Patch "sctp: fix dst refcnt leak in sctp_v4_get_dst" 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

sctp: fix dst refcnt leak in sctp_v4_get_dst

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:
sctp-fix-dst-refcnt-leak-in-sctp_v4_get_dst.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: Tommi Rantala <[email protected]>
Date: Mon, 5 Feb 2018 21:48:14 +0200
Subject: sctp: fix dst refcnt leak in sctp_v4_get_dst

From: Tommi Rantala <[email protected]>

[ Upstream commit 4a31a6b19f9ddf498c81f5c9b089742b7472a6f8 ]

Fix dst reference count leak in sctp_v4_get_dst() introduced in commit 410f03831 ("sctp: add routing output fallback"):

When walking the address_list, successive ip_route_output_key() calls may return the same rt->dst with the reference incremented on each call.

The code would not decrement the dst refcount when the dst pointer was identical from the previous iteration, causing the dst refcnt leak.

Testcase:
ip netns add TEST
ip netns exec TEST ip link set lo up
ip link add dummy0 type dummy
ip link add dummy1 type dummy
ip link add dummy2 type dummy
ip link set dev dummy0 netns TEST
ip link set dev dummy1 netns TEST
ip link set dev dummy2 netns TEST
ip netns exec TEST ip addr add 192.168.1.1/24 dev dummy0
ip netns exec TEST ip link set dummy0 up
ip netns exec TEST ip addr add 192.168.1.2/24 dev dummy1
ip netns exec TEST ip link set dummy1 up
ip netns exec TEST ip addr add 192.168.1.3/24 dev dummy2
ip netns exec TEST ip link set dummy2 up
ip netns exec TEST sctp_test -H 192.168.1.2 -P 20002 -h 192.168.1.1 -p 20000 -s -B 192.168.1.3 ip netns del TEST

In 4.4 and 4.9 kernels this results to:

  [  354.179591] unregister_netdevice: waiting for lo to become free. Usage count = 1
  [  364.419674] unregister_netdevice: waiting for lo to become free. Usage count = 1
  [  374.663664] unregister_netdevice: waiting for lo to become free. Usage count = 1
  [  384.903717] unregister_netdevice: waiting for lo to become free. Usage count = 1
  [  395.143724] unregister_netdevice: waiting for lo to become free. Usage count = 1
  [  405.383645] unregister_netdevice: waiting for lo to become free. Usage count = 1
  ...

---
 net/sctp/protocol.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

@@ -508,22 +508,20 @@ static void sctp_v4_get_dst(struct sctp_
 		if (IS_ERR(rt))
 			continue;
 
-		if (!dst)
-			dst = &rt->dst;
-
 		/* Ensure the src address belongs to the output
 		 * interface.
 		 */
 		odev = __ip_dev_find(sock_net(sk), laddr->a.v4.sin_addr.s_addr,
 				     false);
 		if (!odev || odev->ifindex != fl4->flowi4_oif) {
-			if (&rt->dst != dst)
+			if (!dst)
+				dst = &rt->dst;
+			else
 				dst_release(&rt->dst);
 			continue;
 		}
 
-		if (dst != &rt->dst)
-			dst_release(dst);
+		dst_release(dst);
 		dst = &rt->dst;
 		break;
 	}

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

queue-4.4/sctp-fix-dst-refcnt-leak-in-sctp_v4_get_dst.patch