Patch "packet: hold bind lock when rebinding to fanout hook" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org> know about it.


>From foo@baz Thu Oct 19 14:05:19 CEST 2017
From: Willem de Bruijn <willemb@google.com>
Date: Thu, 14 Sep 2017 17:14:41 -0400
Subject: packet: hold bind lock when rebinding to fanout hook

From: Willem de Bruijn <willemb@google.com>


[ 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.

Fixes: dc99f600698d ("packet: Add fanout support.")
Reported-by: nixioaming <nixiaoming@huawei.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/packet/af_packet.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -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 willemb@google.com 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