Re: [PATCH bpf v2 4/4] selftests/bpf: Add tests to verify the fix of encapsulating VxLAN in lwt

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The fexit program `fexit_lwt_push_ip_encap` is a global hook without filtering, causing test flakiness when tests run concurrently.
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commit 1b1d75b61046d2f71544d30d5afec12a9644a6b0
Author: Leon Hwang <leon.hwang@linux.dev>

selftests/bpf: Add tests to verify the fix of encapsulating VxLAN in lwt

This commit adds two new selftests (IPv4 and IPv6) to verify that the
transport header of an skb is correctly set when encapsulating VxLAN using
the bpf_lwt_push_encap() helper.

> diff --git a/tools/testing/selftests/bpf/progs/test_lwt_ip_encap_fix.c b/tools/testing/selftests/bpf/progs/test_lwt_ip_encap_fix.c
> new file mode 100644
> index 0000000000000..e9043fe654eb7
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_lwt_ip_encap_fix.c
> @@ -0,0 +1,36 @@
[ ... ]
> +SEC("fexit/bpf_lwt_push_ip_encap")
> +int BPF_PROG(fexit_lwt_push_ip_encap, struct sk_buff *skb, void *hdr, u32 len, bool ingress,
> +	     int retval)
> +{
> +	if (retval || fexit_triggered)
> +		return 0;
> +
> +	fexit_triggered = true;
> +	transport_hdr = BPF_CORE_READ(skb, transport_header);

[Severity: Medium]
Will this fexit program cause test flakiness when tests run concurrently?

Since test_progs executes test functions concurrently across multiple workers
by default, this global fexit program might intercept the
bpf_lwt_push_ip_encap call from a different test running simultaneously
(like the existing GRE test).

Because it only captures the first successful execution and has no filtering
for a specific test or network namespace, could it record offsets for the
wrong packet type and lead to random failures in the transport_hdr offset
assertion?

> +	network_hdr   = BPF_CORE_READ(skb, network_header);
> +	return 0;
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260529151351.69911-1-leon.hwang@linux.dev?part=4