diff options
Diffstat (limited to 'net/ipv4/tcp_input.c')
| -rw-r--r-- | net/ipv4/tcp_input.c | 5963 |
1 files changed, 5963 insertions, 0 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c new file mode 100644 index 00000000..7410a8c2 --- /dev/null +++ b/net/ipv4/tcp_input.c @@ -0,0 +1,5963 @@ +/* + * INET An implementation of the TCP/IP protocol suite for the LINUX + * operating system. INET is implemented using the BSD Socket + * interface as the means of communication with the user level. + * + * Implementation of the Transmission Control Protocol(TCP). + * + * Authors: Ross Biro + * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> + * Mark Evans, <evansmp@uhura.aston.ac.uk> + * Corey Minyard <wf-rch!minyard@relay.EU.net> + * Florian La Roche, <flla@stud.uni-sb.de> + * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> + * Linus Torvalds, <torvalds@cs.helsinki.fi> + * Alan Cox, <gw4pts@gw4pts.ampr.org> + * Matthew Dillon, <dillon@apollo.west.oic.com> + * Arnt Gulbrandsen, <agulbra@nvg.unit.no> + * Jorge Cwik, <jorge@laser.satlink.net> + */ + +/* + * Changes: + * Pedro Roque : Fast Retransmit/Recovery. + * Two receive queues. + * Retransmit queue handled by TCP. + * Better retransmit timer handling. + * New congestion avoidance. + * Header prediction. + * Variable renaming. + * + * Eric : Fast Retransmit. + * Randy Scott : MSS option defines. + * Eric Schenk : Fixes to slow start algorithm. + * Eric Schenk : Yet another double ACK bug. + * Eric Schenk : Delayed ACK bug fixes. + * Eric Schenk : Floyd style fast retrans war avoidance. + * David S. Miller : Don't allow zero congestion window. + * Eric Schenk : Fix retransmitter so that it sends + * next packet on ack of previous packet. + * Andi Kleen : Moved open_request checking here + * and process RSTs for open_requests. + * Andi Kleen : Better prune_queue, and other fixes. + * Andrey Savochkin: Fix RTT measurements in the presence of + * timestamps. + * Andrey Savochkin: Check sequence numbers correctly when + * removing SACKs due to in sequence incoming + * data segments. + * Andi Kleen: Make sure we never ack data there is not + * enough room for. Also make this condition + * a fatal error if it might still happen. + * Andi Kleen: Add tcp_measure_rcv_mss to make + * connections with MSS<min(MTU,ann. MSS) + * work without delayed acks. + * Andi Kleen: Process packets with PSH set in the + * fast path. + * J Hadi Salim: ECN support + * Andrei Gurtov, + * Pasi Sarolahti, + * Panu Kuhlberg: Experimental audit of TCP (re)transmission + * engine. Lots of bugs are found. + * Pasi Sarolahti: F-RTO for dealing with spurious RTOs + */ + +#include <linux/mm.h> +#include <linux/slab.h> +#include <linux/module.h> +#include <linux/sysctl.h> +#include <linux/kernel.h> +#include <net/dst.h> +#include <net/tcp.h> +#include <net/inet_common.h> +#include <linux/ipsec.h> +#include <asm/unaligned.h> +#include <net/netdma.h> + +int sysctl_tcp_timestamps __read_mostly = 1; +int sysctl_tcp_window_scaling __read_mostly = 1; +int sysctl_tcp_sack __read_mostly = 1; +int sysctl_tcp_fack __read_mostly = 1; +int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH; +EXPORT_SYMBOL(sysctl_tcp_reordering); +int sysctl_tcp_ecn __read_mostly = 2; +EXPORT_SYMBOL(sysctl_tcp_ecn); +int sysctl_tcp_dsack __read_mostly = 1; +int sysctl_tcp_app_win __read_mostly = 31; +int sysctl_tcp_adv_win_scale __read_mostly = 1; +EXPORT_SYMBOL(sysctl_tcp_adv_win_scale); + +int sysctl_tcp_stdurg __read_mostly; +int sysctl_tcp_rfc1337 __read_mostly; +int sysctl_tcp_max_orphans __read_mostly = NR_FILE; +int sysctl_tcp_frto __read_mostly = 2; +int sysctl_tcp_frto_response __read_mostly; +int sysctl_tcp_nometrics_save __read_mostly; + +int sysctl_tcp_thin_dupack __read_mostly; + +int sysctl_tcp_moderate_rcvbuf __read_mostly = 1; +int sysctl_tcp_abc __read_mostly; + +#define FLAG_DATA 0x01 /* Incoming frame contained data. */ +#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */ +#define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */ +#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */ +#define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */ +#define FLAG_DATA_SACKED 0x20 /* New SACK. */ +#define FLAG_ECE 0x40 /* ECE in this ACK */ +#define FLAG_DATA_LOST 0x80 /* SACK detected data lossage. */ +#define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/ +#define FLAG_ONLY_ORIG_SACKED 0x200 /* SACKs only non-rexmit sent before RTO */ +#define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */ +#define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */ +#define FLAG_NONHEAD_RETRANS_ACKED 0x1000 /* Non-head rexmitted data was ACKed */ +#define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */ + +#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED) +#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED) +#define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE) +#define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED) +#define FLAG_ANY_PROGRESS (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED) + +#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH) +#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH)) + +/* Adapt the MSS value used to make delayed ack decision to the + * real world. + */ +static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + const unsigned int lss = icsk->icsk_ack.last_seg_size; + unsigned int len; + + icsk->icsk_ack.last_seg_size = 0; + + /* skb->len may jitter because of SACKs, even if peer + * sends good full-sized frames. + */ + len = skb_shinfo(skb)->gso_size ? : skb->len; + if (len >= icsk->icsk_ack.rcv_mss) { + icsk->icsk_ack.rcv_mss = len; + } else { + /* Otherwise, we make more careful check taking into account, + * that SACKs block is variable. + * + * "len" is invariant segment length, including TCP header. + */ + len += skb->data - skb_transport_header(skb); + if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) || + /* If PSH is not set, packet should be + * full sized, provided peer TCP is not badly broken. + * This observation (if it is correct 8)) allows + * to handle super-low mtu links fairly. + */ + (len >= TCP_MIN_MSS + sizeof(struct tcphdr) && + !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) { + /* Subtract also invariant (if peer is RFC compliant), + * tcp header plus fixed timestamp option length. + * Resulting "len" is MSS free of SACK jitter. + */ + len -= tcp_sk(sk)->tcp_header_len; + icsk->icsk_ack.last_seg_size = len; + if (len == lss) { + icsk->icsk_ack.rcv_mss = len; + return; + } + } + if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED) + icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2; + icsk->icsk_ack.pending |= ICSK_ACK_PUSHED; + } +} + +static void tcp_incr_quickack(struct sock *sk) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss); + + if (quickacks == 0) + quickacks = 2; + if (quickacks > icsk->icsk_ack.quick) + icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS); +} + +static void tcp_enter_quickack_mode(struct sock *sk) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + tcp_incr_quickack(sk); + icsk->icsk_ack.pingpong = 0; + icsk->icsk_ack.ato = TCP_ATO_MIN; +} + +/* Send ACKs quickly, if "quick" count is not exhausted + * and the session is not interactive. + */ + +static inline int tcp_in_quickack_mode(const struct sock *sk) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong; +} + +static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp) +{ + if (tp->ecn_flags & TCP_ECN_OK) + tp->ecn_flags |= TCP_ECN_QUEUE_CWR; +} + +static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, struct sk_buff *skb) +{ + if (tcp_hdr(skb)->cwr) + tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR; +} + +static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp) +{ + tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR; +} + +static inline void TCP_ECN_check_ce(struct tcp_sock *tp, struct sk_buff *skb) +{ + if (tp->ecn_flags & TCP_ECN_OK) { + if (INET_ECN_is_ce(TCP_SKB_CB(skb)->flags)) + tp->ecn_flags |= TCP_ECN_DEMAND_CWR; + /* Funny extension: if ECT is not set on a segment, + * it is surely retransmit. It is not in ECN RFC, + * but Linux follows this rule. */ + else if (INET_ECN_is_not_ect((TCP_SKB_CB(skb)->flags))) + tcp_enter_quickack_mode((struct sock *)tp); + } +} + +static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, struct tcphdr *th) +{ + if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr)) + tp->ecn_flags &= ~TCP_ECN_OK; +} + +static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, struct tcphdr *th) +{ + if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr)) + tp->ecn_flags &= ~TCP_ECN_OK; +} + +static inline int TCP_ECN_rcv_ecn_echo(struct tcp_sock *tp, struct tcphdr *th) +{ + if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK)) + return 1; + return 0; +} + +/* Buffer size and advertised window tuning. + * + * 1. Tuning sk->sk_sndbuf, when connection enters established state. + */ + +static void tcp_fixup_sndbuf(struct sock *sk) +{ + int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 + + sizeof(struct sk_buff); + + if (sk->sk_sndbuf < 3 * sndmem) { + sk->sk_sndbuf = 3 * sndmem; + if (sk->sk_sndbuf > sysctl_tcp_wmem[2]) + sk->sk_sndbuf = sysctl_tcp_wmem[2]; + } +} + +/* 2. Tuning advertised window (window_clamp, rcv_ssthresh) + * + * All tcp_full_space() is split to two parts: "network" buffer, allocated + * forward and advertised in receiver window (tp->rcv_wnd) and + * "application buffer", required to isolate scheduling/application + * latencies from network. + * window_clamp is maximal advertised window. It can be less than + * tcp_full_space(), in this case tcp_full_space() - window_clamp + * is reserved for "application" buffer. The less window_clamp is + * the smoother our behaviour from viewpoint of network, but the lower + * throughput and the higher sensitivity of the connection to losses. 8) + * + * rcv_ssthresh is more strict window_clamp used at "slow start" + * phase to predict further behaviour of this connection. + * It is used for two goals: + * - to enforce header prediction at sender, even when application + * requires some significant "application buffer". It is check #1. + * - to prevent pruning of receive queue because of misprediction + * of receiver window. Check #2. + * + * The scheme does not work when sender sends good segments opening + * window and then starts to feed us spaghetti. But it should work + * in common situations. Otherwise, we have to rely on queue collapsing. + */ + +/* Slow part of check#2. */ +static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + /* Optimize this! */ + int truesize = tcp_win_from_space(skb->truesize) >> 1; + int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1; + + while (tp->rcv_ssthresh <= window) { + if (truesize <= skb->len) + return 2 * inet_csk(sk)->icsk_ack.rcv_mss; + + truesize >>= 1; + window >>= 1; + } + return 0; +} + +static void tcp_grow_window(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + + /* Check #1 */ + if (tp->rcv_ssthresh < tp->window_clamp && + (int)tp->rcv_ssthresh < tcp_space(sk) && + !tcp_memory_pressure) { + int incr; + + /* Check #2. Increase window, if skb with such overhead + * will fit to rcvbuf in future. + */ + if (tcp_win_from_space(skb->truesize) <= skb->len) + incr = 2 * tp->advmss; + else + incr = __tcp_grow_window(sk, skb); + + if (incr) { + incr = max_t(int, incr, 2 * skb->len); + tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, + tp->window_clamp); + inet_csk(sk)->icsk_ack.quick |= 1; + } + } +} + +/* 3. Tuning rcvbuf, when connection enters established state. */ + +static void tcp_fixup_rcvbuf(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff); + + /* Try to select rcvbuf so that 4 mss-sized segments + * will fit to window and corresponding skbs will fit to our rcvbuf. + * (was 3; 4 is minimum to allow fast retransmit to work.) + */ + while (tcp_win_from_space(rcvmem) < tp->advmss) + rcvmem += 128; + if (sk->sk_rcvbuf < 4 * rcvmem) + sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]); +} + +/* 4. Try to fixup all. It is made immediately after connection enters + * established state. + */ +static void tcp_init_buffer_space(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + int maxwin; + + if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) + tcp_fixup_rcvbuf(sk); + if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) + tcp_fixup_sndbuf(sk); + + tp->rcvq_space.space = tp->rcv_wnd; + + maxwin = tcp_full_space(sk); + + if (tp->window_clamp >= maxwin) { + tp->window_clamp = maxwin; + + if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss) + tp->window_clamp = max(maxwin - + (maxwin >> sysctl_tcp_app_win), + 4 * tp->advmss); + } + + /* Force reservation of one segment. */ + if (sysctl_tcp_app_win && + tp->window_clamp > 2 * tp->advmss && + tp->window_clamp + tp->advmss > maxwin) + tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss); + + tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp); + tp->snd_cwnd_stamp = tcp_time_stamp; +} + +/* 5. Recalculate window clamp after socket hit its memory bounds. */ +static void tcp_clamp_window(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + + icsk->icsk_ack.quick = 0; + + if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] && + !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) && + !tcp_memory_pressure && + atomic_long_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) { + sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc), + sysctl_tcp_rmem[2]); + } + if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) + tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss); +} + +/* Initialize RCV_MSS value. + * RCV_MSS is an our guess about MSS used by the peer. + * We haven't any direct information about the MSS. + * It's better to underestimate the RCV_MSS rather than overestimate. + * Overestimations make us ACKing less frequently than needed. + * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss(). + */ +void tcp_initialize_rcv_mss(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache); + + hint = min(hint, tp->rcv_wnd / 2); + hint = min(hint, TCP_MSS_DEFAULT); + hint = max(hint, TCP_MIN_MSS); + + inet_csk(sk)->icsk_ack.rcv_mss = hint; +} +EXPORT_SYMBOL(tcp_initialize_rcv_mss); + +/* Receiver "autotuning" code. + * + * The algorithm for RTT estimation w/o timestamps is based on + * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL. + * <http://public.lanl.gov/radiant/pubs.html#DRS> + * + * More detail on this code can be found at + * <http://staff.psc.edu/jheffner/>, + * though this reference is out of date. A new paper + * is pending. + */ +static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep) +{ + u32 new_sample = tp->rcv_rtt_est.rtt; + long m = sample; + + if (m == 0) + m = 1; + + if (new_sample != 0) { + /* If we sample in larger samples in the non-timestamp + * case, we could grossly overestimate the RTT especially + * with chatty applications or bulk transfer apps which + * are stalled on filesystem I/O. + * + * Also, since we are only going for a minimum in the + * non-timestamp case, we do not smooth things out + * else with timestamps disabled convergence takes too + * long. + */ + if (!win_dep) { + m -= (new_sample >> 3); + new_sample += m; + } else { + m <<= 3; + if (m < new_sample) + new_sample = m; + } + } else { + /* No previous measure. */ + new_sample = m << 3; + } + + if (tp->rcv_rtt_est.rtt != new_sample) + tp->rcv_rtt_est.rtt = new_sample; +} + +static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp) +{ + if (tp->rcv_rtt_est.time == 0) + goto new_measure; + if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq)) + return; + tcp_rcv_rtt_update(tp, jiffies - tp->rcv_rtt_est.time, 1); + +new_measure: + tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd; + tp->rcv_rtt_est.time = tcp_time_stamp; +} + +static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, + const struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + if (tp->rx_opt.rcv_tsecr && + (TCP_SKB_CB(skb)->end_seq - + TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss)) + tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0); +} + +/* + * This function should be called every time data is copied to user space. + * It calculates the appropriate TCP receive buffer space. + */ +void tcp_rcv_space_adjust(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + int time; + int space; + + if (tp->rcvq_space.time == 0) + goto new_measure; + + time = tcp_time_stamp - tp->rcvq_space.time; + if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0) + return; + + space = 2 * (tp->copied_seq - tp->rcvq_space.seq); + + space = max(tp->rcvq_space.space, space); + + if (tp->rcvq_space.space != space) { + int rcvmem; + + tp->rcvq_space.space = space; + + if (sysctl_tcp_moderate_rcvbuf && + !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) { + int new_clamp = space; + + /* Receive space grows, normalize in order to + * take into account packet headers and sk_buff + * structure overhead. + */ + space /= tp->advmss; + if (!space) + space = 1; + rcvmem = (tp->advmss + MAX_TCP_HEADER + + 16 + sizeof(struct sk_buff)); + while (tcp_win_from_space(rcvmem) < tp->advmss) + rcvmem += 128; + space *= rcvmem; + space = min(space, sysctl_tcp_rmem[2]); + if (space > sk->sk_rcvbuf) { + sk->sk_rcvbuf = space; + + /* Make the window clamp follow along. */ + tp->window_clamp = new_clamp; + } + } + } + +new_measure: + tp->rcvq_space.seq = tp->copied_seq; + tp->rcvq_space.time = tcp_time_stamp; +} + +/* There is something which you must keep in mind when you analyze the + * behavior of the tp->ato delayed ack timeout interval. When a + * connection starts up, we want to ack as quickly as possible. The + * problem is that "good" TCP's do slow start at the beginning of data + * transmission. The means that until we send the first few ACK's the + * sender will sit on his end and only queue most of his data, because + * he can only send snd_cwnd unacked packets at any given time. For + * each ACK we send, he increments snd_cwnd and transmits more of his + * queue. -DaveM + */ +static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + u32 now; + + inet_csk_schedule_ack(sk); + + tcp_measure_rcv_mss(sk, skb); + + tcp_rcv_rtt_measure(tp); + + now = tcp_time_stamp; + + if (!icsk->icsk_ack.ato) { + /* The _first_ data packet received, initialize + * delayed ACK engine. + */ + tcp_incr_quickack(sk); + icsk->icsk_ack.ato = TCP_ATO_MIN; + } else { + int m = now - icsk->icsk_ack.lrcvtime; + + if (m <= TCP_ATO_MIN / 2) { + /* The fastest case is the first. */ + icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2; + } else if (m < icsk->icsk_ack.ato) { + icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m; + if (icsk->icsk_ack.ato > icsk->icsk_rto) + icsk->icsk_ack.ato = icsk->icsk_rto; + } else if (m > icsk->icsk_rto) { + /* Too long gap. Apparently sender failed to + * restart window, so that we send ACKs quickly. + */ + tcp_incr_quickack(sk); + sk_mem_reclaim(sk); + } + } + icsk->icsk_ack.lrcvtime = now; + + TCP_ECN_check_ce(tp, skb); + + if (skb->len >= 128) + tcp_grow_window(sk, skb); +} + +/* Called to compute a smoothed rtt estimate. The data fed to this + * routine either comes from timestamps, or from segments that were + * known _not_ to have been retransmitted [see Karn/Partridge + * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88 + * piece by Van Jacobson. + * NOTE: the next three routines used to be one big routine. + * To save cycles in the RFC 1323 implementation it was better to break + * it up into three procedures. -- erics + */ +static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt) +{ + struct tcp_sock *tp = tcp_sk(sk); + long m = mrtt; /* RTT */ + + /* The following amusing code comes from Jacobson's + * article in SIGCOMM '88. Note that rtt and mdev + * are scaled versions of rtt and mean deviation. + * This is designed to be as fast as possible + * m stands for "measurement". + * + * On a 1990 paper the rto value is changed to: + * RTO = rtt + 4 * mdev + * + * Funny. This algorithm seems to be very broken. + * These formulae increase RTO, when it should be decreased, increase + * too slowly, when it should be increased quickly, decrease too quickly + * etc. I guess in BSD RTO takes ONE value, so that it is absolutely + * does not matter how to _calculate_ it. Seems, it was trap + * that VJ failed to avoid. 