linux-kernel - Re: [PATCH 2/2] seccomp: disallow NEW

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Message-ID: <20190306213000.GI7413@cisco>
Date:   Wed, 6 Mar 2019 14:30:00 -0700
From:   Tycho Andersen <tycho@...ho.ws>
To:     Christian Brauner <christian.brauner@...onical.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 2/2] seccomp: disallow NEW_LISTENER and TSYNC flags

On Wed, Mar 06, 2019 at 10:02:25PM +0100, Christian Brauner wrote:
> On Wed, Mar 6, 2019 at 9:46 PM Tycho Andersen <tycho@...ho.ws> wrote:
> >
> > On Wed, Mar 06, 2019 at 09:39:35PM +0100, Christian Brauner wrote:
> > > > +
> > > >     /* Prepare the new filter before holding any locks. */
> > > >     prepared = seccomp_prepare_user_filter(filter);
> > > >     if (IS_ERR(prepared))
> > > > @@ -1302,7 +1315,7 @@ static long seccomp_set_mode_filter(unsigned int flags,
> > > >             mutex_unlock(&current->signal->cred_guard_mutex);
> > > >  out_put_fd:
> > > >     if (flags & SECCOMP_FILTER_FLAG_NEW_LISTENER) {
> > > > -           if (ret < 0) {
> > > > +           if (ret) {
> > >
> > > Why that change but keep checking if (ret < 0) further up?
> >
> > Not sure what you mean here. The only other place I see that we check
> > something is < 0 in that function is the return value of
> > get_unused_fd_flags(), which looks right to me?
> 
> The change just seemed it had nothing to do with the rest of the patch.
> Just making sure this didn't happen on accident and would cause regressions.

No, not on accident :). See the second half of the patch notes.

I can split it out into two separate patches if that makes more sense.
In fact this hunk alone fixes the UAF, but you still get non-sensical
return results even if it doesn't do anything terrible, hence the
first hunk.

Cheers,

Tycho