Commit 00c83b01 authored Dec 11, 2014 by Marcelo Leitner Committed by David S. Miller Dec 11, 2014

Fix race condition between vxlan_sock_add and vxlan_sock_release



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@redhat.com>
Fixes: 7c47cedf ("vxlan: move IGMP join/leave to work queue")
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 51f83014

drivers/net/vxlan.c

+3 −7

Original line number	Diff line number	Diff line
		@@ -1985,9 +1985,8 @@ static int vxlan_init(struct net_device *dev)
		spin_lock(&vn->sock_lock);
		vs = vxlan_find_sock(vxlan->net, 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 */
		@@ -2389,12 +2388,9 @@ 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)