8) + */ + if (m == 0) + m = 1; + if (tp->srtt != 0) { + m -= (tp->srtt >> 3); /* m is now error in rtt est */ + tp->srtt += m; /* rtt = 7/8 rtt + 1/8 new */ + if (m < 0) { + m = -m; /* m is now abs(error) */ + m -= (tp->mdev >> 2); /* similar update on mdev */ + /* This is similar to one of Eifel findings. + * Eifel blocks mdev updates when rtt decreases. + * This solution is a bit different: we use finer gain + * for mdev in this case (alpha*beta). + * Like Eifel it also prevents growth of rto, + * but also it limits too fast rto decreases, + * happening in pure Eifel. + */ + if (m > 0) + m >>= 3; + } else { + m -= (tp->mdev >> 2); /* similar update on mdev */ + } + tp->mdev += m; /* mdev = 3/4 mdev + 1/4 new */ + if (tp->mdev > tp->mdev_max) { + tp->mdev_max = tp->mdev; + if (tp->mdev_max > tp->rttvar) + tp->rttvar = tp->mdev_max; + } + if (after(tp->snd_una, tp->rtt_seq)) { + if (tp->mdev_max < tp->rttvar) + tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2; + tp->rtt_seq = tp->snd_nxt; + tp->mdev_max = tcp_rto_min(sk); + } + } else { + /* no previous measure. */ + tp->srtt = m << 3; /* take the measured time to be rtt */ + tp->mdev = m << 1; /* make sure rto = 3*rtt */ + tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk)); + tp->rtt_seq = tp->snd_nxt; + } +} + +/* Calculate rto without backoff. This is the second half of Van Jacobson's + * routine referred to above. + */ +static inline void tcp_set_rto(struct sock *sk) +{ + const struct tcp_sock *tp = tcp_sk(sk); + /* Old crap is replaced with new one. 8) + * + * More seriously: + * 1. If rtt variance happened to be less 50msec, it is hallucination. + * It cannot be less due to utterly erratic ACK generation made + * at least by solaris and freebsd. "Erratic ACKs" has _nothing_ + * to do with delayed acks, because at cwnd>2 true delack timeout + * is invisible. Actually, Linux-2.4 also generates erratic + * ACKs in some circumstances. + */ + inet_csk(sk)->icsk_rto = __tcp_set_rto(tp); + + /* 2. Fixups made earlier cannot be right. + * If we do not estimate RTO correctly without them, + * all the algo is pure shit and should be replaced + * with correct one. It is exactly, which we pretend to do. + */ + + /* NOTE: clamping at TCP_RTO_MIN is not required, current algo + * guarantees that rto is higher. + */ + tcp_bound_rto(sk); +} + +/* Save metrics learned by this TCP session. + This function is called only, when TCP finishes successfully + i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE. + */ +void tcp_update_metrics(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct dst_entry *dst = __sk_dst_get(sk); + + if (sysctl_tcp_nometrics_save) + return; + + dst_confirm(dst); + + if (dst && (dst->flags & DST_HOST)) { + const struct inet_connection_sock *icsk = inet_csk(sk); + int m; + unsigned long rtt; + + if (icsk->icsk_backoff || !tp->srtt) { + /* This session failed to estimate rtt. Why? + * Probably, no packets returned in time. + * Reset our results. + */ + if (!(dst_metric_locked(dst, RTAX_RTT))) + dst_metric_set(dst, RTAX_RTT, 0); + return; + } + + rtt = dst_metric_rtt(dst, RTAX_RTT); + m = rtt - tp->srtt; + + /* If newly calculated rtt larger than stored one, + * store new one. Otherwise, use EWMA. Remember, + * rtt overestimation is always better than underestimation. + */ + if (!(dst_metric_locked(dst, RTAX_RTT))) { + if (m <= 0) + set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt); + else + set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3)); + } + + if (!(dst_metric_locked(dst, RTAX_RTTVAR))) { + unsigned long var; + if (m < 0) + m = -m; + + /* Scale deviation to rttvar fixed point */ + m >>= 1; + if (m < tp->mdev) + m = tp->mdev; + + var = dst_metric_rtt(dst, RTAX_RTTVAR); + if (m >= var) + var = m; + else + var -= (var - m) >> 2; + + set_dst_metric_rtt(dst, RTAX_RTTVAR, var); + } + + if (tcp_in_initial_slowstart(tp)) { + /* Slow start still did not finish. */ + if (dst_metric(dst, RTAX_SSTHRESH) && + !dst_metric_locked(dst, RTAX_SSTHRESH) && + (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH)) + dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_cwnd >> 1); + if (!dst_metric_locked(dst, RTAX_CWND) && + tp->snd_cwnd > dst_metric(dst, RTAX_CWND)) + dst_metric_set(dst, RTAX_CWND, tp->snd_cwnd); + } else if (tp->snd_cwnd > tp->snd_ssthresh && + icsk->icsk_ca_state == TCP_CA_Open) { + /* Cong. avoidance phase, cwnd is reliable. */ + if (!dst_metric_locked(dst, RTAX_SSTHRESH)) + dst_metric_set(dst, RTAX_SSTHRESH, + max(tp->snd_cwnd >> 1, tp->snd_ssthresh)); + if (!dst_metric_locked(dst, RTAX_CWND)) + dst_metric_set(dst, RTAX_CWND, + (dst_metric(dst, RTAX_CWND) + + tp->snd_cwnd) >> 1); + } else { + /* Else slow start did not finish, cwnd is non-sense, + ssthresh may be also invalid. + */ + if (!dst_metric_locked(dst, RTAX_CWND)) + dst_metric_set(dst, RTAX_CWND, + (dst_metric(dst, RTAX_CWND) + + tp->snd_ssthresh) >> 1); + if (dst_metric(dst, RTAX_SSTHRESH) && + !dst_metric_locked(dst, RTAX_SSTHRESH) && + tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH)) + dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_ssthresh); + } + + if (!dst_metric_locked(dst, RTAX_REORDERING)) { + if (dst_metric(dst, RTAX_REORDERING) < tp->reordering && + tp->reordering != sysctl_tcp_reordering) + dst_metric_set(dst, RTAX_REORDERING, tp->reordering); + } + } +} + +__u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst) +{ + __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0); + + if (!cwnd) + cwnd = TCP_INIT_CWND; + return min_t(__u32, cwnd, tp->snd_cwnd_clamp); +} + +/* Set slow start threshold and cwnd not falling to slow start */ +void tcp_enter_cwr(struct sock *sk, const int set_ssthresh) +{ + struct tcp_sock *tp = tcp_sk(sk); + const struct inet_connection_sock *icsk = inet_csk(sk); + + tp->prior_ssthresh = 0; + tp->bytes_acked = 0; + if (icsk->icsk_ca_state < TCP_CA_CWR) { + tp->undo_marker = 0; + if (set_ssthresh) + tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); + tp->snd_cwnd = min(tp->snd_cwnd, + tcp_packets_in_flight(tp) + 1U); + tp->snd_cwnd_cnt = 0; + tp->high_seq = tp->snd_nxt; + tp->snd_cwnd_stamp = tcp_time_stamp; + TCP_ECN_queue_cwr(tp); + + tcp_set_ca_state(sk, TCP_CA_CWR); + } +} + +/* + * Packet counting of FACK is based on in-order assumptions, therefore TCP + * disables it when reordering is detected + */ +static void tcp_disable_fack(struct tcp_sock *tp) +{ + /* RFC3517 uses different metric in lost marker => reset on change */ + if (tcp_is_fack(tp)) + tp->lost_skb_hint = NULL; + tp->rx_opt.sack_ok &= ~2; +} + +/* Take a notice that peer is sending D-SACKs */ +static void tcp_dsack_seen(struct tcp_sock *tp) +{ + tp->rx_opt.sack_ok |= 4; +} + +/* Initialize metrics on socket. */ + +static void tcp_init_metrics(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct dst_entry *dst = __sk_dst_get(sk); + + if (dst == NULL) + goto reset; + + dst_confirm(dst); + + if (dst_metric_locked(dst, RTAX_CWND)) + tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND); + if (dst_metric(dst, RTAX_SSTHRESH)) { + tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH); + if (tp->snd_ssthresh > tp->snd_cwnd_clamp) + tp->snd_ssthresh = tp->snd_cwnd_clamp; + } + if (dst_metric(dst, RTAX_REORDERING) && + tp->reordering != dst_metric(dst, RTAX_REORDERING)) { + tcp_disable_fack(tp); + tp->reordering = dst_metric(dst, RTAX_REORDERING); + } + + if (dst_metric(dst, RTAX_RTT) == 0) + goto reset; + + if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3)) + goto reset; + + /* Initial rtt is determined from SYN,SYN-ACK. + * The segment is small and rtt may appear much + * less than real one. Use per-dst memory + * to make it more realistic. + * + * A bit of theory. RTT is time passed after "normal" sized packet + * is sent until it is ACKed. In normal circumstances sending small + * packets force peer to delay ACKs and calculation is correct too. + * The algorithm is adaptive and, provided we follow specs, it + * NEVER underestimate RTT. BUT! If peer tries to make some clever + * tricks sort of "quick acks" for time long enough to decrease RTT + * to low value, and then abruptly stops to do it and starts to delay + * ACKs, wait for troubles. + */ + if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) { + tp->srtt = dst_metric_rtt(dst, RTAX_RTT); + tp->rtt_seq = tp->snd_nxt; + } + if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) { + tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR); + tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk)); + } + tcp_set_rto(sk); + if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp) { +reset: + /* Play conservative. If timestamps are not + * supported, TCP will fail to recalculate correct + * rtt, if initial rto is too small. FORGET ALL AND RESET! + */ + if (!tp->rx_opt.saw_tstamp && tp->srtt) { + tp->srtt = 0; + tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT; + inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT; + } + } + tp->snd_cwnd = tcp_init_cwnd(tp, dst); + tp->snd_cwnd_stamp = tcp_time_stamp; +} + +static void tcp_update_reordering(struct sock *sk, const int metric, + const int ts) +{ + struct tcp_sock *tp = tcp_sk(sk); + if (metric > tp->reordering) { + int mib_idx; + + tp->reordering = min(TCP_MAX_REORDERING, metric); + + /* This exciting event is worth to be remembered. 8) */ + if (ts) + mib_idx = LINUX_MIB_TCPTSREORDER; + else if (tcp_is_reno(tp)) + mib_idx = LINUX_MIB_TCPRENOREORDER; + else if (tcp_is_fack(tp)) + mib_idx = LINUX_MIB_TCPFACKREORDER; + else + mib_idx = LINUX_MIB_TCPSACKREORDER; + + NET_INC_STATS_BH(sock_net(sk), mib_idx); +#if FASTRETRANS_DEBUG > 1 + printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n", + tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state, + tp->reordering, + tp->fackets_out, + tp->sacked_out, + tp->undo_marker ? tp->undo_retrans : 0); +#endif + tcp_disable_fack(tp); + } +} + +/* This must be called before lost_out is incremented */ +static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb) +{ + if ((tp->retransmit_skb_hint == NULL) || + before(TCP_SKB_CB(skb)->seq, + TCP_SKB_CB(tp->retransmit_skb_hint)->seq)) + tp->retransmit_skb_hint = skb; + + if (!tp->lost_out || + after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high)) + tp->retransmit_high = TCP_SKB_CB(skb)->end_seq; +} + +static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb) +{ + if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) { + tcp_verify_retransmit_hint(tp, skb); + + tp->lost_out += tcp_skb_pcount(skb); + TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; + } +} + +static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, + struct sk_buff *skb) +{ + tcp_verify_retransmit_hint(tp, skb); + + if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) { + tp->lost_out += tcp_skb_pcount(skb); + TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; + } +} + +/* This procedure tags the retransmission queue when SACKs arrive. + * + * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L). + * Packets in queue with these bits set are counted in variables + * sacked_out, retrans_out and lost_out, correspondingly. + * + * Valid combinations are: + * Tag InFlight Description + * 0 1 - orig segment is in flight. + * S 0 - nothing flies, orig reached receiver. + * L 0 - nothing flies, orig lost by net. + * R 2 - both orig and retransmit are in flight. + * L|R 1 - orig is lost, retransmit is in flight. + * S|R 1 - orig reached receiver, retrans is still in flight. + * (L|S|R is logically valid, it could occur when L|R is sacked, + * but it is equivalent to plain S and code short-curcuits it to S. + * L|S is logically invalid, it would mean -1 packet in flight 8)) + * + * These 6 states form finite state machine, controlled by the following events: + * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue()) + * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue()) + * 3. Loss detection event of one of three flavors: + * A. Scoreboard estimator decided the packet is lost. + * A'. Reno "three dupacks" marks head of queue lost. + * A''. Its FACK modfication, head until snd.fack is lost. + * B. SACK arrives sacking data transmitted after never retransmitted + * hole was sent out. + * C. SACK arrives sacking SND.NXT at the moment, when the + * segment was retransmitted. + * 4. D-SACK added new rule: D-SACK changes any tag to S. + * + * It is pleasant to note, that state diagram turns out to be commutative, + * so that we are allowed not to be bothered by order of our actions, + * when multiple events arrive simultaneously. (see the function below). + * + * Reordering detection. + * -------------------- + * Reordering metric is maximal distance, which a packet can be displaced + * in packet stream. With SACKs we can estimate it: + * + * 1. SACK fills old hole and the corresponding segment was not + * ever retransmitted -> reordering. Alas, we cannot use it + * when segment was retransmitted. + * 2. The last flaw is solved with D-SACK. D-SACK arrives + * for retransmitted and already SACKed segment -> reordering.. + * Both of these heuristics are not used in Loss state, when we cannot + * account for retransmits accurately. + * + * SACK block validation. + * ---------------------- + * + * SACK block range validation checks that the received SACK block fits to + * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT. + * Note that SND.UNA is not included to the range though being valid because + * it means that the receiver is rather inconsistent with itself reporting + * SACK reneging when it should advance SND.UNA. Such SACK block this is + * perfectly valid, however, in light of RFC2018 which explicitly states + * that "SACK block MUST reflect the newest segment. Even if the newest + * segment is going to be discarded ...", not that it looks very clever + * in case of head skb. Due to potentional receiver driven attacks, we + * choose to avoid immediate execution of a walk in write queue due to + * reneging and defer head skb's loss recovery to standard loss recovery + * procedure that will eventually trigger (nothing forbids us doing this). + * + * Implements also blockage to start_seq wrap-around. Problem lies in the + * fact that though start_seq (s) is before end_seq (i.e., not reversed), + * there's no guarantee that it will be before snd_nxt (n). The problem + * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt + * wrap (s_w): + * + * <- outs wnd -> <- wrapzone -> + * u e n u_w e_w s n_w + * | | | | | | | + * |<------------+------+----- TCP seqno space --------------+---------->| + * ...-- <2^31 ->| |<--------... + * ...---- >2^31 ------>| |<--------... + * + * Current code wouldn't be vulnerable but it's better still to discard such + * crazy SACK blocks. Doing this check for start_seq alone closes somewhat + * similar case (end_seq after snd_nxt wrap) as earlier reversed check in + * snd_nxt wrap -> snd_una region will then become "well defined", i.e., + * equal to the ideal case (infinite seqno space without wrap caused issues). + * + * With D-SACK the lower bound is extended to cover sequence space below + * SND.UNA down to undo_marker, which is the last point of interest. Yet + * again, D-SACK block must not to go across snd_una (for the same reason as + * for the normal SACK blocks, explained above). But there all simplicity + * ends, TCP might receive valid D-SACKs below that. As long as they reside + * fully below undo_marker they do not affect behavior in anyway and can + * therefore be safely ignored. In rare cases (which are more or less + * theoretical ones), the D-SACK will nicely cross that boundary due to skb + * fragmentation and packet reordering past skb's retransmission. To consider + * them correctly, the acceptable range must be extended even more though + * the exact amount is rather hard to quantify. However, tp->max_window can + * be used as an exaggerated estimate. + */ +static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack, + u32 start_seq, u32 end_seq) +{ + /* Too far in future, or reversed (interpretation is ambiguous) */ + if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq)) + return 0; + + /* Nasty start_seq wrap-around check (see comments above) */ + if (!before(start_seq, tp->snd_nxt)) + return 0; + + /* In outstanding window? ...This is valid exit for D-SACKs too. + * start_seq == snd_una is non-sensical (see comments above) + */ + if (after(start_seq, tp->snd_una)) + return 1; + + if (!is_dsack || !tp->undo_marker) + return 0; + + /* ...Then it's D-SACK, and must reside below snd_una completely */ + if (after(end_seq, tp->snd_una)) + return 0; + + if (!before(start_seq, tp->undo_marker)) + return 1; + + /* Too old */ + if (!after(end_seq, tp->undo_marker)) + return 0; + + /* Undo_marker boundary crossing (overestimates a lot). Known already: + * start_seq < undo_marker and end_seq >= undo_marker. + */ + return !before(start_seq, end_seq - tp->max_window); +} + +/* Check for lost retransmit. This superb idea is borrowed from "ratehalving". + * Event "C". Later note: FACK people cheated me again 8), we have to account + * for reordering! Ugly, but should help. + * + * Search retransmitted skbs from write_queue that were sent when snd_nxt was + * less than what is now known to be received by the other end (derived from + * highest SACK block). Also calculate the lowest snd_nxt among the remaining + * retransmitted skbs to avoid some costly processing per ACKs. + */ +static void tcp_mark_lost_retrans(struct sock *sk) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + int cnt = 0; + u32 new_low_seq = tp->snd_nxt; + u32 received_upto = tcp_highest_sack_seq(tp); + + if (!tcp_is_fack(tp) || !tp->retrans_out || + !after(received_upto, tp->lost_retrans_low) || + icsk->icsk_ca_state != TCP_CA_Recovery) + return; + + tcp_for_write_queue(skb, sk) { + u32 ack_seq = TCP_SKB_CB(skb)->ack_seq; + + if (skb == tcp_send_head(sk)) + break; + if (cnt == tp->retrans_out) + break; + if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) + continue; + + if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)) + continue; + + /* TODO: We would like to get rid of tcp_is_fack(tp) only + * constraint here (see above) but figuring out that at + * least tp->reordering SACK blocks reside between ack_seq + * and received_upto is not easy task to do cheaply with + * the available datastructures. + * + * Whether FACK should check here for tp->reordering segs + * in-between one could argue for either way (it would be + * rather simple to implement as we could count fack_count + * during the walk and do tp->fackets_out - fack_count). + */ + if (after(received_upto, ack_seq)) { + TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; + tp->retrans_out -= tcp_skb_pcount(skb); + + tcp_skb_mark_lost_uncond_verify(tp, skb); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT); + } else { + if (before(ack_seq, new_low_seq)) + new_low_seq = ack_seq; + cnt += tcp_skb_pcount(skb); + } + } + + if (tp->retrans_out) + tp->lost_retrans_low = new_low_seq; +} + +static int tcp_check_dsack(struct sock *sk, struct sk_buff *ack_skb, + struct tcp_sack_block_wire *sp, int num_sacks, + u32 prior_snd_una) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq); + u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq); + int dup_sack = 0; + + if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) { + dup_sack = 1; + tcp_dsack_seen(tp); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV); + } else if (num_sacks > 1) { + u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq); + u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq); + + if (!after(end_seq_0, end_seq_1) && + !before(start_seq_0, start_seq_1)) { + dup_sack = 1; + tcp_dsack_seen(tp); + NET_INC_STATS_BH(sock_net(sk), + LINUX_MIB_TCPDSACKOFORECV); + } + } + + /* D-SACK for already forgotten data... Do dumb counting. */ + if (dup_sack && tp->undo_marker && tp->undo_retrans && + !after(end_seq_0, prior_snd_una) && + after(end_seq_0, tp->undo_marker)) + tp->undo_retrans--; + + return dup_sack; +} + +struct tcp_sacktag_state { + int reord; + int fack_count; + int flag; +}; + +/* Check if skb is fully within the SACK block. In presence of GSO skbs, + * the incoming SACK may not exactly match but we can find smaller MSS + * aligned portion of it that matches. Therefore we might need to fragment + * which may fail and creates some hassle (caller must handle error case + * returns). + * + * FIXME: this could be merged to shift decision code + */ +static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb, + u32 start_seq, u32 end_seq) +{ + int in_sack, err; + unsigned int pkt_len; + unsigned int mss; + + in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && + !before(end_seq, TCP_SKB_CB(skb)->end_seq); + + if (tcp_skb_pcount(skb) > 1 && !in_sack && + after(TCP_SKB_CB(skb)->end_seq, start_seq)) { + mss = tcp_skb_mss(skb); + in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq); + + if (!in_sack) { + pkt_len = start_seq - TCP_SKB_CB(skb)->seq; + if (pkt_len < mss) + pkt_len = mss; + } else { + pkt_len = end_seq - TCP_SKB_CB(skb)->seq; + if (pkt_len < mss) + return -EINVAL; + } + + /* Round if necessary so that SACKs cover only full MSSes + * and/or the remaining small portion (if present) + */ + if (pkt_len > mss) { + unsigned int new_len = (pkt_len / mss) * mss; + if (!in_sack && new_len < pkt_len) { + new_len += mss; + if (new_len > skb->len) + return 0; + } + pkt_len = new_len; + } + err = tcp_fragment(sk, skb, pkt_len, mss); + if (err < 0) + return err; + } + + return in_sack; +} + +/* Mark the given newly-SACKed range as such, adjusting counters and hints. */ +static u8 tcp_sacktag_one(struct sock *sk, + struct tcp_sacktag_state *state, u8 sacked, + u32 start_seq, u32 end_seq, + int dup_sack, int pcount) +{ + struct tcp_sock *tp = tcp_sk(sk); + int fack_count = state->fack_count; + + /* Account D-SACK for retransmitted packet. */ + if (dup_sack && (sacked & TCPCB_RETRANS)) { + if (tp->undo_marker && tp->undo_retrans && + after(end_seq, tp->undo_marker)) + tp->undo_retrans--; + if (sacked & TCPCB_SACKED_ACKED) + state->reord = min(fack_count, state->reord); + } + + /* Nothing to do; acked frame is about to be dropped (was ACKed). */ + if (!after(end_seq, tp->snd_una)) + return sacked; + + if (!