scsi: device_handler: Return error pointer in scsi_dh_attached_handler_name()

If scsi_dh_attached_handler_name() fails to allocate the handler name,
dm-multipath (its only caller) assumes there is no attached device
handler, and sets the device up incorrectly. Return an error pointer
instead, so multipath can distinguish between failure, success where
there is no attached device handler, or when the path device is not a
SCSI device at all.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Reviewed-by: Martin Wilck <mwilck@suse.com>
Link: https://patch.msgid.link/20251206010015.1595225-1-bmarzins@redhat.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: bmarzins

drivers/md/dm-mpath.c

@@ -962,6 +962,19 @@ static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps
 
 	q = bdev_get_queue(p->path.dev->bdev);
 	attached_handler_name = scsi_dh_attached_handler_name(q, GFP_KERNEL);
+	if (IS_ERR(attached_handler_name)) {
+		if (PTR_ERR(attached_handler_name) == -ENODEV) {
+			if (m->hw_handler_name) {
+				DMERR("hardware handlers are only allowed for SCSI devices");
+				kfree(m->hw_handler_name);
+				m->hw_handler_name = NULL;
+			}
+			attached_handler_name = NULL;
+		} else {
+			r = PTR_ERR(attached_handler_name);
+			goto bad;
+		}
+	}
 	if (attached_handler_name || m->hw_handler_name) {
 		INIT_DELAYED_WORK(&p->activate_path, activate_path_work);
 		r = setup_scsi_dh(p->path.dev->bdev, m, &attached_handler_name, &ti->error);

drivers/scsi/scsi_dh.c

@@ -353,7 +353,8 @@ EXPORT_SYMBOL_GPL(scsi_dh_attach);
  *      that may have a device handler attached
  * @gfp - the GFP mask used in the kmalloc() call when allocating memory
  *
- * Returns name of attached handler, NULL if no handler is attached.
+ * Returns name of attached handler, NULL if no handler is attached, or
+ * and error pointer if an error occurred.
  * Caller must take care to free the returned string.
  */
 const char *scsi_dh_attached_handler_name(struct request_queue *q, gfp_t gfp)
@@ -363,10 +364,11 @@ const char *scsi_dh_attached_handler_name(struct request_queue *q, gfp_t gfp)
 
 	sdev = scsi_device_from_queue(q);
 	if (!sdev)
-		return NULL;
+		return ERR_PTR(-ENODEV);
 
 	if (sdev->handler)
-		handler_name = kstrdup(sdev->handler->name, gfp);
+		handler_name = kstrdup(sdev->handler->name, gfp) ? :
+			       ERR_PTR(-ENOMEM);
 	put_device(&sdev->sdev_gendev);
 	return handler_name;
 }