Re: [PATCH net 2/2] selftests/net: packetdrill: Verify acceptance of FIN packets when RWIN is 0

[Kuniyuki Iwashima]

On Sun, Feb 22, 2026 at 4:35 AM Simon Baatz via B4 Relay
<devnull+gmbnomis.gmail.com@xxxxxxxxxx> wrote:
>
> From: Simon Baatz <gmbnomis@xxxxxxxxx>
>
> Add a packetdrill test that verifies we accept bare FIN packets when
> the advertised receive window is zero.
>
> Signed-off-by: Simon Baatz <gmbnomis@xxxxxxxxx>

Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>


> ---
>  .../net/packetdrill/tcp_rcv_zero_wnd_fin.pkt       | 27 ++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
>
> diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_zero_wnd_fin.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_zero_wnd_fin.pkt
> new file mode 100644
> index 0000000000000000000000000000000000000000..e245359a1a91d4b6d7ef64496681cea57792cb71
> --- /dev/null
> +++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_zero_wnd_fin.pkt
> @@ -0,0 +1,27 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Some TCP stacks send FINs even though the window is closed. We break
> +// a possible FIN/ACK loop by accepting the FIN.
> +
> +--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 <mss 1460,nop,wscale 0>
> +   +0 < . 1:1(0) ack 1 win 257
> +
> +   +0 accept(3, ..., ...) = 4
> +
> +   +0 < P. 1:60001(60000) ack 1 win 257
> +    * > .  1:1(0) ack 60001 win 0
> +
> +   +0 < F. 60001:60001(0) ack 1 win 257
> +   +0 > . 1:1(0) ack 60002 win 0
>
> --
> 2.53.0
>
>