linux-kernel - Re: [RFC][PATCH 1/4] lsm: Clarify documentation of vm_enough

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Date:   Wed, 16 Nov 2022 20:17:56 +0100
From:   KP Singh <kpsingh@...nel.org>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     Paul Moore <paul@...l-moore.com>, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev,
        song@...nel.org, yhs@...com, john.fastabend@...il.com,
        sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
        revest@...omium.org, jackmanb@...omium.org, jmorris@...ei.org,
        serge@...lyn.com, bpf@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [RFC][PATCH 1/4] lsm: Clarify documentation of vm_enough_memory hook

On Wed, Nov 16, 2022 at 9:06 AM Roberto Sassu
<roberto.sassu@...weicloud.com> 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@...weicloud.com> wrote:
> > > From: Roberto Sassu <roberto.sassu@...wei.com>
> > >
> > > 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@...wei.com>
> > > Reviewed-by: KP Singh <kpsingh@...nel.org>
> > > ---
> > >  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.

>
> Roberto
>