On 27-Mär 08:27, Stephen Smalley wrote:

On 3/26/20 8:24 PM, James Morris wrote:

quoted

On Thu, 26 Mar 2020, KP Singh wrote:

quoted

+int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
+			const struct bpf_prog *prog)
+{
+	/* Only CAP_MAC_ADMIN users are allowed to make changes to LSM hooks
+	 */
+	if (!capable(CAP_MAC_ADMIN))
+		return -EPERM;
+

Stephen, can you confirm that your concerns around this are resolved
(IIRC, by SELinux implementing a bpf_prog callback) ?

I guess the only residual concern I have is that CAP_MAC_ADMIN means
something different to SELinux (ability to get/set file security contexts
unknown to the currently loaded policy), so leaving the CAP_MAC_ADMIN check
here (versus calling a new security hook here and checking CAP_MAC_ADMIN in
the implementation of that hook for the modules that want that) conflates
two very different things.  Prior to this patch, there are no users of
CAP_MAC_ADMIN outside of individual security modules; it is only checked in
module-specific logic within apparmor, safesetid, selinux, and smack, so the
meaning was module-specific.

As we had discussed, We do have a security hook as well:

https://lore.kernel.org/bpf/20200324180652.GA11855@chromium.org/ (local)

The bpf_prog hook which can check for BPF_PROG_TYPE_LSM and implement
module specific logic for LSM programs. I thougt that was okay?

Kees was in favor of keeping the CAP_MAC_ADMIN check here:

https://lore.kernel.org/bpf/202003241133.16C02BE5B@keescook (local)

If you feel strongly and Kees agrees, we can remove the CAP_MAC_ADMIN
check here, but given that we already have a security hook that meets
the requirements, we probably don't need another one.

- KP