From: Ming Lei <ming.lei@redhat.com>
Date: Mon, 21 Dec 2020 04:33:35 +0000 (+0800)
Subject: block: fix use-after-free in disk_part_iter_next
X-Git-Tag: Ubuntu-5.11.0-11.12~671^2~14
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=aebf5db917055b38f4945ed6d621d9f07a44ff30;p=mirror_ubuntu-hirsute-kernel.git

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;
 	}