[CVE-2016-3190] Fix CVE issue

The fill_xrgb32_lerp_opaque_spans() allows remote attackers to cause a denial of service
(out-of-bounds read and application crash) via a negative span length.

Change-Id: Iebce4b5d6fd9ea6435cc88875f314fb60d81bddd

diff --git a/src/cairo-image-compositor.c b/src/cairo-image-compositor.c
index e343d27..1822584 100644 (file)
--- a/src/cairo-image-compositor.c
+++ b/src/cairo-image-compositor.c
@@ -2370,7 +2370,7 @@ _fill_xrgb32_lerp_opaque_spans (void *abstract_renderer, int y, int h,
                        do {
                            int len = spans[1].x - spans[0].x;
                            uint32_t *d = (uint32_t*)(r->u.fill.data + r->u.fill.stride*yy + spans[0].x*4);
-                           while (len--)
+                           while (len-- > 0)
                                *d++ = r->u.fill.pixel;
                            yy++;
                        } while (--hh);
@@ -2380,7 +2380,7 @@ _fill_xrgb32_lerp_opaque_spans (void *abstract_renderer, int y, int h,
                    do {
                        int len = spans[1].x - spans[0].x;
                        uint32_t *d = (uint32_t *)(r->u.fill.data + r->u.fill.stride*yy + spans[0].x*4);
-                       while (len--) {
+                       while (len-- > 0) {
                            *d = lerp8x4 (r->u.fill.pixel, a, *d);
                            d++;
                        }