(sacked & TCPCB_SACKED_ACKED)) { + if (sacked & TCPCB_SACKED_RETRANS) { + /* If the segment is not tagged as lost, + * we do not clear RETRANS, believing + * that retransmission is still in flight. + */ + if (sacked & TCPCB_LOST) { + sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS); + tp->lost_out -= pcount; + tp->retrans_out -= pcount; + } + } else { + if (!(sacked & TCPCB_RETRANS)) { + /* New sack for not retransmitted frame, + * which was in hole. It is reordering. + */ + if (before(start_seq, + tcp_highest_sack_seq(tp))) + state->reord = min(fack_count, + state->reord); + + /* SACK enhanced F-RTO (RFC4138; Appendix B) */ + if (!after(end_seq, tp->frto_highmark)) + state->flag |= FLAG_ONLY_ORIG_SACKED; + } + + if (sacked & TCPCB_LOST) { + sacked &= ~TCPCB_LOST; + tp->lost_out -= pcount; + } + } + + sacked |= TCPCB_SACKED_ACKED; + state->flag |= FLAG_DATA_SACKED; + tp->sacked_out += pcount; + + fack_count += pcount; + + /* Lost marker hint past SACKed? Tweak RFC3517 cnt */ + if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) && + before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq)) + tp->lost_cnt_hint += pcount; + + if (fack_count > tp->fackets_out) + tp->fackets_out = fack_count; + } + + /* D-SACK. We can detect redundant retransmission in S|R and plain R + * frames and clear it. undo_retrans is decreased above, L|R frames + * are accounted above as well. + */ + if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) { + sacked &= ~TCPCB_SACKED_RETRANS; + tp->retrans_out -= pcount; + } + + return sacked; +} + +/* Shift newly-SACKed bytes from this skb to the immediately previous + * already-SACKed sk_buff. Mark the newly-SACKed bytes as such. + */ +static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb, + struct tcp_sacktag_state *state, + unsigned int pcount, int shifted, int mss, + int dup_sack) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *prev = tcp_write_queue_prev(sk, skb); + u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */ + u32 end_seq = start_seq + shifted; /* end of newly-SACKed */ + + BUG_ON(!pcount); + + /* Adjust counters and hints for the newly sacked sequence + * range but discard the return value since prev is already + * marked. We must tag the range first because the seq + * advancement below implicitly advances + * tcp_highest_sack_seq() when skb is highest_sack. + */ + tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked, + start_seq, end_seq, dup_sack, pcount); + + if (skb == tp->lost_skb_hint) + tp->lost_cnt_hint += pcount; + + TCP_SKB_CB(prev)->end_seq += shifted; + TCP_SKB_CB(skb)->seq += shifted; + + skb_shinfo(prev)->gso_segs += pcount; + BUG_ON(skb_shinfo(skb)->gso_segs < pcount); + skb_shinfo(skb)->gso_segs -= pcount; + + /* When we're adding to gso_segs == 1, gso_size will be zero, + * in theory this shouldn't be necessary but as long as DSACK + * code can come after this skb later on it's better to keep + * setting gso_size to something. + */ + if (!skb_shinfo(prev)->gso_size) { + skb_shinfo(prev)->gso_size = mss; + skb_shinfo(prev)->gso_type = sk->sk_gso_type; + } + + /* CHECKME: To clear or not to clear? Mimics normal skb currently */ + if (skb_shinfo(skb)->gso_segs <= 1) { + skb_shinfo(skb)->gso_size = 0; + skb_shinfo(skb)->gso_type = 0; + } + + /* Difference in this won't matter, both ACKed by the same cumul. ACK */ + TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS); + + if (skb->len > 0) { + BUG_ON(!tcp_skb_pcount(skb)); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED); + return 0; + } + + /* Whole SKB was eaten :-) */ + + if (skb == tp->retransmit_skb_hint) + tp->retransmit_skb_hint = prev; + if (skb == tp->scoreboard_skb_hint) + tp->scoreboard_skb_hint = prev; + if (skb == tp->lost_skb_hint) { + tp->lost_skb_hint = prev; + tp->lost_cnt_hint -= tcp_skb_pcount(prev); + } + + TCP_SKB_CB(skb)->flags |= TCP_SKB_CB(prev)->flags; + if (skb == tcp_highest_sack(sk)) + tcp_advance_highest_sack(sk, skb); + + tcp_unlink_write_queue(skb, sk); + sk_wmem_free_skb(sk, skb); + + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED); + + return 1; +} + +/* I wish gso_size would have a bit more sane initialization than + * something-or-zero which complicates things + */ +static int tcp_skb_seglen(struct sk_buff *skb) +{ + return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb); +} + +/* Shifting pages past head area doesn't work */ +static int skb_can_shift(struct sk_buff *skb) +{ + return !skb_headlen(skb) && skb_is_nonlinear(skb); +} + +/* Try collapsing SACK blocks spanning across multiple skbs to a single + * skb. + */ +static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb, + struct tcp_sacktag_state *state, + u32 start_seq, u32 end_seq, + int dup_sack) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *prev; + int mss; + int pcount = 0; + int len; + int in_sack; + + if (!sk_can_gso(sk)) + goto fallback; + + /* Normally R but no L won't result in plain S */ + if (!dup_sack && + (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS) + goto fallback; + if (!skb_can_shift(skb)) + goto fallback; + /* This frame is about to be dropped (was ACKed). */ + if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) + goto fallback; + + /* Can only happen with delayed DSACK + discard craziness */ + if (unlikely(skb == tcp_write_queue_head(sk))) + goto fallback; + prev = tcp_write_queue_prev(sk, skb); + + if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) + goto fallback; + + in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && + !before(end_seq, TCP_SKB_CB(skb)->end_seq); + + if (in_sack) { + len = skb->len; + pcount = tcp_skb_pcount(skb); + mss = tcp_skb_seglen(skb); + + /* TODO: Fix DSACKs to not fragment already SACKed and we can + * drop this restriction as unnecessary + */ + if (mss != tcp_skb_seglen(prev)) + goto fallback; + } else { + if (!after(TCP_SKB_CB(skb)->end_seq, start_seq)) + goto noop; + /* CHECKME: This is non-MSS split case only?, this will + * cause skipped skbs due to advancing loop btw, original + * has that feature too + */ + if (tcp_skb_pcount(skb) <= 1) + goto noop; + + in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq); + if (!in_sack) { + /* TODO: head merge to next could be attempted here + * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)), + * though it might not be worth of the additional hassle + * + * ...we can probably just fallback to what was done + * previously. We could try merging non-SACKed ones + * as well but it probably isn't going to buy off + * because later SACKs might again split them, and + * it would make skb timestamp tracking considerably + * harder problem. + */ + goto fallback; + } + + len = end_seq - TCP_SKB_CB(skb)->seq; + BUG_ON(len < 0); + BUG_ON(len > skb->len); + + /* MSS boundaries should be honoured or else pcount will + * severely break even though it makes things bit trickier. + * Optimize common case to avoid most of the divides + */ + mss = tcp_skb_mss(skb); + + /* TODO: Fix DSACKs to not fragment already SACKed and we can + * drop this restriction as unnecessary + */ + if (mss != tcp_skb_seglen(prev)) + goto fallback; + + if (len == mss) { + pcount = 1; + } else if (len < mss) { + goto noop; + } else { + pcount = len / mss; + len = pcount * mss; + } + } + + /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */ + if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una)) + goto fallback; + + if (!skb_shift(prev, skb, len)) + goto fallback; + if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack)) + goto out; + + /* Hole filled allows collapsing with the next as well, this is very + * useful when hole on every nth skb pattern happens + */ + if (prev == tcp_write_queue_tail(sk)) + goto out; + skb = tcp_write_queue_next(sk, prev); + + if (!skb_can_shift(skb) || + (skb == tcp_send_head(sk)) || + ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) || + (mss != tcp_skb_seglen(skb))) + goto out; + + len = skb->len; + if (skb_shift(prev, skb, len)) { + pcount += tcp_skb_pcount(skb); + tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0); + } + +out: + state->fack_count += pcount; + return prev; + +noop: + return skb; + +fallback: + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK); + return NULL; +} + +static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk, + struct tcp_sack_block *next_dup, + struct tcp_sacktag_state *state, + u32 start_seq, u32 end_seq, + int dup_sack_in) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *tmp; + + tcp_for_write_queue_from(skb, sk) { + int in_sack = 0; + int dup_sack = dup_sack_in; + + if (skb == tcp_send_head(sk)) + break; + + /* queue is in-order => we can short-circuit the walk early */ + if (!before(TCP_SKB_CB(skb)->seq, end_seq)) + break; + + if ((next_dup != NULL) && + before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) { + in_sack = tcp_match_skb_to_sack(sk, skb, + next_dup->start_seq, + next_dup->end_seq); + if (in_sack > 0) + dup_sack = 1; + } + + /* skb reference here is a bit tricky to get right, since + * shifting can eat and free both this skb and the next, + * so not even _safe variant of the loop is enough. + */ + if (in_sack <= 0) { + tmp = tcp_shift_skb_data(sk, skb, state, + start_seq, end_seq, dup_sack); + if (tmp != NULL) { + if (tmp != skb) { + skb = tmp; + continue; + } + + in_sack = 0; + } else { + in_sack = tcp_match_skb_to_sack(sk, skb, + start_seq, + end_seq); + } + } + + if (unlikely(in_sack < 0)) + break; + + if (in_sack) { + TCP_SKB_CB(skb)->sacked = + tcp_sacktag_one(sk, + state, + TCP_SKB_CB(skb)->sacked, + TCP_SKB_CB(skb)->seq, + TCP_SKB_CB(skb)->end_seq, + dup_sack, + tcp_skb_pcount(skb)); + + if (!before(TCP_SKB_CB(skb)->seq, + tcp_highest_sack_seq(tp))) + tcp_advance_highest_sack(sk, skb); + } + + state->fack_count += tcp_skb_pcount(skb); + } + return skb; +} + +/* Avoid all extra work that is being done by sacktag while walking in + * a normal way + */ +static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk, + struct tcp_sacktag_state *state, + u32 skip_to_seq) +{ + tcp_for_write_queue_from(skb, sk) { + if (skb == tcp_send_head(sk)) + break; + + if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq)) + break; + + state->fack_count += tcp_skb_pcount(skb); + } + return skb; +} + +static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb, + struct sock *sk, + struct tcp_sack_block *next_dup, + struct tcp_sacktag_state *state, + u32 skip_to_seq) +{ + if (next_dup == NULL) + return skb; + + if (before(next_dup->start_seq, skip_to_seq)) { + skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq); + skb = tcp_sacktag_walk(skb, sk, NULL, state, + next_dup->start_seq, next_dup->end_seq, + 1); + } + + return skb; +} + +static int tcp_sack_cache_ok(struct tcp_sock *tp, struct tcp_sack_block *cache) +{ + return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache); +} + +static int +tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, + u32 prior_snd_una) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + unsigned char *ptr = (skb_transport_header(ack_skb) + + TCP_SKB_CB(ack_skb)->sacked); + struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2); + struct tcp_sack_block sp[TCP_NUM_SACKS]; + struct tcp_sack_block *cache; + struct tcp_sacktag_state state; + struct sk_buff *skb; + int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3); + int used_sacks; + int found_dup_sack = 0; + int i, j; + int first_sack_index; + + state.flag = 0; + state.reord = tp->packets_out; + + if (!tp->sacked_out) { + if (WARN_ON(tp->fackets_out)) + tp->fackets_out = 0; + tcp_highest_sack_reset(sk); + } + + found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire, + num_sacks, prior_snd_una); + if (found_dup_sack) + state.flag |= FLAG_DSACKING_ACK; + + /* Eliminate too old ACKs, but take into + * account more or less fresh ones, they can + * contain valid SACK info. + */ + if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window)) + return 0; + + if (!tp->packets_out) + goto out; + + used_sacks = 0; + first_sack_index = 0; + for (i = 0; i < num_sacks; i++) { + int dup_sack = !i && found_dup_sack; + + sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq); + sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq); + + if (!tcp_is_sackblock_valid(tp, dup_sack, + sp[used_sacks].start_seq, + sp[used_sacks].end_seq)) { + int mib_idx; + + if (dup_sack) { + if (!tp->undo_marker) + mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO; + else + mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD; + } else { + /* Don't count olds caused by ACK reordering */ + if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) && + !after(sp[used_sacks].end_seq, tp->snd_una)) + continue; + mib_idx = LINUX_MIB_TCPSACKDISCARD; + } + + NET_INC_STATS_BH(sock_net(sk), mib_idx); + if (i == 0) + first_sack_index = -1; + continue; + } + + /* Ignore very old stuff early */ + if (!after(sp[used_sacks].end_seq, prior_snd_una)) + continue; + + used_sacks++; + } + + /* order SACK blocks to allow in order walk of the retrans queue */ + for (i = used_sacks - 1; i > 0; i--) { + for (j = 0; j < i; j++) { + if (after(sp[j].start_seq, sp[j + 1].start_seq)) { + swap(sp[j], sp[j + 1]); + + /* Track where the first SACK block goes to */ + if (j == first_sack_index) + first_sack_index = j + 1; + } + } + } + + skb = tcp_write_queue_head(sk); + state.fack_count = 0; + i = 0; + + if (!tp->sacked_out) { + /* It's already past, so skip checking against it */ + cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache); + } else { + cache = tp->recv_sack_cache; + /* Skip empty blocks in at head of the cache */ + while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq && + !cache->end_seq) + cache++; + } + + while (i < used_sacks) { + u32 start_seq = sp[i].start_seq; + u32 end_seq = sp[i].end_seq; + int dup_sack = (found_dup_sack && (i == first_sack_index)); + struct tcp_sack_block *next_dup = NULL; + + if (found_dup_sack && ((i + 1) == first_sack_index)) + next_dup = &sp[i + 1]; + + /* Event "B" in the comment above. */ + if (after(end_seq, tp->high_seq)) + state.flag |= FLAG_DATA_LOST; + + /* Skip too early cached blocks */ + while (tcp_sack_cache_ok(tp, cache) && + !before(start_seq, cache->end_seq)) + cache++; + + /* Can skip some work by looking recv_sack_cache? */ + if (tcp_sack_cache_ok(tp, cache) && !dup_sack && + after(end_seq, cache->start_seq)) { + + /* Head todo? */ + if (before(start_seq, cache->start_seq)) { + skb = tcp_sacktag_skip(skb, sk, &state, + start_seq); + skb = tcp_sacktag_walk(skb, sk, next_dup, + &state, + start_seq, + cache->start_seq, + dup_sack); + } + + /* Rest of the block already fully processed? */ + if (!after(end_seq, cache->end_seq)) + goto advance_sp; + + skb = tcp_maybe_skipping_dsack(skb, sk, next_dup, + &state, + cache->end_seq); + + /* ...tail remains todo... */ + if (tcp_highest_sack_seq(tp) == cache->end_seq) { + /* ...but better entrypoint exists! */ + skb = tcp_highest_sack(sk); + if (skb == NULL) + break; + state.fack_count = tp->fackets_out; + cache++; + goto walk; + } + + skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq); + /* Check overlap against next cached too (past this one already) */ + cache++; + continue; + } + + if (!before(start_seq, tcp_highest_sack_seq(tp))) { + skb = tcp_highest_sack(sk); + if (skb == NULL) + break; + state.fack_count = tp->fackets_out; + } + skb = tcp_sacktag_skip(skb, sk, &state, start_seq); + +walk: + skb = tcp_sacktag_walk(skb, sk, next_dup, &state, + start_seq, end_seq, dup_sack); + +advance_sp: + /* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct + * due to in-order walk + */ + if (after(end_seq, tp->frto_highmark)) + state.flag &= ~FLAG_ONLY_ORIG_SACKED; + + i++; + } + + /* Clear the head of the cache sack blocks so we can skip it next time */ + for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) { + tp->recv_sack_cache[i].start_seq = 0; + tp->recv_sack_cache[i].end_seq = 0; + } + for (j = 0; j < used_sacks; j++) + tp->recv_sack_cache[i++] = sp[j]; + + tcp_mark_lost_retrans(sk); + + tcp_verify_left_out(tp); + + if ((state.reord < tp->fackets_out) && + ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) && + (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark))) + tcp_update_reordering(sk, tp->fackets_out - state.reord, 0); + +out: + +#if FASTRETRANS_DEBUG > 0 + WARN_ON((int)tp->sacked_out < 0); + WARN_ON((int)tp->lost_out < 0); + WARN_ON((int)tp->retrans_out < 0); + WARN_ON((int)tcp_packets_in_flight(tp) < 0); +#endif + return state.flag; +} + +/* Limits sacked_out so that sum with lost_out isn't ever larger than + * packets_out. Returns zero if sacked_out adjustement wasn't necessary. + */ +static int tcp_limit_reno_sacked(struct tcp_sock *tp) +{ + u32 holes; + + holes = max(tp->lost_out, 1U); + holes = min(holes, tp->packets_out); + + if ((tp->sacked_out + holes) > tp->packets_out) { + tp->sacked_out = tp->packets_out - holes; + return 1; + } + return 0; +} + +/* If we receive more dupacks than we expected counting segments + * in assumption of absent reordering, interpret this as reordering. + * The only another reason could be bug in receiver TCP. + */ +static void tcp_check_reno_reordering(struct sock *sk, const int addend) +{ + struct tcp_sock *tp = tcp_sk(sk); + if (tcp_limit_reno_sacked(tp)) + tcp_update_reordering(sk, tp->packets_out + addend, 0); +} + +/* Emulate SACKs for SACKless connection: account for a new dupack. */ + +static void tcp_add_reno_sack(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + tp->sacked_out++; + tcp_check_reno_reordering(sk, 0); + tcp_verify_left_out(tp); +} + +/* Account for ACK, ACKing some data in Reno Recovery phase. */ + +static void tcp_remove_reno_sacks(struct sock *sk, int acked) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (acked > 0) { + /* One ACK acked hole. The rest eat duplicate ACKs. */ + if (acked - 1 >= tp->sacked_out) + tp->sacked_out = 0; + else + tp->sacked_out -= acked - 1; + } + tcp_check_reno_reordering(sk, acked); + tcp_verify_left_out(tp); +} + +static inline void tcp_reset_reno_sack(struct tcp_sock *tp) +{ + tp->sacked_out = 0; +} + +static int tcp_is_sackfrto(const struct tcp_sock *tp) +{ + return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp); +} + +/* F-RTO can only be used if TCP has never retransmitted anything other than + * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here) + */ +int tcp_use_frto(struct sock *sk) +{ + const struct tcp_sock *tp = tcp_sk(sk); + const struct inet_connection_sock *icsk = inet_csk(sk); + struct sk_buff *skb; + + if (!sysctl_tcp_frto) + return 0; + + /* MTU probe and F-RTO won't really play nicely along currently */ + if (icsk->icsk_mtup.probe_size) + return 0; + + if (tcp_is_sackfrto(tp)) + return 1; + + /* Avoid expensive walking of rexmit queue if possible */ + if (tp->retrans_out > 1) + return 0; + + skb = tcp_write_queue_head(sk); + if (tcp_skb_is_last(sk, skb)) + return 1; + skb = tcp_write_queue_next(sk, skb); /* Skips head */ + tcp_for_write_queue_from(skb, sk) { + if (skb == tcp_send_head(sk)) + break; + if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) + return 0; + /* Short-circuit when first non-SACKed skb has been checked */ + if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) + break; + } + return 1; +} + +/* RTO occurred, but do not yet enter Loss state. Instead, defer RTO + * recovery a bit and use heuristics in tcp_process_frto() to detect if + * the RTO was spurious. Only clear SACKED_RETRANS of the head here to + * keep retrans_out counting accurate (with SACK F-RTO, other than head + * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS + * bits are handled if the Loss state is really to be entered (in + * tcp_enter_frto_loss). + * + * Do like tcp_enter_loss() would; when RTO expires the second time it + * does: + * "Reduce ssthresh if it has not yet been made inside this window." + */ +void tcp_enter_frto(struct sock *sk) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + + if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) || + tp->snd_una == tp->high_seq || + ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) && + !icsk->icsk_retransmits)) { + tp->prior_ssthresh = tcp_current_ssthresh(sk); + /* Our state is too optimistic in ssthresh() call because cwnd + * is not reduced until tcp_enter_frto_loss() when previous F-RTO + * recovery has not yet completed. Pattern would be this: RTO, + * Cumulative ACK, RTO (2xRTO for the same segment does not end + * up here twice). + * RFC4138 should be more specific on what to do, even though + * RTO is quite unlikely to occur after the first Cumulative ACK + * due to back-off and complexity of triggering events ... + */ + if (tp->frto_counter) { + u32 stored_cwnd; + stored_cwnd = tp->snd_cwnd; + tp->snd_cwnd = 2; + tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); + tp->snd_cwnd = stored_cwnd; + } else { + tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); + } + /* ... in theory, cong.control module could do "any