firewire: cdev: disallow receive packets without header

In receive contexts, reject packets with header_length==0.  This would
be an instruction to queue zero packets which would not make sense.

This prevents a division by zero in the OHCI driver.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/core-cdev.c

@@ -968,7 +968,8 @@ static int ioctl_queue_iso(struct client *client, union ioctl_arg *arg)
 			if (ctx->header_size == 0) {
 				if (u.packet.header_length > 0)
 					return -EINVAL;
-			} else if (u.packet.header_length % ctx->header_size != 0) {
+			} else if (u.packet.header_length == 0 ||
+				   u.packet.header_length % ctx->header_size != 0) {
 				return -EINVAL;
 			}
 			header_length = 0;