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

[Paul Moore]

On Mon, Jul 22, 2019 at 12:50 PM Kees Cook <keescook at 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 at redhat.com>
>
> Is this reachable from unprivileged userspace?

I believe it's reachable via selinuxfs under /sys/fs/selinux/context,
and the DAC permissions are for the relevant files are 0666, but the
SELinux policy might restrict that.

> > ---
> >  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?

Yes, definitely.

-- 
paul moore
www.paul-moore.com