net, l2tp: convert l2tp_tunnel.ref_count 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>

net/l2tp/l2tp_core.c

@@ -132,12 +132,12 @@ static inline struct l2tp_net *l2tp_pernet(const struct net *net)
  */
 static inline void l2tp_tunnel_inc_refcount_1(struct l2tp_tunnel *tunnel)
 {
-	atomic_inc(&tunnel->ref_count);
+	refcount_inc(&tunnel->ref_count);
 }
 
 static inline void l2tp_tunnel_dec_refcount_1(struct l2tp_tunnel *tunnel)
 {
-	if (atomic_dec_and_test(&tunnel->ref_count))
+	if (refcount_dec_and_test(&tunnel->ref_count))
 		l2tp_tunnel_free(tunnel);
 }
 #ifdef L2TP_REFCNT_DEBUG
@@ -145,14 +145,14 @@ static inline void l2tp_tunnel_dec_refcount_1(struct l2tp_tunnel *tunnel)
 do {									\
 	pr_debug("l2tp_tunnel_inc_refcount: %s:%d %s: cnt=%d\n",	\
 		 __func__, __LINE__, (_t)->name,			\
-		 atomic_read(&_t->ref_count));				\
+		 refcount_read(&_t->ref_count));			\
 	l2tp_tunnel_inc_refcount_1(_t);					\
 } while (0)
 #define l2tp_tunnel_dec_refcount(_t)					\
 do {									\
 	pr_debug("l2tp_tunnel_dec_refcount: %s:%d %s: cnt=%d\n",	\
 		 __func__, __LINE__, (_t)->name,			\
-		 atomic_read(&_t->ref_count));				\
+		 refcount_read(&_t->ref_count));			\
 	l2tp_tunnel_dec_refcount_1(_t);					\
 } while (0)
 #else
@@ -1353,7 +1353,7 @@ static void l2tp_udp_encap_destroy(struct sock *sk)
  */
 static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel)
 {
-	BUG_ON(atomic_read(&tunnel->ref_count) != 0);
+	BUG_ON(refcount_read(&tunnel->ref_count) != 0);
 	BUG_ON(tunnel->sock != NULL);
 	l2tp_info(tunnel, L2TP_MSG_CONTROL, "%s: free...\n", tunnel->name);
 	kfree_rcu(tunnel, rcu);
@@ -1667,7 +1667,7 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32
 	/* Bump the reference count. The tunnel context is deleted
 	 * only when this drops to zero. Must be done before list insertion
 	 */
-	l2tp_tunnel_inc_refcount(tunnel);
+	refcount_set(&tunnel->ref_count, 1);
 	spin_lock_bh(&pn->l2tp_tunnel_list_lock);
 	list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list);
 	spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
@@ -1706,7 +1706,7 @@ void l2tp_session_free(struct l2tp_session *session)
 {
 	struct l2tp_tunnel *tunnel = session->tunnel;
 
-	BUG_ON(atomic_read(&session->ref_count) != 0);
+	BUG_ON(refcount_read(&session->ref_count) != 0);
 
 	if (tunnel) {
 		BUG_ON(tunnel->magic != L2TP_TUNNEL_MAGIC);

net/l2tp/l2tp_core.h

@@ -7,6 +7,7 @@
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  */
+#include <linux/refcount.h>
 
 #ifndef _L2TP_CORE_H_
 #define _L2TP_CORE_H_
@@ -177,7 +178,7 @@ struct l2tp_tunnel {
 	struct list_head	list;		/* Keep a list of all tunnels */
 	struct net		*l2tp_net;	/* the net we belong to */
 
-	atomic_t		ref_count;
+	refcount_t		ref_count;
 #ifdef CONFIG_DEBUG_FS
 	void (*show)(struct seq_file *m, void *arg);
 #endif

net/l2tp/l2tp_debugfs.c

@@ -145,7 +145,7 @@ static void l2tp_dfs_seq_tunnel_show(struct seq_file *m, void *v)
 		   "");
 	seq_printf(m, " %d sessions, refcnt %d/%d\n", session_count,
 		   tunnel->sock ? refcount_read(&tunnel->sock->sk_refcnt) : 0,
-		   atomic_read(&tunnel->ref_count));
+		   refcount_read(&tunnel->ref_count));
 	seq_printf(m, " %08x rx %ld/%ld/%ld rx %ld/%ld/%ld\n",
 		   tunnel->debug,
 		   atomic_long_read(&tunnel->stats.tx_packets),
@@ -170,7 +170,7 @@ static void l2tp_dfs_seq_session_show(struct seq_file *m, void *v)
 		   "");
 	if (session->send_seq || session->recv_seq)
 		seq_printf(m, "   nr %hu, ns %hu\n", session->nr, session->ns);
-	seq_printf(m, "   refcnt %d\n", atomic_read(&session->ref_count));
+	seq_printf(m, "   refcnt %d\n", refcount_read(&session->ref_count));
 	seq_printf(m, "   config %d/%d/%c/%c/%s/%s %08x %u\n",
 		   session->mtu, session->mru,
 		   session->recv_seq ? 'R' : '-',

net/l2tp/l2tp_ppp.c

@@ -1616,7 +1616,7 @@ static void pppol2tp_seq_tunnel_show(struct seq_file *m, void *v)
 	seq_printf(m, "\nTUNNEL '%s', %c %d\n",
 		   tunnel->name,
 		   (tunnel == tunnel->sock->sk_user_data) ? 'Y' : 'N',
-		   atomic_read(&tunnel->ref_count) - 1);
+		   refcount_read(&tunnel->ref_count) - 1);
 	seq_printf(m, " %08x %ld/%ld/%ld %ld/%ld/%ld\n",
 		   tunnel->debug,
 		   atomic_long_read(&tunnel->stats.tx_packets),