linux/tools/testing/selftests/net/packetdrill, branch master

selftests/net: packetdrill: improve tcp_rcv_neg_window.pkt

2026-03-19T09:26:25Z

The test depends on accepting a packet that is larger than the advertised window and that does not trigger an immediate ACK. Previously, the test might still pass even if kernel behavior changed unexpectedly. Add assertions verifying that the large packet was accepted and no ACK was sent. Suggested-by: Eric Dumazet Signed-off-by: Simon Baatz Link: https://patch.msgid.link/20260316-improve_tcp_neg_usable_wnd_test-v1-1-f16d5e365107@gmail.com Signed-off-by: Paolo Abeni

selftests/net: packetdrill: add tcp_disorder_fin_in_FIN_WAIT.pkt

2026-03-14T20:15:46Z

Commit 795a7dfbc3d9 ("net: tcp: accept old ack during closing") was fixing an old bug, add a test to make sure we won't break this case in future kernels. Signed-off-by: Eric Dumazet Cc: Menglong Dong Link: https://patch.msgid.link/20260313115429.3365751-1-edumazet@google.com Signed-off-by: Jakub Kicinski

selftests/net: packetdrill: add tcp_rcv_neg_window.pkt

2026-03-14T15:02:51Z

The test ensures we correctly apply the maximum advertised window limit when rcv_nxt advances past rcv_mwnd_seq, so that the "usable window" is properly clamped to zero rather than becoming negative. Signed-off-by: Simon Baatz Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260309-tcp_rfc7323_retract_wnd_rfc-v3-6-4c7f96b1ec69@gmail.com Signed-off-by: Jakub Kicinski

selftests/net: packetdrill: add tcp_rcv_wnd_shrink_allowed.pkt

2026-03-14T15:02:51Z

This test verifies the sequence number checks using the maximum advertised window sequence number when net.ipv4.tcp_shrink_window is enabled. Signed-off-by: Simon Baatz Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260309-tcp_rfc7323_retract_wnd_rfc-v3-5-4c7f96b1ec69@gmail.com Signed-off-by: Jakub Kicinski

selftests/net: packetdrill: add tcp_rcv_wnd_shrink_nomem.pkt

2026-03-14T15:02:16Z

This test verifies - the sequence number checks using the maximum advertised window sequence number and - the logic for handling received data in tcp_data_queue() for the cases: 1. The window is reduced to zero because of memory 2. The window grows again but still does not reach the originally advertised window Signed-off-by: Simon Baatz Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260309-tcp_rfc7323_retract_wnd_rfc-v3-4-4c7f96b1ec69@gmail.com Signed-off-by: Jakub Kicinski

tcp: implement RFC 7323 window retraction receiver requirements

2026-03-14T15:01:49Z

By default, the Linux TCP implementation does not shrink the advertised window (RFC 7323 calls this "window retraction") with the following exceptions: - When an incoming segment cannot be added due to the receive buffer running out of memory. Since commit 8c670bdfa58e ("tcp: correct handling of extreme memory squeeze") a zero window will be advertised in this case. It turns out that reaching the required memory pressure is easy when window scaling is in use. In the simplest case, sending a sufficient number of segments smaller than the scale factor to a receiver that does not read data is enough. - Commit b650d953cd39 ("tcp: enforce receive buffer memory limits by allowing the tcp window to shrink") addressed the "eating memory" problem by introducing a sysctl knob that allows shrinking the window before running out of memory. However, RFC 7323 does not only state that shrinking the window is necessary in some cases, it also formulates requirements for TCP implementations when doing so (Section 2.4). This commit addresses the receiver-side requirements: After retracting the window, the peer may have a snd_nxt that lies within a previously advertised window but is now beyond the retracted window. This means that all incoming segments (including pure ACKs) will be rejected until the application happens to read enough data to let the peer's snd_nxt be in window again (which may be never). To comply with RFC 7323, the receiver MUST honor any segment that would have been in window for any ACK sent by the receiver and, when window scaling is in effect, SHOULD track the maximum window sequence number it has advertised. This patch tracks that maximum window sequence number rcv_mwnd_seq throughout the connection and uses it in tcp_sequence() when deciding whether a segment is acceptable. rcv_mwnd_seq is updated together with rcv_wup and rcv_wnd in tcp_select_window(). If we count tcp_sequence() as fast path, it is read in the fast path. Therefore, rcv_mwnd_seq is put into rcv_wnd's cacheline group. The logic for handling received data in tcp_data_queue() is already sufficient and does not need to be updated. Signed-off-by: Simon Baatz Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260309-tcp_rfc7323_retract_wnd_rfc-v3-1-4c7f96b1ec69@gmail.com Signed-off-by: Jakub Kicinski

selftests/net: packetdrill: restore tcp_rcv_big_endseq.pkt

2026-03-03T02:47:46Z

Commit 1cc93c48b5d7 ("selftests/net: packetdrill: remove tests for tcp_rcv_*big") removed the test for the reverted commit 1d2fbaad7cd8 ("tcp: stronger sk_rcvbuf checks") but also the one for commit 9ca48d616ed7 ("tcp: do not accept packets beyond window"). Restore the test with the necessary adaptation: expect a delayed ACK instead of an immediate one, since tcp_can_ingest() does not fail anymore for the last data packet. Signed-off-by: Simon Baatz Link: https://patch.msgid.link/20260301-tcp_rcv_big_endseq-v1-1-86ab7415ab58@gmail.com Signed-off-by: Jakub Kicinski

selftests/net: packetdrill: remove tests for tcp_rcv_*big

2026-02-28T15:55:52Z

Since commit 1d2fbaad7cd8 ("tcp: stronger sk_rcvbuf checks") has been reverted we need to remove the corresponding tests. Link: https://lore.kernel.org/20260227003359.2391017-1-kuba@kernel.org Link: https://patch.msgid.link/20260227033446.2596457-1-kuba@kernel.org Signed-off-by: Jakub Kicinski

selftests/net: packetdrill: Verify acceptance of FIN packets when RWIN is 0

2026-02-26T03:07:02Z

Add a packetdrill test that verifies we accept bare FIN packets when the advertised receive window is zero. Signed-off-by: Simon Baatz Reviewed-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20260224-fix_zero_wnd_fin-v2-2-a16677ea7cea@gmail.com Signed-off-by: Jakub Kicinski

selftests/net: packetdrill: add ipv4-mapped-ipv6 tests

2026-02-19T00:45:30Z

Add ipv4-mapped-ipv6 case to ksft_runner.sh before an upcoming TCP fix in this area. Signed-off-by: Eric Dumazet Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260217142924.1853498-1-edumazet@google.com Signed-off-by: Jakub Kicinski