bug#22883: Trustable "guix pull"

[Vagrant Cascadian <vagrant@debian.org>]

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This isn't exactly pretty, and obviously a better long-term solution is
needed, but I wrote a quick shell script to at least partially addresses
some my biggest fears with guix pull...

Basically, it updates a git checkout, checks the signatures on the
commits, looking for the topmost signed commit by a key in a specific
keyring, and then runs guix pull with that commit.


It relies on a custom gpg directory and assumes any of the keys in the
keyring are valid potential signers of the commits; the web of trust is
essentially ignored.

I really don't like having a custom GNUPGHOME, but I didn't see any
other obvious way to pass arguments to git to use a custom keyring. I
populated this GNUPGHOME with keys from:

  https://savannah.gnu.org/project/memberlist-gpgkeys.php?group=guix&download=1

And then ran gpg --refresh-keys on it, as several keys were
outdated/expired.

(an alternative approach to populate the keyring might be:
https://gitlab.com/Efraim/guix-keyring)


It also assumes a git checkout where "git pull" pulls from the correct
repository.

It assumes guix --version returns a valid git hash, so would require
some more tweaks to get it working from a fresh guix install.

All those caveats aside, it seems to work well enough for me, and
writing this email took longer than writing the script. :)


live well,
  vagrant


#!/bin/sh

set -x
set -e
workdir=/home/vagrant/src/guix
export GNUPGHOME=$workdir/verified-pull/gnupg
cd $workdir
git pull
guixversion=$(guix --version | awk '/^guix/{print $4}')

commits=$(git log ${guixversion}.. --pretty='format:%G?,%H')

# · %G?: show
# "G" for a good (valid) signature,
# "B" for a bad · %signature,
# "U" for a good signature with unknown validity,
# "X" for a good · %signature that has expired,
# "Y" for a good signature made by an expired · %key,
# "R" for a good signature made by a revoked key,
# "E" if the · %signature cannot be checked (e.g. missing key) and
# "N" for no signature

for commitlog in $commits ; do
    commitverify=$(echo $commitlog | cut -d , -f 1)
    commit=$(echo $commitlog | cut -d , -f 2)
    case $commitverify in
	G|U) git verify-commit $commit && \
		   guix pull --url=file://$workdir --commit=$commit && \
		   exit 0 ;;
    esac
done

echo unable to find signed commit
exit 1

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