~samiam/MaraDNS

MaraDNS is a small open source DNS server
e008519f — Sam Trenholme 2 months ago
Automatic update of DwRandPrime.h on 2024-05-10
e272277f — Sam Trenholme a month ago
Sam Discusses Lunacy: 2024-05-16
ab6a8411 — Sam Trenholme 2 months ago
Sam Discusses Lunacy: 2024-04-27 version

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https://git.sr.ht/~samiam/MaraDNS
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git@git.sr.ht:~samiam/MaraDNS

You can also use your local clone with git send-email.

#What is MaraDNS

MaraDNS is a free open-source computer program written by Sam Trenholme.

MaraDNS implements the Domain Name System (DNS), an essential internet service. MaraDNS is open source software: This means that anyone is free to download, use, and modify the program free of charge, as per its license.

People like MaraDNS because it’s small, lightweight, easy to set up, and remarkably secure. It’s also cross platform — the program runs both in Windows and in UNIX clones.

MaraDNS has a web page and blog at https://maradns.samiam.org. MaraDNS’s Git tree is hosted at GitHub, GitLab, Bitbucket, Codeberg, and SourceHut (Please use GitHub discussions for bug reports).

#ABOUT

MaraDNS is a small and lightweight cross-platform open-source DNS server. The server is remarkably easy to configure for someone comfortable editing text configuration files. MaraDNS is released under a BSD license.

I initially wrote MaraDNS while I was a college student and a travelling English teacher during the first 2000s decade.

Since the COVID-19 pandemic, I have been actively adding new features to MaraDNS, most notably the new coLunacyDNS service which uses Lua to customize DNS replies.

Versions of some MaraDNS programs compiled as Windows binaries (without needing Cygwin or another POSIX emulation library) are in the folder maradns-win32/

#Building MaraDNS

To build MaraDNS, one needs a POSIX system with:

  • A POSIX compatible shell
  • A POSIX compatible implementation of make, which has the POSIX202X feature of allowing a make target to have a / in it.
  • Other standard POSIX utilities (awk, etc.)
  • A current C compiler which can support, via stdint, 8-bit, 16-bit, 32-bit, and 64-bit sized integers.
  • A POSIX C library with both POSIX and Berkeley socket support.

(To build some of the documentation, the non-standard but widely available unix2dos text conversion utility is used.)

Then, do this:

./configure
CC=cc # Change this to gcc/clang/tcc as desired
export CC
make

Note that most implementations of make will set $CC to cc if it’s not already set, but the POSIX spec says that the default value should be c99, a compiler which will not compile MaraDNS. A POSIX program like MaraDNS will not compile with a strictly ISO compliant C compiler (the POSIX system calls will fail to compile). However, all of the C programs here compile with gcc, clang, and tcc, and should compile with any reasonable POSIX C compiler.

All of these are very standard tools which are included with the vast majority of Linux and BSD distributions; packages usually have names like:

  • clang (which uses llvm) for the C compiler
  • libc-dev for the development C standard library, which will have sockets
  • make for make; if one does not wish to use GNU make (the Linux standard), other make implementations exist, e.g. https://github.com/samboy/maramake
  • POSIX compatible implementations of sh, awk, and other utilities are also almost always included as part of a Linux base install.

MaraDNS successfully compiles with gcc, clang, and tcc; it successfully builds with GNU make, bmake, pdpmake (as long as non-POSIX and/or POSIX202X extensions are enabled and CC has the value cc), and maramake. The version of make used to compile MaraDNS needs to have the command name make. MaraDNS compiles and runs with both Busybox versions of the core POSIX utilities and GNU coreutils.

#Supported OSes

MaraDNS is built and runs on Ubuntu 22.04 as of late 2022.

I currently use Ubuntu 22.04 to develop MaraDNS, both Ubuntu 22.04 and Alpine Linux 3.14 to test that MaraDNS builds and passes all automated regressions, and a Windows XP virtual machine to make the Windows binaries.

#Please use systemd

While MaraDNS does have scripts for starting up MaraDNS at system boot time on sysvinit systems, these scripts are no longer fully supported, since most major Linux distributions have moved on to systemd, which is a lot better than the older sysvinit process for starting up the MaraDNS related services.

While make install is only guaranteed to get MaraDNS to start up at system boot time on Ubuntu 22.04, it should do the right thing in Rocky Linux, Debian, RedHat, CentOS, Fedora, and other Linux distributions which use systemd.

There is some scaffolding for getting MaraDNS to run without systemd. There is a helper, duende, to make MaraDNS a daemon on systems with classic *NIX style init. While, with systemd, it’s no longer needed to use this Duende helper, I will keep Duende around for sysvinit and some level of OpenRC compatibility. There are also shell scripts for starting MaraDNS on sysvinit systems which may or may not work with other init systems.

systemd handles the daemonization of the MaraDNS services the way duende does (did?) on sysvinit and similar systems. The systemd way is much simpler at the development level, since systemd now handles a lot of complexity the old init systems forced networking services to handle.

