Re: [PATCH bpf-next v3 2/2] selftests/bpf: verify kallsyms entries for token-loaded subprograms

[sashiko-bot@kernel.org]

Sashiko AI review found 1 potential issue(s):
- [Medium] Unchecked return values of `sysctl_set()` in `serial_test_token()` can lead to confusing test failures.
--

commit e7dc629b9f37dc08742ff9bbddeaaf65c1e34956
Author: Eduard Zingerman <eddyz87@gmail.com>

selftests/bpf: verify kallsyms entries for token-loaded subprograms

This commit adds a test to verify that both the main XDP program and its
global subprogram appear in /proc/kallsyms when loaded using a user
namespace BPF token. It also introduces a sysctl_set utility to configure
system parameters needed to read kallsyms.

> diff --git a/tools/testing/selftests/bpf/prog_tests/token.c b/tools/testing/selftests/bpf/prog_tests/token.c
> index b81dde283052e..cf5b94512cff4 100644
> --- a/tools/testing/selftests/bpf/prog_tests/token.c
> +++ b/tools/testing/selftests/bpf/prog_tests/token.c

[ ... ]

> @@ -1194,4 +1252,23 @@ void test_token(void)
>  
>  		subtest_userns(&opts, userns_bpf_token_info);
>  	}
> +	if (test__start_subtest("obj_priv_prog_kallsyms")) {
> +		char perf_paranoid_orig[32] = {};
> +		char kptr_restrict_orig[32] = {};
> +		struct bpffs_opts opts = {
> +			.cmds = bit(BPF_BTF_LOAD) | bit(BPF_PROG_LOAD),
> +			.progs = bit(BPF_PROG_TYPE_XDP),
> +			.attachs = ~0ULL,
> +		};
> +
> +		sysctl_set("/proc/sys/kernel/perf_event_paranoid", perf_paranoid_orig, "0");
> +		sysctl_set("/proc/sys/kernel/kptr_restrict", kptr_restrict_orig, "0");

Should the return values of these sysctl_set calls be checked?

If the test is executed in an environment where these sysctls are read-only
or inaccessible (such as inside a container), sysctl_set will silently fail.

This would cause load_kallsyms_local to read zeroed addresses because
kptr_restrict wasn't successfully disabled, resulting in confusing test
failures later at ASSERT_TRUE instead of catching the setup failure early.

Would it be better to wrap these with ASSERT_OK?

> +
> +		subtest_userns(&opts, userns_obj_priv_prog_kallsyms);
> +
> +		if (perf_paranoid_orig[0])
> +			sysctl_set("/proc/sys/kernel/perf_event_paranoid", NULL, perf_paranoid_orig);
> +		if (kptr_restrict_orig[0])
> +			sysctl_set("/proc/sys/kernel/kptr_restrict", NULL, kptr_restrict_orig);
> +	}
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260415-subprog-token-fix-v3-0-6fefe1d51646@gmail.com?part=2