[cff] Integer overflow.

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=2089

* src/cff/cffload.c (cff_blend_doBlend): User OVERFLOW_ADD_INT32.

ChangeLog

@@ -1,3 +1,13 @@
+2017-06-05  Werner Lemberg  <wl@gnu.org>
+
+	[cff] Integer overflow.
+
+	Reported as
+
+	  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=2089
+
+	* src/cff/cffload.c (cff_blend_doBlend): User OVERFLOW_ADD_INT32.
+
 2017-06-04  Werner Lemberg  <wl@gnu.org>
 
 	[cff, truetype] Integer overflows.

src/cff/cffload.c

@@ -1352,9 +1352,12 @@
       sum = cff_parse_num( parser, &parser->stack[i + base] ) * 65536;
 
       for ( j = 1; j < blend->lenBV; j++ )
-        sum += FT_MulFix( *weight++,
-                          cff_parse_num( parser,
-                                         &parser->stack[delta++] ) * 65536 );
+        sum = OVERFLOW_ADD_INT32(
+                sum,
+                FT_MulFix(
+                  *weight++,
+                  cff_parse_num( parser,
+                                 &parser->stack[delta++] ) * 65536 ) );
 
       /* point parser stack to new value on blend_stack */
       parser->stack[i + base] = subFont->blend_top;