ublk: detach gendisk from ublk device if add_disk() fails

Inside ublk_abort_requests(), gendisk is grabbed for aborting all
inflight requests. And ublk_abort_requests() is called when exiting
the uring context or handling timeout.

If add_disk() fails, the gendisk may have been freed when calling
ublk_abort_requests(), so use-after-free can be caused when getting
disk's reference in ublk_abort_requests().

Fixes the bug by detaching gendisk from ublk device if add_disk() fails.

Fixes: bd23f6c ("ublk: quiesce request queue when aborting queue")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20241225110640.351531-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Ming Lei

drivers/block/ublk_drv.c

@@ -1618,6 +1618,21 @@ static void ublk_unquiesce_dev(struct ublk_device *ub)
 	blk_mq_kick_requeue_list(ub->ub_disk->queue);
 }
 
+static struct gendisk *ublk_detach_disk(struct ublk_device *ub)
+{
+	struct gendisk *disk;
+
+	/* Sync with ublk_abort_queue() by holding the lock */
+	spin_lock(&ub->lock);
+	disk = ub->ub_disk;
+	ub->dev_info.state = UBLK_S_DEV_DEAD;
+	ub->dev_info.ublksrv_pid = -1;
+	ub->ub_disk = NULL;
+	spin_unlock(&ub->lock);
+
+	return disk;
+}
+
 static void ublk_stop_dev(struct ublk_device *ub)
 {
 	struct gendisk *disk;
@@ -1631,14 +1646,7 @@ static void ublk_stop_dev(struct ublk_device *ub)
 		ublk_unquiesce_dev(ub);
 	}
 	del_gendisk(ub->ub_disk);
-
-	/* Sync with ublk_abort_queue() by holding the lock */
-	spin_lock(&ub->lock);
-	disk = ub->ub_disk;
-	ub->dev_info.state = UBLK_S_DEV_DEAD;
-	ub->dev_info.ublksrv_pid = -1;
-	ub->ub_disk = NULL;
-	spin_unlock(&ub->lock);
+	disk = ublk_detach_disk(ub);
 	put_disk(disk);
  unlock:
 	mutex_unlock(&ub->mutex);
@@ -2336,7 +2344,7 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub, struct io_uring_cmd *cmd)
 
 out_put_cdev:
 	if (ret) {
-		ub->dev_info.state = UBLK_S_DEV_DEAD;
+		ublk_detach_disk(ub);
 		ublk_put_device(ub);
 	}
 	if (ret)