Bluetooth: convert rfcomm_dlc.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: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/rfcomm.h

@@ -21,6 +21,8 @@
    SOFTWARE IS DISCLAIMED.
 */
 
+#include <linux/refcount.h>
+
 #ifndef __RFCOMM_H
 #define __RFCOMM_H
 
@@ -174,7 +176,7 @@ struct rfcomm_dlc {
 	struct mutex  lock;
 	unsigned long state;
 	unsigned long flags;
-	atomic_t      refcnt;
+	refcount_t    refcnt;
 	u8            dlci;
 	u8            addr;
 	u8            priority;
@@ -247,12 +249,12 @@ struct rfcomm_dlc *rfcomm_dlc_exists(bdaddr_t *src, bdaddr_t *dst, u8 channel);
 
 static inline void rfcomm_dlc_hold(struct rfcomm_dlc *d)
 {
-	atomic_inc(&d->refcnt);
+	refcount_inc(&d->refcnt);
 }
 
 static inline void rfcomm_dlc_put(struct rfcomm_dlc *d)
 {
-	if (atomic_dec_and_test(&d->refcnt))
+	if (refcount_dec_and_test(&d->refcnt))
 		rfcomm_dlc_free(d);
 }
 

net/bluetooth/rfcomm/core.c

@@ -311,7 +311,7 @@ struct rfcomm_dlc *rfcomm_dlc_alloc(gfp_t prio)
 
 	skb_queue_head_init(&d->tx_queue);
 	mutex_init(&d->lock);
-	atomic_set(&d->refcnt, 1);
+	refcount_set(&d->refcnt, 1);
 
 	rfcomm_dlc_clear_state(d);
 
@@ -342,7 +342,7 @@ static void rfcomm_dlc_unlink(struct rfcomm_dlc *d)
 {
 	struct rfcomm_session *s = d->session;
 
-	BT_DBG("dlc %p refcnt %d session %p", d, atomic_read(&d->refcnt), s);
+	BT_DBG("dlc %p refcnt %d session %p", d, refcount_read(&d->refcnt), s);
 
 	list_del(&d->list);
 	d->session = NULL;