From: Marcelo Leitner <mleitner@redhat.com>
Date: Thu, 11 Dec 2014 12:02:22 +0000 (-0200)
Subject: Fix race condition between vxlan_sock_add and vxlan_sock_release
X-Git-Tag: omap-for-v3.20/drop-legacy-3517~122^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=00c83b01d58068dfeb2e1351cca6fccf2a83fa8f;p=pandora-kernel.git

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: 7c47cedf43a8b3 ("vxlan: move IGMP join/leave to work queue")
Signed-off-by: David S. Miller <davem@davemloft.net>
---

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