From c699a0db2d62e3bbb7f0bf35c87edbc8d23e3062 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Mon, 10 May 2021 14:49:05 -0400
Subject: [PATCH] dm snapshot: fix crash with transient storage and zero chunk
 size
Git-commit: c699a0db2d62e3bbb7f0bf35c87edbc8d23e3062
Patch-mainline: v5.13-rc3
References: git-fixes

The following commands will crash the kernel:

modprobe brd rd_size=1048576
dmsetup create o --table "0 `blockdev --getsize /dev/ram0` snapshot-origin /dev/ram0"
dmsetup create s --table "0 `blockdev --getsize /dev/ram0` snapshot /dev/ram0 /dev/ram1 N 0"

The reason is that when we test for zero chunk size, we jump to the label
bad_read_metadata without setting the "r" variable. The function
snapshot_ctr destroys all the structures and then exits with "r == 0". The
kernel then crashes because it falsely believes that snapshot_ctr
succeeded.

In order to fix the bug, we set the variable "r" to -EINVAL.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Coly Li <colyli@suse.de>

---
 drivers/md/dm-snap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 2a51ddd840b4..b8e4d31124ea 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1408,6 +1408,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
 	if (!s->store->chunk_size) {
 		ti->error = "Chunk size not set";
+		r = -EINVAL;
 		goto bad_read_metadata;
 	}
 
-- 
2.35.3