Reject names that are longer than 255 characters, to avoid problems with...

Reject names that are longer than 255 characters, to avoid problems with strict or buggy DNS server implementations. (Patch from the Google tree)

ares/ares_mkquery.c

@@ -108,6 +108,23 @@ int ares_mkquery(const char *name, int dnsclass, int type, unsigned short id,
   if (*name && *(p - 1) != '.')
     len++;
 
+  /* Immediately reject names that are longer than the maximum of 255
+   * bytes that's specified in RFC 1035 ("To simplify implementations,
+   * the total length of a domain name (i.e., label octets and label
+   * length octets) is restricted to 255 octets or less."). We aren't
+   * doing this just to be a stickler about RFCs. For names that are
+   * too long, 'dnscache' closes its TCP connection to us immediately
+   * (when using TCP) and ignores the request when using UDP, and
+   * BIND's named returns ServFail (TCP or UDP). Sending a request
+   * that we know will cause 'dnscache' to close the TCP connection is
+   * painful, since that makes any other outstanding requests on that
+   * connection fail. And sending a UDP request that we know
+   * 'dnscache' will ignore is bad because resources will be tied up
+   * until we time-out the request.
+   */
+  if (len > MAXCDNAME)
+    return ARES_EBADNAME;
+
   *buflen = len + HFIXEDSZ + QFIXEDSZ;
   *buf = malloc(*buflen);
   if (!*buf)