On Tue, Jun 09, 2015 at 12:37:21PM -0300, Marcelo Ricardo Leitner wrote:
> On Mon, Jun 08, 2015 at 10:09:50PM +0200, Hannes Frederic Sowa wrote:
> > On Fr, 2015-06-05 at 14:08 -0300, mleitner@xxxxxxxxxx wrote:
> > > if (sp->do_auto_asconf) {
> > > + spin_lock_bh(&sock_net(sk)->sctp.addr_wq_lock);
> > > sp->do_auto_asconf = 0;
> > > - list_del(&sp->auto_asconf_list);
> > > + list_del_rcu(&sp->auto_asconf_list);
> > > + spin_unlock_bh(&sock_net(sk)->sctp.addr_wq_lock);
> > > }
> >
> > This also looks a bit unsafe to me:
> >
> > My proposal would be to sock_hold/sock_put the sockets when pushing them
> > onto the auto_asconf_list and defer the modifications on the list until
> ^^^^^^^^^^^^--- you lost me here
>
> > we don't need to hold socket lock anymore (in syscalls we do have a reference
> > anyway).
>
> Yup.. seems we have a use-after-free with this rcu usage on
> auto_asconf_splist, because if the socket was destroyed by the time the
> timeout handler is running, it may still see that socket and thus we
> would need two additional procedures a) to take a sock_hold() when it is
> inserted on that list, and release it via call_rcu() and b) to know how
> to identify such dead sockets, most likely just by checking
> sp->do_auto_asconf, and skip from acting on them.
>
> Neil, WDYT?
>
That seems like a reasonable approach.
> > addr_wq_lock then is only used either without lock_sock at all or only
> > in order addr_wq_lock -> lock_sock, which does not cause any locking
> > ordering issues.
>
> No because we have to update this list on sctp_destroy_sock(), which is
> called with lock_sock() held. If we add the precautions above, I think
> it will be fine.
>
Agreed.
> Thanks,
> Marcelo
>
>
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