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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>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Mike Snitzer <snitzer@redhat.com>,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Subject: [PATCH 4.4 175/190] dm ioctl: fix out of bounds array access when no devices
Date:   Thu, 20 May 2021 11:23:59 +0200
Message-Id: <20210520092107.957446529@linuxfoundation.org>
In-Reply-To: <20210520092102.149300807@linuxfoundation.org>
References: <20210520092102.149300807@linuxfoundation.org>
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From: Mikulas Patocka <mpatocka@redhat.com>

commit 4edbe1d7bcffcd6269f3b5eb63f710393ff2ec7a upstream.

If there are not any dm devices, we need to zero the "dev" argument in
the first structure dm_name_list. However, this can cause out of
bounds write, because the "needed" variable is zero and len may be
less than eight.

Fix this bug by reporting DM_BUFFER_FULL_FLAG if the result buffer is
too small to hold the "nl->dev" value.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
[iwamatsu: Adjust context]
Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/md/dm-ioctl.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -524,7 +524,7 @@ static int list_devices(struct dm_ioctl
 	 * Grab our output buffer.
 	 */
 	nl = get_result_buffer(param, param_size, &len);
-	if (len < needed) {
+	if (len < needed || len < sizeof(nl->dev)) {
 		param->flags |= DM_BUFFER_FULL_FLAG;
 		goto out;
 	}