[bind10-dev] MessageTooShort and SERVFAIL

[JINMEI Tatuya / 神明達哉]

At Wed, 07 Nov 2012 14:44:27 +0000,
Francis Dupont <fdupont at isc.org> wrote:

> On a request shorter than a DNS message header, Message::fromWire
> raises the MessageTooShort exception which is translated (as it is
> not a DNSProtocolError) into a SERVFAIL response. IMHO it should
> be more a FORMERR (as bind 9 does)?

Did you confirm the behavior by actually seeing the response in the
wire, or is it based on code inspection?  I believe in this case it
results in silent discard:

    // First, check the header part.  If we fail even for the base header,
    // just drop the message.
    try {
        message.parseHeader(request_buffer);
	...
    } catch (const Exception& ex) {
        LOG_DEBUG(auth_logger, DBG_AUTH_DETAIL, AUTH_HEADER_PARSE_FAIL)
                  .arg(ex.what());
        impl_->resumeServer(server, message, stats_attrs, false);
        return;
    }

And, in fact, whether it's SERVFAIL or FORMERR, it wouldn't even make
sense to try sending any response if it doesn't even have a complete
header.

---
JINMEI, Tatuya