From 250fad18b0c959b137ad745428fb411f1ac1bbc6 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 14 Jun 2024 13:06:15 +0000 Subject: [PATCH] tcp: clear tp->retrans_stamp in tcp_rcv_fastopen_synack() commit 9e046bb111f13461d3f9331e24e974324245140e upstream. Some applications were reporting ETIMEDOUT errors on apparently good looking flows, according to packet dumps. We were able to root cause the issue to an accidental setting of tp->retrans_stamp in the following scenario: - client sends TFO SYN with data. - server has TFO disabled, ACKs only SYN but not payload. - client receives SYNACK covering only SYN. - tcp_ack() eats SYN and sets tp->retrans_stamp to 0. - tcp_rcv_fastopen_synack() calls tcp_xmit_retransmit_queue() to retransmit TFO payload w/o SYN, sets tp->retrans_stamp to "now", but we are not in any loss recovery state. - TFO payload is ACKed. - we are not in any loss recovery state, and don't see any dupacks, so we don't get to any code path that clears tp->retrans_stamp. - tp->retrans_stamp stays non-zero for the lifetime of the connection. - after first RTO, tcp_clamp_rto_to_user_timeout() clamps second RTO to 1 jiffy due to bogus tp->retrans_stamp. - on clamped RTO with non-zero icsk_retransmits, retransmits_timed_out() sets start_ts from tp->retrans_stamp from TFO payload retransmit hours/days ago, and computes bogus long elapsed time for loss recovery, and suffers ETIMEDOUT early. Fixes: a7abf3cd76e1 ("tcp: consider using standard rtx logic in tcp_rcv_fastopen_synack()") CC: stable@vger.kernel.org Co-developed-by: Neal Cardwell Signed-off-by: Neal Cardwell Co-developed-by: Yuchung Cheng Signed-off-by: Yuchung Cheng Signed-off-by: Eric Dumazet Link: https://lore.kernel.org/r/20240614130615.396837-1-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_input.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index f938442b202d..abd6e95d2dca 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -6176,6 +6176,7 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack, skb_rbtree_walk_from(data) tcp_mark_skb_lost(sk, data); tcp_xmit_retransmit_queue(sk); + tp->retrans_stamp = 0; NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL); return true;