net, atm: convert lec_arp_table.usage 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/atm/lec.c

@@ -101,12 +101,12 @@ static void lec_vcc_close(struct lec_priv *priv, struct atm_vcc *vcc);
 /* must be done under lec_arp_lock */
 static inline void lec_arp_hold(struct lec_arp_table *entry)
 {
-	atomic_inc(&entry->usage);
+	refcount_inc(&entry->usage);
 }
 
 static inline void lec_arp_put(struct lec_arp_table *entry)
 {
-	if (atomic_dec_and_test(&entry->usage))
+	if (refcount_dec_and_test(&entry->usage))
 		kfree(entry);
 }
 
@@ -1564,7 +1564,7 @@ static struct lec_arp_table *make_entry(struct lec_priv *priv,
 	to_return->last_used = jiffies;
 	to_return->priv = priv;
 	skb_queue_head_init(&to_return->tx_wait);
-	atomic_set(&to_return->usage, 1);
+	refcount_set(&to_return->usage, 1);
 	return to_return;
 }
 

net/atm/lec_arpc.h

@@ -47,7 +47,7 @@ struct lec_arp_table {
 					 * the length of the tlvs array
 					 */
 	struct sk_buff_head tx_wait;	/* wait queue for outgoing packets */
-	atomic_t usage;			/* usage count */
+	refcount_t usage;		/* usage count */
 };
 
 /*