[PATCH 5.10 090/221] dm ioctl: fix out of bounds array access when no devices

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 <redacted>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <redacted>
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

@@ -529,7 +529,7 @@ static int list_devices(struct file *fil
 	 * Grab our output buffer.
 	 */
 	nl = orig_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;
 	}