f_modown and LSM inconsistency (was [PATCH v2 1/4] Landlock: Add signal control)

[Paul Moore]

On Mon, Aug 12, 2024 at 9:09 AM Jann Horn <jannh at google.com> wrote:
> On Mon, Aug 12, 2024 at 12:04 AM Paul Moore <paul at paul-moore.com> wrote:

...

> > From a LSM perspective I suspect we are always going to need some sort
> > of hook in the F_SETOWN code path as the LSM needs to potentially
> > capture state/attributes/something-LSM-specific at that
> > context/point-in-time.
>
> The only thing LSMs currently do there is capture state from
> current->cred. So if the VFS takes care of capturing current->cred
> there, we should be able to rip out all the file_set_fowner stuff.
> Something like this (totally untested):

I've very hesitant to drop the LSM hook from the F_SETOWN path both
because it is reasonable that other LSMs may want to do other things
here, and adding a LSM hook to the kernel, even if it is re-adding a
hook that was previously removed, is a difficult and painful process
with an uncertain outcome.

-- 
paul-moore.com