Apply a patch to prevent an integer overflow in expat.

third_party/expat/files/lib/xmlparse.c

Index: third_party/expat/files/lib/xmlparse.c
diff --git a/third_party/expat/files/lib/xmlparse.c b/third_party/expat/files/lib/xmlparse.c
index f35aa36ba8a7fce3bae90f31b20354435b15d2f2..ede7b5bb6673eed3fecbe83056da3a906cdafe41 100644
--- a/third_party/expat/files/lib/xmlparse.c
+++ b/third_party/expat/files/lib/xmlparse.c
@@ -1678,6 +1678,12 @@ XML_ParseBuffer(XML_Parser parser, int len, int isFinal)
 void * XMLCALL
 XML_GetBuffer(XML_Parser parser, int len)
 {
+/* BEGIN MOZILLA CHANGE (sanity check len) */
+  if (len < 0) {
+    errorCode = XML_ERROR_NO_MEMORY;
+    return NULL;
+  }
+/* END MOZILLA CHANGE */
   switch (ps_parsing) {
   case XML_SUSPENDED:
     errorCode = XML_ERROR_SUSPENDED;
@@ -1689,8 +1695,13 @@ XML_GetBuffer(XML_Parser parser, int len)
   }
 
   if (len > bufferLim - bufferEnd) {
-    /* FIXME avoid integer overflow */
     int neededSize = len + (int)(bufferEnd - bufferPtr);

[wrowe, 2015/08/06 18:45:51]

Moving the patch below up one line (prior to int neededSize) will restore this
file as C89 compatible, with no side effect.

[daniel.gutson, 2015/09/01 13:17:04]

May I ask why are you using signed types? A size should always be positive;
moreover, the type should be size_t

+/* BEGIN MOZILLA CHANGE (sanity check neededSize) */
+    if (neededSize < 0) {
+      errorCode = XML_ERROR_NO_MEMORY;
+      return NULL;
+    }
+/* END MOZILLA CHANGE */
 #ifdef XML_CONTEXT_BYTES
     int keep = (int)(bufferPtr - buffer);
 
@@ -1719,7 +1730,15 @@ XML_GetBuffer(XML_Parser parser, int len)
         bufferSize = INIT_BUFFER_SIZE;
       do {
         bufferSize *= 2;
-      } while (bufferSize < neededSize);
+/* BEGIN MOZILLA CHANGE (prevent infinite loop on overflow) */

[VZ, 2015/07/26 22:35:06]

This change doesn't seem to be ideal as it will result in returning an
out-of-memory error for neededSize just slightly larger than INT_MAX/2 which is
not that much under 32 bit architectures.

Wouldn't it be better to just set bufferSize to neededSize if it's big enough
(e.g. >= INT_MAX/2)?

+      } while (bufferSize < neededSize && bufferSize > 0);
+/* END MOZILLA CHANGE */
+/* BEGIN MOZILLA CHANGE (sanity check bufferSize) */
+      if (bufferSize <= 0) {
+        errorCode = XML_ERROR_NO_MEMORY;
+        return NULL;
+      }
+/* END MOZILLA CHANGE */
       newBuf = (char *)MALLOC(bufferSize);
       if (newBuf == 0) {
         errorCode = XML_ERROR_NO_MEMORY;