selftests: net: check timestamp echo after an old ACK

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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: 83f72d3f90
Assisted-by: LLM
Signed-off-by: Jeff Jo <jeffjo@openai.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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Jeff Jo 2026-09-24 15:44:59 -07:00 • committed by David S. Miller

parent 1b92780ae4

commit 81fe707ae5

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tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.pkt

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