On 8/31/22 8:50 PM, Serge E. Hallyn wrote:

On Wed, Aug 31, 2022 at 06:24:14PM +0300, Yauheni Kaliuta wrote:

quoted

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.

The selinux mentions probably aren't really necessary.  The more
concise way to say it is that bpf_jit_blinding_enabled() should
be permitted with CAP_BPF, that full CAP_SYS_ADMIN is not needed.
(Assuming that that is the case)

quoted

Signed-off-by: Yauheni Kaliuta <redacted>
---

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())

I think lowering this requirement is fine here. These days given unpriv eBPF is
disabled by default, I see the main users for constant blinding coming from unpriv
in particular via cBPF -> eBPF migration (e.g. old-style socket filters).

quoted

  		return false;
  
  	return true;

Please also update Documentation/admin-guide/sysctl/net.rst to clarify cap details.

Thanks,
Daniel