libxml: Fix undefined behavior due to integer overflow when parsing uri port.

third_party/libxml/src/uri.c

Index: third_party/libxml/src/uri.c
diff --git a/third_party/libxml/src/uri.c b/third_party/libxml/src/uri.c
index ff47abbecb1d0fc0f4161d3596e2840a6970ffaa..3e51255e61cd85a79eb4955dffea496d09f3c687 100644
--- a/third_party/libxml/src/uri.c
+++ b/third_party/libxml/src/uri.c
@@ -314,7 +314,7 @@ xmlParse3986Query(xmlURIPtr uri, const char **str)
  * @uri:  pointer to an URI structure
  * @str:  the string to analyze
  *
- * Parse a port  part and fills in the appropriate fields
+ * Parse a port part and fills in the appropriate fields
  * of the @uri structure
  *
  * port          = *DIGIT
@@ -327,13 +327,13 @@ xmlParse3986Port(xmlURIPtr uri, const char **str)
     const char *cur = *str;
 
     if (ISA_DIGIT(cur)) {
-	if (uri != NULL)
-	    uri->port = 0;
+	unsigned port = 0; /* unsigned for defined overflow behavior */
 	while (ISA_DIGIT(cur)) {
-	    if (uri != NULL)
-		uri->port = uri->port * 10 + (*cur - '0');
+	    port = port * 10 + (*cur - '0');
 	    cur++;
 	}
+	if (uri != NULL)
+	    uri->port = port & INT_MAX; /* port value modulo INT_MAX+1 */
 	*str = cur;
 	return(0);
     }