from Hacker News

How to Write Software with Zero bugs – 25 years after qmail 1.0 – D. Bernstein [pdf]

by bykhun on 8/22/23, 8:48 PM with 29 comments

  • by hdmoore on 8/22/23, 10:32 PM

    Erm, qmail had lots of bugs[1], when compiled for 64-bit processors (lots of integer overflows), but djb pushed back and said 64-bit wasn't supported. If anything, qmail is known as the most annoying MTA to package, since no modifications to the source are permitted, and the application has to be built using a massive patch tree instead. The quirky management daemons required to run qmail were also obnoxious and at odds with everything else on the system.

    Salient quote below:

    >In May 2005, Georgi Guninski published "64 bit qmail fun", three vulnerabilities in qmail (CVE-2005-1513, CVE-2005-1514, CVE-2005-1515):

    [snip]

    >Surprisingly, we re-discovered these vulnerabilities during a recent qmail audit; they have never been fixed because, as stated by qmail's author Daniel J. Bernstein (in https://cr.yp.to/qmail/guarantee.html):

    >>"This claim is denied. Nobody gives gigabytes of memory to each qmail-smtpd process, so there is no problem with qmail's assumption that allocated array lengths fit comfortably into 32 bits."

    1. https://www.qualys.com/2020/05/19/cve-2005-1513/remote-code-...

    edit: added quote from referenced url

  • by kens on 8/22/23, 10:48 PM

    The title of the actual paper is "Some thoughts on security after ten years of qmail 1.0". The post currently has the made-up title "How to Write Software with Zero bugs – 25 years after qmail 1.0 – D. Bernstein [pdf]".

  • by jongjong on 8/22/23, 11:33 PM

    I agree with the argument about reducing lines of code. Whenever I write code, I spend quite a bit of time thinking about different ways of implementing it before I start coding and the most important characteristic I look for in a solution is succinctness.

    Correct code is easy to read because it's close to its theoretical minimum size. It reminds me of the quote "Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away."

  • by gerdesj on 8/22/23, 11:26 PM

    I ran several Qmail systems. Daemontools worked rather well. They had a habit of delivering email reliably. "Life with Qmail" was a very decent primer.

    I also ran several other mail systems at the same time (and still do). Exchange's smtpd is still a bit of a pain and I never put it on the internet directly.

    Nowadays (last 15 years) I use Exim for a MTA/proxy - at home and at work.

  • by lockhouse on 8/23/23, 12:59 AM

    Why is this flagged? This is one of the few posts that are actually on topic for HN.

  • by latenightcoding on 8/22/23, 10:33 PM

    Classic paper but what the hell is this title .

  • by daneel_w on 8/22/23, 10:30 PM

    Does anyone know how qmail has fared since this PDF was written in 2007? Did it make it to 2023 without any bugs surfacing?

  • by technick on 8/22/23, 11:16 PM

    I have PTSD from listening to my friends complain about qmail back in the early 2000's.

  • by johnea on 8/23/23, 1:46 AM

    Good to see the DJBway here.

    So much could be learned in modern *nix distributions from this philosophy...