Re: [PATCH v2 bpf-next 2/2] selftests/bpf: Add linked_externs test for externs in allocated sections

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] selftests/bpf: unhandled mkstemp() failure in test_relink()
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commit e2fcaeeb4be58f57f9657902a9e400bc15e30412
Author: Andrii Nakryiko <andrii@kernel.org>

selftests/bpf: Add linked_externs test for externs in allocated sections

This commit adds a selftest to verify that the BPF linker correctly handles
extern variables in allocated sections (like arena and maps). It tests the
behavior both via the BPF skeleton and by directly driving the libbpf linker
API.

> diff --git a/tools/testing/selftests/bpf/prog_tests/linked_externs.c b/tools/testing/selftests/bpf/prog_tests/linked_externs.c
> new file mode 100644
> index 0000000000000..29358c82dc356
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/linked_externs.c
[ ... ]
> +/* link in1 on its own first, then link the result with in2 */
> +static void test_relink(const char *in1, const char *in2, const char *sec_name)
> +{
> +	char out1[] = "/tmp/linked_externs.XXXXXX", out2[] = "/tmp/linked_externs.XXXXXX";
> +	const struct btf_var_secinfo *vi;
> +	struct bpf_object *obj = NULL;
> +	const struct btf_type *t;
> +	struct btf *btf;
> +	int i, id, n;
> +
> +	close(mkstemp(out1));
> +	close(mkstemp(out2));

[Severity: Medium]
What happens if mkstemp() fails here?

If it returns -1, it will be passed directly to close() which will just fail,
but the template strings will remain undefined (typically unmodified). The
test would then continue using the predictable string
"/tmp/linked_externs.XXXXXX" for file operations.

Could this cause collisions with other concurrent test runs or leave leftover
predictable files in /tmp?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260926000243.2830819-1-andrii@kernel.org?part=2