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

On Wed, 2026-04-15 at 01:21 +0000, [email protected] wrote:
> 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 <[email protected]>
> 
> 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?

I don't think that we have tests that rely on these parameters atm,
but suggestion makes sense.

> 
> > +
> > +		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);
> > +	}
> >  }