2022-11-15 13:55:49

by Yu Kuai

Subject: [PATCH v3 08/10] block: fix use after free for bd_holder_dir

From: Yu Kuai <[email protected]>

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 <[email protected]>
---
block/holder.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/block/holder.c b/block/holder.c
index dd9327b43ce0..c8e462053f49 100644
--- a/block/holder.c
+++ b/block/holder.c
@@ -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);
--
2.31.1

2022-11-16 07:23:03

by Christoph Hellwig

Subject: Re: [PATCH v3 08/10] block: fix use after free for bd_holder_dir

Looks good:

Reviewed-by: Christoph Hellwig <[email protected]>