tricks" in + * ssthresh(), which means that ca_state, lost bits and lost_out + * counter would have to be faked before the call occurs. We + * consider that too expensive, unlikely and hacky, so modules + * using these in ssthresh() must deal these incompatibility + * issues if they receives CA_EVENT_FRTO and frto_counter != 0 + */ + tcp_ca_event(sk, CA_EVENT_FRTO); + } + + tp->undo_marker = tp->snd_una; + tp->undo_retrans = 0; + + skb = tcp_write_queue_head(sk); + if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) + tp->undo_marker = 0; + if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) { + TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; + tp->retrans_out -= tcp_skb_pcount(skb); + } + tcp_verify_left_out(tp); + + /* Too bad if TCP was application limited */ + tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1); + + /* Earlier loss recovery underway (see RFC4138; Appendix B). + * The last condition is necessary at least in tp->frto_counter case. + */ + if (tcp_is_sackfrto(tp) && (tp->frto_counter || + ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) && + after(tp->high_seq, tp->snd_una)) { + tp->frto_highmark = tp->high_seq; + } else { + tp->frto_highmark = tp->snd_nxt; + } + tcp_set_ca_state(sk, TCP_CA_Disorder); + tp->high_seq = tp->snd_nxt; + tp->frto_counter = 1; +} + +/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO, + * which indicates that we should follow the traditional RTO recovery, + * i.e. mark everything lost and do go-back-N retransmission. + */ +static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + + tp->lost_out = 0; + tp->retrans_out = 0; + if (tcp_is_reno(tp)) + tcp_reset_reno_sack(tp); + + tcp_for_write_queue(skb, sk) { + if (skb == tcp_send_head(sk)) + break; + + TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; + /* + * Count the retransmission made on RTO correctly (only when + * waiting for the first ACK and did not get it)... + */ + if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) { + /* For some reason this R-bit might get cleared? */ + if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) + tp->retrans_out += tcp_skb_pcount(skb); + /* ...enter this if branch just for the first segment */ + flag |= FLAG_DATA_ACKED; + } else { + if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) + tp->undo_marker = 0; + TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; + } + + /* Marking forward transmissions that were made after RTO lost + * can cause unnecessary retransmissions in some scenarios, + * SACK blocks will mitigate that in some but not in all cases. + * We used to not mark them but it was causing break-ups with + * receivers that do only in-order receival. + * + * TODO: we could detect presence of such receiver and select + * different behavior per flow. + */ + if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) { + TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; + tp->lost_out += tcp_skb_pcount(skb); + tp->retransmit_high = TCP_SKB_CB(skb)->end_seq; + } + } + tcp_verify_left_out(tp); + + tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments; + tp->snd_cwnd_cnt = 0; + tp->snd_cwnd_stamp = tcp_time_stamp; + tp->frto_counter = 0; + tp->bytes_acked = 0; + + tp->reordering = min_t(unsigned int, tp->reordering, + sysctl_tcp_reordering); + tcp_set_ca_state(sk, TCP_CA_Loss); + tp->high_seq = tp->snd_nxt; + TCP_ECN_queue_cwr(tp); + + tcp_clear_all_retrans_hints(tp); +} + +static void tcp_clear_retrans_partial(struct tcp_sock *tp) +{ + tp->retrans_out = 0; + tp->lost_out = 0; + + tp->undo_marker = 0; + tp->undo_retrans = 0; +} + +void tcp_clear_retrans(struct tcp_sock *tp) +{ + tcp_clear_retrans_partial(tp); + + tp->fackets_out = 0; + tp->sacked_out = 0; +} + +/* Enter Loss state. If "how" is not zero, forget all SACK information + * and reset tags completely, otherwise preserve SACKs. If receiver + * dropped its ofo queue, we will know this due to reneging detection. + */ +void tcp_enter_loss(struct sock *sk, int how) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + + /* Reduce ssthresh if it has not yet been made inside this window. */ + if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq || + (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) { + tp->prior_ssthresh = tcp_current_ssthresh(sk); + tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); + tcp_ca_event(sk, CA_EVENT_LOSS); + } + tp->snd_cwnd = 1; + tp->snd_cwnd_cnt = 0; + tp->snd_cwnd_stamp = tcp_time_stamp; + + tp->bytes_acked = 0; + tcp_clear_retrans_partial(tp); + + if (tcp_is_reno(tp)) + tcp_reset_reno_sack(tp); + + if (!how) { + /* Push undo marker, if it was plain RTO and nothing + * was retransmitted. */ + tp->undo_marker = tp->snd_una; + } else { + tp->sacked_out = 0; + tp->fackets_out = 0; + } + tcp_clear_all_retrans_hints(tp); + + tcp_for_write_queue(skb, sk) { + if (skb == tcp_send_head(sk)) + break; + + if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) + tp->undo_marker = 0; + TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED; + if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) { + TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED; + TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; + tp->lost_out += tcp_skb_pcount(skb); + tp->retransmit_high = TCP_SKB_CB(skb)->end_seq; + } + } + tcp_verify_left_out(tp); + + tp->reordering = min_t(unsigned int, tp->reordering, + sysctl_tcp_reordering); + tcp_set_ca_state(sk, TCP_CA_Loss); + tp->high_seq = tp->snd_nxt; + TCP_ECN_queue_cwr(tp); + /* Abort F-RTO algorithm if one is in progress */ + tp->frto_counter = 0; +} + +/* If ACK arrived pointing to a remembered SACK, it means that our + * remembered SACKs do not reflect real state of receiver i.e. + * receiver _host_ is heavily congested (or buggy). + * + * Do processing similar to RTO timeout. + */ +static int tcp_check_sack_reneging(struct sock *sk, int flag) +{ + if (flag & FLAG_SACK_RENEGING) { + struct inet_connection_sock *icsk = inet_csk(sk); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING); + + tcp_enter_loss(sk, 1); + icsk->icsk_retransmits++; + tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); + inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, + icsk->icsk_rto, TCP_RTO_MAX); + return 1; + } + return 0; +} + +static inline int tcp_fackets_out(struct tcp_sock *tp) +{ + return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out; +} + +/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs + * counter when SACK is enabled (without SACK, sacked_out is used for + * that purpose). + * + * Instead, with FACK TCP uses fackets_out that includes both SACKed + * segments up to the highest received SACK block so far and holes in + * between them. + * + * With reordering, holes may still be in flight, so RFC3517 recovery + * uses pure sacked_out (total number of SACKed segments) even though + * it violates the RFC that uses duplicate ACKs, often these are equal + * but when e.g. out-of-window ACKs or packet duplication occurs, + * they differ. Since neither occurs due to loss, TCP should really + * ignore them. + */ +static inline int tcp_dupack_heuristics(struct tcp_sock *tp) +{ + return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1; +} + +static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb) +{ + return tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto; +} + +static inline int tcp_head_timedout(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + return tp->packets_out && + tcp_skb_timedout(sk, tcp_write_queue_head(sk)); +} + +/* Linux NewReno/SACK/FACK/ECN state machine. + * -------------------------------------- + * + * "Open" Normal state, no dubious events, fast path. + * "Disorder" In all the respects it is "Open", + * but requires a bit more attention. It is entered when + * we see some SACKs or dupacks. It is split of "Open" + * mainly to move some processing from fast path to slow one. + * "CWR" CWND was reduced due to some Congestion Notification event. + * It can be ECN, ICMP source quench, local device congestion. + * "Recovery" CWND was reduced, we are fast-retransmitting. + * "Loss" CWND was reduced due to RTO timeout or SACK reneging. + * + * tcp_fastretrans_alert() is entered: + * - each incoming ACK, if state is not "Open" + * - when arrived ACK is unusual, namely: + * * SACK + * * Duplicate ACK. + * * ECN ECE. + * + * Counting packets in flight is pretty simple. + * + * in_flight = packets_out - left_out + retrans_out + * + * packets_out is SND.NXT-SND.UNA counted in packets. + * + * retrans_out is number of retransmitted segments. + * + * left_out is number of segments left network, but not ACKed yet. + * + * left_out = sacked_out + lost_out + * + * sacked_out: Packets, which arrived to receiver out of order + * and hence not ACKed. With SACKs this number is simply + * amount of SACKed data. Even without SACKs + * it is easy to give pretty reliable estimate of this number, + * counting duplicate ACKs. + * + * lost_out: Packets lost by network. TCP has no explicit + * "loss notification" feedback from network (for now). + * It means that this number can be only _guessed_. + * Actually, it is the heuristics to predict lossage that + * distinguishes different algorithms. + * + * F.e. after RTO, when all the queue is considered as lost, + * lost_out = packets_out and in_flight = retrans_out. + * + * Essentially, we have now two algorithms counting + * lost packets. + * + * FACK: It is the simplest heuristics. As soon as we decided + * that something is lost, we decide that _all_ not SACKed + * packets until the most forward SACK are lost. I.e. + * lost_out = fackets_out - sacked_out and left_out = fackets_out. + * It is absolutely correct estimate, if network does not reorder + * packets. And it loses any connection to reality when reordering + * takes place. We use FACK by default until reordering + * is suspected on the path to this destination. + * + * NewReno: when Recovery is entered, we assume that one segment + * is lost (classic Reno). While we are in Recovery and + * a partial ACK arrives, we assume that one more packet + * is lost (NewReno). This heuristics are the same in NewReno + * and SACK. + * + * Imagine, that's all! Forget about all this shamanism about CWND inflation + * deflation etc. CWND is real congestion window, never inflated, changes + * only according to classic VJ rules. + * + * Really tricky (and requiring careful tuning) part of algorithm + * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue(). + * The first determines the moment _when_ we should reduce CWND and, + * hence, slow down forward transmission. In fact, it determines the moment + * when we decide that hole is caused by loss, rather than by a reorder. + * + * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill + * holes, caused by lost packets. + * + * And the most logically complicated part of algorithm is undo + * heuristics. We detect false retransmits due to both too early + * fast retransmit (reordering) and underestimated RTO, analyzing + * timestamps and D-SACKs. When we detect that some segments were + * retransmitted by mistake and CWND reduction was wrong, we undo + * window reduction and abort recovery phase. This logic is hidden + * inside several functions named tcp_try_undo_<something>. + */ + +/* This function decides, when we should leave Disordered state + * and enter Recovery phase, reducing congestion window. + * + * Main question: may we further continue forward transmission + * with the same cwnd? + */ +static int tcp_time_to_recover(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + __u32 packets_out; + + /* Do not perform any recovery during F-RTO algorithm */ + if (tp->frto_counter) + return 0; + + /* Trick#1: The loss is proven. */ + if (tp->lost_out) + return 1; + + /* Not-A-Trick#2 : Classic rule... */ + if (tcp_dupack_heuristics(tp) > tp->reordering) + return 1; + + /* Trick#3 : when we use RFC2988 timer restart, fast + * retransmit can be triggered by timeout of queue head. + */ + if (tcp_is_fack(tp) && tcp_head_timedout(sk)) + return 1; + + /* Trick#4: It is still not OK... But will it be useful to delay + * recovery more? + */ + packets_out = tp->packets_out; + if (packets_out <= tp->reordering && + tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) && + !tcp_may_send_now(sk)) { + /* We have nothing to send. This connection is limited + * either by receiver window or by application. + */ + return 1; + } + + /* If a thin stream is detected, retransmit after first + * received dupack. Employ only if SACK is supported in order + * to avoid possible corner-case series of spurious retransmissions + * Use only if there are no unsent data. + */ + if ((tp->thin_dupack || sysctl_tcp_thin_dupack) && + tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 && + tcp_is_sack(tp) && !tcp_send_head(sk)) + return 1; + + return 0; +} + +/* New heuristics: it is possible only after we switched to restart timer + * each time when something is ACKed. Hence, we can detect timed out packets + * during fast retransmit without falling to slow start. + * + * Usefulness of this as is very questionable, since we should know which of + * the segments is the next to timeout which is relatively expensive to find + * in general case unless we add some data structure just for that. The + * current approach certainly won't find the right one too often and when it + * finally does find _something_ it usually marks large part of the window + * right away (because a retransmission with a larger timestamp blocks the + * loop from advancing). -ij + */ +static void tcp_timeout_skbs(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + + if (!tcp_is_fack(tp) || !tcp_head_timedout(sk)) + return; + + skb = tp->scoreboard_skb_hint; + if (tp->scoreboard_skb_hint == NULL) + skb = tcp_write_queue_head(sk); + + tcp_for_write_queue_from(skb, sk) { + if (skb == tcp_send_head(sk)) + break; + if (!tcp_skb_timedout(sk, skb)) + break; + + tcp_skb_mark_lost(tp, skb); + } + + tp->scoreboard_skb_hint = skb; + + tcp_verify_left_out(tp); +} + +/* Mark head of queue up as lost. With RFC3517 SACK, the packets is + * is against sacked "cnt", otherwise it's against facked "cnt" + */ +static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + int cnt, oldcnt; + int err; + unsigned int mss; + + WARN_ON(packets > tp->packets_out); + if (tp->lost_skb_hint) { + skb = tp->lost_skb_hint; + cnt = tp->lost_cnt_hint; + /* Head already handled? */ + if (mark_head && skb != tcp_write_queue_head(sk)) + return; + } else { + skb = tcp_write_queue_head(sk); + cnt = 0; + } + + tcp_for_write_queue_from(skb, sk) { + if (skb == tcp_send_head(sk)) + break; + /* TODO: do this better */ + /* this is not the most efficient way to do this... */ + tp->lost_skb_hint = skb; + tp->lost_cnt_hint = cnt; + + if (after(TCP_SKB_CB(skb)->end_seq, tp->high_seq)) + break; + + oldcnt = cnt; + if (tcp_is_fack(tp) || tcp_is_reno(tp) || + (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) + cnt += tcp_skb_pcount(skb); + + if (cnt > packets) { + if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) || + (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) || + (oldcnt >= packets)) + break; + + mss = skb_shinfo(skb)->gso_size; + err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss); + if (err < 0) + break; + cnt = packets; + } + + tcp_skb_mark_lost(tp, skb); + + if (mark_head) + break; + } + tcp_verify_left_out(tp); +} + +/* Account newly detected lost packet(s) */ + +static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tcp_is_reno(tp)) { + tcp_mark_head_lost(sk, 1, 1); + } else if (tcp_is_fack(tp)) { + int lost = tp->fackets_out - tp->reordering; + if (lost <= 0) + lost = 1; + tcp_mark_head_lost(sk, lost, 0); + } else { + int sacked_upto = tp->sacked_out - tp->reordering; + if (sacked_upto >= 0) + tcp_mark_head_lost(sk, sacked_upto, 0); + else if (fast_rexmit) + tcp_mark_head_lost(sk, 1, 1); + } + + tcp_timeout_skbs(sk); +} + +/* CWND moderation, preventing bursts due to too big ACKs + * in dubious situations. + */ +static inline void tcp_moderate_cwnd(struct tcp_sock *tp) +{ + tp->snd_cwnd = min(tp->snd_cwnd, + tcp_packets_in_flight(tp) + tcp_max_burst(tp)); + tp->snd_cwnd_stamp = tcp_time_stamp; +} + +/* Lower bound on congestion window is slow start threshold + * unless congestion avoidance choice decides to overide it. + */ +static inline u32 tcp_cwnd_min(const struct sock *sk) +{ + const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops; + + return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh; +} + +/* Decrease cwnd each second ack. */ +static void tcp_cwnd_down(struct sock *sk, int flag) +{ + struct tcp_sock *tp = tcp_sk(sk); + int decr = tp->snd_cwnd_cnt + 1; + + if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) || + (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) { + tp->snd_cwnd_cnt = decr & 1; + decr >>= 1; + + if (decr && tp->snd_cwnd > tcp_cwnd_min(sk)) + tp->snd_cwnd -= decr; + + tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1); + tp->snd_cwnd_stamp = tcp_time_stamp; + } +} + +/* Nothing was retransmitted or returned timestamp is less + * than timestamp of the first retransmission. + */ +static inline int tcp_packet_delayed(struct tcp_sock *tp) +{ + return !tp->retrans_stamp || + (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && + before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp)); +} + +/* Undo procedures. */ + +#if FASTRETRANS_DEBUG > 1 +static void DBGUNDO(struct sock *sk, const char *msg) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_sock *inet = inet_sk(sk); + + if (sk->sk_family == AF_INET) { + printk(KERN_DEBUG "Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n", + msg, + &inet->inet_daddr, ntohs(inet->inet_dport), + tp->snd_cwnd, tcp_left_out(tp), + tp->snd_ssthresh, tp->prior_ssthresh, + tp->packets_out); + } +#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) + else if (sk->sk_family == AF_INET6) { + struct ipv6_pinfo *np = inet6_sk(sk); + printk(KERN_DEBUG "Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n", + msg, + &np->daddr, ntohs(inet->inet_dport), + tp->snd_cwnd, tcp_left_out(tp), + tp->snd_ssthresh, tp->prior_ssthresh, + tp->packets_out); + } +#endif +} +#else +#define DBGUNDO(x...) do { } while (0) +#endif + +static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tp->prior_ssthresh) { + const struct inet_connection_sock *icsk = inet_csk(sk); + + if (icsk->icsk_ca_ops->undo_cwnd) + tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk); + else + tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1); + + if (undo_ssthresh && tp->prior_ssthresh > tp->snd_ssthresh) { + tp->snd_ssthresh = tp->prior_ssthresh; + TCP_ECN_withdraw_cwr(tp); + } + } else { + tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh); + } + tp->snd_cwnd_stamp = tcp_time_stamp; +} + +static inline int tcp_may_undo(struct tcp_sock *tp) +{ + return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp)); +} + +/* People celebrate: "We love our President!" */ +static int tcp_try_undo_recovery(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tcp_may_undo(tp)) { + int mib_idx; + + /* Happy end! We did not retransmit anything + * or our original transmission succeeded. + */ + DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans"); + tcp_undo_cwr(sk, true); + if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss) + mib_idx = LINUX_MIB_TCPLOSSUNDO; + else + mib_idx = LINUX_MIB_TCPFULLUNDO; + + NET_INC_STATS_BH(sock_net(sk), mib_idx); + tp->undo_marker = 0; + } + if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) { + /* Hold old state until something *above* high_seq + * is ACKed. For Reno it is MUST to prevent false + * fast retransmits (RFC2582). SACK TCP is safe. */ + tcp_moderate_cwnd(tp); + return 1; + } + tcp_set_ca_state(sk, TCP_CA_Open); + return 0; +} + +/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */ +static void tcp_try_undo_dsack(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tp->undo_marker && !tp->undo_retrans) { + DBGUNDO(sk, "D-SACK"); + tcp_undo_cwr(sk, true); + tp->undo_marker = 0; + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO); + } +} + +/* We can clear retrans_stamp when there are no retransmissions in the + * window. It would seem that it is trivially available for us in + * tp->retrans_out, however, that kind of assumptions doesn't consider + * what will happen if errors occur when sending retransmission for the + * second time. ...It could the that such segment has only + * TCPCB_EVER_RETRANS set at the present time. It seems that checking + * the head skb is enough except for some reneging corner cases that + * are not worth the effort. + * + * Main reason for all this complexity is the fact that connection dying + * time now depends on the validity of the retrans_stamp, in particular, + * that successive retransmissions of a segment must not advance + * retrans_stamp under any conditions. + */ +static int tcp_any_retrans_done(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + + if (tp->retrans_out) + return 1; + + skb = tcp_write_queue_head(sk); + if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS)) + return 1; + + return 0; +} + +/* Undo during fast recovery after partial