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Commit c9b929f7 authored by Aananth V's avatar Aananth V Committed by Greg Kroah-Hartman
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tcp: call tcp_try_undo_recovery when an RTOd TFO SYNACK is ACKed 



[ 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: default avatarAananth V <aananthv@google.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 25eaef1d

net/ipv4/tcp_input.c

+5 −4
Original line number Diff line number Diff line
@@ -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);