#Important note for Windows users

Users of Microsoft Windows are better off downloading a prebuilt Windows binary: http://maradns.samiam.org/download.html (or, look in the folder maradns-win32 here) Be sure to download the file with the .zip extension.

Only Deadwood and coLunacyDNS binaries are provided.

Deadwood has passed Y2038 tests in Windows 10.

#What is DNS

The internet uses numbers, not names, to find computers. DNS is the internet’s directory service: It takes a name, like “www.maradns.org”, and converts that name in to an “IP” number that your computer can use to connect to www.maradns.org.

DNS is one of these things many take for granted that is essential to using today’s internet. Without DNS, the internet breaks. It is critical that a DNS server keeps the internet working in a secure and stable manner.

#MaraDNS' History

MaraDNS was started in 2001 in response to concerns that there were only two freely available DNS servers (BIND and DjbDNS) at the time. MaraDNS 1.0 was released in mid-2002, MaraDNS 1.2 was released in late 2005, MaraDNS 2.0 was released in the fall of 2010, and MaraDNS had a version number jump up to 3.3 in 2019 in order to have the same version number as Deadwood.

MaraDNS 1.0 used a recursive DNS server that was implemented rather quickly and had difficult-to-maintain code. This code was completely rewritten for the MaraDNS 2.0 release, which now uses a separate recursive DNS server.

#Overview

MaraDNS 3.5 consists of three primary components: A UDP-only authoritative DNS server for hosting domains, a UDP recursive DNS server called Deadwood for finding domains on the internet, and a Lua-powered DNS server called coLunacyDNS. MaraDNS’ recursive DNS server Deadwood shares no code with MaraDNS’ authoritative DNS server.

coLunacyDNS is a Lua-based name server which uses a combination of C (for the heavy lifting of binding to DNS sockets, processing DNS requests, and handling pending replies from upstream DNS servers) and Lua (for deciding how to respond to a given query) to have both performance and flexibility.

In more detail: MaraDNS has one daemon, the authoritative daemon (called maradns), that provides information to recursive DNS servers on the internet, and another daemon, the recursive daemon (called Deadwood), that gets DNS information from the internet for web browsers and other internet clients.

A simplified way to look at it: MaraDNS puts your web page on the Internet; Deadwood looks for web pages on the Internet.

Since MaraDNS’ authoritative daemon does not support TCP, MaraDNS includes a separate DNS-over-TCP server called zoneserver that supports both standard DNS-over-TCP and DNS zone transfers.

Neither MaraDNS nor the UNIX version of Deadwood have support for daemonization; this is handled by a separate program included with MaraDNS called Duende. Deadwood's Windows port, on the other hand, includes support for running as a Windows service.

MaraDNS also includes a simple DNS querying tool called askmara and a number of other miscellaneous tools: Lua 5.1 scripts for processing MaraDNS' documentation (since MaraDNS comes with a fork of Lua 5.1, these scripts do not have an external dependency), some Unicode conversion utilities, scripts for building and installing MaraDNS, automated SQA tests, etc.

MaraDNS is a native UNIX program which can run in Windows via cygwin. Both Deadwood, MaraDNS' recursive resolver, and coLunacyDNS, a DNS server configured with a Lua 5.1 script, are cross-platform applications with full Windows ports.

MaraDNS 2.0 has full (albeit not fully tested) IPv6 support.

#Internals

MaraDNS 3.5’s authoritative server uses code going all the way back to 2001. The core DNS-over-UDP server has a number of components, including two different zone file parsers, a mararc parser, a secure random number generator, and so on.

MaraDNS is written entirely in C. No objective C nor C++ classes are used in MaraDNS’ code.

MaraDNS 2.0’s “Deadwood” recursive server was started in 2007 and has far cleaner code. Its random number generator, for example, uses a smaller, simpler, and more secure cryptographic algorithm; its configuration file parser uses a finite state machine interpreter; its handling of multiple simultaneous pending connections is done using select() and a state machine instead of with threads.

#Other DNS servers

The landscape of open-source DNS servers has changed greatly since 2001 when MaraDNS was started. There are now a number of different DNS servers still actively developed and maintained: BIND, Power DNS, NSD/Unbound, as well as MaraDNS. DjbDNS is no longer being updated and the unofficial forks have limited support; notably it took nearly five months for someone to come up with a patch for CVE-2012-1191.

MaraDNS’ strength is that it’s a remarkably small, lightweight, easy to configure, and mostly cross-platform DNS server. Deadwood is a tiny DNS server with full recursion support, perfect for embedded systems.

MaraDNS’ weakness is that it does not have some features other DNS servers have. For example, while Deadwood has the strongest spoof protection available without cryptography, it does not have support for DNSSEC.

As another example, MaraDNS does not have full zone transfer support; while MaraDNS can both serve zones and receive external zone files from other DNS servers, MaraDNS needs to be restarted to update its database of DNS records.

#MaraDNS’ future

MaraDNS is a mature application. Being open source code, the amount of time I have to devote to MaraDNS is highly variable. Right now, I am concentrating my efforts to revamp MaraDNS so that it can continue to compile and run for as long as possible, minimizing the number of external dependencies so that outside changes are unlikely to break MaraDNS.