ACK. */ + +static int tcp_try_undo_partial(struct sock *sk, int acked) +{ + struct tcp_sock *tp = tcp_sk(sk); + /* Partial ACK arrived. Force Hoe's retransmit. */ + int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering); + + if (tcp_may_undo(tp)) { + /* Plain luck! Hole if filled with delayed + * packet, rather than with a retransmit. + */ + if (!tcp_any_retrans_done(sk)) + tp->retrans_stamp = 0; + + tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1); + + DBGUNDO(sk, "Hoe"); + tcp_undo_cwr(sk, false); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO); + + /* So... Do not make Hoe's retransmit yet. + * If the first packet was delayed, the rest + * ones are most probably delayed as well. + */ + failed = 0; + } + return failed; +} + +/* Undo during loss recovery after partial ACK. */ +static int tcp_try_undo_loss(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tcp_may_undo(tp)) { + struct sk_buff *skb; + tcp_for_write_queue(skb, sk) { + if (skb == tcp_send_head(sk)) + break; + TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; + } + + tcp_clear_all_retrans_hints(tp); + + DBGUNDO(sk, "partial loss"); + tp->lost_out = 0; + tcp_undo_cwr(sk, true); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO); + inet_csk(sk)->icsk_retransmits = 0; + tp->undo_marker = 0; + if (tcp_is_sack(tp)) + tcp_set_ca_state(sk, TCP_CA_Open); + return 1; + } + return 0; +} + +static inline void tcp_complete_cwr(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + /* Do not moderate cwnd if it's already undone in cwr or recovery */ + if (tp->undo_marker && tp->snd_cwnd > tp->snd_ssthresh) { + tp->snd_cwnd = tp->snd_ssthresh; + tp->snd_cwnd_stamp = tcp_time_stamp; + } + tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR); +} + +static void tcp_try_keep_open(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + int state = TCP_CA_Open; + + if (tcp_left_out(tp) || tcp_any_retrans_done(sk) || tp->undo_marker) + state = TCP_CA_Disorder; + + if (inet_csk(sk)->icsk_ca_state != state) { + tcp_set_ca_state(sk, state); + tp->high_seq = tp->snd_nxt; + } +} + +static void tcp_try_to_open(struct sock *sk, int flag) +{ + struct tcp_sock *tp = tcp_sk(sk); + + tcp_verify_left_out(tp); + + if (!tp->frto_counter && !tcp_any_retrans_done(sk)) + tp->retrans_stamp = 0; + + if (flag & FLAG_ECE) + tcp_enter_cwr(sk, 1); + + if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) { + tcp_try_keep_open(sk); + tcp_moderate_cwnd(tp); + } else { + tcp_cwnd_down(sk, flag); + } +} + +static void tcp_mtup_probe_failed(struct sock *sk) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + + icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1; + icsk->icsk_mtup.probe_size = 0; +} + +static void tcp_mtup_probe_success(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + + /* FIXME: breaks with very large cwnd */ + tp->prior_ssthresh = tcp_current_ssthresh(sk); + tp->snd_cwnd = tp->snd_cwnd * + tcp_mss_to_mtu(sk, tp->mss_cache) / + icsk->icsk_mtup.probe_size; + tp->snd_cwnd_cnt = 0; + tp->snd_cwnd_stamp = tcp_time_stamp; + tp->snd_ssthresh = tcp_current_ssthresh(sk); + + icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size; + icsk->icsk_mtup.probe_size = 0; + tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); +} + +/* Do a simple retransmit without using the backoff mechanisms in + * tcp_timer. This is used for path mtu discovery. + * The socket is already locked here. + */ +void tcp_simple_retransmit(struct sock *sk) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + unsigned int mss = tcp_current_mss(sk); + u32 prior_lost = tp->lost_out; + + tcp_for_write_queue(skb, sk) { + if (skb == tcp_send_head(sk)) + break; + if (tcp_skb_seglen(skb) > mss && + !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) { + if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) { + TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; + tp->retrans_out -= tcp_skb_pcount(skb); + } + tcp_skb_mark_lost_uncond_verify(tp, skb); + } + } + + tcp_clear_retrans_hints_partial(tp); + + if (prior_lost == tp->lost_out) + return; + + if (tcp_is_reno(tp)) + tcp_limit_reno_sacked(tp); + + tcp_verify_left_out(tp); + + /* Don't muck with the congestion window here. + * Reason is that we do not increase amount of _data_ + * in network, but units changed and effective + * cwnd/ssthresh really reduced now. + */ + if (icsk->icsk_ca_state != TCP_CA_Loss) { + tp->high_seq = tp->snd_nxt; + tp->snd_ssthresh = tcp_current_ssthresh(sk); + tp->prior_ssthresh = 0; + tp->undo_marker = 0; + tcp_set_ca_state(sk, TCP_CA_Loss); + } + tcp_xmit_retransmit_queue(sk); +} +EXPORT_SYMBOL(tcp_simple_retransmit); + +/* Process an event, which can update packets-in-flight not trivially. + * Main goal of this function is to calculate new estimate for left_out, + * taking into account both packets sitting in receiver's buffer and + * packets lost by network. + * + * Besides that it does CWND reduction, when packet loss is detected + * and changes state of machine. + * + * It does _not_ decide what to send, it is made in function + * tcp_xmit_retransmit_queue(). + */ +static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + int is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP)); + int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) && + (tcp_fackets_out(tp) > tp->reordering)); + int fast_rexmit = 0, mib_idx; + + if (WARN_ON(!tp->packets_out && tp->sacked_out)) + tp->sacked_out = 0; + if (WARN_ON(!tp->sacked_out && tp->fackets_out)) + tp->fackets_out = 0; + + /* Now state machine starts. + * A. ECE, hence prohibit cwnd undoing, the reduction is required. */ + if (flag & FLAG_ECE) + tp->prior_ssthresh = 0; + + /* B. In all the states check for reneging SACKs. */ + if (tcp_check_sack_reneging(sk, flag)) + return; + + /* C. Process data loss notification, provided it is valid. */ + if (tcp_is_fack(tp) && (flag & FLAG_DATA_LOST) && + before(tp->snd_una, tp->high_seq) && + icsk->icsk_ca_state != TCP_CA_Open && + tp->fackets_out > tp->reordering) { + tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering, 0); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSS); + } + + /* D. Check consistency of the current state. */ + tcp_verify_left_out(tp); + + /* E. Check state exit conditions. State can be terminated + * when high_seq is ACKed. */ + if (icsk->icsk_ca_state == TCP_CA_Open) { + WARN_ON(tp->retrans_out != 0); + tp->retrans_stamp = 0; + } else if (!before(tp->snd_una, tp->high_seq)) { + switch (icsk->icsk_ca_state) { + case TCP_CA_Loss: + icsk->icsk_retransmits = 0; + if (tcp_try_undo_recovery(sk)) + return; + break; + + case TCP_CA_CWR: + /* CWR is to be held something *above* high_seq + * is ACKed for CWR bit to reach receiver. */ + if (tp->snd_una != tp->high_seq) { + tcp_complete_cwr(sk); + tcp_set_ca_state(sk, TCP_CA_Open); + } + break; + + case TCP_CA_Disorder: + tcp_try_undo_dsack(sk); + if (!tp->undo_marker || + /* For SACK case do not Open to allow to undo + * catching for all duplicate ACKs. */ + tcp_is_reno(tp) || tp->snd_una != tp->high_seq) { + tp->undo_marker = 0; + tcp_set_ca_state(sk, TCP_CA_Open); + } + break; + + case TCP_CA_Recovery: + if (tcp_is_reno(tp)) + tcp_reset_reno_sack(tp); + if (tcp_try_undo_recovery(sk)) + return; + tcp_complete_cwr(sk); + break; + } + } + + /* F. Process state. */ + switch (icsk->icsk_ca_state) { + case TCP_CA_Recovery: + if (!(flag & FLAG_SND_UNA_ADVANCED)) { + if (tcp_is_reno(tp) && is_dupack) + tcp_add_reno_sack(sk); + } else + do_lost = tcp_try_undo_partial(sk, pkts_acked); + break; + case TCP_CA_Loss: + if (flag & FLAG_DATA_ACKED) + icsk->icsk_retransmits = 0; + if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED) + tcp_reset_reno_sack(tp); + if (!tcp_try_undo_loss(sk)) { + tcp_moderate_cwnd(tp); + tcp_xmit_retransmit_queue(sk); + return; + } + if (icsk->icsk_ca_state != TCP_CA_Open) + return; + /* Loss is undone; fall through to processing in Open state. */ + default: + if (tcp_is_reno(tp)) { + if (flag & FLAG_SND_UNA_ADVANCED) + tcp_reset_reno_sack(tp); + if (is_dupack) + tcp_add_reno_sack(sk); + } + + if (icsk->icsk_ca_state == TCP_CA_Disorder) + tcp_try_undo_dsack(sk); + + if (!tcp_time_to_recover(sk)) { + tcp_try_to_open(sk, flag); + return; + } + + /* MTU probe failure: don't reduce cwnd */ + if (icsk->icsk_ca_state < TCP_CA_CWR && + icsk->icsk_mtup.probe_size && + tp->snd_una == tp->mtu_probe.probe_seq_start) { + tcp_mtup_probe_failed(sk); + /* Restores the reduction we did in tcp_mtup_probe() */ + tp->snd_cwnd++; + tcp_simple_retransmit(sk); + return; + } + + /* Otherwise enter Recovery state */ + + if (tcp_is_reno(tp)) + mib_idx = LINUX_MIB_TCPRENORECOVERY; + else + mib_idx = LINUX_MIB_TCPSACKRECOVERY; + + NET_INC_STATS_BH(sock_net(sk), mib_idx); + + tp->high_seq = tp->snd_nxt; + tp->prior_ssthresh = 0; + tp->undo_marker = tp->snd_una; + tp->undo_retrans = tp->retrans_out; + + if (icsk->icsk_ca_state < TCP_CA_CWR) { + if (!(flag & FLAG_ECE)) + tp->prior_ssthresh = tcp_current_ssthresh(sk); + tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); + TCP_ECN_queue_cwr(tp); + } + + tp->bytes_acked = 0; + tp->snd_cwnd_cnt = 0; + tcp_set_ca_state(sk, TCP_CA_Recovery); + fast_rexmit = 1; + } + + if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk))) + tcp_update_scoreboard(sk, fast_rexmit); + tcp_cwnd_down(sk, flag); + tcp_xmit_retransmit_queue(sk); +} + +static void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt) +{ + tcp_rtt_estimator(sk, seq_rtt); + tcp_set_rto(sk); + inet_csk(sk)->icsk_backoff = 0; +} + +/* Read draft-ietf-tcplw-high-performance before mucking + * with this code. (Supersedes RFC1323) + */ +static void tcp_ack_saw_tstamp(struct sock *sk, int flag) +{ + /* RTTM Rule: A TSecr value received in a segment is used to + * update the averaged RTT measurement only if the segment + * acknowledges some new data, i.e., only if it advances the + * left edge of the send window. + * + * See draft-ietf-tcplw-high-performance-00, section 3.3. + * 1998/04/10 Andrey V. Savochkin <saw@msu.ru> + * + * Changed: reset backoff as soon as we see the first valid sample. + * If we do not, we get strongly overestimated rto. With timestamps + * samples are accepted even from very old segments: f.e., when rtt=1 + * increases to 8, we retransmit 5 times and after 8 seconds delayed + * answer arrives rto becomes 120 seconds! If at least one of segments + * in window is lost... Voila. --ANK (010210) + */ + struct tcp_sock *tp = tcp_sk(sk); + + tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr); +} + +static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag) +{ + /* We don't have a timestamp. Can only use + * packets that are not retransmitted to determine + * rtt estimates. Also, we must not reset the + * backoff for rto until we get a non-retransmitted + * packet. This allows us to deal with a situation + * where the network delay has increased suddenly. + * I.e. Karn's algorithm. (SIGCOMM '87, p5.) + */ + + if (flag & FLAG_RETRANS_DATA_ACKED) + return; + + tcp_valid_rtt_meas(sk, seq_rtt); +} + +static inline void tcp_ack_update_rtt(struct sock *sk, const int flag, + const s32 seq_rtt) +{ + const struct tcp_sock *tp = tcp_sk(sk); + /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */ + if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) + tcp_ack_saw_tstamp(sk, flag); + else if (seq_rtt >= 0) + tcp_ack_no_tstamp(sk, seq_rtt, flag); +} + +static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight); + tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp; +} + +/* Restart timer after forward progress on connection. + * RFC2988 recommends to restart timer to now+rto. + */ +static void tcp_rearm_rto(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (!tp->packets_out) { + inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS); + } else { + inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, + inet_csk(sk)->icsk_rto, TCP_RTO_MAX); + } +} + +/* If we get here, the whole TSO packet has not been acked. */ +static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 packets_acked; + + BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)); + + packets_acked = tcp_skb_pcount(skb); + if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) + return 0; + packets_acked -= tcp_skb_pcount(skb); + + if (packets_acked) { + BUG_ON(tcp_skb_pcount(skb) == 0); + BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)); + } + + return packets_acked; +} + +/* Remove acknowledged frames from the retransmission queue. If our packet + * is before the ack sequence we can discard it as it's confirmed to have + * arrived at the other end. + */ +static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets, + u32 prior_snd_una) +{ + struct tcp_sock *tp = tcp_sk(sk); + const struct inet_connection_sock *icsk = inet_csk(sk); + struct sk_buff *skb; + u32 now = tcp_time_stamp; + int fully_acked = 1; + int flag = 0; + u32 pkts_acked = 0; + u32 reord = tp->packets_out; + u32 prior_sacked = tp->sacked_out; + s32 seq_rtt = -1; + s32 ca_seq_rtt = -1; + ktime_t last_ackt = net_invalid_timestamp(); + + while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) { + struct tcp_skb_cb *scb = TCP_SKB_CB(skb); + u32 acked_pcount; + u8 sacked = scb->sacked; + + /* Determine how many packets and what bytes were acked, tso and else */ + if (after(scb->end_seq, tp->snd_una)) { + if (tcp_skb_pcount(skb) == 1 || + !after(tp->snd_una, scb->seq)) + break; + + acked_pcount = tcp_tso_acked(sk, skb); + if (!acked_pcount) + break; + + fully_acked = 0; + } else { + acked_pcount = tcp_skb_pcount(skb); + } + + if (sacked & TCPCB_RETRANS) { + if (sacked & TCPCB_SACKED_RETRANS) + tp->retrans_out -= acked_pcount; + flag |= FLAG_RETRANS_DATA_ACKED; + ca_seq_rtt = -1; + seq_rtt = -1; + if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1)) + flag |= FLAG_NONHEAD_RETRANS_ACKED; + } else { + ca_seq_rtt = now - scb->when; + last_ackt = skb->tstamp; + if (seq_rtt < 0) { + seq_rtt = ca_seq_rtt; + } + if (!(sacked & TCPCB_SACKED_ACKED)) + reord = min(pkts_acked, reord); + } + + if (sacked & TCPCB_SACKED_ACKED) + tp->sacked_out -= acked_pcount; + if (sacked & TCPCB_LOST) + tp->lost_out -= acked_pcount; + + tp->packets_out -= acked_pcount; + pkts_acked += acked_pcount; + + /* Initial outgoing SYN's get put onto the write_queue + * just like anything else we transmit. It is not + * true data, and if we misinform our callers that + * this ACK acks real data, we will erroneously exit + * connection startup slow start one packet too + * quickly. This is severely frowned upon behavior. + */ + if (!(scb->flags & TCPHDR_SYN)) { + flag |= FLAG_DATA_ACKED; + } else { + flag |= FLAG_SYN_ACKED; + tp->retrans_stamp = 0; + } + + if (!fully_acked) + break; + + tcp_unlink_write_queue(skb, sk); + sk_wmem_free_skb(sk, skb); + tp->scoreboard_skb_hint = NULL; + if (skb == tp->retransmit_skb_hint) + tp->retransmit_skb_hint = NULL; + if (skb == tp->lost_skb_hint) + tp->lost_skb_hint = NULL; + } + + if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una))) + tp->snd_up = tp->snd_una; + + if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) + flag |= FLAG_SACK_RENEGING; + + if (flag & FLAG_ACKED) { + const struct tcp_congestion_ops *ca_ops + = inet_csk(sk)->icsk_ca_ops; + + if (unlikely(icsk->icsk_mtup.probe_size && + !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) { + tcp_mtup_probe_success(sk); + } + + tcp_ack_update_rtt(sk, flag, seq_rtt); + tcp_rearm_rto(sk); + + if (tcp_is_reno(tp)) { + tcp_remove_reno_sacks(sk, pkts_acked); + } else { + int delta; + + /* Non-retransmitted hole got filled? That's reordering */ + if (reord < prior_fackets) + tcp_update_reordering(sk, tp->fackets_out - reord, 0); + + delta = tcp_is_fack(tp) ? pkts_acked : + prior_sacked - tp->sacked_out; + tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta); + } + + tp->fackets_out -= min(pkts_acked, tp->fackets_out); + + if (ca_ops->pkts_acked) { + s32 rtt_us = -1; + + /* Is the ACK triggering packet unambiguous? */ + if (!(flag & FLAG_RETRANS_DATA_ACKED)) { + /* High resolution needed and available? */ + if (ca_ops->flags & TCP_CONG_RTT_STAMP && + !ktime_equal(last_ackt, + net_invalid_timestamp())) + rtt_us = ktime_us_delta(ktime_get_real(), + last_ackt); + else if (ca_seq_rtt >= 0) + rtt_us = jiffies_to_usecs(ca_seq_rtt); + } + + ca_ops->pkts_acked(sk, pkts_acked, rtt_us); + } + } + +#if FASTRETRANS_DEBUG > 0 + WARN_ON((int)tp->sacked_out < 0); + WARN_ON((int)tp->lost_out < 0); + WARN_ON((int)tp->retrans_out < 0); + if (!tp->packets_out && tcp_is_sack(tp)) { + icsk = inet_csk(sk); + if (tp->lost_out) { + printk(KERN_DEBUG "Leak l=%u %d\n", + tp->lost_out, icsk->icsk_ca_state); + tp->lost_out = 0; + } + if (tp->sacked_out) { + printk(KERN_DEBUG "Leak s=%u %d\n", + tp->sacked_out, icsk->icsk_ca_state); + tp->sacked_out = 0; + } + if (tp->retrans_out) { + printk(KERN_DEBUG "Leak r=%u %d\n", + tp->retrans_out, icsk->icsk_ca_state); + tp->retrans_out = 0; + } + } +#endif + return flag; +} + +static void tcp_ack_probe(struct sock *sk) +{ + const struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + + /* Was it a usable window open? */ + + if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) { + icsk->icsk_backoff = 0; + inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0); + /* Socket must be waked up by subsequent tcp_data_snd_check(). + * This function is not for random using! + */ + } else { + inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, + min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX), + TCP_RTO_MAX); + } +} + +static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag) +{ + return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) || + inet_csk(sk)->icsk_ca_state != TCP_CA_Open; +} + +static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag) +{ + const struct tcp_sock *tp = tcp_sk(sk); + return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) && + !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR)); +} + +/* Check that window update is acceptable. + * The function assumes that snd_una<=ack<=snd_next. + */ +static inline int tcp_may_update_window(const struct tcp_sock *tp, + const u32 ack, const u32 ack_seq, + const u32 nwin) +{ + return after(ack, tp->snd_una) || + after(ack_seq, tp->snd_wl1) || + (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd); +} + +/* Update our send window. + * + * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2 + * and in FreeBSD. NetBSD's one is even worse.) is wrong. + */ +static int tcp_ack_update_window(struct sock *sk, struct sk_buff *skb, u32 ack, + u32 ack_seq) +{ + struct tcp_sock *tp = tcp_sk(sk); + int flag = 0; + u32 nwin = ntohs(tcp_hdr(skb)->window); + + if (likely(!tcp_hdr(skb)->syn)) + nwin <<= tp->rx_opt.snd_wscale; + + if (tcp_may_update_window(tp, ack, ack_seq, nwin)) { + flag |= FLAG_WIN_UPDATE; + tcp_update_wl(tp, ack_seq); + + if (tp->snd_wnd != nwin) { + tp->snd_wnd = nwin; + + /* Note, it is the only place, where + * fast path is recovered for sending TCP. + */ + tp->pred_flags = 0; + tcp_fast_path_check(sk); + + if (nwin > tp->max_window) { + tp->max_window = nwin; + tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie); + } + } + } + + tp->snd_una = ack; + + return flag; +} + +/* A very conservative spurious RTO response algorithm: reduce cwnd and + * continue in congestion avoidance. + */ +static void tcp_conservative_spur_to_response(struct tcp_sock *tp) +{ + tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh); + tp->snd_cwnd_cnt = 0; + tp->bytes_acked = 0; + TCP_ECN_queue_cwr(tp); + tcp_moderate_cwnd(tp); +} + +/* A conservative spurious RTO response algorithm: reduce cwnd using + * rate halving and continue in congestion avoidance. + */ +static void tcp_ratehalving_spur_to_response(struct sock *sk) +{ + tcp_enter_cwr(sk, 0); +} + +static void tcp_undo_spur_to_response(struct sock *sk, int flag) +{ + if (flag & FLAG_ECE) + tcp_ratehalving_spur_to_response(sk); + else + tcp_undo_cwr(sk, true); +} + +/* F-RTO spurious RTO detection algorithm (RFC4138) + * + * F-RTO affects during two new ACKs following RTO (well, almost, see inline + * comments). State (ACK number) is kept in frto_counter. When ACK advances + * window (but not to or beyond highest sequence sent before RTO): + * On First ACK, send two new segments out. + * On Second ACK, RTO was likely spurious. Do spurious response (response + * algorithm is not part of the F-RTO detection algorithm + * given in RFC4138 but can be selected separately). + * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss + * and TCP falls back to conventional RTO recovery. F-RTO allows overriding + * of Nagle, this is done using frto_counter states 2 and 3, when a new data + * segment of any size sent during F-RTO, state 2 is upgraded to 3. + * + * Rationale: if the RTO was spurious, new ACKs should arrive from the + * original window even after we transmit two new data segments. + * + * SACK version: + * on first step, wait until first cumulative ACK arrives, then move to + * the second step. In second step, the next ACK decides. + * + * F-RTO is implemented (mainly) in four functions: + * - tcp_use_frto() is used to determine if TCP is can use F-RTO + * - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is + * called when tcp_use_frto() showed green light + * - tcp_process_frto() handles incoming ACKs during F-RTO algorithm + * - tcp_enter_frto_loss() is called if there is not enough evidence + * to prove that the RTO is indeed spurious. It transfers the control + * from F-RTO to the conventional RTO recovery + */ +static int tcp_process_frto(struct sock *sk, int flag) +{ + struct tcp_sock *tp = tcp_sk(sk); + + tcp_verify_left_out(tp); + + /* Duplicate the behavior from Loss state (fastretrans_alert) */ + if (flag & FLAG_DATA_ACKED) + inet_csk(sk)->icsk_retransmits = 0; + + if ((flag & FLAG_NONHEAD_RETRANS_ACKED) || + ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED))) + tp->undo_marker = 0; + + if (!before(tp->snd_una, tp->frto_highmark)) { + tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag); + return 1; + } + + if (!tcp_is_sackfrto(tp)) { + /* RFC4138 shortcoming in step 2; should also have case c): + * ACK isn't duplicate nor advances window, e.g., opposite dir + * data, winupdate + */ + if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP)) + return 1; + + if (!