On Tue, Mar 24, 2020 at 03:51:55PM +0100, KP Singh wrote:

On 24-Mär 10:51, Stephen Smalley wrote:

quoted

On Tue, Mar 24, 2020 at 10:42 AM KP Singh [off-list ref] wrote:

quoted

On 24-Mär 10:37, Stephen Smalley wrote:

quoted

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

quoted

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

quoted

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?

We can still do that if it does not work for SELinux.

Would it be okay to add bpf as LSM_ORDER_LAST?

LSMs like Landlock can then add LSM_ORDER_UNPRIVILEGED to even end up
after bpf?

I guess the question is whether we need an explicit LSM_ORDER_LAST or
can just handle it via the default
values for the lsm= parameter, where you are already placing bpf last
IIUC?  If someone can mess with the kernel boot
parameters, they already have options to mess with SELinux, so it is no worse...

Yeah, we do add BPF as the last LSM in the default list. So, I will
avoid adding LSM_ORDER_LAST for now.

FWIW, this is my preference as well. If there ends up being a stronger
need, then we can implement LSM_ORDER_LAST at that time.

-- 
Kees Cook