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 --- block/partition-generic.c | 6 ++++++ 1 file changed, 6 insertions(+)

diff --git a/block/partition-generic.c b/block/partition-generic.c index db57cced9b98..68bd04d044b9 100644 --- a/block/partition-generic.c +++ b/block/partition-generic.c @@ -270,6 +270,7 @@ void delete_partition(struct gendisk *disk, int partno) 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; @@ -283,6 +284,11 @@ void delete_partition(struct gendisk *disk, int partno) kobject_put(part->holder_dir); device_del(part_to_dev(part));

+ bdev = bdget(part_devt(part)); + if (bdev) { + remove_inode_hash(bdev->bd_inode); + bdput(bdev); + } hd_struct_kill(part); }