Re: [PATCH bpf-next v2 2/2] selftests/bpf: verify kallsyms entries for token-loaded subprograms

[sashiko-bot@kernel.org]

Sashiko AI review found 1 potential issue(s):
- [Medium] The test modifies global sysctls (`perf_event_paranoid` and `kptr_restrict`) while running in parallel, causing race conditions and potential host state leakage.
--

commit 9e0a167112286dfb5b44d5686732b8297533a10b
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 program and its global
subprogram appear in /proc/kallsyms when loaded using a user namespace BPF
token. It temporarily modifies global sysctl variables to allow reading
kallsym addresses.

> diff --git a/tools/testing/selftests/bpf/prog_tests/token.c b/tools/testing/selftests/bpf/prog_tests/token.c
> index b81dde283052e..89da527ed9304 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");

The BPF selftest framework executes test_token() concurrently with other
tests because it lacks the serial_test_ prefix.

If another parallel test modifies or relies on these sysctls simultaneously,
can this create a race condition where the parallel test reads the
already-modified "0" as its original state? 

This could result in the host permanently retaining the lowered security
settings once the tests complete.

Should this test be renamed to serial_test_token() to prevent concurrent
modification of global system state?

> +
> +		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/20260414-subprog-token-fix-v2-0-59146c31f6f1@gmail.com?part=2