compositor-x11: fix title overflow in x11_backend_create_output

sprintf can overflow the fixed length title which is char[32]. This
patch change title to dynamically allocated char array using asprintf or
strdup. If one of them fail we leave returning NULL to indicate the
failure.

Signed-off-by: Benoit Gschwind <gschwind@gnu-log.net>
Reviewed-by: Yong Bakos <ybakos@humanoriented.com>
Tested-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
Signed-off-by: Daniel Stone <daniels@collabora.com>

libweston/compositor-x11.c

@@ -782,7 +782,7 @@ x11_backend_create_output(struct x11_backend *b, int x, int y,
 {
 	static const char name[] = "Weston Compositor";
 	static const char class[] = "weston-1\0Weston Compositor";
-	char title[32];
+	char *title = NULL;
 	struct x11_output *output;
 	xcb_screen_t *screen;
 	struct wm_normal_hints normal_hints;
@@ -800,11 +800,6 @@ x11_backend_create_output(struct x11_backend *b, int x, int y,
 	output_width = width * scale;
 	output_height = height * scale;
 
-	if (configured_name)
-		sprintf(title, "%s - %s", name, configured_name);
-	else
-		strcpy(title, name);
-
 	if (!no_input)
 		values[0] |=
 			XCB_EVENT_MASK_KEY_PRESS |
@@ -871,9 +866,24 @@ x11_backend_create_output(struct x11_backend *b, int x, int y,
 	}
 
 	/* Set window name.  Don't bother with non-EWMH WMs. */
+	if (configured_name) {
+		if (asprintf(&title, "%s - %s", name, configured_name) < 0)
+			title = NULL;
+	} else {
+		title = strdup(name);
+	}
+
+	if (title) {
 		xcb_change_property(b->conn, XCB_PROP_MODE_REPLACE, output->window,
 				    b->atom.net_wm_name, b->atom.utf8_string, 8,
 				    strlen(title), title);
+		free(title);
+	} else {
+		xcb_destroy_window(b->conn, output->window);
+		free(output);
+		return NULL;
+	}
+
 	xcb_change_property(b->conn, XCB_PROP_MODE_REPLACE, output->window,
 			    b->atom.wm_class, b->atom.string, 8,
 			    sizeof class, class);