From 81fe707ae58e67e5a029a9778c4b0c1b478bcb97 Mon Sep 17 00:00:00 2001 From: Jeff Jo Date: Thu, 24 Sep 2026 15:44:59 -0700 Subject: [PATCH] selftests: net: check timestamp echo after an old ACK Add a regression test for a gap-filling packet whose acknowledgment has become old. Linux first sends data to the peer. Deliver two peer data packets out of order: the later packet acknowledges Linux's data, while the delayed packet still carries the earlier acknowledgment. Require the ACK that closes the receive gap to echo the delayed packet's timestamp, 301000. Without the fix, Linux accepts the data but still echoes the previously saved timestamp, 1000. Also check that the application can read all 34 bytes. Use a large jump in peer timestamps to represent the idle interval, with no real wait, loss or retransmission. The test directly checks the outgoing timestamp echo. It requires packetdrill's merged TSecr verification fix (linked below); older tools incorrectly pass on an unfixed kernel. Use the existing packetdrill selftest runner for IPv4, IPv6 and IPv4-mapped IPv6. Link: https://github.com/google/packetdrill/commit/83f72d3f9085d0e26eb4d206fe4d7cfab5b6d872 Assisted-by: LLM Signed-off-by: Jeff Jo Reviewed-by: Eric Dumazet Signed-off-by: David S. Miller --- .../net/packetdrill/tcp_old_ack_ts.pkt | 22 +++++++++++++++++++ 1 file changed, 22 insertions(+) create mode 100644 tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.pkt diff --git a/tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.pkt b/tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.pkt new file mode 100644 index 000000000000..f072e5e4c449 --- /dev/null +++ b/tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.pkt @@ -0,0 +1,22 @@ +// SPDX-License-Identifier: GPL-2.0 +// An out-of-order segment advances SND.UNA. The gap filler still carries +// its original, older ACK. The reply must echo the gap filler's timestamp. +--tcp_ts_tick_usecs=1000 + +`./defaults.sh` + +0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 ++0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 ++0 bind(3, ..., ...) = 0 ++0 listen(3, 1) = 0 +0.100 < S 0:0(0) win 20000 ++0 > S. 0:0(0) ack 1 +0.200 < . 1:1(0) ack 1 win 20000 ++0 accept(3, ..., ...) = 4 +0.300 write(4, ..., 17) = 17 ++0 > P. 1:18(17) ack 1 +0.310 < P. 18:35(17) ack 18 win 20000 ++0 > . 18:18(0) ack 1 +0.320 < P. 1:18(17) ack 1 win 20000 ++0 > . 18:18(0) ack 35 ++0 read(4, ..., 34) = 34