Re: [RFC][PATCH 1/4] lsm: Clarify documentation of vm_enough_memory hook

[Paul Moore]

On Wed, Nov 16, 2022 at 2:18 PM KP Singh <kpsingh@xxxxxxxxxx> wrote:
> On Wed, Nov 16, 2022 at 9:06 AM Roberto Sassu
> <roberto.sassu@xxxxxxxxxxxxxxx> wrote:
> >
> > On Tue, 2022-11-15 at 21:11 -0500, Paul Moore wrote:
> > > On Tue, Nov 15, 2022 at 12:57 PM Roberto Sassu
> > > <roberto.sassu@xxxxxxxxxxxxxxx> wrote:
> > > > From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> > > >
> > > > include/linux/lsm_hooks.h reports the result of the LSM infrastructure to
> > > > the callers, not what LSMs should return to the LSM infrastructure.
> > > >
> > > > Clarify that and add that returning 1 from the LSMs means calling
> > > > __vm_enough_memory() with cap_sys_admin set, 0 without.
> > > >
> > > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> > > > Reviewed-by: KP Singh <kpsingh@xxxxxxxxxx>
> > > > ---
> > > >  include/linux/lsm_hooks.h | 4 +++-
> > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> > > > index 4ec80b96c22e..f40b82ca91e7 100644
> > > > --- a/include/linux/lsm_hooks.h
> > > > +++ b/include/linux/lsm_hooks.h
> > > > @@ -1411,7 +1411,9 @@
> > > >   *     Check permissions for allocating a new virtual mapping.
> > > >   *     @mm contains the mm struct it is being added to.
> > > >   *     @pages contains the number of pages.
> > > > - *     Return 0 if permission is granted.
> > > > + *     Return 0 if permission is granted by LSMs to the caller. LSMs should
> > > > + *     return 1 if __vm_enough_memory() should be called with
> > > > + *     cap_sys_admin set, 0 if not.
> > >
> > > I think this is a nice addition, but according to the code, any value
> > > greater than zero will trigger the caller-should-have-CAP_SYS_ADMIN
> > > behavior, not just 1.  I suggest updating the comment.
> >
> > Ok, yes. Thanks.
>
> Also, this is an unrelated patch and you can probably send it
> independently, especially
> since the other changes will now land mostly via BPF.

Yes, the doc/comment changes really have nothing to do with the other
stuff we are discussing in this patchset.

-- 
paul-moore.com