Re: [PATCH v7 5/6] seccomp: add a way to pass FDs via a notification fd

Tycho Andersen
2018-09-27T22:50:03Z

On Fri, Sep 28, 2018 at 12:17:07AM +0200, Jann Horn wrote:
> On Fri, Sep 28, 2018 at 12:14 AM Tycho Andersen <tycho@tycho.ws> wrote:
> > On Thu, Sep 27, 2018 at 09:28:07PM +0200, Jann Horn wrote:
> > > On Thu, Sep 27, 2018 at 5:11 PM Tycho Andersen <tycho@tycho.ws> wrote:
> > > > This patch adds a way to insert FDs into the tracee's process (also
> > > > close/overwrite fds for the tracee). This functionality is necessary to
> > > > mock things like socketpair() or dup2() or similar, but since it depends on
> > > > external (vfs) patches, I've left it as a separate patch as before so the
> > > > core functionality can still be merged while we argue about this. Except
> > > > this time it doesn't add any ugliness to the API :)
> > > [...]
> > > > +static long seccomp_notify_put_fd(struct seccomp_filter *filter,
> > > > + unsigned long arg)
> > > > +{
> > > > + struct seccomp_notif_put_fd req;
> > > > + void __user *buf = (void __user *)arg;
> > > > + struct seccomp_knotif *knotif = NULL;
> > > > + long ret;
> > > > +
> > > > + if (copy_from_user(&req, buf, sizeof(req)))
> > > > + return -EFAULT;
> > > > +
> > > > + if (req.fd < 0 && req.to_replace < 0)
> > > > + return -EINVAL;
> > > > +
> > > > + ret = mutex_lock_interruptible(&filter->notify_lock);
> > > > + if (ret < 0)
> > > > + return ret;
> > > > +
> > > > + ret = -ENOENT;
> > > > + list_for_each_entry(knotif, &filter->notif->notifications, list) {
> > > > + struct file *file = NULL;
> > > > +
> > > > + if (knotif->id != req.id)
> > > > + continue;
> > >
> > > Are you intentionally permitting non-SENT states here? It shouldn't
> > > make a big difference, but I think it'd be nice to at least block the
> > > use of notifications in SECCOMP_NOTIFY_REPLIED state.
> >
> > Agreed, I'll block everything besides REPLIED.
>
> Do you mean SENT? In REPLIED state, seccomp_notify_put_fd()
> is racy because the target task is in the process of waking up, right?

Yes, sorry, I mean SENT.

Tycho