Cairo: Fix Denial-of-Service Attack due to Logical Problem in Program

https://bugs.freedesktop.org/show_bug.cgi?id=100763

CVE: CVE-2017-7475
Upstream-Status: Submitted

Signed-off-by: Fan Xin <fan.xin@jp.fujitsu.com>

Index: cairo-1.15.4/src/cairo-ft-font.c
===================================================================
--- cairo-1.15.4.orig/src/cairo-ft-font.c
+++ cairo-1.15.4/src/cairo-ft-font.c
@@ -1149,7 +1149,7 @@ _get_bitmap_surface (FT_Bitmap		     *bi
     width = bitmap->width;
     height = bitmap->rows;
 
-    if (width == 0 || height == 0) {
+    if (width == 0 || height == 0 || bitmap->buffer == NULL) {
 	*surface = (cairo_image_surface_t *)
 	    cairo_image_surface_create_for_data (NULL, format, 0, 0, 0);
 	return (*surface)->base.status;
