lib: Prevent integer overflow on m_groupSize in function doProlog (CV…

…E-2021-46143)

expat/lib/xmlparse.c

@@ -5046,6 +5046,11 @@ doProlog(XML_Parser parser, const ENCODING *enc, const char *s, const char *end,
       if (parser->m_prologState.level >= parser->m_groupSize) {
         if (parser->m_groupSize) {
           {
+            /* Detect and prevent integer overflow */
+            if (parser->m_groupSize > (unsigned int)(-1) / 2u) {
+              return XML_ERROR_NO_MEMORY;
+            }
+
             char *const new_connector = (char *)REALLOC(
                 parser, parser->m_groupConnector, parser->m_groupSize *= 2);
             if (new_connector == NULL) {
@@ -5056,6 +5061,16 @@ doProlog(XML_Parser parser, const ENCODING *enc, const char *s, const char *end,
           }
 
           if (dtd->scaffIndex) {
+            /* Detect and prevent integer overflow.
+             * The preprocessor guard addresses the "always false" warning
+             * from -Wtype-limits on platforms where
+             * sizeof(unsigned int) < sizeof(size_t), e.g. on x86_64. */
+#if UINT_MAX >= SIZE_MAX
+            if (parser->m_groupSize > (size_t)(-1) / sizeof(int)) {
+              return XML_ERROR_NO_MEMORY;
+            }
+#endif
+
             int *const new_scaff_index = (int *)REALLOC(
                 parser, dtd->scaffIndex, parser->m_groupSize * sizeof(int));
             if (new_scaff_index == NULL)