block: fix use after free for bd_holder_dir

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60Q98
CVE: NA

--------------------------------

Currently, the caller of bd_link_disk_holer() get 'bdev' by
blkdev_get_by_dev(), which will look up 'bdev' by inode number 'dev'.
Howerver, it's possible that del_gendisk() can be called currently, and
'bd_holder_dir' can be freed before bd_link_disk_holer() access it, thus
use after free is triggered.

t1:				t2:
bdev = blkdev_get_by_dev
				del_gendisk
				 kobject_put(bd_holder_dir)
				  kobject_free()
bd_link_disk_holder

Fix the problem by checking disk is still live and grabbing a reference
to 'bd_holder_dir' first in bd_link_disk_holder().

Link: https://lore.kernel.org/all/20221103025541.1875809-3-yukuai1@huaweicloud.com/Signed-off-by: NYu Kuai <yukuai3@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

fs/block_dev.c

@@ -1266,16 +1266,31 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	struct bd_holder_disk *holder;
 	int ret = 0;
 
-	mutex_lock(&bdev->bd_mutex);
+	/*
+	 * bdev could be deleted beneath us which would implicitly destroy
+	 * the holder directory.  Hold on to it.
+	 */
+	down_read(&bdev->bd_disk->lookup_sem);
+	if (!(disk->flags & GENHD_FL_UP)) {
+		up_read(&bdev->bd_disk->lookup_sem);
+		return -ENODEV;
+	}
 
+	kobject_get(bdev->bd_part->holder_dir);
+	up_read(&bdev->bd_disk->lookup_sem);
+
+	mutex_lock(&bdev->bd_mutex);
 	WARN_ON_ONCE(!bdev->bd_holder);
 
 	/* FIXME: remove the following once add_disk() handles errors */
-	if (WARN_ON(!disk->slave_dir || !bdev->bd_part->holder_dir))
+	if (WARN_ON(!disk->slave_dir || !bdev->bd_part->holder_dir)) {
+		kobject_put(bdev->bd_part->holder_dir);
 		goto out_unlock;
+	}
 
 	holder = bd_find_holder_disk(bdev, disk);
 	if (holder) {
+		kobject_put(bdev->bd_part->holder_dir);
 		holder->refcnt++;
 		goto out_unlock;
 	}
@@ -1297,11 +1312,6 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	ret = add_symlink(bdev->bd_part->holder_dir, &disk_to_dev(disk)->kobj);
 	if (ret)
 		goto out_del;
-	/*
-	 * bdev could be deleted beneath us which would implicitly destroy
-	 * the holder directory.  Hold on to it.
-	 */
-	kobject_get(bdev->bd_part->holder_dir);
 
 	list_add(&holder->list, &bdev->bd_holder_disks);
 	goto out_unlock;
@@ -1312,6 +1322,8 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	kfree(holder);
 out_unlock:
 	mutex_unlock(&bdev->bd_mutex);
+	if (ret)
+		kobject_put(bdev->bd_part->holder_dir);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(bd_link_disk_holder);