(flag & FLAG_DATA_ACKED)) { + tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3), + flag); + return 1; + } + } else { + if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) { + /* Prevent sending of new data. */ + tp->snd_cwnd = min(tp->snd_cwnd, + tcp_packets_in_flight(tp)); + return 1; + } + + if ((tp->frto_counter >= 2) && + (!(flag & FLAG_FORWARD_PROGRESS) || + ((flag & FLAG_DATA_SACKED) && + !(flag & FLAG_ONLY_ORIG_SACKED)))) { + /* RFC4138 shortcoming (see comment above) */ + if (!(flag & FLAG_FORWARD_PROGRESS) && + (flag & FLAG_NOT_DUP)) + return 1; + + tcp_enter_frto_loss(sk, 3, flag); + return 1; + } + } + + if (tp->frto_counter == 1) { + /* tcp_may_send_now needs to see updated state */ + tp->snd_cwnd = tcp_packets_in_flight(tp) + 2; + tp->frto_counter = 2; + + if (!tcp_may_send_now(sk)) + tcp_enter_frto_loss(sk, 2, flag); + + return 1; + } else { + switch (sysctl_tcp_frto_response) { + case 2: + tcp_undo_spur_to_response(sk, flag); + break; + case 1: + tcp_conservative_spur_to_response(tp); + break; + default: + tcp_ratehalving_spur_to_response(sk); + break; + } + tp->frto_counter = 0; + tp->undo_marker = 0; + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS); + } + return 0; +} + +/* This routine deals with incoming acks, but not outgoing ones. */ +static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + u32 prior_snd_una = tp->snd_una; + u32 ack_seq = TCP_SKB_CB(skb)->seq; + u32 ack = TCP_SKB_CB(skb)->ack_seq; + u32 prior_in_flight; + u32 prior_fackets; + int prior_packets; + int frto_cwnd = 0; + + /* If the ack is older than previous acks + * then we can probably ignore it. + */ + if (before(ack, prior_snd_una)) + goto old_ack; + + /* If the ack includes data we haven't sent yet, discard + * this segment (RFC793 Section 3.9). + */ + if (after(ack, tp->snd_nxt)) + goto invalid_ack; + + if (after(ack, prior_snd_una)) + flag |= FLAG_SND_UNA_ADVANCED; + + if (sysctl_tcp_abc) { + if (icsk->icsk_ca_state < TCP_CA_CWR) + tp->bytes_acked += ack - prior_snd_una; + else if (icsk->icsk_ca_state == TCP_CA_Loss) + /* we assume just one segment left network */ + tp->bytes_acked += min(ack - prior_snd_una, + tp->mss_cache); + } + + prior_fackets = tp->fackets_out; + prior_in_flight = tcp_packets_in_flight(tp); + + if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) { + /* Window is constant, pure forward advance. + * No more checks are required. + * Note, we use the fact that SND.UNA>=SND.WL2. + */ + tcp_update_wl(tp, ack_seq); + tp->snd_una = ack; + flag |= FLAG_WIN_UPDATE; + + tcp_ca_event(sk, CA_EVENT_FAST_ACK); + + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS); + } else { + if (ack_seq != TCP_SKB_CB(skb)->end_seq) + flag |= FLAG_DATA; + else + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS); + + flag |= tcp_ack_update_window(sk, skb, ack, ack_seq); + + if (TCP_SKB_CB(skb)->sacked) + flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una); + + if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb))) + flag |= FLAG_ECE; + + tcp_ca_event(sk, CA_EVENT_SLOW_ACK); + } + + /* We passed data and got it acked, remove any soft error + * log. Something worked... + */ + sk->sk_err_soft = 0; + icsk->icsk_probes_out = 0; + tp->rcv_tstamp = tcp_time_stamp; + prior_packets = tp->packets_out; + if (!prior_packets) + goto no_queue; + + /* See if we can take anything off of the retransmit queue. */ + flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una); + + if (tp->frto_counter) + frto_cwnd = tcp_process_frto(sk, flag); + /* Guarantee sacktag reordering detection against wrap-arounds */ + if (before(tp->frto_highmark, tp->snd_una)) + tp->frto_highmark = 0; + + if (tcp_ack_is_dubious(sk, flag)) { + /* Advance CWND, if state allows this. */ + if ((flag & FLAG_DATA_ACKED) && !frto_cwnd && + tcp_may_raise_cwnd(sk, flag)) + tcp_cong_avoid(sk, ack, prior_in_flight); + tcp_fastretrans_alert(sk, prior_packets - tp->packets_out, + flag); + } else { + if ((flag & FLAG_DATA_ACKED) && !frto_cwnd) + tcp_cong_avoid(sk, ack, prior_in_flight); + } + + if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) + dst_confirm(__sk_dst_get(sk)); + + return 1; + +no_queue: + /* If this ack opens up a zero window, clear backoff. It was + * being used to time the probes, and is probably far higher than + * it needs to be for normal retransmission. + */ + if (tcp_send_head(sk)) + tcp_ack_probe(sk); + return 1; + +invalid_ack: + SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt); + return -1; + +old_ack: + if (TCP_SKB_CB(skb)->sacked) { + tcp_sacktag_write_queue(sk, skb, prior_snd_una); + if (icsk->icsk_ca_state == TCP_CA_Open) + tcp_try_keep_open(sk); + } + + SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt); + return 0; +} + +/* Look for tcp options. Normally only called on SYN and SYNACK packets. + * But, this can also be called on packets in the established flow when + * the fast version below fails. + */ +void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, + u8 **hvpp, int estab) +{ + unsigned char *ptr; + struct tcphdr *th = tcp_hdr(skb); + int length = (th->doff * 4) - sizeof(struct tcphdr); + + ptr = (unsigned char *)(th + 1); + opt_rx->saw_tstamp = 0; + + while (length > 0) { + int opcode = *ptr++; + int opsize; + + switch (opcode) { + case TCPOPT_EOL: + return; + case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */ + length--; + continue; + default: + opsize = *ptr++; + if (opsize < 2) /* "silly options" */ + return; + if (opsize > length) + return; /* don't parse partial options */ + switch (opcode) { + case TCPOPT_MSS: + if (opsize == TCPOLEN_MSS && th->syn && !estab) { + u16 in_mss = get_unaligned_be16(ptr); + if (in_mss) { + if (opt_rx->user_mss && + opt_rx->user_mss < in_mss) + in_mss = opt_rx->user_mss; + opt_rx->mss_clamp = in_mss; + } + } + break; + case TCPOPT_WINDOW: + if (opsize == TCPOLEN_WINDOW && th->syn && + !estab && sysctl_tcp_window_scaling) { + __u8 snd_wscale = *(__u8 *)ptr; + opt_rx->wscale_ok = 1; + if (snd_wscale > 14) { + if (net_ratelimit()) + printk(KERN_INFO "tcp_parse_options: Illegal window " + "scaling value %d >14 received.\n", + snd_wscale); + snd_wscale = 14; + } + opt_rx->snd_wscale = snd_wscale; + } + break; + case TCPOPT_TIMESTAMP: + if ((opsize == TCPOLEN_TIMESTAMP) && + ((estab && opt_rx->tstamp_ok) || + (!estab && sysctl_tcp_timestamps))) { + opt_rx->saw_tstamp = 1; + opt_rx->rcv_tsval = get_unaligned_be32(ptr); + opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4); + } + break; + case TCPOPT_SACK_PERM: + if (opsize == TCPOLEN_SACK_PERM && th->syn && + !estab && sysctl_tcp_sack) { + opt_rx->sack_ok = 1; + tcp_sack_reset(opt_rx); + } + break; + + case TCPOPT_SACK: + if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) && + !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) && + opt_rx->sack_ok) { + TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th; + } + break; +#ifdef CONFIG_TCP_MD5SIG + case TCPOPT_MD5SIG: + /* + * The MD5 Hash has already been + * checked (see tcp_v{4,6}_do_rcv()). + */ + break; +#endif + case TCPOPT_COOKIE: + /* This option is variable length. + */ + switch (opsize) { + case TCPOLEN_COOKIE_BASE: + /* not yet implemented */ + break; + case TCPOLEN_COOKIE_PAIR: + /* not yet implemented */ + break; + case TCPOLEN_COOKIE_MIN+0: + case TCPOLEN_COOKIE_MIN+2: + case TCPOLEN_COOKIE_MIN+4: + case TCPOLEN_COOKIE_MIN+6: + case TCPOLEN_COOKIE_MAX: + /* 16-bit multiple */ + opt_rx->cookie_plus = opsize; + *hvpp = ptr; + break; + default: + /* ignore option */ + break; + } + break; + } + + ptr += opsize-2; + length -= opsize; + } + } +} +EXPORT_SYMBOL(tcp_parse_options); + +static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, struct tcphdr *th) +{ + __be32 *ptr = (__be32 *)(th + 1); + + if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) + | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) { + tp->rx_opt.saw_tstamp = 1; + ++ptr; + tp->rx_opt.rcv_tsval = ntohl(*ptr); + ++ptr; + tp->rx_opt.rcv_tsecr = ntohl(*ptr); + return 1; + } + return 0; +} + +/* Fast parse options. This hopes to only see timestamps. + * If it is wrong it falls back on tcp_parse_options(). + */ +static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th, + struct tcp_sock *tp, u8 **hvpp) +{ + /* In the spirit of fast parsing, compare doff directly to constant + * values. Because equality is used, short doff can be ignored here. + */ + if (th->doff == (sizeof(*th) / 4)) { + tp->rx_opt.saw_tstamp = 0; + return 0; + } else if (tp->rx_opt.tstamp_ok && + th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) { + if (tcp_parse_aligned_timestamp(tp, th)) + return 1; + } + tcp_parse_options(skb, &tp->rx_opt, hvpp, 1); + return 1; +} + +#ifdef CONFIG_TCP_MD5SIG +/* + * Parse MD5 Signature option + */ +u8 *tcp_parse_md5sig_option(struct tcphdr *th) +{ + int length = (th->doff << 2) - sizeof (*th); + u8 *ptr = (u8*)(th + 1); + + /* If the TCP option is too short, we can short cut */ + if (length < TCPOLEN_MD5SIG) + return NULL; + + while (length > 0) { + int opcode = *ptr++; + int opsize; + + switch(opcode) { + case TCPOPT_EOL: + return NULL; + case TCPOPT_NOP: + length--; + continue; + default: + opsize = *ptr++; + if (opsize < 2 || opsize > length) + return NULL; + if (opcode == TCPOPT_MD5SIG) + return opsize == TCPOLEN_MD5SIG ? ptr : NULL; + } + ptr += opsize - 2; + length -= opsize; + } + return NULL; +} +EXPORT_SYMBOL(tcp_parse_md5sig_option); +#endif + +static inline void tcp_store_ts_recent(struct tcp_sock *tp) +{ + tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval; + tp->rx_opt.ts_recent_stamp = get_seconds(); +} + +static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq) +{ + if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) { + /* PAWS bug workaround wrt. ACK frames, the PAWS discard + * extra check below makes sure this can only happen + * for pure ACK frames. -DaveM + * + * Not only, also it occurs for expired timestamps. + */ + + if (tcp_paws_check(&tp->rx_opt, 0)) + tcp_store_ts_recent(tp); + } +} + +/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM + * + * It is not fatal. If this ACK does _not_ change critical state (seqs, window) + * it can pass through stack. So, the following predicate verifies that + * this segment is not used for anything but congestion avoidance or + * fast retransmit. Moreover, we even are able to eliminate most of such + * second order effects, if we apply some small "replay" window (~RTO) + * to timestamp space. + * + * All these measures still do not guarantee that we reject wrapped ACKs + * on networks with high bandwidth, when sequence space is recycled fastly, + * but it guarantees that such events will be very rare and do not affect + * connection seriously. This doesn't look nice, but alas, PAWS is really + * buggy extension. + * + * [ Later note. Even worse! It is buggy for segments _with_ data. RFC + * states that events when retransmit arrives after original data are rare. + * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is + * the biggest problem on large power networks even with minor reordering. + * OK, let's give it small replay window. If peer clock is even 1hz, it is safe + * up to bandwidth of 18Gigabit/sec. 8) ] + */ + +static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct tcphdr *th = tcp_hdr(skb); + u32 seq = TCP_SKB_CB(skb)->seq; + u32 ack = TCP_SKB_CB(skb)->ack_seq; + + return (/* 1. Pure ACK with correct sequence number. */ + (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) && + + /* 2. ... and duplicate ACK. */ + ack == tp->snd_una && + + /* 3. ... and does not update window. */ + !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) && + + /* 4. ... and sits in replay window. */ + (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ); +} + +static inline int tcp_paws_discard(const struct sock *sk, + const struct sk_buff *skb) +{ + const struct tcp_sock *tp = tcp_sk(sk); + + return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) && + !tcp_disordered_ack(sk, skb); +} + +/* Check segment sequence number for validity. + * + * Segment controls are considered valid, if the segment + * fits to the window after truncation to the window. Acceptability + * of data (and SYN, FIN, of course) is checked separately. + * See tcp_data_queue(), for example. + * + * Also, controls (RST is main one) are accepted using RCV.WUP instead + * of RCV.NXT. Peer still did not advance his SND.UNA when we + * delayed ACK, so that hisSND.UNA<=ourRCV.WUP. + * (borrowed from freebsd) + */ + +static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq) +{ + return !before(end_seq, tp->rcv_wup) && + !after(seq, tp->rcv_nxt + tcp_receive_window(tp)); +} + +/* When we get a reset we do this. */ +static void tcp_reset(struct sock *sk) +{ + /* We want the right error as BSD sees it (and indeed as we do). */ + switch (sk->sk_state) { + case TCP_SYN_SENT: + sk->sk_err = ECONNREFUSED; + break; + case TCP_CLOSE_WAIT: + sk->sk_err = EPIPE; + break; + case TCP_CLOSE: + return; + default: + sk->sk_err = ECONNRESET; + } + /* This barrier is coupled with smp_rmb() in tcp_poll() */ + smp_wmb(); + + if (!sock_flag(sk, SOCK_DEAD)) + sk->sk_error_report(sk); + + tcp_done(sk); +} + +/* + * Process the FIN bit. This now behaves as it is supposed to work + * and the FIN takes effect when it is validly part of sequence + * space. Not before when we get holes. + * + * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT + * (and thence onto LAST-ACK and finally, CLOSE, we never enter + * TIME-WAIT) + * + * If we are in FINWAIT-1, a received FIN indicates simultaneous + * close and we go into CLOSING (and later onto TIME-WAIT) + * + * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT. + */ +static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th) +{ + struct tcp_sock *tp = tcp_sk(sk); + + inet_csk_schedule_ack(sk); + + sk->sk_shutdown |= RCV_SHUTDOWN; + sock_set_flag(sk, SOCK_DONE); + + switch (sk->sk_state) { + case TCP_SYN_RECV: + case TCP_ESTABLISHED: + /* Move to CLOSE_WAIT */ + tcp_set_state(sk, TCP_CLOSE_WAIT); + inet_csk(sk)->icsk_ack.pingpong = 1; + break; + + case TCP_CLOSE_WAIT: + case TCP_CLOSING: + /* Received a retransmission of the FIN, do + * nothing. + */ + break; + case TCP_LAST_ACK: + /* RFC793: Remain in the LAST-ACK state. */ + break; + + case TCP_FIN_WAIT1: + /* This case occurs when a simultaneous close + * happens, we must ack the received FIN and + * enter the CLOSING state. + */ + tcp_send_ack(sk); + tcp_set_state(sk, TCP_CLOSING); + break; + case TCP_FIN_WAIT2: + /* Received a FIN -- send ACK and enter TIME_WAIT. */ + tcp_send_ack(sk); + tcp_time_wait(sk, TCP_TIME_WAIT, 0); + break; + default: + /* Only TCP_LISTEN and TCP_CLOSE are left, in these + * cases we should never reach this piece of code. + */ + printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n", + __func__, sk->sk_state); + break; + } + + /* It _is_ possible, that we have something out-of-order _after_ FIN. + * Probably, we should reset in this case. For now drop them. + */ + __skb_queue_purge(&tp->out_of_order_queue); + if (tcp_is_sack(tp)) + tcp_sack_reset(&tp->rx_opt); + sk_mem_reclaim(sk); + + if (!sock_flag(sk, SOCK_DEAD)) { + sk->sk_state_change(sk); + + /* Do not send POLL_HUP for half duplex close. */ + if (sk->sk_shutdown == SHUTDOWN_MASK || + sk->sk_state == TCP_CLOSE) + sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP); + else + sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN); + } +} + +static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, + u32 end_seq) +{ + if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) { + if (before(seq, sp->start_seq)) + sp->start_seq = seq; + if (after(end_seq, sp->end_seq)) + sp->end_seq = end_seq; + return 1; + } + return 0; +} + +static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tcp_is_sack(tp) && sysctl_tcp_dsack) { + int mib_idx; + + if (before(seq, tp->rcv_nxt)) + mib_idx = LINUX_MIB_TCPDSACKOLDSENT; + else + mib_idx = LINUX_MIB_TCPDSACKOFOSENT; + + NET_INC_STATS_BH(sock_net(sk), mib_idx); + + tp->rx_opt.dsack = 1; + tp->duplicate_sack[0].start_seq = seq; + tp->duplicate_sack[0].end_seq = end_seq; + } +} + +static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (!tp->rx_opt.dsack) + tcp_dsack_set(sk, seq, end_seq); + else + tcp_sack_extend(tp->duplicate_sack, seq, end_seq); +} + +static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && + before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST); + tcp_enter_quickack_mode(sk); + + if (tcp_is_sack(tp) && sysctl_tcp_dsack) { + u32 end_seq = TCP_SKB_CB(skb)->end_seq; + + if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) + end_seq = tp->rcv_nxt; + tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq); + } + } + + tcp_send_ack(sk); +} + +/* These routines update the SACK block as out-of-order packets arrive or + * in-order packets close up the sequence space. + */ +static void tcp_sack_maybe_coalesce(struct tcp_sock *tp) +{ + int this_sack; + struct tcp_sack_block *sp = &tp->selective_acks[0]; + struct tcp_sack_block *swalk = sp + 1; + + /* See if the recent change to the first SACK eats into + * or hits the sequence space of other SACK blocks, if so coalesce. + */ + for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) { + if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) { + int i; + + /* Zap SWALK, by moving every further SACK up by one slot. + * Decrease num_sacks. + */ + tp->rx_opt.num_sacks--; + for (i = this_sack; i < tp->rx_opt.num_sacks; i++) + sp[i] = sp[i + 1]; + continue; + } + this_sack++, swalk++; + } +} + +static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct tcp_sack_block *sp = &tp->selective_acks[0]; + int cur_sacks = tp->rx_opt.num_sacks; + int this_sack; + + if (!cur_sacks) + goto new_sack; + + for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) { + if (tcp_sack_extend(sp, seq, end_seq)) { + /* Rotate this_sack to the first one. */ + for (; this_sack > 0; this_sack--, sp--) + swap(*sp, *(sp - 1)); + if (cur_sacks > 1) + tcp_sack_maybe_coalesce(tp); + return; + } + } + + /* Could not find an adjacent existing SACK, build a new one, + * put it at the front, and shift everyone else down. We + * always know there is at least one SACK present already here. + * + * If the sack array is full, forget about the last one. + */ + if (this_sack >= TCP_NUM_SACKS) { + this_sack--; + tp->rx_opt.num_sacks--; + sp--; + } + for (; this_sack > 0; this_sack--, sp--) + *sp = *(sp - 1); + +new_sack: + /* Build the new head SACK, and we're done. */ + sp->start_seq = seq; + sp->end_seq = end_seq; + tp->rx_opt.num_sacks++; +} + +/* RCV.NXT advances, some SACKs should be eaten. */ + +static void tcp_sack_remove(struct tcp_sock *tp) +{ + struct tcp_sack_block *sp = &tp->selective_acks[0]; + int num_sacks = tp->rx_opt.num_sacks; + int this_sack; + + /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */ + if (skb_queue_empty(&tp->out_of_order_queue)) { + tp->rx_opt.num_sacks = 0; + return; + } + + for (this_sack = 0; this_sack < num_sacks;) { + /* Check if the start of the sack is covered by RCV.NXT. */ + if (!before(tp->rcv_nxt, sp->start_seq)) { + int i; + + /* RCV.NXT must cover all the block! */ + WARN_ON(before(tp->rcv_nxt, sp->end_seq)); + + /* Zap this SACK, by moving forward any other SACKS. */ + for (i=this_sack+1; i < num_sacks; i++) + tp->selective_acks[i-1] = tp->selective_acks[i]; + num_sacks--; + continue; + } + this_sack++; + sp++; + } + tp->rx_opt.num_sacks = num_sacks; +} + +/* This one checks to see if we can put data from the + * out_of_order queue into the receive_queue. + */ +static void tcp_ofo_queue(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + __u32 dsack_high = tp->rcv_nxt; + struct sk_buff *skb; + + while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) { + if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) + break; + + if (before(TCP_SKB_CB(skb)->seq, dsack_high)) { + __u32 dsack = dsack_high; + if (before(TCP_SKB_CB(skb)->end_seq, dsack_high)) + dsack_high = TCP_SKB_CB(skb)->end_seq; + tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack); + } + + if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) { + SOCK_DEBUG(sk, "ofo packet was already received\n"); + __skb_unlink(skb, &tp->out_of_order_queue); + __kfree_skb(skb); + continue; + } + SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n", + tp->rcv_nxt, TCP_SKB_CB(skb)->seq, + TCP_SKB_CB(skb)->end_seq); + + __skb_unlink(skb, &tp->out_of_order_queue); + __skb_queue_tail(&sk->sk_receive_queue, skb); + tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; + if (tcp_hdr(skb)->fin) + tcp_fin(skb, sk, tcp_hdr(skb)); + } +} + +static int tcp_prune_ofo_queue(struct sock *sk); +static int tcp_prune_queue(struct sock *sk); + +static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size) +{ + if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf || + !sk_rmem_schedule(sk, size)) { + + if (tcp_prune_queue(sk) < 0) + return -1; + + if (!sk_rmem_schedule(sk, size)) { + if (!tcp_prune_ofo_queue(sk)) + return -1; + + if (!sk_rmem_schedule(sk, size)) + return -1; + } + } + return 0; +} + +static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) +{ + struct tcphdr *th = tcp_hdr(skb); + struct tcp_sock *tp = tcp_sk(sk); + int eaten = -1; + + if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) + goto drop; + + skb_dst_drop(skb); + __skb_pull(skb, th->doff * 4); + + TCP_ECN_accept_cwr(tp, skb); + + tp->rx_opt.dsack = 0; + + /* Queue data for delivery to the user. + * Packets in sequence go to the receive queue. + * Out of sequence packets to the out_of_order_queue. + */ + if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) { + if (tcp_receive_window(tp) == 0) + goto out_of_window; + + /* Ok. In sequence. In window. */ + if (tp->ucopy.task == current && + tp->copied_seq == tp->rcv_nxt && tp->ucopy.len && + sock_owned_by_user(sk) && !tp->urg_data) { + int chunk = min_t(unsigned int, skb->len, + tp->ucopy.len); + + __set_current_state(TASK_RUNNING); + + local_bh_enable(); + if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) { + tp->ucopy.len -= chunk; + tp->copied_seq += chunk; + eaten = (chunk == skb->len); + tcp_rcv_space_adjust(sk); + } + local_bh_disable(); + } + + if (eaten <= 0) { +queue_and_out: + if (eaten < 0 && + tcp_try_rmem_schedule(sk, skb->truesize)) + goto drop; + + skb_set_owner_r(skb, sk); + __skb_queue_tail(&sk->sk_receive_queue, skb); + } + tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; + if (skb->len) + tcp_event_data_recv(sk, skb); + if (th->fin) + tcp_fin(skb, sk, th); + + if (!skb_queue_empty(&tp->out_of_order_queue)) { + tcp_ofo_queue(sk); + + /* RFC2581. 