6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Neal Cardwell <ncardwell@xxxxxxxxxx>
[ Upstream commit 27c80efcc20486c82698f05f00e288b44513c86b ]
Fix tcp_rcv_synrecv_state_fastopen() to not zero retrans_stamp
if retransmits are outstanding.
tcp_fastopen_synack_timer() sets retrans_stamp, so typically we'll
need to zero retrans_stamp here to prevent spurious
retransmits_timed_out(). The logic to zero retrans_stamp is from this
2019 commit:
commit cd736d8b67fb ("tcp: fix retrans timestamp on passive Fast Open")
However, in the corner case where the ACK of our TFO SYNACK carried
some SACK blocks that caused us to enter TCP_CA_Recovery then that
non-zero retrans_stamp corresponds to the active fast recovery, and we
need to leave retrans_stamp with its current non-zero value, for
correct ETIMEDOUT and undo behavior.
Fixes: cd736d8b67fb ("tcp: fix retrans timestamp on passive Fast Open")
Signed-off-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: Yuchung Cheng <ycheng@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://patch.msgid.link/20241001200517.2756803-4-ncardwell.sw@xxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
net/ipv4/tcp_input.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d472f7052cd32..fb053942dba2a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6554,10 +6554,17 @@ static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss && !tp->packets_out)
tcp_try_undo_recovery(sk);
- /* Reset rtx states to prevent spurious retransmits_timed_out() */
tcp_update_rto_time(tp);
- tp->retrans_stamp = 0;
inet_csk(sk)->icsk_retransmits = 0;
+ /* In tcp_fastopen_synack_timer() on the first SYNACK RTO we set
+ * retrans_stamp but don't enter CA_Loss, so in case that happened we
+ * need to zero retrans_stamp here to prevent spurious
+ * retransmits_timed_out(). However, if the ACK of our SYNACK caused us
+ * to enter CA_Recovery then we need to leave retrans_stamp as it was
+ * set entering CA_Recovery, for correct retransmits_timed_out() and
+ * undo behavior.
+ */
+ tcp_retrans_stamp_cleanup(sk);
/* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1,
* we no longer need req so release it.
--
2.43.0
