Patch "packet: in packet_do_bind, test fanout with bind_lock held" 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

packet: in packet_do_bind, test fanout with bind_lock held

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:
packet-in-packet_do_bind-test-fanout-with-bind_lock-held.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: Willem de Bruijn <[email protected]>
Date: Tue, 26 Sep 2017 12:19:37 -0400
Subject: packet: in packet_do_bind, test fanout with bind_lock held

From: Willem de Bruijn <[email protected]>

[ Upstream commit 4971613c1639d8e5f102c4e797c3bf8f83a5a69e ]

Once a socket has po->fanout set, it remains a member of the group until it is destroyed. The prot_hook must be constant and identical across sockets in the group.

If fanout_add races with packet_do_bind between the test of po->fanout and taking the lock, the bind call may make type or dev inconsistent with that of the fanout group.

Hold po->bind_lock when testing po->fanout to avoid this race.

I had to introduce artificial delay (local_bh_enable) to actually observe the race.

---
 net/packet/af_packet.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

@@ -2944,13 +2944,15 @@ static int packet_do_bind(struct sock *s
 	int ret = 0;
 	bool unlisted = false;
 
-	if (po->fanout)
-		return -EINVAL;
-
 	lock_sock(sk);
 	spin_lock(&po->bind_lock);
 	rcu_read_lock();
 
+	if (po->fanout) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
 	if (name) {
 		dev = dev_get_by_name_rcu(sock_net(sk), name);
 		if (!dev) {

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

queue-4.4/packet-in-packet_do_bind-test-fanout-with-bind_lock-held.patch queue-4.4/packet-only-test-po-has_vnet_hdr-once-in-packet_snd.patch queue-4.4/packet-hold-bind-lock-when-rebinding-to-fanout-hook.patch