Patch "packet: hold bind lock when rebinding to fanout hook" 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: hold bind lock when rebinding to fanout hook

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-hold-bind-lock-when-rebinding-to-fanout-hook.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: Thu, 14 Sep 2017 17:14:41 -0400
Subject: packet: hold bind lock when rebinding to fanout hook

From: Willem de Bruijn <[email protected]>

[ Upstream commit 008ba2a13f2d04c947adc536d19debb8fe66f110 ]

Packet socket bind operations must hold the po->bind_lock. This keeps po->running consistent with whether the socket is actually on a ptype list to receive packets.

fanout_add unbinds a socket and its packet_rcv/tpacket_rcv call, then binds the fanout object to receive through packet_rcv_fanout.

Make it hold the po->bind_lock when testing po->running and rebinding. Else, it can race with other rebind operations, such as that in packet_set_ring from packet_rcv to tpacket_rcv. Concurrent updates can result in a socket being added to a fanout group twice, causing use-after-free KASAN bug reports, among others.

Reported independently by both trinity and syzkaller. Verified that the syzkaller reproducer passes after this patch.

---
 net/packet/af_packet.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

@@ -1652,10 +1652,6 @@ static int fanout_add(struct sock *sk, u
 
 	mutex_lock(&fanout_mutex);
 
-	err = -EINVAL;
-	if (!po->running)
-		goto out;
-
 	err = -EALREADY;
 	if (po->fanout)
 		goto out;

@@ -1704,7 +1700,10 @@ static int fanout_add(struct sock *sk, u
 		list_add(&match->list, &fanout_list);
 	}
 	err = -EINVAL;
-	if (match->type == type &&
+
+	spin_lock(&po->bind_lock);
+	if (po->running &&
+	    match->type == type &&
 	    match->prot_hook.type == po->prot_hook.type &&
 	    match->prot_hook.dev == po->prot_hook.dev) {
 		err = -ENOSPC;

@@ -1716,6 +1715,13 @@ static int fanout_add(struct sock *sk, u
 			err = 0;
 		}
 	}
+	spin_unlock(&po->bind_lock);
+
+	if (err && !refcount_read(&match->sk_ref)) {
+		list_del(&match->list);
+		kfree(match);
+	}
+
 out:
 	if (err && rollover) {
 		kfree(rollover);

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