Subject: bug#60782: Channels and dependency confusion

From: Simon Tournier <[email-masked]>
Date: Mon, 16 Jan 2023 12:18:58 +0100

Hi,

On lun., 16 janv. 2023 at 10:00, Ludovic Courtès <[email-masked]> wrote:

>> Well, the assumption for a similar attack using Guix channels is that
>> the user first adds the channel to their channel list.  Therefore, they
>> trust what they consider able to be trust. ;-)
>
> Right, users would have to explicitly add the offending channel to their
> channel list in the first place.  (And there are many other ways channel
> code could mess up with one’s machine.)

To be precise, the user must add a compromised channel; either
compromised by the packages which this channel offers or either by some
dependencies channel of this very same channel.

For instance, consider the user adds the channel guix-bimsb which
contains this .guix-channel [1] file:

--8<---------------cut here---------------start------------->8---
(channel
 (version 0)
 (dependencies
  (channel
   (name guix-past)
   (url "https://gitlab.inria.fr/guix-hpc/guix-past"))
  (channel
   (name guix-science)
   (url "https://github.com/guix-science/guix-science.git"))))
--8<---------------cut here---------------end--------------->8---

Here, the user could be compromised if the attacker is able to
compromise guix-past or guix-science.  The user who trusts guix-bimsb is
maybe not aware of this recursive dependencies; but because they trust
guix-bimsb in the first place, somehow it means they trust people behind
guix-bimsb to check that guix-past or guix-science is not compromised.

Well, somehow it is a web of trust.

And if all channels are using authentication, then the attack is hard,
no?

1: <https://github.com/BIMSBbioinfo/guix-bimsb/blob/master/.guix-channel>

Cheers,
simon