[PATCH RFC net-next v2 5/5] selftests/net: packetdrill: add tcp_rcv_neg_window.pkt

[Simon Baatz via B4 Relay]

From: Simon Baatz <gmbnomis@xxxxxxxxx>

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 <gmbnomis@xxxxxxxxx>
---
 .../net/packetdrill/tcp_rcv_neg_window.pkt         | 26 ++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_neg_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_neg_window.pkt
new file mode 100644
index 0000000000000000000000000000000000000000..15a9b4938f16d175ac54f3fd192ed2b59b0a4399
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_neg_window.pkt
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+
+--mss=1000
+
+`./defaults.sh`
+
+// Establish a connection.
+   +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [20000], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:0(0) win 32792 <mss 1000,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 18980 <mss 1460,nop,wscale 0>
+  +.1 < . 1:1(0) ack 1 win 257
+
+   +0 accept(3, ..., ...) = 4
+
+// A too big packet is accepted if the receive queue is empty
+   +0 < P. 1:20001(20000) ack 1 win 257
+// Send a RST immediately so that there is no rcv_wup/rcv_mwnd_seq update yet
+   +0 < R. 20001:20001(0) ack 1 win 257
+
+  +.1 %{ assert tcpi_state == TCP_CLOSE, tcpi_state }%
+

-- 
2.53.0