5.4-stable review patch. If anyone has any objections, please let me know.
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From: Aananth V aananthv@google.com
[ Upstream commit e326578a21414738de45f77badd332fb00bd0f58 ]
For passive TCP Fast Open sockets that had SYN/ACK timeout and did not send more data in SYN_RECV, upon receiving the final ACK in 3WHS, the congestion state may awkwardly stay in CA_Loss mode unless the CA state was undone due to TCP timestamp checks. However, if tcp_rcv_synrecv_state_fastopen() decides not to undo, then we should enter CA_Open, because at that point we have received an ACK covering the retransmitted SYNACKs. Currently, the icsk_ca_state is only set to CA_Open after we receive an ACK for a data-packet. This is because tcp_ack does not call tcp_fastretrans_alert (and tcp_process_loss) if !prior_packets
Note that tcp_process_loss() calls tcp_try_undo_recovery(), so having tcp_rcv_synrecv_state_fastopen() decide that if we're in CA_Loss we should call tcp_try_undo_recovery() is consistent with that, and low risk.
Fixes: dad8cea7add9 ("tcp: fix TFO SYNACK undo to avoid double-timestamp-undo") Signed-off-by: Aananth V aananthv@google.com Signed-off-by: Neal Cardwell ncardwell@google.com Signed-off-by: Yuchung Cheng ycheng@google.com Reviewed-by: Eric Dumazet edumazet@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp_input.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index c3f227c4c3567..fe5ef114beba5 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -6176,22 +6176,23 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
static void tcp_rcv_synrecv_state_fastopen(struct sock *sk) { + struct tcp_sock *tp = tcp_sk(sk); struct request_sock *req;
/* If we are still handling the SYNACK RTO, see if timestamp ECR allows * undo. If peer SACKs triggered fast recovery, we can't undo here. */ - if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss) - tcp_try_undo_loss(sk, false); + 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_sk(sk)->retrans_stamp = 0; + tp->retrans_stamp = 0; inet_csk(sk)->icsk_retransmits = 0;
/* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1, * we no longer need req so release it. */ - req = rcu_dereference_protected(tcp_sk(sk)->fastopen_rsk, + req = rcu_dereference_protected(tp->fastopen_rsk, lockdep_sock_is_held(sk)); reqsk_fastopen_remove(sk, req, false);