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

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Date:	Sat, 6 Oct 2012 17:46:06 +0200
From:	Krzysztof Mazur <krzysiek@...lesie.net>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	mitch@...oth.com, netdev@...r.kernel.org, davem@...emloft.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pppoatm: don't send frames to destroyed vcc

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
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