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: v4.4.252~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a09652089d496a4ecb925e2cb95a6523f22ae538;p=thirdparty%2Fkernel%2Fstable.git

block: fix use-after-free in disk_part_iter_next

commit aebf5db917055b38f4945ed6d621d9f07a44ff30 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/block/genhd.c b/block/genhd.c
index 3032453a89e63..0b8c65e51adf4 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -158,14 +158,17 @@ struct hd_struct *disk_part_iter_next(struct disk_part_iter *piter)
 		part = rcu_dereference(ptbl->part[piter->idx]);
 		if (!part)
 			continue;
+		get_device(part_to_dev(part));
+		piter->part = part;
 		if (!part_nr_sects_read(part) &&
 		    !(piter->flags & DISK_PITER_INCL_EMPTY) &&
 		    !(piter->flags & DISK_PITER_INCL_EMPTY_PART0 &&
-		      piter->idx == 0))
+		      piter->idx == 0)) {
+			put_device(part_to_dev(part));
+			piter->part = NULL;
 			continue;
+		}
 
-		get_device(part_to_dev(part));
-		piter->part = part;
 		piter->idx += inc;
 		break;
 	}