Hi
在 2022/10/30 23:31, Christoph Hellwig 写道:
We hold a reference to the holder kobject for each bd_holder_disk,
so to make the code a bit more robust, use a reference to it instead
of the block_device. As long as no one clears ->bd_holder_dir in
before freeing the disk, this isn't strictly required, but it does
make the code more clear and more robust.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
block/holder.c | 23 ++++++++++-------------
1 file changed, 10 insertions(+), 13 deletions(-)
diff --git a/block/holder.c b/block/holder.c
index dd9327b43ce05..a8c355b9d0806 100644
--- a/block/holder.c
+++ b/block/holder.c
@@ -4,7 +4,7 @@
struct bd_holder_disk {
struct list_head list;
- struct block_device *bdev;
+ struct kobject *holder_dir;
int refcnt;
};
@@ -14,7 +14,7 @@ static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
struct bd_holder_disk *holder;
list_for_each_entry(holder, &disk->slave_bdevs, list)
- if (holder->bdev == bdev)
+ if (holder->holder_dir == bdev->bd_holder_dir)
return holder;
return NULL;
}
@@ -82,27 +82,24 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
}
INIT_LIST_HEAD(&holder->list);
- holder->bdev = bdev;
holder->refcnt = 1;
+ holder->holder_dir = kobject_get(bdev->bd_holder_dir);
I wonder is this safe here, if kobject reference is 0 here and
bd_holder_dir is about to be freed. Here in kobject_get, kref_get() will
warn about uaf, and kobject_get will return a address that is about to
be freed.
Thansk,
Kuai
+
ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
if (ret)
- goto out_free_holder;
- ret = add_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
+ goto out_put_holder_dir;
+ ret = add_symlink(holder->holder_dir, &disk_to_dev(disk)->kobj);
if (ret)
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;
out_del_symlink:
del_symlink(disk->slave_dir, bdev_kobj(bdev));
-out_free_holder:
+out_put_holder_dir:
+ kobject_put(holder->holder_dir);
kfree(holder);
out_unlock:
mutex_unlock(&disk->open_mutex);
@@ -131,8 +128,8 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
holder = bd_find_holder_disk(bdev, disk);
if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
del_symlink(disk->slave_dir, bdev_kobj(bdev));
- del_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
- kobject_put(bdev->bd_holder_dir);
+ del_symlink(holder->holder_dir, &disk_to_dev(disk)->kobj);
+ kobject_put(holder->holder_dir);
list_del_init(&holder->list);
kfree(holder);
}
--
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