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tcp: initialize send sequence numbers before deferring TFO

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TCP_FASTOPEN_CONNECT can return from connect() before tcp_connect_init()
when a cached cookie or cookieless Fast Open allows deferring the SYN.
At this point write_seq contains the initial sequence number, while
snd_una and snd_nxt have not been initialized to that sequence number.

Consequently, inet_diag and /proc/net/tcp{,6} report the initial
sequence number as the send queue length despite no SYN or payload being
queued.

Initialize snd_una and snd_nxt to write_seq before marking the
connection as deferred. Both sequence-based queue lengths then remain
zero until the first write starts the connection and runs
tcp_connect_init().

Fixes: 19f6d3f3c8 ("net/tcp-fastopen: Add new API support")
Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
Reviewed-by: Eric Dumazet <edumazet@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Link: https://patch.msgid.link/20261102035943.9700-1-qingfang.deng@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Qingfang Deng 2026-11-02 11:59:43 +08:00 committed by Paolo Abeni
parent 37dfd0efbf
commit 57889a8f6d
1 changed files with 2 additions and 0 deletions
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2
net/ipv4/tcp_fastopen.c
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@ -545,6 +545,8 @@ bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
if (tp->fastopen_connect && !tp->fastopen_req) {
if (tcp_fastopen_cookie_check(sk, &mss, &cookie)) {
WRITE_ONCE(tp->snd_una, tp->write_seq);
WRITE_ONCE(tp->snd_nxt, tp->write_seq);
inet_set_bit(DEFER_CONNECT, sk);
return true;
}