selftests/bpf: Introduce __caps_unpriv annotation for tests

Add a __caps_unpriv annotation so that tests requiring specific
capabilities while dropping the rest can conveniently specify them
during selftest declaration instead of munging with capabilities at
runtime from the testing binary.

While at it, let us convert test_verifier_mtu to use this new support
instead.

Since we do not want to include linux/capability.h, we only defined the
four main capabilities BPF subsystem deals with in bpf_misc.h for use in
tests. If the user passes a CAP_SYS_NICE or anything else that's not
defined in the header, capability parsing code will return a warning.

Also reject strtol returning 0. CAP_CHOWN = 0 but we'll never need to
use it, and strtol doesn't errno on failed conversion. Fail the test in
such a case.

The original diff for this idea is available at link [0].

  [0]: https://lore.kernel.org/bpf/a1e48f5d9ae133e19adc6adf27e19d585e06bab4.camel@gmail.com

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
[ Kartikeya: rebase on bpf-next, add warn to parse_caps, convert test_verifier_mtu ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20241204044757.1483141-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 1 insertions, 18 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
index d9f65adb456b..3ee40ee9413a 100644
--- a/tools/testing/selftests/bpf/prog_tests/verifier.c
+++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
@@ -225,24 +225,7 @@ void test_verifier_xdp(void)                  { RUN(verifier_xdp); }
 void test_verifier_xdp_direct_packet_access(void) { RUN(verifier_xdp_direct_packet_access); }
 void test_verifier_bits_iter(void) { RUN(verifier_bits_iter); }
 void test_verifier_lsm(void)                  { RUN(verifier_lsm); }
-
-void test_verifier_mtu(void)
-{
-	__u64 caps = 0;
-	int ret;
-
-	/* In case CAP_BPF and CAP_PERFMON is not set */
-	ret = cap_enable_effective(1ULL << CAP_BPF | 1ULL << CAP_NET_ADMIN, &caps);
-	if (!ASSERT_OK(ret, "set_cap_bpf_cap_net_admin"))
-		return;
-	ret = cap_disable_effective(1ULL << CAP_SYS_ADMIN | 1ULL << CAP_PERFMON, NULL);
-	if (!ASSERT_OK(ret, "disable_cap_sys_admin"))
-		goto restore_cap;
-	RUN(verifier_mtu);
-restore_cap:
-	if (caps)
-		cap_enable_effective(caps, NULL);
-}
+void test_verifier_mtu(void)		      { RUN(verifier_mtu); }
 
 static int init_test_val_map(struct bpf_object *obj, char *map_name)
 {