diff options
Diffstat (limited to 'target/linux/generic/patches-4.4/096-tcp-make-challenge-acks-less-predictable.patch')
| -rw-r--r-- | target/linux/generic/patches-4.4/096-tcp-make-challenge-acks-less-predictable.patch | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/target/linux/generic/patches-4.4/096-tcp-make-challenge-acks-less-predictable.patch b/target/linux/generic/patches-4.4/096-tcp-make-challenge-acks-less-predictable.patch new file mode 100644 index 0000000000..a783c6ebbc --- /dev/null +++ b/target/linux/generic/patches-4.4/096-tcp-make-challenge-acks-less-predictable.patch @@ -0,0 +1,76 @@ +From 75ff39ccc1bd5d3c455b6822ab09e533c551f758 Mon Sep 17 00:00:00 2001 +From: Eric Dumazet <edumazet@google.com> +Date: Sun, 10 Jul 2016 10:04:02 +0200 +Subject: [PATCH] tcp: make challenge acks less predictable + +Yue Cao claims that current host rate limiting of challenge ACKS +(RFC 5961) could leak enough information to allow a patient attacker +to hijack TCP sessions. He will soon provide details in an academic +paper. + +This patch increases the default limit from 100 to 1000, and adds +some randomization so that the attacker can no longer hijack +sessions without spending a considerable amount of probes. + +Based on initial analysis and patch from Linus. + +Note that we also have per socket rate limiting, so it is tempting +to remove the host limit in the future. + +v2: randomize the count of challenge acks per second, not the period. + +Fixes: 282f23c6ee34 ("tcp: implement RFC 5961 3.2") +Reported-by: Yue Cao <ycao009@ucr.edu> +Signed-off-by: Eric Dumazet <edumazet@google.com> +Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> +Cc: Yuchung Cheng <ycheng@google.com> +Cc: Neal Cardwell <ncardwell@google.com> +Acked-by: Neal Cardwell <ncardwell@google.com> +Acked-by: Yuchung Cheng <ycheng@google.com> +Signed-off-by: David S. Miller <davem@davemloft.net> +--- + net/ipv4/tcp_input.c | 15 ++++++++++----- + 1 file changed, 10 insertions(+), 5 deletions(-) + +--- a/net/ipv4/tcp_input.c ++++ b/net/ipv4/tcp_input.c +@@ -89,7 +89,7 @@ int sysctl_tcp_adv_win_scale __read_most + EXPORT_SYMBOL(sysctl_tcp_adv_win_scale); + + /* rfc5961 challenge ack rate limiting */ +-int sysctl_tcp_challenge_ack_limit = 100; ++int sysctl_tcp_challenge_ack_limit = 1000; + + int sysctl_tcp_stdurg __read_mostly; + int sysctl_tcp_rfc1337 __read_mostly; +@@ -3427,7 +3427,7 @@ static void tcp_send_challenge_ack(struc + static u32 challenge_timestamp; + static unsigned int challenge_count; + struct tcp_sock *tp = tcp_sk(sk); +- u32 now; ++ u32 count, now; + + /* First check our per-socket dupack rate limit. */ + if (tcp_oow_rate_limited(sock_net(sk), skb, +@@ -3435,13 +3435,18 @@ static void tcp_send_challenge_ack(struc + &tp->last_oow_ack_time)) + return; + +- /* Then check the check host-wide RFC 5961 rate limit. */ ++ /* Then check host-wide RFC 5961 rate limit. */ + now = jiffies / HZ; + if (now != challenge_timestamp) { ++ u32 half = (sysctl_tcp_challenge_ack_limit + 1) >> 1; ++ + challenge_timestamp = now; +- challenge_count = 0; ++ WRITE_ONCE(challenge_count, half + ++ prandom_u32_max(sysctl_tcp_challenge_ack_limit)); + } +- if (++challenge_count <= sysctl_tcp_challenge_ack_limit) { ++ count = READ_ONCE(challenge_count); ++ if (count > 0) { ++ WRITE_ONCE(challenge_count, count - 1); + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK); + tcp_send_ack(sk); + } |