On 3/27/20 8:41 AM, KP Singh wrote:
On 27-Mär 08:27, Stephen Smalley wrote:
On 3/26/20 8:24 PM, James Morris wrote:
On Thu, 26 Mar 2020, KP Singh wrote:
+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@xxxxxxxxxxxx/
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
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.
I would favor removing the CAP_MAC_ADMIN check here, and implementing it
in a bpf_prog hook for Smack and AppArmor if they want that. SELinux
would implement its own check in its existing bpf_prog hook.
