From 00c83b01d58068dfeb2e1351cca6fccf2a83fa8f Mon Sep 17 00:00:00 2001 From: Marcelo Leitner Date: Thu, 11 Dec 2014 10:02:22 -0200 Subject: [PATCH] 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 Fixes: 7c47cedf43a8b3 ("vxlan: move IGMP join/leave to work queue") Signed-off-by: David S. Miller --- 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 31ecb03368c6..49d9f2291998 100644 --- a/drivers/net/vxlan.c +++ b/drivers/net/vxlan.c @@ -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) -- 2.20.1