[PATCH 5.4 4/9] block: unhash blkdev part inode when the part is deleted

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: 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 big 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.

Backported from the following 5.10.y commit:

5f2f77560591 ("block: unhash blkdev part inode when the part is deleted")

Reported-by: Shiwei Cui <cuishw@inspur.com>
Tested-by: Shiwei Cui <cuishw@inspur.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 block/partition-generic.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -272,6 +272,7 @@ void delete_partition(struct gendisk *di
 	struct disk_part_tbl *ptbl =
 		rcu_dereference_protected(disk->part_tbl, 1);
 	struct hd_struct *part;
+	struct block_device *bdev;
 
 	if (partno >= ptbl->len)
 		return;
@@ -292,6 +293,12 @@ void delete_partition(struct gendisk *di
 	 * "in-use" until we really free the gendisk.
 	 */
 	blk_invalidate_devt(part_devt(part));
+
+	bdev = bdget(part_devt(part));
+	if (bdev) {
+		remove_inode_hash(bdev->bd_inode);
+		bdput(bdev);
+	}
 	hd_struct_kill(part);
 }