Re: [PATCH] selinux: check sidtab limit before adding a new entry

[Ondrej Mosnacek <omosnace@redhat.com>]

On Mon, Jul 22, 2019 at 6:50 PM Kees Cook <keescook@chromium.org> wrote:
> On Mon, Jul 22, 2019 at 03:21:11PM +0200, Ondrej Mosnacek wrote:
> > We need to error out when trying to add an entry above SIDTAB_MAX in
> > sidtab_reverse_lookup() to avoid overflow on the odd chance that this
> > happens.
> >
> > Fixes: ee1a84fdfeed ("selinux: overhaul sidtab to fix bug and improve performance")
> > Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
>
> Is this reachable from unprivileged userspace?
>
> > ---
> >  security/selinux/ss/sidtab.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
> > index e63a90ff2728..54c1ba1e79ab 100644
> > --- a/security/selinux/ss/sidtab.c
> > +++ b/security/selinux/ss/sidtab.c
> > @@ -286,6 +286,11 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
> >               ++count;
> >       }
> >
> > +     /* bail out if we already reached max entries */
> > +     rc = -ENOMEM;
> > +     if (count == SIDTAB_MAX)
>
> Do you want to use >= here instead?

Makes sense. Also staged for v2.

>
> -Kees
>
> > +             goto out_unlock;
> > +
> >       /* insert context into new entry */
> >       rc = -ENOMEM;
> >       dst = sidtab_do_lookup(s, count, 1);
> > --
> > 2.21.0
> >
>
> --
> Kees Cook

Thanks,
-- 
Ondrej Mosnacek <omosnace at redhat dot com>
Software Engineer, Security Technologies
Red Hat, Inc.