[PATCH v5 2/5] Smack: Prepare for PTRACE_MODE_SCHED

[Jann Horn]

+Jiri

On Thu, Sep 27, 2018 at 12:54 AM Schaufler, Casey
<casey.schaufler at intel.com> wrote:
> > -----Original Message-----
> > From: Jann Horn [mailto:jannh at google.com]
> > Sent: Wednesday, September 26, 2018 2:31 PM
> > To: Schaufler, Casey <casey.schaufler at intel.com>
> > Cc: Kernel Hardening <kernel-hardening at lists.openwall.com>; kernel list
> > <linux-kernel at vger.kernel.org>; linux-security-module <linux-security-
> > module at vger.kernel.org>; selinux at tycho.nsa.gov; Hansen, Dave
> > <dave.hansen at intel.com>; Dock, Deneen T <deneen.t.dock at intel.com>;
> > kristen at linux.intel.com; Arjan van de Ven <arjan at linux.intel.com>
> > Subject: Re: [PATCH v5 2/5] Smack: Prepare for PTRACE_MODE_SCHED
> >
> > On Wed, Sep 26, 2018 at 10:35 PM Casey Schaufler
> > <casey.schaufler at intel.com> wrote:
> > > A ptrace access check with mode PTRACE_MODE_SCHED gets called
> > > from process switching code. This precludes the use of audit,
> > > as the locking is incompatible. Don't do audit in the PTRACE_MODE_SCHED
> > > case.
> > >
> > > Signed-off-by: Casey Schaufler <casey.schaufler at intel.com>
> > > ---
> > >  security/smack/smack_lsm.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> > > index 340fc30ad85d..ffa95bcab599 100644
> > > --- a/security/smack/smack_lsm.c
> > > +++ b/security/smack/smack_lsm.c
> > > @@ -422,7 +422,8 @@ static int smk_ptrace_rule_check(struct task_struct
> > *tracer,
> > >         struct task_smack *tsp;
> > >         struct smack_known *tracer_known;
> > >
> > > -       if ((mode & PTRACE_MODE_NOAUDIT) == 0) {
> > > +       if ((mode & PTRACE_MODE_NOAUDIT) == 0 &&
> > > +           (mode & PTRACE_MODE_SCHED) == 0) {
> >
> > If you ORed PTRACE_MODE_NOAUDIT into the flags when calling the
> > security hook, you could drop this patch, right?
>
> Yes. Since the PTRACE_MODE_NOAUDIT was in PTRACE_MODE_IBPB
> in Jiri's previous patch set and not in PTRACE_MODE_SCHED in this one
> I assumed that there was a good reason for it.

Jiri, was there a good reason for it, and if so, what was it?