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

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Message-ID: <18e375adfe53f8ce5fb38a6a146ad06eaec71a5e.camel@huaweicloud.com>
Date:   Wed, 16 Nov 2022 09:06:02 +0100
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, 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 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.

Roberto