Fix overflow when comparing two ints by promoting the sum to 64-bits.

drWulf · andi34 · commit 968454f69b9c · 2016-06-07T19:00:28.000+02:00
R=reed@google.com, scroggo@google.com Author: djsollen@google.com Review URL: https://codereview.chromium.org/505153003 bug: 17265206 Change-Id: Id74fc6d165b55258dbd980d9d36afe1377e7a162
diff --git a/src/images/SkImageDecoder_libico.cpp b/src/images/SkImageDecoder_libico.cpp
@@ -150,7 +150,8 @@ bool SkICOImageDecoder::onDecode(SkStream* stream, SkBitmap* bm, Mode mode)
     //int fakeBitCount = read2Bytes(buf, 12 + choice*16); //should be real - usually 0
     const size_t size = read4Bytes(buf, 14 + choice*16);           //matters?
     const size_t offset = read4Bytes(buf, 18 + choice*16);
-    if ((offset + size) > length) {
+    // promote the sum to 64-bits to avoid overflow
+    if (((uint64_t)offset + size) > length) {
         return false;
     }
 

Original file line number	Diff line number	Diff line change
`@@ -150,7 +150,8 @@ bool SkICOImageDecoder::onDecode(SkStream* stream, SkBitmap* bm, Mode mode)`
`150`	`150`	`//int fakeBitCount = read2Bytes(buf, 12 + choice*16); //should be real - usually 0`
`151`	`151`	`const size_t size = read4Bytes(buf, 14 + choice*16); //matters?`
`152`	`152`	`const size_t offset = read4Bytes(buf, 18 + choice*16);`
`153`		`- if ((offset + size) > length) {`
	`153`	`+ // promote the sum to 64-bits to avoid overflow`
	`154`	`+ if (((uint64_t)offset + size) > length) {`
`154`	`155`	`return false;`
`155`	`156`	`}`
`156`	`157`