Re: [PATCH bpf-next v5 5/7] bpf: lsm: Initialize the BPF LSM hooks

On Mon, Mar 23, 2020 at 9:52 PM KP Singh [off-list ref] wrote:

On 23-Mär 18:13, Casey Schaufler wrote:

quoted

On 3/23/2020 9:44 AM, KP Singh wrote:

quoted

From: KP Singh <redacted>

The bpf_lsm_ nops are initialized into the LSM framework like any other
LSM.  Some LSM hooks do not have 0 as their default return value. The
__weak symbol for these hooks is overridden by a corresponding
definition in security/bpf/hooks.c

+   return 0;

[...]

quoted

quoted

+}
+
+DEFINE_LSM(bpf) = {
+   .name = "bpf",
+   .init = bpf_lsm_init,

Have you given up on the "BPF must be last" requirement?

Yes, we dropped it for as the BPF programs require CAP_SYS_ADMIN
anwyays so the position ~shouldn't~ matter. (based on some of the
discussions we had on the BPF_MODIFY_RETURN patches).

However, This can be added later (in a separate patch) if really
deemed necessary.

It matters for SELinux, as I previously explained.  A process that has
CAP_SYS_ADMIN is not assumed to be able to circumvent MAC policy.
And executing prior to SELinux allows the bpf program to access and
potentially leak to userspace information that wouldn't be visible to
the
process itself. However, I thought you were handling the order issue
by putting it last in the list of lsms?