Re: [PATCH net-next 12/14] selftests/bpf: Test skb_ext read from seg6local End.BPF hook

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The assertion `ASSERT_GE(tc_hook.ifindex, 0)` incorrectly accepts 0 as a valid interface index, masking `if_nametoindex()` failures.
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--- Patch [12]: [PATCH net-next 12/14] selftests/bpf: Test skb_ext read from seg6local End.BPF hook ---
commit b36d673a00ed1b242e3b7537fce3622d564183f9
Author: Jakub Sitnicki <[email protected]>

selftests/bpf: Test skb_ext read from seg6local End.BPF hook

This patch adds a test for reading skb_ext from an lwt_seg6local context.
It sets up a three-namespace topology to verify that an skb_ext written
at TC egress can be successfully read back by a seg6local End.BPF hook
running in a different namespace.

> diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
> index 7a7537ef80e75..5f9247941aa01 100644
> --- a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
> +++ b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
[ ... ]
> +	/* NS1: write skb_ext at TC egress on veth1, then send.
> +	 * TC egress fires after seg6 encap, on the encapped packet.
> +	 */
> +	nstoken = open_netns("seg6_1");
> +	if (!ASSERT_OK_PTR(nstoken, "open seg6_1"))
> +		goto cleanup;
> +
> +	tc_hook.ifindex = if_nametoindex("veth1");
> +	if (!ASSERT_GE(tc_hook.ifindex, 0, "ifindex veth1"))

[Severity: Medium]
Does this assertion properly detect an interface lookup failure? 

When if_nametoindex() fails to find the network interface, it returns 0. 
Using ASSERT_GE(..., 0) allows a return value of 0 to pass the check. If the 
interface is missing, the test will proceed and likely fail later in 
bpf_tc_hook_create(), which could obfuscate the true failure point.

Would it be better to ensure the index is strictly greater than 0 here?

> +		goto cleanup;
> +
> +	ret = bpf_tc_hook_create(&tc_hook);
> +	if (!ASSERT_OK(ret, "bpf_tc_hook_create"))
> +		goto cleanup;
> +
> +	tc_opts.prog_fd = bpf_program__fd(skel->progs.tc_skb_ext_write);

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Sashiko AI review · https://sashiko.dev/#/patchset/20260814-bpf-meta-inside-skb-ext-v1-0-767edd862656@cloudflare.com?part=12