scsi: libiscsi: qedi: convert iscsi_task.refcount 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>
Acked-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/libiscsi.c

@@ -517,13 +517,13 @@ static void iscsi_free_task(struct iscsi_task *task)
 
 void __iscsi_get_task(struct iscsi_task *task)
 {
-	atomic_inc(&task->refcount);
+	refcount_inc(&task->refcount);
 }
 EXPORT_SYMBOL_GPL(__iscsi_get_task);
 
 void __iscsi_put_task(struct iscsi_task *task)
 {
-	if (atomic_dec_and_test(&task->refcount))
+	if (refcount_dec_and_test(&task->refcount))
 		iscsi_free_task(task);
 }
 EXPORT_SYMBOL_GPL(__iscsi_put_task);
@@ -745,7 +745,7 @@ __iscsi_conn_send_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
 	 * released by the lld when it has transmitted the task for
 	 * pdus we do not expect a response for.
 	 */
-	atomic_set(&task->refcount, 1);
+	refcount_set(&task->refcount, 1);
 	task->conn = conn;
 	task->sc = NULL;
 	INIT_LIST_HEAD(&task->running);
@@ -1617,7 +1617,7 @@ static inline struct iscsi_task *iscsi_alloc_task(struct iscsi_conn *conn,
 	sc->SCp.phase = conn->session->age;
 	sc->SCp.ptr = (char *) task;
 
-	atomic_set(&task->refcount, 1);
+	refcount_set(&task->refcount, 1);
 	task->state = ISCSI_TASK_PENDING;
 	task->conn = conn;
 	task->sc = sc;

drivers/scsi/qedi/qedi_iscsi.c

@@ -1372,7 +1372,7 @@ static void qedi_cleanup_task(struct iscsi_task *task)
 {
 	if (!task->sc || task->state == ISCSI_TASK_PENDING) {
 		QEDI_INFO(NULL, QEDI_LOG_IO, "Returning ref_cnt=%d\n",
-			  atomic_read(&task->refcount));
+			  refcount_read(&task->refcount));
 		return;
 	}
 

include/scsi/libiscsi.h

@@ -29,6 +29,7 @@
 #include <linux/timer.h>
 #include <linux/workqueue.h>
 #include <linux/kfifo.h>
+#include <linux/refcount.h>
 #include <scsi/iscsi_proto.h>
 #include <scsi/iscsi_if.h>
 #include <scsi/scsi_transport_iscsi.h>
@@ -139,7 +140,7 @@ struct iscsi_task {
 
 	/* state set/tested under session->lock */
 	int			state;
-	atomic_t		refcount;
+	refcount_t		refcount;
 	struct list_head	running;	/* running cmd list */
 	void			*dd_data;	/* driver/transport data */
 };