[3.13.y-ckt stable] Patch "Fix race condition between vxlan_sock_add and vxlan_sock_release" has been added to staging queue

[Kamal Mostafa]

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

    Fix race condition between vxlan_sock_add and vxlan_sock_release

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt13.

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

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 6f1ff3032adb6c3f39afbd6fae23cdc35a0b7b43 Mon Sep 17 00:00:00 2001
From: Marcelo Leitner <mleitner at redhat.com>
Date: Thu, 11 Dec 2014 10:02:22 -0200
Subject: Fix race condition between vxlan_sock_add and vxlan_sock_release

[ Upstream commit 00c83b01d58068dfeb2e1351cca6fccf2a83fa8f ]

Currently, when trying to reuse a socket, vxlan_sock_add will grab
vn->sock_lock, locate a reusable socket, inc refcount and release
vn->sock_lock.

But vxlan_sock_release() will first decrement refcount, and then grab
that lock. refcnt operations are atomic but as currently we have
deferred works which hold vs->refcnt each, this might happen, leading to
a use after free (specially after vxlan_igmp_leave):

  CPU 1                            CPU 2

deferred work                    vxlan_sock_add
  ...                              ...
                                   spin_lock(&vn->sock_lock)
                                   vs = vxlan_find_sock();
  vxlan_sock_release
    dec vs->refcnt, reaches 0
    spin_lock(&vn->sock_lock)
                                   vxlan_sock_hold(vs), refcnt=1
                                   spin_unlock(&vn->sock_lock)
    hlist_del_rcu(&vs->hlist);
    vxlan_notify_del_rx_port(vs)
    spin_unlock(&vn->sock_lock)

So when we look for a reusable socket, we check if it wasn't freed
already before reusing it.

Signed-off-by: Marcelo Ricardo Leitner <mleitner at redhat.com>
Fixes: 7c47cedf43a8b3 ("vxlan: move IGMP join/leave to work queue")
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/net/vxlan.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index e7da1c4..045876f 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2006,9 +2006,8 @@ static int vxlan_init(struct net_device *dev)
 	spin_lock(&vn->sock_lock);
 	vs = vxlan_find_sock(dev_net(dev), ipv6 ? AF_INET6 : AF_INET,
 			     vxlan->dst_port);
-	if (vs) {
+	if (vs && atomic_add_unless(&vs->refcnt, 1, 0)) {
 		/* If we have a socket with same port already, reuse it */
-		atomic_inc(&vs->refcnt);
 		vxlan_vs_add_dev(vs, vxlan);
 	} else {
 		/* otherwise make new socket outside of RTNL */
@@ -2448,12 +2447,9 @@ struct vxlan_sock *vxlan_sock_add(struct net *net, __be16 port,

 	spin_lock(&vn->sock_lock);
 	vs = vxlan_find_sock(net, ipv6 ? AF_INET6 : AF_INET, port);
-	if (vs) {
-		if (vs->rcv == rcv)
-			atomic_inc(&vs->refcnt);
-		else
+	if (vs && ((vs->rcv != rcv) ||
+		   !atomic_add_unless(&vs->refcnt, 1, 0)))
 			vs = ERR_PTR(-EBUSY);
-	}
 	spin_unlock(&vn->sock_lock);

 	if (!vs)
--
1.9.1