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Commit f7020c43 authored Jan 15, 2021 by Enke Chen Committed by Greg Kroah-Hartman Jan 27, 2021

tcp: fix TCP_USER_TIMEOUT with zero window



commit 9d9b1ee0b2d1c9e02b2338c4a4b0a062d2d3edac upstream.

The TCP session does not terminate with TCP_USER_TIMEOUT when data
remain untransmitted due to zero window.

The number of unanswered zero-window probes (tcp_probes_out) is
reset to zero with incoming acks irrespective of the window size,
as described in tcp_probe_timer():

    RFC 1122 4.2.2.17 requires the sender to stay open indefinitely
    as long as the receiver continues to respond probes. We support
    this by default and reset icsk_probes_out with incoming ACKs.

This counter, however, is the wrong one to be used in calculating the
duration that the window remains closed and data remain untransmitted.
Thanks to Jonathan Maxwell <jmaxwell37@gmail.com> for diagnosing the
actual issue.

In this patch a new timestamp is introduced for the socket in order to
track the elapsed time for the zero-window probes that have not been
answered with any non-zero window ack.

Fixes: 9721e709 ("tcp: simplify window probe aborting on USER_TIMEOUT")
Reported-by: William McCall <william.mccall@gmail.com>
Co-developed-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Enke Chen <enchen@paloaltonetworks.com>
Reviewed-by: Yuchung Cheng <ycheng@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20210115223058.GA39267@localhost.localdomain


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 945d182a

include/net/inet_connection_sock.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -83,6 +83,8 @@ struct inet_connection_sock_af_ops {
		* @icsk_ext_hdr_len: Network protocol overhead (IP/IPv6 options)
		* @icsk_ack: Delayed ACK control data
		* @icsk_mtup; MTU probing control data
		* @icsk_probes_tstamp: Probe timestamp (cleared by non-zero window ack)
		* @icsk_user_timeout: TCP_USER_TIMEOUT value
		*/
		struct inet_connection_sock {
		/* inet_sock has to be the first member! */
		@@ -133,6 +135,7 @@ struct inet_connection_sock {

		u32 probe_timestamp;
		} icsk_mtup;
		u32 icsk_probes_tstamp;
		u32 icsk_user_timeout;

		u64 icsk_ca_priv[104 / sizeof(u64)];

net/ipv4/inet_connection_sock.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -840,6 +840,7 @@ struct sock inet_csk_clone_lock(const struct sock sk,
		newicsk->icsk_retransmits = 0;
		newicsk->icsk_backoff = 0;
		newicsk->icsk_probes_out = 0;
		newicsk->icsk_probes_tstamp = 0;

		/* Deinitialize accept_queue to trap illegal accesses. */
		memset(&newicsk->icsk_accept_queue, 0, sizeof(newicsk->icsk_accept_queue));

net/ipv4/tcp.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -2627,6 +2627,7 @@ int tcp_disconnect(struct sock *sk, int flags)
		icsk->icsk_backoff = 0;
		tp->snd_cwnd = 2;
		icsk->icsk_probes_out = 0;
		icsk->icsk_probes_tstamp = 0;
		icsk->icsk_rto = TCP_TIMEOUT_INIT;
		tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
		tp->snd_cwnd = TCP_INIT_CWND;

net/ipv4/tcp_input.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -3286,6 +3286,7 @@ static void tcp_ack_probe(struct sock *sk)
		return;
		if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
		icsk->icsk_backoff = 0;
		icsk->icsk_probes_tstamp = 0;
		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
		/* Socket must be waked up by subsequent tcp_data_snd_check().
		* This function is not for random using!

net/ipv4/tcp_output.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -3835,6 +3835,7 @@ void tcp_send_probe0(struct sock *sk)
		/* Cancel probe timer, if it is not required. */
		icsk->icsk_probes_out = 0;
		icsk->icsk_backoff = 0;
		icsk->icsk_probes_tstamp = 0;
		return;
		}