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block: fix use after free for bd_holder_dir

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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: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221115141054.1051801-9-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Yu Kuai 2022-11-15 22:10:52 +08:00 committed by Jens Axboe
parent 7abc077788
commit 62f535e1f0
1 changed files with 15 additions and 6 deletions
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21
block/holder.c
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@ -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);