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
Client-side DNS call handling with GSS-TSIG
Unix SMB/CIFS implementation
Dimitrios Gravanis (C) 2017
Based on the existing work by Samba Team
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
Project libcli/dns structure:
For more information on the project goals, read the GSoC proposal here.
The project timeline and development journal is documented in its dedicated blogspot.
- 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
- 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.
- 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.
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.
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.
- cmocka-tests/test-fn: wscript needs to be properly configured to enable standalone test builds for the feature libraries.
- cmocka-tests/cli_tests.c: TCP/UDP callbacks may be additionally tested for internal error output in their respective test functions.