4.2. SHOULD send immediate ACK, when + * gap in queue is filled. + */ + if (skb_queue_empty(&tp->out_of_order_queue)) + inet_csk(sk)->icsk_ack.pingpong = 0; + } + + if (tp->rx_opt.num_sacks) + tcp_sack_remove(tp); + + tcp_fast_path_check(sk); + + if (eaten > 0) + __kfree_skb(skb); + else if (!sock_flag(sk, SOCK_DEAD)) + sk->sk_data_ready(sk, 0); + return; + } + + if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) { + /* A retransmit, 2nd most common case. Force an immediate ack. */ + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST); + tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); + +out_of_window: + tcp_enter_quickack_mode(sk); + inet_csk_schedule_ack(sk); +drop: + __kfree_skb(skb); + return; + } + + /* Out of window. F.e. zero window probe. */ + if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp))) + goto out_of_window; + + tcp_enter_quickack_mode(sk); + + if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { + /* Partial packet, seq < rcv_next < end_seq */ + SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n", + tp->rcv_nxt, TCP_SKB_CB(skb)->seq, + TCP_SKB_CB(skb)->end_seq); + + tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt); + + /* If window is closed, drop tail of packet. But after + * remembering D-SACK for its head made in previous line. + */ + if (!tcp_receive_window(tp)) + goto out_of_window; + goto queue_and_out; + } + + TCP_ECN_check_ce(tp, skb); + + if (tcp_try_rmem_schedule(sk, skb->truesize)) + goto drop; + + /* Disable header prediction. */ + tp->pred_flags = 0; + inet_csk_schedule_ack(sk); + + SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n", + tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); + + skb_set_owner_r(skb, sk); + + if (!skb_peek(&tp->out_of_order_queue)) { + /* Initial out of order segment, build 1 SACK. */ + if (tcp_is_sack(tp)) { + tp->rx_opt.num_sacks = 1; + tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq; + tp->selective_acks[0].end_seq = + TCP_SKB_CB(skb)->end_seq; + } + __skb_queue_head(&tp->out_of_order_queue, skb); + } else { + struct sk_buff *skb1 = skb_peek_tail(&tp->out_of_order_queue); + u32 seq = TCP_SKB_CB(skb)->seq; + u32 end_seq = TCP_SKB_CB(skb)->end_seq; + + if (seq == TCP_SKB_CB(skb1)->end_seq) { + __skb_queue_after(&tp->out_of_order_queue, skb1, skb); + + if (!tp->rx_opt.num_sacks || + tp->selective_acks[0].end_seq != seq) + goto add_sack; + + /* Common case: data arrive in order after hole. */ + tp->selective_acks[0].end_seq = end_seq; + return; + } + + /* Find place to insert this segment. */ + while (1) { + if (!after(TCP_SKB_CB(skb1)->seq, seq)) + break; + if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) { + skb1 = NULL; + break; + } + skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1); + } + + /* Do skb overlap to previous one? */ + if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) { + if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) { + /* All the bits are present. Drop. */ + __kfree_skb(skb); + tcp_dsack_set(sk, seq, end_seq); + goto add_sack; + } + if (after(seq, TCP_SKB_CB(skb1)->seq)) { + /* Partial overlap. */ + tcp_dsack_set(sk, seq, + TCP_SKB_CB(skb1)->end_seq); + } else { + if (skb_queue_is_first(&tp->out_of_order_queue, + skb1)) + skb1 = NULL; + else + skb1 = skb_queue_prev( + &tp->out_of_order_queue, + skb1); + } + } + if (!skb1) + __skb_queue_head(&tp->out_of_order_queue, skb); + else + __skb_queue_after(&tp->out_of_order_queue, skb1, skb); + + /* And clean segments covered by new one as whole. */ + while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) { + skb1 = skb_queue_next(&tp->out_of_order_queue, skb); + + if (!after(end_seq, TCP_SKB_CB(skb1)->seq)) + break; + if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) { + tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq, + end_seq); + break; + } + __skb_unlink(skb1, &tp->out_of_order_queue); + tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq, + TCP_SKB_CB(skb1)->end_seq); + __kfree_skb(skb1); + } + +add_sack: + if (tcp_is_sack(tp)) + tcp_sack_new_ofo_skb(sk, seq, end_seq); + } +} + +static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb, + struct sk_buff_head *list) +{ + struct sk_buff *next = NULL; + + if (!skb_queue_is_last(list, skb)) + next = skb_queue_next(list, skb); + + __skb_unlink(skb, list); + __kfree_skb(skb); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED); + + return next; +} + +/* Collapse contiguous sequence of skbs head..tail with + * sequence numbers start..end. + * + * If tail is NULL, this means until the end of the list. + * + * Segments with FIN/SYN are not collapsed (only because this + * simplifies code) + */ +static void +tcp_collapse(struct sock *sk, struct sk_buff_head *list, + struct sk_buff *head, struct sk_buff *tail, + u32 start, u32 end) +{ + struct sk_buff *skb, *n; + bool end_of_skbs; + + /* First, check that queue is collapsible and find + * the point where collapsing can be useful. */ + skb = head; +restart: + end_of_skbs = true; + skb_queue_walk_from_safe(list, skb, n) { + if (skb == tail) + break; + /* No new bits? It is possible on ofo queue. */ + if (!before(start, TCP_SKB_CB(skb)->end_seq)) { + skb = tcp_collapse_one(sk, skb, list); + if (!skb) + break; + goto restart; + } + + /* The first skb to collapse is: + * - not SYN/FIN and + * - bloated or contains data before "start" or + * overlaps to the next one. + */ + if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin && + (tcp_win_from_space(skb->truesize) > skb->len || + before(TCP_SKB_CB(skb)->seq, start))) { + end_of_skbs = false; + break; + } + + if (!skb_queue_is_last(list, skb)) { + struct sk_buff *next = skb_queue_next(list, skb); + if (next != tail && + TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) { + end_of_skbs = false; + break; + } + } + + /* Decided to skip this, advance start seq. */ + start = TCP_SKB_CB(skb)->end_seq; + } + if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin) + return; + + while (before(start, end)) { + struct sk_buff *nskb; + unsigned int header = skb_headroom(skb); + int copy = SKB_MAX_ORDER(header, 0); + + /* Too big header? This can happen with IPv6. */ + if (copy < 0) + return; + if (end - start < copy) + copy = end - start; + nskb = alloc_skb(copy + header, GFP_ATOMIC); + if (!nskb) + return; + + skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head); + skb_set_network_header(nskb, (skb_network_header(skb) - + skb->head)); + skb_set_transport_header(nskb, (skb_transport_header(skb) - + skb->head)); + skb_reserve(nskb, header); + memcpy(nskb->head, skb->head, header); + memcpy(nskb->cb, skb->cb, sizeof(skb->cb)); + TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start; + __skb_queue_before(list, skb, nskb); + skb_set_owner_r(nskb, sk); + + /* Copy data, releasing collapsed skbs. */ + while (copy > 0) { + int offset = start - TCP_SKB_CB(skb)->seq; + int size = TCP_SKB_CB(skb)->end_seq - start; + + BUG_ON(offset < 0); + if (size > 0) { + size = min(copy, size); + if (skb_copy_bits(skb, offset, skb_put(nskb, size), size)) + BUG(); + TCP_SKB_CB(nskb)->end_seq += size; + copy -= size; + start += size; + } + if (!before(start, TCP_SKB_CB(skb)->end_seq)) { + skb = tcp_collapse_one(sk, skb, list); + if (!skb || + skb == tail || + tcp_hdr(skb)->syn || + tcp_hdr(skb)->fin) + return; + } + } + } +} + +/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs + * and tcp_collapse() them until all the queue is collapsed. + */ +static void tcp_collapse_ofo_queue(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb = skb_peek(&tp->out_of_order_queue); + struct sk_buff *head; + u32 start, end; + + if (skb == NULL) + return; + + start = TCP_SKB_CB(skb)->seq; + end = TCP_SKB_CB(skb)->end_seq; + head = skb; + + for (;;) { + struct sk_buff *next = NULL; + + if (!skb_queue_is_last(&tp->out_of_order_queue, skb)) + next = skb_queue_next(&tp->out_of_order_queue, skb); + skb = next; + + /* Segment is terminated when we see gap or when + * we are at the end of all the queue. */ + if (!skb || + after(TCP_SKB_CB(skb)->seq, end) || + before(TCP_SKB_CB(skb)->end_seq, start)) { + tcp_collapse(sk, &tp->out_of_order_queue, + head, skb, start, end); + head = skb; + if (!skb) + break; + /* Start new segment */ + start = TCP_SKB_CB(skb)->seq; + end = TCP_SKB_CB(skb)->end_seq; + } else { + if (before(TCP_SKB_CB(skb)->seq, start)) + start = TCP_SKB_CB(skb)->seq; + if (after(TCP_SKB_CB(skb)->end_seq, end)) + end = TCP_SKB_CB(skb)->end_seq; + } + } +} + +/* + * Purge the out-of-order queue. + * Return true if queue was pruned. + */ +static int tcp_prune_ofo_queue(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + int res = 0; + + if (!skb_queue_empty(&tp->out_of_order_queue)) { + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED); + __skb_queue_purge(&tp->out_of_order_queue); + + /* Reset SACK state. A conforming SACK implementation will + * do the same at a timeout based retransmit. When a connection + * is in a sad state like this, we care only about integrity + * of the connection not performance. + */ + if (tp->rx_opt.sack_ok) + tcp_sack_reset(&tp->rx_opt); + sk_mem_reclaim(sk); + res = 1; + } + return res; +} + +/* Reduce allocated memory if we can, trying to get + * the socket within its memory limits again. + * + * Return less than zero if we should start dropping frames + * until the socket owning process reads some of the data + * to stabilize the situation. + */ +static int tcp_prune_queue(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq); + + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED); + + if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) + tcp_clamp_window(sk); + else if (tcp_memory_pressure) + tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss); + + tcp_collapse_ofo_queue(sk); + if (!skb_queue_empty(&sk->sk_receive_queue)) + tcp_collapse(sk, &sk->sk_receive_queue, + skb_peek(&sk->sk_receive_queue), + NULL, + tp->copied_seq, tp->rcv_nxt); + sk_mem_reclaim(sk); + + if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) + return 0; + + /* Collapsing did not help, destructive actions follow. + * This must not ever occur. */ + + tcp_prune_ofo_queue(sk); + + if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) + return 0; + + /* If we are really being abused, tell the caller to silently + * drop receive data on the floor. It will get retransmitted + * and hopefully then we'll have sufficient space. + */ + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED); + + /* Massive buffer overcommit. */ + tp->pred_flags = 0; + return -1; +} + +/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto. + * As additional protections, we do not touch cwnd in retransmission phases, + * and if application hit its sndbuf limit recently. + */ +void tcp_cwnd_application_limited(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open && + sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) { + /* Limited by application or receiver window. */ + u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk)); + u32 win_used = max(tp->snd_cwnd_used, init_win); + if (win_used < tp->snd_cwnd) { + tp->snd_ssthresh = tcp_current_ssthresh(sk); + tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1; + } + tp->snd_cwnd_used = 0; + } + tp->snd_cwnd_stamp = tcp_time_stamp; +} + +static int tcp_should_expand_sndbuf(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + /* If the user specified a specific send buffer setting, do + * not modify it. + */ + if (sk->sk_userlocks & SOCK_SNDBUF_LOCK) + return 0; + + /* If we are under global TCP memory pressure, do not expand. */ + if (tcp_memory_pressure) + return 0; + + /* If we are under soft global TCP memory pressure, do not expand. */ + if (atomic_long_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0]) + return 0; + + /* If we filled the congestion window, do not expand. */ + if (tp->packets_out >= tp->snd_cwnd) + return 0; + + return 1; +} + +/* When incoming ACK allowed to free some skb from write_queue, + * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket + * on the exit from tcp input handler. + * + * PROBLEM: sndbuf expansion does not work well with largesend. + */ +static void tcp_new_space(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tcp_should_expand_sndbuf(sk)) { + int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) + + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff); + int demanded = max_t(unsigned int, tp->snd_cwnd, + tp->reordering + 1); + sndmem *= 2 * demanded; + if (sndmem > sk->sk_sndbuf) + sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]); + tp->snd_cwnd_stamp = tcp_time_stamp; + } + + sk->sk_write_space(sk); +} + +static void tcp_check_space(struct sock *sk) +{ + if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) { + sock_reset_flag(sk, SOCK_QUEUE_SHRUNK); + if (sk->sk_socket && + test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) + tcp_new_space(sk); + } +} + +static inline void tcp_data_snd_check(struct sock *sk) +{ + tcp_push_pending_frames(sk); + tcp_check_space(sk); +} + +/* + * Check if sending an ack is needed. + */ +static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible) +{ + struct tcp_sock *tp = tcp_sk(sk); + + /* More than one full frame received... */ + if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss && + /* ... and right edge of window advances far enough. + * (tcp_recvmsg() will send ACK otherwise). Or... + */ + __tcp_select_window(sk) >= tp->rcv_wnd) || + /* We ACK each frame or... */ + tcp_in_quickack_mode(sk) || + /* We have out of order data. */ + (ofo_possible && skb_peek(&tp->out_of_order_queue))) { + /* Then ack it now */ + tcp_send_ack(sk); + } else { + /* Else, send delayed ack. */ + tcp_send_delayed_ack(sk); + } +} + +static inline void tcp_ack_snd_check(struct sock *sk) +{ + if (!inet_csk_ack_scheduled(sk)) { + /* We sent a data segment already. */ + return; + } + __tcp_ack_snd_check(sk, 1); +} + +/* + * This routine is only called when we have urgent data + * signaled. Its the 'slow' part of tcp_urg. It could be + * moved inline now as tcp_urg is only called from one + * place. We handle URGent data wrong. We have to - as + * BSD still doesn't use the correction from RFC961. + * For 1003.1g we should support a new option TCP_STDURG to permit + * either form (or just set the sysctl tcp_stdurg). + */ + +static void tcp_check_urg(struct sock *sk, struct tcphdr *th) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 ptr = ntohs(th->urg_ptr); + + if (ptr && !sysctl_tcp_stdurg) + ptr--; + ptr += ntohl(th->seq); + + /* Ignore urgent data that we've already seen and read. */ + if (after(tp->copied_seq, ptr)) + return; + + /* Do not replay urg ptr. + * + * NOTE: interesting situation not covered by specs. + * Misbehaving sender may send urg ptr, pointing to segment, + * which we already have in ofo queue. We are not able to fetch + * such data and will stay in TCP_URG_NOTYET until will be eaten + * by recvmsg(). Seems, we are not obliged to handle such wicked + * situations. But it is worth to think about possibility of some + * DoSes using some hypothetical application level deadlock. + */ + if (before(ptr, tp->rcv_nxt)) + return; + + /* Do we already have a newer (or duplicate) urgent pointer? */ + if (tp->urg_data && !after(ptr, tp->urg_seq)) + return; + + /* Tell the world about our new urgent pointer. */ + sk_send_sigurg(sk); + + /* We may be adding urgent data when the last byte read was + * urgent. To do this requires some care. We cannot just ignore + * tp->copied_seq since we would read the last urgent byte again + * as data, nor can we alter copied_seq until this data arrives + * or we break the semantics of SIOCATMARK (and thus sockatmark()) + * + * NOTE. Double Dutch. Rendering to plain English: author of comment + * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB); + * and expect that both A and B disappear from stream. This is _wrong_. + * Though this happens in BSD with high probability, this is occasional. + * Any application relying on this is buggy. Note also, that fix "works" + * only in this artificial test. Insert some normal data between A and B and we will + * decline of BSD again. Verdict: it is better to remove to trap + * buggy users. + */ + if (tp->urg_seq == tp->copied_seq && tp->urg_data && + !