From: Simon Baatz Date: Mon, 9 Mar 2026 08:02:30 +0000 (+0100) Subject: selftests/net: packetdrill: add tcp_rcv_wnd_shrink_allowed.pkt X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ba58b3e70b86cd64fe8bb9c52f1111667a448908;p=thirdparty%2Flinux.git selftests/net: packetdrill: add tcp_rcv_wnd_shrink_allowed.pkt 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 --- diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt new file mode 100644 index 0000000000000..6af0e0eb183a0 --- /dev/null +++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt @@ -0,0 +1,40 @@ +// SPDX-License-Identifier: GPL-2.0 + +--mss=1000 + +`./defaults.sh +sysctl -q net.ipv4.tcp_shrink_window=1 +sysctl -q net.ipv4.tcp_rmem="4096 32768 $((32*1024*1024))"` + + 0 `nstat -n` + +// Establish a connection. + +0 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 < S 0:0(0) win 32792 + +0 > S. 0:0(0) ack 1 + +0 < . 1:1(0) ack 1 win 257 + + +0 accept(3, ..., ...) = 4 + + +0 < P. 1:10001(10000) ack 1 win 257 + * > . 1:1(0) ack 10001 win 15 + + +0 < P. 10001:11024(1023) ack 1 win 257 + * > . 1:1(0) ack 11024 win 13 + +// Max window seq advertised 10001 + 15*1024 = 25361, last advertised: 11024 + 13*1024 = 24336 + +// Segment beyond the max window is dropped + +0 < P. 11024:25362(14338) ack 1 win 257 + * > . 1:1(0) ack 11024 win 13 + +// Segment using the max window is accepted + +0 < P. 11024:25361(14337) ack 1 win 257 + * > . 1:1(0) ack 25361 win 0 + +// Check LINUX_MIB_BEYOND_WINDOW has been incremented once + +0 `nstat | grep TcpExtBeyondWindow | grep -q " 1 "`