Multiple integer overflows in the XML_GetBuffer function in Expat 
through 2.1.0, allow remote attackers to cause a denial of service 
(heap-based buffer overflow) or possibly have unspecified other 
impact via crafted XML data.

CVSSv2:  (AV:N/AC:M/Au:N/C:P/I:P/A:P)

CVE: CVE-2015-1283
Upstream-Status: Backport

Signed-off-by: Eric Rahm <erahm@mozilla.com>
Signed-off-by: Zhixiong Chi <zhixiong.chi@windirver.com>

Index: expat-2.1.0/lib/xmlparse.c
===================================================================
--- expat-2.1.0.orig/lib/xmlparse.c	2012-03-11 13:13:12.000000000 +0800
+++ expat-2.1.0/lib/xmlparse.c	2015-12-23 10:29:07.347361329 +0800
@@ -1678,6 +1678,12 @@
 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 @@
   }
 
   if (len > bufferLim - bufferEnd) {
-    /* FIXME avoid integer overflow */
     int neededSize = len + (int)(bufferEnd - bufferPtr);
+/* 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 @@
         bufferSize = INIT_BUFFER_SIZE;
       do {
         bufferSize *= 2;
-      } while (bufferSize < neededSize);
+/* BEGIN MOZILLA CHANGE (prevent infinite loop on overflow) */
+      } 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;