Re: [PATCH net v5 7/8] selftests: drv-net: psp: test that ipv4 psp packets aren't fragmented

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] selftests: drv-net: psp: open-coded ctl_file_write() in
  data_send_ipv4_frags()
--

commit f2ab5974348f0d91190d725cd849415716fc0e2e
Author: Todd Freed <toddfreed@meta.com>

selftests: drv-net: psp: test that ipv4 psp packets aren't fragmented

This commit adds a selftest verifying that IPv4 TCP packets on a PSP
socket that exceed the device MTU are dropped rather than fragmented and
sent unencrypted.

> diff --git a/tools/testing/selftests/drivers/net/psp.py b/tools/testing/selftests/drivers/net/psp.py
> index 7e251439a2fd9..5dac62ad96b0b 100755
> --- a/tools/testing/selftests/drivers/net/psp.py
> +++ b/tools/testing/selftests/drivers/net/psp.py

[ ... ]

> @@ -799,6 +801,105 @@ def data_send_ipv6_exthdr(cfg, opt, val):

[ ... ]

> +def data_send_ipv4_frags(cfg):

[ ... ]

> +    # With MTU probing on, TCP caps the MSS at the probing base, whatever
> +    # the route MTU
> +    probing_path = "/proc/sys/net/ipv4/tcp_mtu_probing"
> +    with open(probing_path, encoding="utf-8") as fp:
> +        probing = fp.read().strip()
> +    if int(probing) > 1:
> +        def set_probing(val):
> +            with open(probing_path, "w", encoding="utf-8") as fp:
> +                fp.write(val)
> +        set_probing("0")
> +        defer(set_probing, probing)

[Severity: Low]
Could this use ctl_file_write("/proc/sys/net/ipv4/tcp_mtu_probing", 0)
from lib.py instead of open-coding the read, write, and deferred restore?

Also, only clearing tcp_mtu_probing when it is greater than 1 leaves blackhole
detection (1) enabled, which can still enable MTU probing and lower the socket
MSS during the 3-second s.sendall() timeout window if retransmissions pass
tcp_retries1.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111001831.3710881-1-toddfreed@meta.com?part=7