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

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Message-ID: <CAG48ez1+9Bfadu4y4TzPYJfFpLk+N8w7GdCE+xwNCM5TfQ8W8Q@mail.gmail.com>
Date:   Thu, 27 Sep 2018 00:58:00 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Casey Schaufler <casey.schaufler@...el.com>,
        Jiri Kosina <jikos@...nel.org>
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, Dave Hansen <dave.hansen@...el.com>,
        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

+Jiri

On Thu, Sep 27, 2018 at 12:54 AM Schaufler, Casey
<casey.schaufler@...el.com> wrote:
> > -----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.

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