Re: Bad signature on commit 6a34f4ccc8a5d (gnu: python-prompt-toolkit: Update to 1.0.9.)

[Leo Famulari <leo@famulari.name>]

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On Thu, Dec 29, 2016 at 04:04:49AM +0100, Tobias Geerinckx-Rice wrote:
> Signing seems to fail both seldom and pseudo-randomly. Oh, and
> silently[1]. My favourite kind of bug.
> 
> I'm guessing this is what happens:
> 
>   $
>   $ git commit, am or cherry-pick && git log --show-signatures
>       ...everything looks good and signed! Let's push!
>   $ git fetch --all && git rebase upstream/master
>       ...now signing some non-HEAD commit silently fails...
>   $ git push upstream
>       ...badness.
> 
> Good night,
> 
> T G-R
> 
> [1]: until you check the log, of course.
> 
> PS:
>   nckx@ubuntu~$ $ /usr/bin/gpg2 --version
>   gpg (GnuPG) 2.1.15
>   libgcrypt 1.7.2-beta
> but I doubt that matters much now. I don't use Guix's gpg [yet].

It would be nice to figure out why it fails. It seems specific to your
setup somehow (since there are no other broken signatures in the log),
but I have no idea where to start. Perhaps with the beta version of
libgcrypt.

Especially since it seems specific to your setup, can you evaluate the
pre-push hook that's attached, and start using the hook if you're
satisfied that it's correct?

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#!/bin/sh

# A hook script that prevents the user from pushing unsigned commits.

# Called by "git push" after it has checked the remote status, but before
# anything has been pushed.  If this script exits with a non-zero status nothing
# will be pushed.
#
# This hook is called with the following parameters:
#
# $1 -- Name of the remote to which the push is being done
# $2 -- URL to which the push is being done
#
# If pushing without using a named remote those arguments will be equal.
#
# Information about the commits which are being pushed is supplied as lines to
# the standard input in the form:
#
#   <local ref> <local sha1> <remote ref> <remote sha1>

z40=0000000000000000000000000000000000000000

# Only use the hook when pushing to Savannah.
case "$2" in
*git.sv.gnu.org*)
	break
	;;
*)
	exit 0
	;;
esac

while read local_ref local_sha remote_ref remote_sha
do
	if [ "$local_sha" = $z40 ]
	then
		# Handle delete
		:
	else
		if [ "$remote_sha" = $z40 ]
		then
			# New branch, examine all commits
			range="$local_sha"
		else
			# Update to existing branch, examine new commits
			range="$remote_sha..$local_sha"
		fi

		# Check if push candidate commits are PGP signed.
		git verify-commit $(git rev-list $range) >/dev/null 2>&1

		exit $?
	fi
done

exit 0

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