For MaraDNS to break, either the C language would have to change to break programs that compile with few to no warnings here in the 2020s, or the POSIX standard would have to change to the point that POSIX compliant scripts which run here in the 2020s no longer run. Both of these are very unlikely to happen.

#Y2038 statement

MaraDNS is fully Y2038 compliant on systems with a 64-bit time_t. Here in the 2020s, even 32-bit Linux distributions, such as Alpine Linux, have a 64-bit time_t.

Deadwood, in addition, for its Windows 32-bit binary, uses Windows filetime to generate internal timestamps; filetime stamps will not run over until the year 30827 or so.

coLunacyDNS, likewise, uses Windows filetime for timestamps with its Win32 binary.

On *NIX systems with a 32-bit time_t, some features which depend on OS-level time and date libraries are disabled. MaraDNS has support for showing a human readable timestamp with the timestamp_type parameter; this parameter is disabled on systems with a 32-bit time_t since the underlying libraries MaraDNS uses will probably fail at the Y2038 cutoff. Likewise, MaraDNS has support for generating a human-readable SOA serial number with the synth_soa_serial parameter, but this feature is disabled if time_t is 32-bit. In both cases, the feature in question is, by default, disabled in MaraDNS, so only users who have explicitly enabled these features will see any change in behavior.

MaraDNS has the ability to generate a synthetic SOA serial number if a zone file does not have a SOA record. The SOA serial is based on the timestamp for the zone file. If time_t is 32-bit, MaraDNS assumes that the stat call will return a negative timestamp after the Y2038 cutoff, and will adjust timestamps from before 2001 (the year MaraDNS was first developed) to be after the Y2038 cutoff. If there are systems out there where a stat call for a file’s modification time fail after the Y2038 cutoff, one can avoid Y2038 issues by having a SOA record with a serial number in zone files. The Windows port of MaraDNS, as of 3.5.0028, uses Windows Y2038 compliant system calls instead of POSIX calls to get zone file timestamps.

Both Deadwood and coLunacyDNS make some effort to generate accurate timestamps on *NIX systems with a 32-bit time_t until later than 2106; this code assumes that 32-bit systems will have the time stamp “wrap around” after 2038 but still have the 32-bit time be updated.

#Cyber Resilience Act statement

MaraDNS is a project developed on a strictly volunteer, non-commercial basis. It has been developed outside the course of a commercial activity, developed entirely in the Americas (i.e. outside of Europe) and therefore is not subject to the restrictions or conditions of the proposed EU Cyber Resilience Act. Someone selling a product that uses any component of MaraDNS may be subject to this act and may need to handle any and all necessary compliance.

MaraDNS, as always, is provided free of charge but with no warranty.

#Updates

#2022 Updates

MaraDNS was updated in 2022 to have its automated tests run in an Ubuntu 22.04 Docker container instead of an Ubuntu 20.04 Docker container. The tests have also been updated to be more portable, running in both Alpine Linux (Busybox-based Linux distro) and Ubuntu 22.04.

I also fixed a minor security issue, which also affected other DNS servers, where a clever attacker with access to the recurisve DNS server could had kept records in the cache longer than desired.

min_ttl now correctly sets a minimum TTL for direct answers to queries. I have backported the min_ttl parameter to the older legacy 3.4 version of MaraDNS.

While using Deadwood as a fully recursive server is not guaranteed to be fully supported, I have fixed a long standing bug with how Deadwood handled certain CNAME chains, and have added tests to make sure this bug stays fixed.

MaraDNS no longer uses non-POSIX scripting languages not included with MaraDNS:

  • MaraDNS’s documentation system, EJ, has been updated to use Lua 5.1 (included with MaraDNS with the name lunacy in coLunacyDNS/lunacy) instead of Perl scripts.
  • The old bind2csv2.py tool has been removed, so that MaraDNS no longer needs Python to run any of its components.

#2021 Updates

Deadwood has a new parameter: source_ip4. This optional parameter is used to specify the source IP when sending queries upstream. The majority of users should be able to leave this untouched; this is for cases when Deadwood is multi-homed and we need to specify which IP to use when querying root or upstream DNS servers.

One line change to zoneserver.c to make it work better with systemd.

Synthetic IP generator example added to coLunacyDNS

#2020 Updates

I have updated things so that the Git version of MaraDNS is the authoritative “One source of truth” for MaraDNS’s source code. The Git code is, every time a new MaraDNS release is made, converted in to tarballs (with full Git history) which can be downloaded at Sourceforge and MaraDNS’s web page.

I have added block list support to Deadwood, to allow a large list of host names to be blocked.

I have created a new service: coLunacyDNS, a simple Lua-based DNS server which can return IPv4 (A) and IPv6 (AAAA) DNS records. It has the ability to query other DNS servers, and customize the answer given to the client based on the contents of a Lua script. All programs have IPv6 support in Linux as well as *NIX clones, and the Windows 32-bit binary of coLunacyDNS has IPv6 support.