[RFC PATCH v2] bpf: use bpf_capable() instead of CAP_SYS_ADMIN for blinding decision

[Yauheni Kaliuta <ykaliuta@redhat.com>]

The capability check can cause SELinux denial.

For example, in ptp4l, setsockopt() with the SO_ATTACH_FILTER option
raises sk_attach_filter() to run a bpf program. SELinux hooks into
capable() calls and performs an additional check if the task's
SELinux domain has permission to "use" the given capability. ptp4l_t
already has CAP_BPF granted by SELinux, so if the function used
bpf_capable() as most BPF code does, there would be no change needed
in selinux-policy.

Signed-off-by: Yauheni Kaliuta <ykaliuta@redhat.com>
---

v2: put the reasoning in the commit message

---
 include/linux/filter.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index a5f21dc3c432..3de96b1a736b 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1100,7 +1100,7 @@ static inline bool bpf_jit_blinding_enabled(struct bpf_prog *prog)
 		return false;
 	if (!bpf_jit_harden)
 		return false;
-	if (bpf_jit_harden == 1 && capable(CAP_SYS_ADMIN))
+	if (bpf_jit_harden == 1 && bpf_capable())
 		return false;
 
 	return true;
-- 
2.34.1