Hi,
在 2022/11/03 16:12, Christoph Hellwig 写道:
On Thu, Nov 03, 2022 at 10:55:41AM +0800, Yu Kuai wrote:
From: Yu Kuai <yukuai3@xxxxxxxxxx>
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().
Looks good with some minor stilistic nipicks:
+ if (!disk_live(bdev->bd_disk)) {
+ mutex_unlock(&bdev->bd_disk->open_mutex);
+ return -ENODEV;
+ }
This can use a goto out_unlock;
This lock is different from current 'out_unlock', add a new lable will
make the code more complex, I think.
holder->refcnt++;
+ kobject_put(bdev->bd_holder_dir);
goto out_unlock;
}
holder = kzalloc(sizeof(*holder), GFP_KERNEL);
if (!holder) {
ret = -ENOMEM;
+ kobject_put(bdev->bd_holder_dir);
goto out_unlock;
}
@@ -101,16 +114,12 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
ret = __link_disk_holder(bdev, disk);
if (ret) {
kfree(holder);
+ kobject_put(bdev->bd_holder_dir);
And I think a goto out_put_holder and out_free_holder would clean this up
nicely.
Yes, you're right.
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);
.. with this then jumping straight to out_unlock.
Ok, I'll do that in next version.
We should repost a series with my first 7 patches and your two. I can do
that, but it might take some time as I just got through (minor) knee
surgery and am still at the hospital, so if you have spare cycles feel
free to do it.
I'm glad to do that, and have a good rest 😄
Thanks,
Kuai
.
