Re: [PATCH 2/2] seccomp: disallow NEW_LISTENER and TSYNC flags

[Tycho Andersen]

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@xxxxxxxx> 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