Re: [PATCH] pppoatm: don't send frames to destroyed vcc

Krzysztof Mazur
2012-10-06T15:46:06Z

On Sat, Oct 06, 2012 at 05:38:04PM +0200, Krzysztof Mazur wrote:
> On Sat, Oct 06, 2012 at 02:32:50PM +0100, David Woodhouse wrote:
> > On Sat, 2012-10-06 at 14:19 +0200, Krzysztof Mazur wrote:
> > > Now pppoatm_send(), like vcc_sendmsg(), checks for vcc flags that
> > > indicate that vcc is not ready.
> >
> > And what locking prevents the flag from being set immediately after we
> > check it?
> >
>
> nothing, this patch should fix this.
>

I think there is another problem here. The pppoatm gets a reference
to atmvcc, but I don't see anything that protects against removal
of that vcc.

The vcc uses vcc->sk socket for reference counting, so sock_hold()
and sock_put() should be used by pppoatm.

diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c
index 29afc68..126f57f 100644
--- a/net/atm/pppoatm.c
+++ b/net/atm/pppoatm.c
@@ -154,6 +154,7 @@ static void pppoatm_unassign_vcc(struct atm_vcc *atmvcc)
tasklet_kill(&pvcc->wakeup_tasklet);
ppp_unregister_channel(&pvcc->chan);
atmvcc->user_back = NULL;
+ sock_put(sk_atm(pvcc->atmvcc));
kfree(pvcc);
/* Gee, I hope we have the big kernel lock here... */
module_put(THIS_MODULE);
@@ -371,6 +372,7 @@ static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
if (pvcc == NULL)
return -ENOMEM;
pvcc->atmvcc = atmvcc;
+ sock_hold(sk_atm(atmvcc));

/* Maximum is zero, so that we can use atomic_inc_not_zero() */
atomic_set(&pvcc->inflight, NONE_INFLIGHT);
@@ -385,6 +387,7 @@ static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
pvcc->wakeup_tasklet.data = (unsigned long) &pvcc->chan;
err = ppp_register_channel(&pvcc->chan);
if (err != 0) {
+ sock_put(sk_atm(atmvcc));
kfree(pvcc);
return err;
}

--
Krzysiek