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Why don't they upload packages to the normal package repository? Is this a general convention (IE, do other distros separate the repositories also)?

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I'd suggest not having other distro's as that could possibly be excessively long, also by archive to you mean package repo? I'm guessing you do, but making sure you don't mean an svn/git branch or something. –  xenoterracide Nov 22 '10 at 11:57

3 Answers 3

up vote 13 down vote accepted

Debian has a distribution channel that provides security updates only so that administrators can choose to run a stable system with only the absolute minimum of changes. Additionally, this distribution channel is kept somewhat separate from the normal channel: all security updates are fed directly from security.debian.org, whereas it is recommended to use mirrors for everything else. This has a number of advantages. (I don't remember which of these are official motivations I read on Debian mailing lists and which are my own mini-analysis. Some of these are touched on in the Debian security FAQ.)

  • Security updates are spread immediately, without the delay incurred by mirror updates (which can add about 1 day of propagation time).
  • Mirrors can go stale. Direct distribution avoids that problem.
  • There is less infrastructure to maintain as a critical service. Even if most of Debian's servers are unavailable and people can't install new packages, as long as security.debian.org points to a working server, security updates can be distributed.
  • Mirrors can be compromised (this has happened in the past). It's easier to watch a single distribution point. If an attacker managed to upload a malicious package somewhere, security.debian.org could push a package with a more recent version number. Depending on the nature of the exploit and the timeliness of the response, this could be enough to keep some machines uninfected or at least warn administrators.
  • Fewer people have upload rights on security.debian.org. This limits the possibilities for an attacker trying to subvert an account or machine in order to inject a malicious package.
  • Servers that don't need ordinary web access can be kept behind a firewall that only allows security.debian.org through.
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The security repo pre-dates signing the release files for repositories, so mirroring it was discouraged, as it diluted the implicit trust of downloading from security.debian.org. That argument has gone away to some extent now that package metadata is signed. –  jmtd Jan 24 '11 at 13:50
    
host security.debian.org does resolve to a bunch of addresses, so maybe it is a pool of machines, even if it technically does not have mirrors. –  Faheem Mitha Nov 7 at 1:53

I'm pretty sure Debian puts security updates in the regular repo as well.

The reason to have a separate repo that only contains security updates is so you can set up a server, only point it at the security repo, and automate updates. Now you've got a server that is guaranteed to have the latest security patches without accidentally introducing bugs caused by incompatible versions, etc.

I'm not sure if this exact mechanism is used by other distros. There's a yum plugin to handle this kind of thing for CentOS, and Gentoo currently has a security mailing list (portage is currently being modified to support security-only updates). FreeBSD and NetBSD both provide ways to do security audits of installed ports/packages, which integrate well with the built-in update mechanisms. All told, Debian's approach (and probably Ubuntu's, since they're so closely related) is one of the slicker solutions to this problem.

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yes because a security patch could never possibly introduce another bug. –  xenoterracide Nov 22 '10 at 23:00
    
"s. Now you've got a server that is guaranteed to have the latest security patches without accidentally introducing bugs caused by incompatible versions, etc." is that not what that means? I suppose I could sat that incompat versions is the arguable point... what does that mean exactly... most of the time people who backport only security patches aren't doing it because they feel that ABI/API is the only thing they're looking at. –  xenoterracide Nov 24 '10 at 0:18
    
@xeno Are you critisizing the idea of splitting these repos up, or are you alerting us that there are no guarantees? –  Tshepang Nov 26 '10 at 7:27
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@xeno Depending on how upstream handles things, bugfix patches can be too intrusive for a 'stable' release. –  Tshepang Nov 26 '10 at 8:24
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The vast majority of security patches are trivially small: re-ordering the arguments to a memset, fixing a bounds check on a strncmp or what-have-you. Of course, they could plausibly introduce other bugs, but the risk is very small and theoretical, whereas the discovered security bug is very much practical. –  jmtd Jan 24 '11 at 13:49

It helps with two things:

  1. safety - first get your security fixes, then you are at lower risk while updating the rest
  2. security updates should be stored at a high security level, as you tend to rely on them to protect the rest of your system, so it could be that this repo has stronger security controls to prevent compromise

there could well be other reasons, but those are the two I would find useful

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You sure about stored at a high security level? I say that because you express doubt, could be. –  Tshepang Dec 19 '10 at 8:12
    
Well spotted Tshepang - I haven't got visibility of the environment that repo exists in, but that is they way I would set it up :-) –  Rory Alsop Dec 19 '10 at 12:05
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There is at least some form of higher security level: only the security team can push a package onto security.debian.org. I don't know the implementation details. –  Gilles Dec 19 '10 at 16:21

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