The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From aebf5db917055b38f4945ed6d621d9f07a44ff30 Mon Sep 17 00:00:00 2001

From: Ming Lei ming.lei@redhat.com Date: Mon, 21 Dec 2020 12:33:35 +0800 Subject: [PATCH] block: fix use-after-free in disk_part_iter_next

Make sure that bdgrab() is done on the 'block_device' instance before referring to it for avoiding use-after-free.

Cc: stable@vger.kernel.org Reported-by: syzbot+825f0f9657d4e528046e@syzkaller.appspotmail.com Signed-off-by: Ming Lei ming.lei@redhat.com Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/block/genhd.c b/block/genhd.c index 73faec438e49..419548e92d82 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -246,15 +246,18 @@ struct block_device *disk_part_iter_next(struct disk_part_iter *piter) part = rcu_dereference(ptbl->part[piter->idx]); if (!part) continue; + piter->part = bdgrab(part); + if (!piter->part) + continue; if (!bdev_nr_sectors(part) && !(piter->flags & DISK_PITER_INCL_EMPTY) && !(piter->flags & DISK_PITER_INCL_EMPTY_PART0 && - piter->idx == 0)) + piter->idx == 0)) { + bdput(piter->part); + piter->part = NULL; continue; + }

- piter->part = bdgrab(part); - if (!piter->part) - continue; piter->idx += inc; break; }