Patch "ppp: defer netns reference release for ppp channel" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

ppp: defer netns reference release for ppp channel

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ppp-defer-netns-reference-release-for-ppp-channel.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: WANG Cong <[email protected]>
Date: Tue, 5 Jul 2016 22:12:36 -0700
Subject: ppp: defer netns reference release for ppp channel

From: WANG Cong <[email protected]>

commit 205e1e255c479f3fd77446415706463b282f94e4 upstream.

Matt reported that we have a NULL pointer dereference in ppp_pernet() from ppp_connect_channel(), i.e. pch->chan_net is NULL.

This is due to that a parallel ppp_unregister_channel() could happen while we are in ppp_connect_channel(), during which pch->chan_net set to NULL. Since we need a reference to net per channel, it makes sense to sync the refcnt with the life time of the channel, therefore we should release this reference when we destroy it.

---
 drivers/net/ppp/ppp_generic.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

@@ -2390,8 +2390,6 @@ ppp_unregister_channel(struct ppp_channe
 	spin_lock_bh(&pn->all_channels_lock);
 	list_del(&pch->list);
 	spin_unlock_bh(&pn->all_channels_lock);
-	put_net(pch->chan_net);
-	pch->chan_net = NULL;
 
 	pch->file.dead = 1;
 	wake_up_interruptible(&pch->file.rwait);

@@ -2984,6 +2982,9 @@ ppp_disconnect_channel(struct channel *p
  */
 static void ppp_destroy_channel(struct channel *pch)
 {
+	put_net(pch->chan_net);
+	pch->chan_net = NULL;
+
 	atomic_dec(&channel_count);
 
 	if (!pch->file.dead) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/ppp-defer-netns-reference-release-for-ppp-channel.patch