From e971ceb803e147e47c15cbb7c5b84327c6453786 Mon Sep 17 00:00:00 2001 From: Fernando Fernandez Mancera Date: Mon, 15 Jul 2019 21:31:49 +0200 Subject: [PATCH] netfilter: synproxy: fix rst sequence number mismatch 14:51:00.024418 IP 192.168.122.1.41462 > netfilter.90: Flags [S], seq 4023580551, 14:51:00.024454 IP netfilter.90 > 192.168.122.1.41462: Flags [S.], seq 727560212, ack 4023580552, 14:51:00.024524 IP 192.168.122.1.41462 > netfilter.90: Flags [.], ack 1, Note: here, synproxy will send a SYN to the real server, as the 3whs was completed sucessfully. Instead of a syn/ack that we can intercept, we instead received a reset packet from the real backend, that we forward to the original client. However, we don't use the correct sequence number, so the reset is not effective in closing the connection coming from the client. 14:51:00.024550 IP netfilter.90 > 192.168.122.1.41462: Flags [R.], seq 3567407084, 14:51:00.231196 IP 192.168.122.1.41462 > netfilter.90: Flags [.], ack 1, 14:51:00.647911 IP 192.168.122.1.41462 > netfilter.90: Flags [.], ack 1, 14:51:01.474395 IP 192.168.122.1.41462 > netfilter.90: Flags [.], ack 1, Fixes: 48b1de4c110a ("netfilter: add SYNPROXY core/target") Signed-off-by: Fernando Fernandez Mancera Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_synproxy_core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c index 09718e5a9e41..c769462a839e 100644 --- a/net/netfilter/nf_synproxy_core.c +++ b/net/netfilter/nf_synproxy_core.c @@ -687,7 +687,7 @@ ipv4_synproxy_hook(void *priv, struct sk_buff *skb, state = &ct->proto.tcp; switch (state->state) { case TCP_CONNTRACK_CLOSE: - if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) { + if (th->rst && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) { nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq) + 1); break; @@ -1111,7 +1111,7 @@ ipv6_synproxy_hook(void *priv, struct sk_buff *skb, state = &ct->proto.tcp; switch (state->state) { case TCP_CONNTRACK_CLOSE: - if (th->rst && !test_bit(IPS_SEEN_REPLY_BIT, &ct->status)) { + if (th->rst && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) { nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq) + 1); break;