linux-kernel - Re: [PATCH v5 1/5] AppArmor: Prepare for PTRACE_MODE

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Message-ID: <CAG48ez15jcFQT1NdZekRuo9_GKLru_R1HpgF0TNKUKAZ8_6UNA@mail.gmail.com>
Date:   Wed, 26 Sep 2018 23:18:35 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Casey Schaufler <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, 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 1/5] AppArmor: Prepare for PTRACE_MODE_SCHED

On Wed, Sep 26, 2018 at 11:16 PM Jann Horn <jannh@...gle.com> wrote:
>
> 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.
>
> Why is this separate from PTRACE_MODE_NOAUDIT? It looks like
> apparmor_ptrace_access_check() currently ignores PTRACE_MODE_NOAUDIT.
> Could you, instead of adding a new flag, fix the handling of
> PTRACE_MODE_NOAUDIT?

Er, after looking at more of the series, I see that PTRACE_MODE_SCHED
is necessary; but could you handle the "don't audit" part for AppArmor
using PTRACE_MODE_NOAUDIT instead?

> > Signed-off-by: Casey Schaufler <casey.schaufler@...el.com>
> > ---
> >  security/apparmor/domain.c      | 2 +-
> >  security/apparmor/include/ipc.h | 2 +-
> >  security/apparmor/ipc.c         | 8 +++++---
> >  security/apparmor/lsm.c         | 5 +++--
> >  4 files changed, 10 insertions(+), 7 deletions(-)
> >
> > diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
> > index 08c88de0ffda..28300f4c3ef9 100644
> > --- a/security/apparmor/domain.c
> > +++ b/security/apparmor/domain.c
> > @@ -77,7 +77,7 @@ static int may_change_ptraced_domain(struct aa_label *to_label,
> >         if (!tracer || unconfined(tracerl))
> >                 goto out;
> >
> > -       error = aa_may_ptrace(tracerl, to_label, PTRACE_MODE_ATTACH);
> > +       error = aa_may_ptrace(tracerl, to_label, PTRACE_MODE_ATTACH, true);
> >
> >  out:
> >         rcu_read_unlock();
> > diff --git a/security/apparmor/include/ipc.h b/security/apparmor/include/ipc.h
> > index 5ffc218d1e74..299d1c45fef0 100644
> > --- a/security/apparmor/include/ipc.h
> > +++ b/security/apparmor/include/ipc.h
> > @@ -34,7 +34,7 @@ struct aa_profile;
> >         "xcpu xfsz vtalrm prof winch io pwr sys emt lost"
> >
> >  int aa_may_ptrace(struct aa_label *tracer, struct aa_label *tracee,
> > -                 u32 request);
> > +                 u32 request, bool audit);
> >  int aa_may_signal(struct aa_label *sender, struct aa_label *target, int sig);
> >
> >  #endif /* __AA_IPC_H */
> > diff --git a/security/apparmor/ipc.c b/security/apparmor/ipc.c
> > index 527ea1557120..9ed110afc822 100644
> > --- a/security/apparmor/ipc.c
> > +++ b/security/apparmor/ipc.c
> > @@ -121,15 +121,17 @@ static int profile_tracer_perm(struct aa_profile *tracer,
> >   * Returns: %0 else error code if permission denied or error
> >   */
> >  int aa_may_ptrace(struct aa_label *tracer, struct aa_label *tracee,
> > -                 u32 request)
> > +                 u32 request, bool audit)
> >  {
> >         struct aa_profile *profile;
> >         u32 xrequest = request << PTRACE_PERM_SHIFT;
> >         DEFINE_AUDIT_DATA(sa, LSM_AUDIT_DATA_NONE, OP_PTRACE);
> >
> >         return xcheck_labels(tracer, tracee, profile,
> > -                       profile_tracer_perm(profile, tracee, request, &sa),
> > -                       profile_tracee_perm(profile, tracer, xrequest, &sa));
> > +                       profile_tracer_perm(profile, tracee, request,
> > +                                           audit ? &sa : NULL),
> > +                       profile_tracee_perm(profile, tracer, xrequest,
> > +                                           audit ? &sa : NULL));
> >  }
> >
> >
> > diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> > index 8b8b70620bbe..da9d0b228857 100644
> > --- a/security/apparmor/lsm.c
> > +++ b/security/apparmor/lsm.c
> > @@ -118,7 +118,8 @@ static int apparmor_ptrace_access_check(struct task_struct *child,
> >         tracee = aa_get_task_label(child);
> >         error = aa_may_ptrace(tracer, tracee,
> >                         (mode & PTRACE_MODE_READ) ? AA_PTRACE_READ
> > -                                                 : AA_PTRACE_TRACE);
> > +                                                 : AA_PTRACE_TRACE,
> > +                       !(mode & PTRACE_MODE_SCHED));
> >         aa_put_label(tracee);
> >         end_current_label_crit_section(tracer);
> >
> > @@ -132,7 +133,7 @@ static int apparmor_ptrace_traceme(struct task_struct *parent)
> >
> >         tracee = begin_current_label_crit_section();
> >         tracer = aa_get_task_label(parent);
> > -       error = aa_may_ptrace(tracer, tracee, AA_PTRACE_TRACE);
> > +       error = aa_may_ptrace(tracer, tracee, AA_PTRACE_TRACE, true);
> >         aa_put_label(tracer);
> >         end_current_label_crit_section(tracee);
> >
> > --
> > 2.17.1
> >