[Bug 54998] New: DnsQuery(DNS_TYPE_SRV) fails to parse some of the server answers

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=54998

Bug ID: 54998
           Summary: DnsQuery(DNS_TYPE_SRV) fails to parse some of the
                    server answers
           Product: Wine
           Version: 8.9
          Hardware: x86-64
                OS: Linux
            Status: NEW
          Keywords: patch, source
          Severity: normal
          Priority: P2
         Component: dnsapi
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

Created attachment 74551
  --> https://bugs.winehq.org/attachment.cgi?id=74551
patch

An application that uses ActiveDs sometimes fails to get domain DC using
DsGetDcNameW(). That's caused by a failing call to
DnsQuery("_ldap._tcp.dc._msdcs.domain.com", DNS_TYPE_SRV)
which in turn fails because DnsExtractRecordsFromMessage_UTF8() fails to parse
some of the server answers.

It looks like this happens because in the DNS_TYPE_SRV record name is the last
element, and in that case get_name() uses wrong boundary check and returns
NULL.

Just in case it will be useful I'm attaching my version of the fix with some
tests.

It seems that skip_name() also uses wrong boundary check, however usually some
other data follows the skipped name, so it currently doesn't cause failures.