70 lines
2.3 KiB
Diff
70 lines
2.3 KiB
Diff
From 238c69f9af458e41dea5ad8c988dbf65b05b5172 Mon Sep 17 00:00:00 2001
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From: Stefano Brivio <sbrivio@redhat.com>
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Date: Tue, 19 Nov 2024 20:53:44 +0100
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Subject: [PATCH] tcp: Acknowledge keep-alive segments, ignore them for the
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rest
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RFC 9293, 3.8.4 says:
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Implementers MAY include "keep-alives" in their TCP implementations
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(MAY-5), although this practice is not universally accepted. Some
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TCP implementations, however, have included a keep-alive mechanism.
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To confirm that an idle connection is still active, these
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implementations send a probe segment designed to elicit a response
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from the TCP peer. Such a segment generally contains SEG.SEQ =
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SND.NXT-1 and may or may not contain one garbage octet of data. If
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keep-alives are included, the application MUST be able to turn them
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on or off for each TCP connection (MUST-24), and they MUST default to
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off (MUST-25).
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but currently, tcp_data_from_tap() is not aware of this and will
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schedule a fast re-transmit on the second keep-alive (because it's
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also a duplicate ACK), ignoring the fact that the sequence number was
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rewinded to SND.NXT-1.
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ACK these keep-alive segments, reset the activity timeout, and ignore
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them for the rest.
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At some point, we could think of implementing an approximation of
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keep-alive segments on outbound sockets, for example by setting
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TCP_KEEPIDLE to 1, and a large TCP_KEEPINTVL, so that we send a single
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keep-alive segment at approximately the same time, and never reset the
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connection. That's beyond the scope of this fix, though.
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Reported-by: Tim Besard <tim.besard@gmail.com>
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Link: https://github.com/containers/podman/discussions/24572
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Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
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Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
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---
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tcp.c | 14 ++++++++++++++
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1 file changed, 14 insertions(+)
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diff --git a/tcp.c b/tcp.c
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index f357920..1eb85bb 100644
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--- a/tcp.c
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+++ b/tcp.c
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@@ -1763,6 +1763,20 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn,
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continue;
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seq = ntohl(th->seq);
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+ if (SEQ_LT(seq, conn->seq_from_tap) && len <= 1) {
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+ flow_trace(conn,
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+ "keep-alive sequence: %u, previous: %u",
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+ seq, conn->seq_from_tap);
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+
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+ tcp_send_flag(c, conn, ACK);
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+ tcp_timer_ctl(c, conn);
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+
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+ if (p->count == 1)
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+ return 1;
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+
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+ continue;
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+ }
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+
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ack_seq = ntohl(th->ack_seq);
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if (th->ack) {
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--
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2.43.5
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