linux-kernel - RE: [PATCH v5 2/5] Smack: Prepare for PTRACE_MODE

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Date:   Wed, 26 Sep 2018 22:53:27 +0000
From:   "Schaufler, Casey" <casey.schaufler@...el.com>
To:     Jann Horn <jannh@...gle.com>
CC:     Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        "selinux@...ho.nsa.gov" <selinux@...ho.nsa.gov>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Dock, Deneen T" <deneen.t.dock@...el.com>,
        "kristen@...ux.intel.com" <kristen@...ux.intel.com>,
        Arjan van de Ven <arjan@...ux.intel.com>
Subject: RE: [PATCH v5 2/5] Smack: Prepare for PTRACE_MODE_SCHED

> -----Original Message-----
> From: Jann Horn [mailto:jannh@...gle.com]
> Sent: Wednesday, September 26, 2018 2:31 PM
> To: Schaufler, Casey <casey.schaufler@...el.com>
> Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>; kernel list
> <linux-kernel@...r.kernel.org>; linux-security-module <linux-security-
> module@...r.kernel.org>; selinux@...ho.nsa.gov; Hansen, Dave
> <dave.hansen@...el.com>; Dock, Deneen T <deneen.t.dock@...el.com>;
> kristen@...ux.intel.com; Arjan van de Ven <arjan@...ux.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@...el.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@...el.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.