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) { + struct sk_buff *skb = skb_peek(&sk->sk_receive_queue); + tp->copied_seq++; + if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) { + __skb_unlink(skb, &sk->sk_receive_queue); + __kfree_skb(skb); + } + } + + tp->urg_data = TCP_URG_NOTYET; + tp->urg_seq = ptr; + + /* Disable header prediction. */ + tp->pred_flags = 0; +} + +/* This is the 'fast' part of urgent handling. */ +static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th) +{ + struct tcp_sock *tp = tcp_sk(sk); + + /* Check if we get a new urgent pointer - normally not. */ + if (th->urg) + tcp_check_urg(sk, th); + + /* Do we wait for any urgent data? - normally not... */ + if (tp->urg_data == TCP_URG_NOTYET) { + u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) - + th->syn; + + /* Is the urgent pointer pointing into this packet? */ + if (ptr < skb->len) { + u8 tmp; + if (skb_copy_bits(skb, ptr, &tmp, 1)) + BUG(); + tp->urg_data = TCP_URG_VALID | tmp; + if (!sock_flag(sk, SOCK_DEAD)) + sk->sk_data_ready(sk, 0); + } + } +} + +static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen) +{ + struct tcp_sock *tp = tcp_sk(sk); + int chunk = skb->len - hlen; + int err; + + local_bh_enable(); + if (skb_csum_unnecessary(skb)) + err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk); + else + err = skb_copy_and_csum_datagram_iovec(skb, hlen, + tp->ucopy.iov); + + if (!err) { + tp->ucopy.len -= chunk; + tp->copied_seq += chunk; + tcp_rcv_space_adjust(sk); + } + + local_bh_disable(); + return err; +} + +static __sum16 __tcp_checksum_complete_user(struct sock *sk, + struct sk_buff *skb) +{ + __sum16 result; + + if (sock_owned_by_user(sk)) { + local_bh_enable(); + result = __tcp_checksum_complete(skb); + local_bh_disable(); + } else { + result = __tcp_checksum_complete(skb); + } + return result; +} + +static inline int tcp_checksum_complete_user(struct sock *sk, + struct sk_buff *skb) +{ + return !skb_csum_unnecessary(skb) && + __tcp_checksum_complete_user(sk, skb); +} + +#ifdef CONFIG_NET_DMA +static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb, + int hlen) +{ + struct tcp_sock *tp = tcp_sk(sk); + int chunk = skb->len - hlen; + int dma_cookie; + int copied_early = 0; + + if (tp->ucopy.wakeup) + return 0; + + if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list) + tp->ucopy.dma_chan = dma_find_channel(DMA_MEMCPY); + + if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) { + + dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan, + skb, hlen, + tp->ucopy.iov, chunk, + tp->ucopy.pinned_list); + + if (dma_cookie < 0) + goto out; + + tp->ucopy.dma_cookie = dma_cookie; + copied_early = 1; + + tp->ucopy.len -= chunk; + tp->copied_seq += chunk; + tcp_rcv_space_adjust(sk); + + if ((tp->ucopy.len == 0) || + (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) || + (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) { + tp->ucopy.wakeup = 1; + sk->sk_data_ready(sk, 0); + } + } else if (chunk > 0) { + tp->ucopy.wakeup = 1; + sk->sk_data_ready(sk, 0); + } +out: + return copied_early; +} +#endif /* CONFIG_NET_DMA */ + +/* Does PAWS and seqno based validation of an incoming segment, flags will + * play significant role here. + */ +static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, + struct tcphdr *th, int syn_inerr) +{ + u8 *hash_location; + struct tcp_sock *tp = tcp_sk(sk); + + /* RFC1323: H1. Apply PAWS check first. */ + if (tcp_fast_parse_options(skb, th, tp, &hash_location) && + tp->rx_opt.saw_tstamp && + tcp_paws_discard(sk, skb)) { + if (!th->rst) { + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); + tcp_send_dupack(sk, skb); + goto discard; + } + /* Reset is accepted even if it did not pass PAWS. */ + } + + /* Step 1: check sequence number */ + if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) { + /* RFC793, page 37: "In all states except SYN-SENT, all reset + * (RST) segments are validated by checking their SEQ-fields." + * And page 69: "If an incoming segment is not acceptable, + * an acknowledgment should be sent in reply (unless the RST + * bit is set, if so drop the segment and return)". + */ + if (!th->rst) + tcp_send_dupack(sk, skb); + goto discard; + } + + /* Step 2: check RST bit */ + if (th->rst) { + tcp_reset(sk); + goto discard; + } + + /* ts_recent update must be made after we are sure that the packet + * is in window. + */ + tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); + + /* step 3: check security and precedence [ignored] */ + + /* step 4: Check for a SYN in window. */ + if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { + if (syn_inerr) + TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONSYN); + tcp_reset(sk); + return -1; + } + + return 1; + +discard: + __kfree_skb(skb); + return 0; +} + +/* + * TCP receive function for the ESTABLISHED state. + * + * It is split into a fast path and a slow path. The fast path is + * disabled when: + * - A zero window was announced from us - zero window probing + * is only handled properly in the slow path. + * - Out of order segments arrived. + * - Urgent data is expected. + * - There is no buffer space left + * - Unexpected TCP flags/window values/header lengths are received + * (detected by checking the TCP header against pred_flags) + * - Data is sent in both directions. Fast path only supports pure senders + * or pure receivers (this means either the sequence number or the ack + * value must stay constant) + * - Unexpected TCP option. + * + * When these conditions are not satisfied it drops into a standard + * receive procedure patterned after RFC793 to handle all cases. + * The first three cases are guaranteed by proper pred_flags setting, + * the rest is checked inline. Fast processing is turned on in + * tcp_data_queue when everything is OK. + */ +int tcp_rcv_established(struct sock *sk, struct sk_buff *skb, + struct tcphdr *th, unsigned len) +{ + struct tcp_sock *tp = tcp_sk(sk); + int res; + + /* + * Header prediction. + * The code loosely follows the one in the famous + * "30 instruction TCP receive" Van Jacobson mail. + * + * Van's trick is to deposit buffers into socket queue + * on a device interrupt, to call tcp_recv function + * on the receive process context and checksum and copy + * the buffer to user space. smart... + * + * Our current scheme is not silly either but we take the + * extra cost of the net_bh soft interrupt processing... + * We do checksum and copy also but from device to kernel. + */ + + tp->rx_opt.saw_tstamp = 0; + + /* pred_flags is 0xS?10 << 16 + snd_wnd + * if header_prediction is to be made + * 'S' will always be tp->tcp_header_len >> 2 + * '?' will be 0 for the fast path, otherwise pred_flags is 0 to + * turn it off (when there are holes in the receive + * space for instance) + * PSH flag is ignored. + */ + + if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags && + TCP_SKB_CB(skb)->seq == tp->rcv_nxt && + !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) { + int tcp_header_len = tp->tcp_header_len; + + /* Timestamp header prediction: tcp_header_len + * is automatically equal to th->doff*4 due to pred_flags + * match. + */ + + /* Check timestamp */ + if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) { + /* No? Slow path! */ + if (!tcp_parse_aligned_timestamp(tp, th)) + goto slow_path; + + /* If PAWS failed, check it more carefully in slow path */ + if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0) + goto slow_path; + + /* DO NOT update ts_recent here, if checksum fails + * and timestamp was corrupted part, it will result + * in a hung connection since we will drop all + * future packets due to the PAWS test. + */ + } + + if (len <= tcp_header_len) { + /* Bulk data transfer: sender */ + if (len == tcp_header_len) { + /* Predicted packet is in window by definition. + * seq == rcv_nxt and rcv_wup <= rcv_nxt. + * Hence, check seq<=rcv_wup reduces to: + */ + if (tcp_header_len == + (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && + tp->rcv_nxt == tp->rcv_wup) + tcp_store_ts_recent(tp); + + /* We know that such packets are checksummed + * on entry. + */ + tcp_ack(sk, skb, 0); + __kfree_skb(skb); + tcp_data_snd_check(sk); + return 0; + } else { /* Header too small */ + TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS); + goto discard; + } + } else { + int eaten = 0; + int copied_early = 0; + + if (tp->copied_seq == tp->rcv_nxt && + len - tcp_header_len <= tp->ucopy.len) { +#ifdef CONFIG_NET_DMA + if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) { + copied_early = 1; + eaten = 1; + } +#endif + if (tp->ucopy.task == current && + sock_owned_by_user(sk) && !copied_early) { + __set_current_state(TASK_RUNNING); + + if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) + eaten = 1; + } + if (eaten) { + /* Predicted packet is in window by definition. + * seq == rcv_nxt and rcv_wup <= rcv_nxt. + * Hence, check seq<=rcv_wup reduces to: + */ + if (tcp_header_len == + (sizeof(struct tcphdr) + + TCPOLEN_TSTAMP_ALIGNED) && + tp->rcv_nxt == tp->rcv_wup) + tcp_store_ts_recent(tp); + + tcp_rcv_rtt_measure_ts(sk, skb); + + __skb_pull(skb, tcp_header_len); + tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER); + } + if (copied_early) + tcp_cleanup_rbuf(sk, skb->len); + } + if (!eaten) { + if (tcp_checksum_complete_user(sk, skb)) + goto csum_error; + + /* Predicted packet is in window by definition. + * seq == rcv_nxt and rcv_wup <= rcv_nxt. + * Hence, check seq<=rcv_wup reduces to: + */ + if (tcp_header_len == + (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && + tp->rcv_nxt == tp->rcv_wup) + tcp_store_ts_recent(tp); + + tcp_rcv_rtt_measure_ts(sk, skb); + + if ((int)skb->truesize > sk->sk_forward_alloc) + goto step5; + + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS); + + /* Bulk data transfer: receiver */ + __skb_pull(skb, tcp_header_len); + __skb_queue_tail(&sk->sk_receive_queue, skb); + skb_set_owner_r(skb, sk); + tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; + } + + tcp_event_data_recv(sk, skb); + + if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) { + /* Well, only one small jumplet in fast path... */ + tcp_ack(sk, skb, FLAG_DATA); + tcp_data_snd_check(sk); + if (!inet_csk_ack_scheduled(sk)) + goto no_ack; + } + + if (!copied_early || tp->rcv_nxt != tp->rcv_wup) + __tcp_ack_snd_check(sk, 0); +no_ack: +#ifdef CONFIG_NET_DMA + if (copied_early) + __skb_queue_tail(&sk->sk_async_wait_queue, skb); + else +#endif + if (eaten) + __kfree_skb(skb); + else + sk->sk_data_ready(sk, 0); + return 0; + } + } + +slow_path: + if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb)) + goto csum_error; + + /* + * Standard slow path. + */ + + res = tcp_validate_incoming(sk, skb, th, 1); + if (res <= 0) + return -res; + +step5: + if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0) + goto discard; + + tcp_rcv_rtt_measure_ts(sk, skb); + + /* Process urgent data. */ + tcp_urg(sk, skb, th); + + /* step 7: process the segment text */ + tcp_data_queue(sk, skb); + + tcp_data_snd_check(sk); + tcp_ack_snd_check(sk); + return 0; + +csum_error: + TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS); + +discard: + __kfree_skb(skb); + return 0; +} +EXPORT_SYMBOL(tcp_rcv_established); + +static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, + struct tcphdr *th, unsigned len) +{ + u8 *hash_location; + struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + struct tcp_cookie_values *cvp = tp->cookie_values; + int saved_clamp = tp->rx_opt.mss_clamp; + + tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0); + + if (th->ack) { + /* rfc793: + * "If the state is SYN-SENT then + * first check the ACK bit + * If the ACK bit is set + * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send + * a reset (unless the RST bit is set, if so drop + * the segment and return)" + * + * We do not send data with SYN, so that RFC-correct + * test reduces to: + */ + if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt) + goto reset_and_undo; + + if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && + !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp, + tcp_time_stamp)) { + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED); + goto reset_and_undo; + } + + /* Now ACK is acceptable. + * + * "If the RST bit is set + * If the ACK was acceptable then signal the user "error: + * connection reset", drop the segment, enter CLOSED state, + * delete TCB, and return." + */ + + if (th->rst) { + tcp_reset(sk); + goto discard; + } + + /* rfc793: + * "fifth, if neither of the SYN or RST bits is set then + * drop the segment and return." + * + * See note below! + * --ANK(990513) + */ + if (!th->syn) + goto discard_and_undo; + + /* rfc793: + * "If the SYN bit is on ... + * are acceptable then ... + * (our SYN has been ACKed), change the connection + * state to ESTABLISHED..." + */ + + TCP_ECN_rcv_synack(tp, th); + + tp->snd_wl1 = TCP_SKB_CB(skb)->seq; + tcp_ack(sk, skb, FLAG_SLOWPATH); + + /* Ok.. it's good. Set up sequence numbers and + * move to established. + */ + tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; + tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; + + /* RFC1323: The window in SYN & SYN/ACK segments is + * never scaled. + */ + tp->snd_wnd = ntohs(th->window); + tcp_init_wl(tp, TCP_SKB_CB(skb)->seq); + + if (!tp->rx_opt.wscale_ok) { + tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0; + tp->window_clamp = min(tp->window_clamp, 65535U); + } + + if (tp->rx_opt.saw_tstamp) { + tp->rx_opt.tstamp_ok = 1; + tp->tcp_header_len = + sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; + tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; + tcp_store_ts_recent(tp); + } else { + tp->tcp_header_len = sizeof(struct tcphdr); + } + + if (tcp_is_sack(tp) && sysctl_tcp_fack) + tcp_enable_fack(tp); + + tcp_mtup_init(sk); + tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); + tcp_initialize_rcv_mss(sk); + + /* Remember, tcp_poll() does not lock socket! + * Change state from SYN-SENT only after copied_seq + * is initialized. */ + tp->copied_seq = tp->rcv_nxt; + + if (cvp != NULL && + cvp->cookie_pair_size > 0 && + tp->rx_opt.cookie_plus > 0) { + int cookie_size = tp->rx_opt.cookie_plus + - TCPOLEN_COOKIE_BASE; + int cookie_pair_size = cookie_size + + cvp->cookie_desired; + + /* A cookie extension option was sent and returned. + * Note that each incoming SYNACK replaces the + * Responder cookie. The initial exchange is most + * fragile, as protection against spoofing relies + * entirely upon the sequence and timestamp (above). + * This replacement strategy allows the correct pair to + * pass through, while any others will be filtered via + * Responder verification later. + */ + if (sizeof(cvp->cookie_pair) >= cookie_pair_size) { + memcpy(&cvp->cookie_pair[cvp->cookie_desired], + hash_location, cookie_size); + cvp->cookie_pair_size = cookie_pair_size; + } + } + + smp_mb(); + tcp_set_state(sk, TCP_ESTABLISHED); + + security_inet_conn_established(sk, skb); + + /* Make sure socket is routed, for correct metrics. */ + icsk->icsk_af_ops->rebuild_header(sk); + + tcp_init_metrics(sk); + + tcp_init_congestion_control(sk); + + /* Prevent spurious tcp_cwnd_restart() on first data + * packet. + */ + tp->lsndtime = tcp_time_stamp; + + tcp_init_buffer_space(sk); + + if (sock_flag(sk, SOCK_KEEPOPEN)) + inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp)); + + if (!tp->rx_opt.snd_wscale) + __tcp_fast_path_on(tp, tp->snd_wnd); + else + tp->pred_flags = 0; + + if (!sock_flag(sk, SOCK_DEAD)) { + sk->sk_state_change(sk); + sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT); + } + + if (sk->sk_write_pending || + icsk->icsk_accept_queue.rskq_defer_accept || + icsk->icsk_ack.pingpong) { + /* Save one ACK. Data will be ready after + * several ticks, if write_pending is set. + * + * It may be deleted, but with this feature tcpdumps + * look so _wonderfully_ clever, that I was not able + * to stand against the temptation 8) --ANK + */ + inet_csk_schedule_ack(sk); + icsk->icsk_ack.lrcvtime = tcp_time_stamp; + icsk->icsk_ack.ato = TCP_ATO_MIN; + tcp_incr_quickack(sk); + tcp_enter_quickack_mode(sk); + inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, + TCP_DELACK_MAX, TCP_RTO_MAX); + +discard: + __kfree_skb(skb); + return 0; + } else { + tcp_send_ack(sk); + } + return -1; + } + + /* No ACK in the segment */ + + if (th->rst) { + /* rfc793: + * "If the RST bit is set + * + * Otherwise (no ACK) drop the segment and return." + */ + + goto discard_and_undo; + } + + /* PAWS check. */ + if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && + tcp_paws_reject(&tp->rx_opt, 0)) + goto discard_and_undo; + + if (th->syn) { + /* We see SYN without ACK. It is attempt of + * simultaneous connect with crossed SYNs. + * Particularly, it can be connect to self. + */ + tcp_set_state(sk, TCP_SYN_RECV); + + if (tp->rx_opt.saw_tstamp) { + tp->rx_opt.tstamp_ok = 1; + tcp_store_ts_recent(tp); + tp->tcp_header_len = + sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; + } else { + tp->tcp_header_len = sizeof(struct tcphdr); + } + + tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; + tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; + + /* RFC1323: The window in SYN & SYN/ACK segments is + * never scaled. + */ + tp->snd_wnd = ntohs(th->window); + tp->snd_wl1 = TCP_SKB_CB(skb)->seq; + tp->max_window = tp->snd_wnd; + + TCP_ECN_rcv_syn(tp, th); + + tcp_mtup_init(sk); + tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); + tcp_initialize_rcv_mss(sk); + + tcp_send_synack(sk); +#if 0 + /* Note, we could accept data and URG from this segment. + * There are no obstacles to make this. + * + * However, if we ignore data in ACKless segments sometimes, + * we have no reasons to accept it sometimes. + * Also, seems the code doing it in step6 of tcp_rcv_state_process + * is not flawless. So, discard packet for sanity. + * Uncomment this return to process the data. + */ + return -1; +#else + goto discard; +#endif + } + /* "fifth, if neither of the SYN or RST bits is set then + * drop the segment and return." + */ + +discard_and_undo: + tcp_clear_options(&tp->rx_opt); + tp->rx_opt.mss_clamp = saved_clamp; + goto discard; + +reset_and_undo: + tcp_clear_options(&tp->rx_opt); + tp->rx_opt.mss_clamp = saved_clamp; + return 1; +} + +/* + * This function implements the receiving procedure of RFC 793 for + * all states except ESTABLISHED and TIME_WAIT. + * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be + * address independent. + */ + +int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, + struct tcphdr *th, unsigned len) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + int queued = 0; + int res; + + tp->rx_opt.saw_tstamp = 0; + + switch (sk->sk_state) { + case TCP_CLOSE: + goto discard; + + case TCP_LISTEN: + if (th->ack) + return 1; + + if (th->rst) + goto discard; + + if (th->syn) { + if (icsk->icsk_af_ops->conn_request(sk, skb) < 0) + return 1; + + /* Now we have several options: In theory there is + * nothing else in the frame. KA9Q has an option to + * send data with the syn, BSD accepts data with the + * syn up to the [to be] advertised window and + * Solaris 2.1 gives you a protocol error. For now + * we just ignore it, that fits the spec precisely + * and avoids incompatibilities. It would be nice in + * future to drop through and process the data. + * + * Now that TTCP is starting to be used we ought to + * queue this data. + * But, this leaves one open to an easy denial of + * service attack, and SYN cookies can't defend + * against this problem. So, we drop the data + * in the interest of security over speed unless + * it's still in use. + */ + kfree_skb(skb); + return 0; + } + goto discard; + + case TCP_SYN_SENT: + queued = tcp_rcv_synsent_state_process(sk, skb, th, len); + if (queued >= 0) + return queued; + + /* Do step6 onward by hand. */ + tcp_urg(sk, skb, th); + __kfree_skb(skb); + tcp_data_snd_check(sk); + return 0; + } + + res = tcp_validate_incoming(sk, skb, th, 0); + if (res <= 0) + return -res; + + /* step 5: check the ACK field */ + if (th->ack) { + int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH) > 0; + + switch (sk->sk_state) { + case TCP_SYN_RECV: + if (acceptable) { + tp->copied_seq = tp->rcv_nxt; + smp_mb(); + tcp_set_state(sk, TCP_ESTABLISHED); + sk->sk_state_change(sk); + + /* Note, that this wakeup is only for marginal + * crossed SYN case. Passively open sockets + * are not waked up, because sk->sk_sleep == + * NULL and sk->sk_socket == NULL. + */ + if (sk->sk_socket) + sk_wake_async(sk, + SOCK_WAKE_IO, POLL_OUT); + + tp->snd_una = TCP_SKB_CB(skb)->ack_seq; + tp->snd_wnd = ntohs(th->window) << + tp->rx_opt.snd_wscale; + tcp_init_wl(tp, TCP_SKB_CB(skb)->seq); + + /* tcp_ack considers this ACK as duplicate + * and does not calculate rtt. + * Force it here. + */ + tcp_ack_update_rtt(sk, 0, 0); + + if (tp->rx_opt.tstamp_ok) + tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; + + /* Make sure socket is routed, for + * correct metrics. + */ + icsk->icsk_af_ops->rebuild_header(sk); + + tcp_init_metrics(sk); + + tcp_init_congestion_control(sk); + + /* Prevent spurious tcp_cwnd_restart() on + * first data packet. + */ + tp->lsndtime = tcp_time_stamp; + + tcp_mtup_init(sk); + tcp_initialize_rcv_mss(sk); + tcp_init_buffer_space(sk); + tcp_fast_path_on(tp); + } else { + return 1; + } + break; + + case TCP_FIN_WAIT1: + if (tp->snd_una == tp->write_seq) { + tcp_set_state(sk, TCP_FIN_WAIT2); + sk->sk_shutdown |= SEND_SHUTDOWN; + dst_confirm(__sk_dst_get(sk)); + + if (!sock_flag(sk, SOCK_DEAD)) + /* Wake up lingering close() */ + sk->sk_state_change(sk); + else { + int tmo; + + if (tp->linger2 < 0 || + (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && + after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) { + tcp_done(sk); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA); + return 1; + } + + tmo = tcp_fin_time(sk); + if (tmo > TCP_TIMEWAIT_LEN) { + inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN); + } else if (th->fin || sock_owned_by_user(sk)) { + /* Bad case. We could lose such FIN otherwise. + * It is not a big problem, but it looks confusing + * and not so rare event. We still can lose it now, + * if it spins in bh_lock_sock(), but it is really + * marginal case. + */ + inet_csk_reset_keepalive_timer(sk, tmo); + } else { + tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); + goto discard; + } + } + } + break; + + case TCP_CLOSING: + if (tp->snd_una == tp->write_seq) { + tcp_time_wait(sk, TCP_TIME_WAIT, 0); + goto discard; + } + break; + + case TCP_LAST_ACK: + if (tp->snd_una == tp->write_seq) { + tcp_update_metrics(sk); + tcp_done(sk); + goto discard; + } + break; + } + } else + goto discard; + + /* step 6: check the URG bit */ + tcp_urg(sk, skb, th); + + /* step 7: process the segment text */ + switch (sk->sk_state) { + case TCP_CLOSE_WAIT: + case TCP_CLOSING: + case TCP_LAST_ACK: + if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) + break; + case TCP_FIN_WAIT1: + case TCP_FIN_WAIT2: + /* RFC 793 says to queue data in these states, + * RFC 1122 says we MUST send a reset. + * BSD 4.4 also does reset. + */ + if (sk->sk_shutdown & RCV_SHUTDOWN) { + if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && + after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) { + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA); + tcp_reset(sk); + return 1; + } + } + /* Fall through */ + case TCP_ESTABLISHED: + tcp_data_queue(sk, skb); + queued = 1; + break; + } + + /* tcp_data could move socket to TIME-WAIT */ + if (sk->sk_state != TCP_CLOSE) { + tcp_data_snd_check(sk); + tcp_ack_snd_check(sk); + } + + if (!queued) { +discard: + __kfree_skb(skb); + } + return 0; +} +EXPORT_SYMBOL(tcp_rcv_state_process); |