xen: xenbus_dev_frontend: Really return response string

xenbus_command_reply() did not actually copy the response string and
leaked stack content instead.

Fixes: 9a6161f ("xen: return xenstore command failures via response instead of rc")
Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/xenbus/xenbus_dev_frontend.c

@@ -403,7 +403,7 @@ static int xenbus_command_reply(struct xenbus_file_priv *u,
 {
 	struct {
 		struct xsd_sockmsg hdr;
-		const char body[16];
+		char body[16];
 	} msg;
 	int rc;
 
@@ -412,6 +412,7 @@ static int xenbus_command_reply(struct xenbus_file_priv *u,
 	msg.hdr.len = strlen(reply) + 1;
 	if (msg.hdr.len > sizeof(msg.body))
 		return -E2BIG;
+	memcpy(&msg.body, reply, msg.hdr.len);
 
 	mutex_lock(&u->reply_mutex);
 	rc = queue_reply(&u->read_buffers, &msg, sizeof(msg.hdr) + msg.hdr.len);