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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Mikulas Patocka <mpatocka@redhat.com>,
        Mike Snitzer <snitzer@redhat.com>
Subject: [PATCH 5.12 094/127] dm snapshot: fix crash with transient storage and zero chunk size
Date:   Mon, 24 May 2021 17:26:51 +0200
Message-Id: <20210524152338.035594414@linuxfoundation.org>
In-Reply-To: <20210524152334.857620285@linuxfoundation.org>
References: <20210524152334.857620285@linuxfoundation.org>
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From: Mikulas Patocka <mpatocka@redhat.com>

commit c699a0db2d62e3bbb7f0bf35c87edbc8d23e3062 upstream.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/md/dm-snap.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1407,6 +1407,7 @@ static int snapshot_ctr(struct dm_target
 
 	if (!s->store->chunk_size) {
 		ti->error = "Chunk size not set";
+		r = -EINVAL;
 		goto bad_read_metadata;
 	}