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Fix race condition between vxlan_sock_add and vxlan_sock_release

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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: 7c47cedf43 ("vxlan: move IGMP join/leave to work queue")
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Marcelo Leitner 2014-12-11 10:02:22 -02:00 committed by David S. Miller
parent 51f8301485
commit 00c83b01d5
1 changed files with 3 additions and 7 deletions
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10
drivers/net/vxlan.c
View file

@ -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)