* Re: [PATCH] selinux: check sidtab limit before adding a new entry
2019-07-22 16:50 ` [PATCH] selinux: check sidtab limit before adding a new entry Kees Cook
@ 2019-07-23 0:36 ` Paul Moore
2019-07-23 6:48 ` Ondrej Mosnacek
1 sibling, 0 replies; 3+ messages in thread
From: Paul Moore @ 2019-07-23 0:36 UTC (permalink / raw)
To: Kees Cook
Cc: Ondrej Mosnacek, selinux, NitinGote, kernel-hardening,
linux-security-module
On Mon, Jul 22, 2019 at 12:50 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?
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
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] selinux: check sidtab limit before adding a new entry
2019-07-22 16:50 ` [PATCH] selinux: check sidtab limit before adding a new entry Kees Cook
2019-07-23 0:36 ` Paul Moore
@ 2019-07-23 6:48 ` Ondrej Mosnacek
1 sibling, 0 replies; 3+ messages in thread
From: Ondrej Mosnacek @ 2019-07-23 6:48 UTC (permalink / raw)
To: Kees Cook
Cc: SElinux list, Paul Moore, NitinGote, kernel-hardening,
Linux Security Module list
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.
^ permalink raw reply [flat|nested] 3+ messages in thread