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

[Schaufler, Casey]

> -----Original Message-----
> From: Jann Horn [mailto:jannh@xxxxxxxxxx]
> Sent: Wednesday, September 26, 2018 2:31 PM
> To: Schaufler, Casey <casey.schaufler@xxxxxxxxx>
> Cc: Kernel Hardening <kernel-hardening@xxxxxxxxxxxxxxxxxx>; kernel list
> <linux-kernel@xxxxxxxxxxxxxxx>; linux-security-module <linux-security-
> module@xxxxxxxxxxxxxxx>; selinux@xxxxxxxxxxxxx; Hansen, Dave
> <dave.hansen@xxxxxxxxx>; Dock, Deneen T <deneen.t.dock@xxxxxxxxx>;
> kristen@xxxxxxxxxxxxxxx; Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
> 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@xxxxxxxxx> 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@xxxxxxxxx>
> > ---
> >  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.