net, sctp: convert sctp_transport.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>

include/net/sctp/structs.h

@@ -735,7 +735,7 @@ struct sctp_transport {
 	struct rhlist_head node;
 
 	/* Reference counting. */
-	atomic_t refcnt;
+	refcount_t refcnt;
 		/* RTO-Pending : A flag used to track if one of the DATA
 		 *		chunks sent to this address is currently being
 		 *		used to compute a RTT. If this flag is 0,

net/sctp/transport.c

@@ -99,7 +99,7 @@ static struct sctp_transport *sctp_transport_init(struct net *net,
 	/* Initialize the 64-bit random nonce sent with heartbeat. */
 	get_random_bytes(&peer->hb_nonce, sizeof(peer->hb_nonce));
 
-	atomic_set(&peer->refcnt, 1);
+	refcount_set(&peer->refcnt, 1);
 
 	return peer;
 }
@@ -172,7 +172,7 @@ static void sctp_transport_destroy_rcu(struct rcu_head *head)
  */
 static void sctp_transport_destroy(struct sctp_transport *transport)
 {
-	if (unlikely(atomic_read(&transport->refcnt))) {
+	if (unlikely(refcount_read(&transport->refcnt))) {
 		WARN(1, "Attempt to destroy undead transport %p!\n", transport);
 		return;
 	}
@@ -311,15 +311,15 @@ void sctp_transport_route(struct sctp_transport *transport,
 /* Hold a reference to a transport.  */
 int sctp_transport_hold(struct sctp_transport *transport)
 {
-	return atomic_add_unless(&transport->refcnt, 1, 0);
+	return refcount_inc_not_zero(&transport->refcnt);
 }
 
 /* Release a reference to a transport and clean up
  * if there are no more references.
  */
 void sctp_transport_put(struct sctp_transport *transport)
 {
-	if (atomic_dec_and_test(&transport->refcnt))
+	if (refcount_dec_and_test(&transport->refcnt))
 		sctp_transport_destroy(transport);
 }