SoC/2017

Revision as of 09:54, 27 August 2017 by Dimgrav (talk | contribs) (About)

Improve libcli/dns

Samba comes with its own asynchronous DNS parser framework developed for the internal DNS server. Basic calls have been implemented for a client-side library as well, but a more fleshed out implementation would be needed. The goal of this project is to implement more high-level calls handling DNS requests, such as UDP/TCP switchover and client-side GSS-TSIG cryptography. A test suite excercising all the functions is required and can be used to cross-check and complement the existing DNS server tests already shipped by Samba. This testsuite should use cmocka.

  • Difficulty: Medium
  • Language(s): C
  • Mentors: Kai Blin, David Disseldorp
  • Student: Dimitris Gravanis


Project Information


Client-side DNS call handling with GSS-TSIG

Unix SMB/CIFS implementation

Dimitrios Gravanis (C) 2017

Based on the existing work by Samba Team


About

For the Samba AD DC, libcli/dns is a library that allows the handling of DNS calls (send/receive requests) and generates GSS-TSIG type encryption signature for signed packets, to accomodate encrypted client-server communication.

The project goal was to enhance client-server communication, by implementing TCP request send/receive handling and sign client-side packets with GSS-TSIG signatures, to provide security.

It consists of its respective function and structure libraries, that provide definitions for client-side functionality.


Initial libcli/dns structure

  • dns.c
  • dns.h
  • libdns.h
  • wscript_build


Project libcli/dns structure:

  • cli-fn/
    • README.md
    • client_crypto.c
    • dns_tcp.c
    • dns_udp.c
  • cmocka-tests/
    • test-fn
      • cli_crypto_test.c
      • dns_tcp_test.c
      • dns_udp_test.c
      • wscript
    • README.md
    • cli_tests.c
    • wscript_build
  • README.md
  • cli_dns.c
  • dns.h
  • libtcp.h
  • libudp.h
  • libtsig.h
  • libwrap.h
  • wrap_cli.c
  • wscript_build


For more information on the project goals, read the GSoC proposal here.

The project timeline and development journal is documented in its dedicated blogspot.


Repositories

  • Individual project "mirror" repository (requires Samba source code for integration - NOT STANDALONE): link
  • Samba GitHub repository: link
  • Personal samba-team/samba fork with integrated changes in libcli/dns: link


Commits

  • dimgrav/samba (fork): link
DNS Client (with wrapper support)

Handles TCP and UDP requests.

The client may use either TCP or UDP protocols to send a DNS name request to the server, then handle the reception of the appropriate server response.

Features:

  • UDP request send/receive
  • TCP request send/receive
  • GSS-TSIG generation
  • DNS name packet parsing and signing

The library consists of cli_dns.c, that includes functions, and dns.h, libtcp.h, libtsig.h, libudp.h, that provide definitions and structures.


Wrapping

wrap_cli.c provides multiple wrapping of the above functionality, to hide buffer creation, DNS packet parsing and signature generation. Definitions of the wrapped functions are provided in libwrap.h.


Test suite

In cmocka-tests, cli_tests.c provides a test suite for the complete client-side functionality, as defined by the functions in libcli/dns/cli_dns.c. The API used for unit testing is Cmocka.

In cmocka-tests/test-fn, there are individual unit tests for every feature library in libcli/dns. All of these tests are incorporated in cmocka-tests/cli_tests.c These tests can be built by using waf-samba and the intended configuration in cmocka-tests/test-fn/wscript. The purpose of these test suites is to facilitate future additions and features in Samba client-side code, without the necessity to integrate them directly to cli_dns.c, thus making changes easier to test and encourage future contributions.


To-do list

Tests

  1. cmocka-tests/test-fn: wscript needs to be properly configured to enable standalone test builds for the feature libraries.
  2. cmocka-tests/cli_tests.c: TCP/UDP callbacks may be additionally tested for internal error output in their respective test functions.