[PATCH 3.17 30/47] Fix race condition between vxlan_sock_add and vxlan_sock_release

Greg Kroah-Hartman
2014-12-14T20:24:22Z

From: Marcelo Leitner <mleitner@redhat.com>

[ 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@redhat.com>
Fixes: 7c47cedf43a8b3 ("vxlan: move IGMP join/leave to work queue")
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/vxlan.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)

--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2050,9 +2050,8 @@ static int vxlan_init(struct net_device
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 */
@@ -2459,12 +2458,9 @@ struct vxlan_sock *vxlan_sock_add(struct

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)