scsi: libfc: convert fc_fcp_pkt.ref_cnt 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 <[e-mail]>
Signed-off-by: Hans Liljestrand <[e-mail]>
Signed-off-by: Kees Cook <[e-mail]>
Signed-off-by: David Windsor <[e-mail]>
Acked-by: Johannes Thumshirn <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/libfc/fc_fcp.c

···
 		memset(fsp, 0, sizeof(*fsp));
 		fsp->lp = lport;
 		fsp->xfer_ddp = FC_XID_UNKNOWN;
-		atomic_set(&fsp->ref_cnt, 1);
+		refcount_set(&fsp->ref_cnt, 1);
 		init_timer(&fsp->timer);
 		fsp->timer.data = (unsigned long)fsp;
 		INIT_LIST_HEAD(&fsp->list);
···
  */
 static void fc_fcp_pkt_release(struct fc_fcp_pkt *fsp)
 {
-	if (atomic_dec_and_test(&fsp->ref_cnt)) {
+	if (refcount_dec_and_test(&fsp->ref_cnt)) {
 		struct fc_fcp_internal *si = fc_get_scsi_internal(fsp->lp);
 
 		mempool_free(fsp, si->scsi_pkt_pool);
···
  */
 static void fc_fcp_pkt_hold(struct fc_fcp_pkt *fsp)
 {
-	atomic_inc(&fsp->ref_cnt);
+	refcount_inc(&fsp->ref_cnt);
 }
 
 /**

include/scsi/libfc.h

···
 #include <linux/timer.h>
 #include <linux/if.h>
 #include <linux/percpu.h>
+#include <linux/refcount.h>
 
 #include <scsi/scsi_transport.h>
 #include <scsi/scsi_transport_fc.h>
···
  */
 struct fc_fcp_pkt {
 	spinlock_t	  scsi_pkt_lock;
-	atomic_t	  ref_cnt;
+	refcount_t	  ref_cnt;
 
 	/* SCSI command and data transfer information */
 	u32		  data_len;