6.6-stable review patch. If anyone has any objections, please let me know.
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From: Neal Cardwell ncardwell@google.com
[ 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@google.com Signed-off-by: Yuchung Cheng ycheng@google.com Signed-off-by: Eric Dumazet edumazet@google.com Link: https://patch.msgid.link/20241001200517.2756803-4-ncardwell.sw@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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.