[4.2.y-ckt stable] Patch "netlink: don't send NETLINK_URELEASE for unbound sockets" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    netlink: don't send NETLINK_URELEASE for unbound sockets

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 01e894d5ea6ccacf67a20178837d8a2107a92867 Mon Sep 17 00:00:00 2001
From: Dmitry Ivanov <dmitrijs.ivanovs at ubnt.com>
Date: Thu, 7 Apr 2016 09:31:38 +0200
Subject: netlink: don't send NETLINK_URELEASE for unbound sockets

commit e27260203912b40751fa353d009eaa5a642c739f upstream.

All existing users of NETLINK_URELEASE use it to clean up resources that
were previously allocated to a socket via some command. As a result, no
users require getting this notification for unbound sockets.

Sending it for unbound sockets, however, is a problem because any user
(including unprivileged users) can create a socket that uses the same ID
as an existing socket. Binding this new socket will fail, but if the
NETLINK_URELEASE notification is generated for such sockets, the users
thereof will be tricked into thinking the socket that they allocated the
resources for is closed.

In the nl80211 case, this will cause destruction of virtual interfaces
that still belong to an existing hostapd process; this is the case that
Dmitry noticed. In the NFC case, it will cause a poll abort. In the case
of netlink log/queue it will cause them to stop reporting events, as if
NFULNL_CFG_CMD_UNBIND/NFQNL_CFG_CMD_UNBIND had been called.

Fix this problem by checking that the socket is bound before generating
the NETLINK_URELEASE notification.

Signed-off-by: Dmitry Ivanov <dima at ubnt.com>
Signed-off-by: Johannes Berg <johannes.berg at intel.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/netlink/af_netlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index f7cb8c6..08bd219 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1293,7 +1293,7 @@ static int netlink_release(struct socket *sock)

 	skb_queue_purge(&sk->sk_write_queue);

-	if (nlk->portid) {
+	if (nlk->portid && nlk->bound) {
 		struct netlink_notify n = {
 						.net = sock_net(sk),
 						.protocol = sk->sk_protocol,
--
2.7.4