From b8835ba8c029b5c9ada5666754526c2b00f7ea80 Mon Sep 17 00:00:00 2001 From: Pablo Neira Ayuso Date: Tue, 17 May 2022 10:44:14 +0200 Subject: netfilter: flowtable: fix TCP flow teardown [ Upstream commit e5eaac2beb54f0a16ff851125082d9faeb475572 ] This patch addresses three possible problems: 1. ct gc may race to undo the timeout adjustment of the packet path, leaving the conntrack entry in place with the internal offload timeout (one day). 2. ct gc removes the ct because the IPS_OFFLOAD_BIT is not set and the CLOSE timeout is reached before the flow offload del. 3. tcp ct is always set to ESTABLISHED with a very long timeout in flow offload teardown/delete even though the state might be already CLOSED. Also as a remark we cannot assume that the FIN or RST packet is hitting flow table teardown as the packet might get bumped to the slow path in nftables. This patch resets IPS_OFFLOAD_BIT from flow_offload_teardown(), so conntrack handles the tcp rst/fin packet which triggers the CLOSE/FIN state transition. Moreover, teturn the connection's ownership to conntrack upon teardown by clearing the offload flag and fixing the established timeout value. The flow table GC thread will asynchonrnously free the flow table and hardware offload entries. Before this patch, the IPS_OFFLOAD_BIT remained set for expired flows on which is also misleading since the flow is back to classic conntrack path. If nf_ct_delete() removes the entry from the conntrack table, then it calls nf_ct_put() which decrements the refcnt. This is not a problem because the flowtable holds a reference to the conntrack object from flow_offload_alloc() path which is released via flow_offload_free(). This patch also updates nft_flow_offload to skip packets in SYN_RECV state. Since we might miss or bump packets to slow path, we do not know what will happen there while we are still in SYN_RECV, this patch postpones offload up to the next packet which also aligns to the existing behaviour in tc-ct. flow_offload_teardown() does not reset the existing tcp state from flow_offload_fixup_tcp() to ESTABLISHED anymore, packets bump to slow path might have already update the state to CLOSE/FIN. Joint work with Oz and Sven. Fixes: 1e5b2471bcc4 ("netfilter: nf_flow_table: teardown flow timeout race") Signed-off-by: Oz Shlomo Signed-off-by: Sven Auhagen Signed-off-by: Pablo Neira Ayuso Signed-off-by: Sasha Levin --- net/netfilter/nf_flow_table_core.c | 33 +++++++----------------------- net/netfilter/nft_flow_offload.c | 3 ++- 2 files changed, 9 insertions(+), 27 deletions(-) --- a/net/netfilter/nf_flow_table_core.c +++ b/net/netfilter/nf_flow_table_core.c @@ -173,12 +173,11 @@ EXPORT_SYMBOL_GPL(flow_offload_route_ini static void flow_offload_fixup_tcp(struct ip_ct_tcp *tcp) { - tcp->state = TCP_CONNTRACK_ESTABLISHED; tcp->seen[0].td_maxwin = 0; tcp->seen[1].td_maxwin = 0; } -static void flow_offload_fixup_ct_timeout(struct nf_conn *ct) +static void flow_offload_fixup_ct(struct nf_conn *ct) { struct net *net = nf_ct_net(ct); int l4num = nf_ct_protonum(ct); @@ -187,7 +186,9 @@ static void flow_offload_fixup_ct_timeou if (l4num == IPPROTO_TCP) { struct nf_tcp_net *tn = nf_tcp_pernet(net); - timeout = tn->timeouts[TCP_CONNTRACK_ESTABLISHED]; + flow_offload_fixup_tcp(&ct->proto.tcp); + + timeout = tn->timeouts[ct->proto.tcp.state]; timeout -= tn->offload_timeout; } else if (l4num == IPPROTO_UDP) { struct nf_udp_net *tn = nf_udp_pernet(net); @@ -205,18 +206,6 @@ static void flow_offload_fixup_ct_timeou WRITE_ONCE(ct->timeout, nfct_time_stamp + timeout); } -static void flow_offload_fixup_ct_state(struct nf_conn *ct) -{ - if (nf_ct_protonum(ct) == IPPROTO_TCP) - flow_offload_fixup_tcp(&ct->proto.tcp); -} - -static void flow_offload_fixup_ct(struct nf_conn *ct) -{ - flow_offload_fixup_ct_state(ct); - flow_offload_fixup_ct_timeout(ct); -} - static void flow_offload_route_release(struct flow_offload *flow) { nft_flow_dst_release(flow, FLOW_OFFLOAD_DIR_ORIGINAL); @@ -353,22 +342,14 @@ static void flow_offload_del(struct nf_f rhashtable_remove_fast(&flow_table->rhashtable, &flow->tuplehash[FLOW_OFFLOAD_DIR_REPLY].node, nf_flow_offload_rhash_params); - - clear_bit(IPS_OFFLOAD_BIT, &flow->ct->status); - - if (nf_flow_has_expired(flow)) - flow_offload_fixup_ct(flow->ct); - else - flow_offload_fixup_ct_timeout(flow->ct); - flow_offload_free(flow); } void flow_offload_teardown(struct flow_offload *flow) { + clear_bit(IPS_OFFLOAD_BIT, &flow->ct->status); set_bit(NF_FLOW_TEARDOWN, &flow->flags); - - flow_offload_fixup_ct_state(flow->ct); + flow_offload_fixup_ct(flow->ct); } EXPORT_SYMBOL_GPL(flow_offload_teardown); @@ -437,7 +418,7 @@ static void nf_flow_offload_gc_step(stru if (nf_flow_has_expired(flow) || nf_ct_is_dying(flow->ct)) - set_bit(NF_FLOW_TEARDOWN, &flow->flags); + flow_offload_teardown(flow); if (test_bit(NF_FLOW_TEARDOWN, &flow->flags)) { if (test_bit(NF_FLOW_HW, &flow->flags)) { --- a/net/netfilter/nft_flow_offload.c +++ b/net/netfilter/nft_flow_offload.c @@ -268,6 +268,12 @@ static bool nft_flow_offload_skip(struct return false; } +static bool nf_conntrack_tcp_established(const struct nf_conn *ct) +{ + return ct->proto.tcp.state == TCP_CONNTRACK_ESTABLISHED && + test_bit(IPS_ASSURED_BIT, &ct->status); +} + static void nft_flow_offload_eval(const struct nft_expr *expr, struct nft_regs *regs, const struct nft_pktinfo *pkt) @@ -293,7 +299,8 @@ static void nft_flow_offload_eval(const case IPPROTO_TCP: tcph = skb_header_pointer(pkt->skb, pkt->xt.thoff, sizeof(_tcph), &_tcph); - if (unlikely(!tcph || tcph->fin || tcph->rst)) + if (unlikely(!tcph || tcph->fin || tcph->rst || + !nf_conntrack_tcp_established(ct))) goto out; break; case IPPROTO_UDP: