net, vxlan: convert vxlan_sock.refcnt from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -1034,11 +1034,11 @@ static bool vxlan_group_used(struct vxlan_net *vn, struct vxlan_dev *dev)
 	/* The vxlan_sock is only used by dev, leaving group has
 	 * no effect on other vxlan devices.
 	 */
-	if (family == AF_INET && sock4 && atomic_read(&sock4->refcnt) == 1)
+	if (family == AF_INET && sock4 && refcount_read(&sock4->refcnt) == 1)
 		return false;
 #if IS_ENABLED(CONFIG_IPV6)
 	sock6 = rtnl_dereference(dev->vn6_sock);
-	if (family == AF_INET6 && sock6 && atomic_read(&sock6->refcnt) == 1)
+	if (family == AF_INET6 && sock6 && refcount_read(&sock6->refcnt) == 1)
 		return false;
 #endif
 
@@ -1075,7 +1075,7 @@ static bool __vxlan_sock_release_prep(struct vxlan_sock *vs)
 
 	if (!vs)
 		return false;
-	if (!atomic_dec_and_test(&vs->refcnt))
+	if (!refcount_dec_and_test(&vs->refcnt))
 		return false;
 
 	vn = net_generic(sock_net(vs->sock->sk), vxlan_net_id);
@@ -2825,7 +2825,7 @@ static struct vxlan_sock *vxlan_socket_create(struct net *net, bool ipv6,
 	}
 
 	vs->sock = sock;
-	atomic_set(&vs->refcnt, 1);
+	refcount_set(&vs->refcnt, 1);
 	vs->flags = (flags & VXLAN_F_RCV_FLAGS);
 
 	spin_lock(&vn->sock_lock);
@@ -2860,7 +2860,7 @@ static int __vxlan_sock_add(struct vxlan_dev *vxlan, bool ipv6)
 		spin_lock(&vn->sock_lock);
 		vs = vxlan_find_sock(vxlan->net, ipv6 ? AF_INET6 : AF_INET,
 				     vxlan->cfg.dst_port, vxlan->cfg.flags);
-		if (vs && !atomic_add_unless(&vs->refcnt, 1, 0)) {
+		if (vs && !refcount_inc_not_zero(&vs->refcnt)) {
 			spin_unlock(&vn->sock_lock);
 			return -EBUSY;
 		}

include/net/vxlan.h

@@ -183,7 +183,7 @@ struct vxlan_sock {
 	struct hlist_node hlist;
 	struct socket	 *sock;
 	struct hlist_head vni_list[VNI_HASH_SIZE];
-	atomic_t	  refcnt;
+	refcount_t	  refcnt;
 	u32		  flags;
 };