[PATCH 5.10.y stable] block: unhash blkdev part inode when the part is deleted

[Ming Lei <ming.lei@redhat.com>]

v5.11 changes the blkdev lookup mechanism completely since commit
22ae8ce8b892 ("block: simplify bdev/disk lookup in blkdev_get"),
and small part of the change is to unhash part bdev inode when
deleting partition. Turns out this kind of change does fix one
nasty issue in case of BLOCK_EXT_MAJOR:

1) when one partition is deleted & closed, disk_put_part() is always
called before bdput(bdev), see blkdev_put(); so the part's devt can
be freed & re-used before the inode is dropped

2) then new partition with same devt can be created just before the
inode in 1) is dropped, then the old inode/bdev structurein 1) is
re-used for this new partition, this way causes use-after-free and
kernel panic.

It isn't possible to backport the whole fbig patchset of "merge struct
block_device and struct hd_struct v4" for addressing this issue.

https://lore.kernel.org/linux-block/20201128161510.347752-1-hch@lst.de/

So fixes it by unhashing part bdev in delete_partition(), and this way
is actually aligned with v5.11+'s behavior.

Reported-by: cuishw@inspur.com
Tested-by: cuishw@inspur.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/partitions/core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/block/partitions/core.c b/block/partitions/core.c
index a02e22411594..e3d61ec4a5a6 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -329,6 +329,7 @@ void delete_partition(struct hd_struct *part)
 	struct gendisk *disk = part_to_disk(part);
 	struct disk_part_tbl *ptbl =
 		rcu_dereference_protected(disk->part_tbl, 1);
+	struct block_device *bdev;
 
 	/*
 	 * ->part_tbl is referenced in this part's release handler, so
@@ -346,6 +347,12 @@ void delete_partition(struct hd_struct *part)
 	 * "in-use" until we really free the gendisk.
 	 */
 	blk_invalidate_devt(part_devt(part));
+
+	bdev = bdget_part(part);
+	if (bdev) {
+		remove_inode_hash(bdev->bd_inode);
+		bdput(bdev);
+	}
 	percpu_ref_kill(&part->ref);
 }
 
-- 
2.37.3