diff options
| author | Eric Dumazet <edumazet@google.com> | 2026-06-08 15:14:52 +0000 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-06-13 13:40:37 -0700 |
| commit | 91934d44468d8d674248c4dfd93a8999e0b4594f (patch) | |
| tree | fe2ef3aaf21a4a5d4b7bbc19a93a76d4d8255431 /net | |
| parent | 0969af4b649e6bf65298988d4d4389dda64a6e62 (diff) | |
| download | ath-91934d44468d8d674248c4dfd93a8999e0b4594f.tar.gz | |
tcp: refine tcp_sequence() for the FIN exception
Commit 0e24d17bd966 ("tcp: implement RFC 7323 window retraction
receiver requirements") removed the special FIN case that
was added in commit 1e3bb184e941 ("tcp: re-enable acceptance of
FIN packets when RWIN is 0").
If a peer sends a segment containing data and a FIN flag before
it learns about our window retraction and has a buggy TCP stack,
it might place the FIN one byte beyond what it thinks is the
right edge of the window (i.e., max_window_edge + 1).
The data portion (end_seq - th->fin) will end exactly at max_window_edge.
In this case, we will drop the packet if our receive queue is not empty,
even though the data was sent within the window we previously allowed.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Simon Baatz <gmbnomis@gmail.com>
Link: https://patch.msgid.link/20260608151452.706822-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net')
| -rw-r--r-- | net/ipv4/tcp_input.c | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index ab7a4e5435a8a..8560a9c6d3820 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4812,18 +4812,20 @@ static enum skb_drop_reason tcp_sequence(const struct sock *sk, const struct tcphdr *th) { const struct tcp_sock *tp = tcp_sk(sk); + u32 seq_limit; if (before(end_seq, tp->rcv_wup)) return SKB_DROP_REASON_TCP_OLD_SEQUENCE; - if (unlikely(after(end_seq, tp->rcv_nxt + tcp_max_receive_window(tp)))) { + seq_limit = tp->rcv_nxt + tcp_max_receive_window(tp); + if (unlikely(after(end_seq, seq_limit))) { /* Some stacks are known to handle FIN incorrectly; allow the * FIN to extend beyond the window and check it in detail later. */ - if (!after(end_seq - th->fin, tp->rcv_nxt + tcp_receive_window(tp))) + if (!after(end_seq - th->fin, seq_limit)) return SKB_NOT_DROPPED_YET; - if (after(seq, tp->rcv_nxt + tcp_max_receive_window(tp))) + if (after(seq, seq_limit)) return SKB_DROP_REASON_TCP_INVALID_SEQUENCE; /* Only accept this packet if receive queue is empty. */ |