Commit 62f535e1 authored by Yu Kuai's avatar Yu Kuai Committed by Jens Axboe
Browse files

block: fix use after free for bd_holder_dir 



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().

Signed-off-by: default avatarYu Kuai <yukuai3@huawei.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221115141054.1051801-9-yukuai1@huaweicloud.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 7abc0777

block/holder.c

+15 −6
Original line number Diff line number Diff line
@@ -65,12 +65,24 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk) 
	if (WARN_ON_ONCE(!disk->slave_dir))

		return -EINVAL;



	mutex_lock(&disk->open_mutex);

	/*

	 * del_gendisk drops the initial reference to bd_holder_dir, so we

	 * need to keep our own here to allow for cleanup past that point.

	 */

	mutex_lock(&bdev->bd_disk->open_mutex);

	if (!disk_live(bdev->bd_disk)) {

		mutex_unlock(&bdev->bd_disk->open_mutex);

		return -ENODEV;

	}

	kobject_get(bdev->bd_holder_dir);

	mutex_unlock(&bdev->bd_disk->open_mutex);



	mutex_lock(&disk->open_mutex);

	WARN_ON_ONCE(!bdev->bd_holder);



	holder = bd_find_holder_disk(bdev, disk);

	if (holder) {

		kobject_put(bdev->bd_holder_dir);

		holder->refcnt++;

		goto out_unlock;

	}
@@ -92,11 +104,6 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk) 
		goto out_del_symlink;

	list_add(&holder->list, &disk->slave_bdevs);



	/*

	 * del_gendisk drops the initial reference to bd_holder_dir, so we need

	 * to keep our own here to allow for cleanup past that point.

	 */

	kobject_get(bdev->bd_holder_dir);

	mutex_unlock(&disk->open_mutex);

	return 0;
@@ -106,6 +113,8 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk) 
	kfree(holder);

out_unlock:

	mutex_unlock(&disk->open_mutex);

	if (ret)

		kobject_put(bdev->bd_holder_dir);

	return ret;

}

EXPORT_SYMBOL_GPL(bd_link_disk_holder);