[ Upstream commit 959b69ef57db00cb33e9c4777400ae7183ebddd3 ]
Jakub Jankowski reported following oddity:
After 3 way handshake completes, timeout of new connection is set to max_retrans (300s) instead of established (5 days).
shortened excerpt from pcap provided: 25.070622 IP (flags [DF], proto TCP (6), length 52) 10.8.5.4.1025 > 10.8.1.2.80: Flags [S], seq 11, win 64240, [wscale 8] 26.070462 IP (flags [DF], proto TCP (6), length 48) 10.8.1.2.80 > 10.8.5.4.1025: Flags [S.], seq 82, ack 12, win 65535, [wscale 3] 27.070449 IP (flags [DF], proto TCP (6), length 40) 10.8.5.4.1025 > 10.8.1.2.80: Flags [.], ack 83, win 512, length 0
Turns out the last_win is of u16 type, but we store the scaled value: 512 << 8 (== 0x20000) becomes 0 window.
The Fixes tag is not correct, as the bug has existed forever, but without that change all that this causes might cause is to mistake a window update (to-nonzero-from-zero) for a retransmit.
Fixes: fbcd253d2448b8 ("netfilter: conntrack: lower timeout to RETRANS seconds if window is 0") Reported-by: Jakub Jankowski shasta@toxcorp.com Tested-by: Jakub Jankowski shasta@toxcorp.com Signed-off-by: Florian Westphal fw@strlen.de Acked-by: Jozsef Kadlecsik kadlec@blackhole.kfki.hu Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/netfilter/nf_conntrack_proto_tcp.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index 1e2cc83ff5da8..ae1f8c6b3a974 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -472,6 +472,7 @@ static bool tcp_in_window(const struct nf_conn *ct, struct ip_ct_tcp_state *receiver = &state->seen[!dir]; const struct nf_conntrack_tuple *tuple = &ct->tuplehash[dir].tuple; __u32 seq, ack, sack, end, win, swin; + u16 win_raw; s32 receiver_offset; bool res, in_recv_win;
@@ -480,7 +481,8 @@ static bool tcp_in_window(const struct nf_conn *ct, */ seq = ntohl(tcph->seq); ack = sack = ntohl(tcph->ack_seq); - win = ntohs(tcph->window); + win_raw = ntohs(tcph->window); + win = win_raw; end = segment_seq_plus_len(seq, skb->len, dataoff, tcph);
if (receiver->flags & IP_CT_TCP_FLAG_SACK_PERM) @@ -655,14 +657,14 @@ static bool tcp_in_window(const struct nf_conn *ct, && state->last_seq == seq && state->last_ack == ack && state->last_end == end - && state->last_win == win) + && state->last_win == win_raw) state->retrans++; else { state->last_dir = dir; state->last_seq = seq; state->last_ack = ack; state->last_end = end; - state->last_win = win; + state->last_win = win_raw; state->retrans = 0; } }