[Intel-gfx] [maintainer-tools PATCH] dim: Sign commits in addition to tags

[Eric Anholt]

Sean Paul <seanpaul at chromium.org> writes:

> On Wed, Nov 1, 2017 at 7:12 AM, Gustavo Padovan <gustavo at padovan.org> wrote:
>> 2017-10-31 Sean Paul <seanpaul at chromium.org>:
>>
>>> On Tue, Oct 31, 2017 at 1:31 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
>>> > On Tue, Oct 31, 2017 at 5:14 PM, Sean Paul <seanpaul at chromium.org> wrote:
>>> >> On Tue, Oct 31, 2017 at 4:27 AM, Jani Nikula
>>> >> <jani.nikula at linux.intel.com> wrote:
>>> >>>
>>> >>> Reminder, we have this new list dim-tools at lists.freedesktop.org for
>>> >>> maintainer tools patches. Cc'd.
>>> >>>
>>> >>
>>> >> Ahh, cool. I didn't realize dim grew up!
>>> >>
>>> >>> On Mon, 30 Oct 2017, Sean Paul <seanpaul at chromium.org> wrote:
>>> >>>> Expanding on Jani's work to sign tags, this patch adds signing for git
>>> >>>> commit/am.
>>> >>>
>>> >>> I guess I'd like more rationale here. Is this something we should be
>>> >>> doing? Is anyone else doing this?
>>> >>>
>>> >>
>>> >> Sure thing. Signing commits allows Dave to use --verify-signatures
>>> >> when pulling. If something is not signed, we'll know it was either not
>>> >> applied with dim, or was altered on fdo (both warrant investigation).
>>> >>
>>> >> I suspect no one else is doing this since most trees are single
>>> >> maintainer, and it's not possible to sign commits via git send-email.
>>> >> Since we have the committer model, and a bunch of people with access
>>> >> to fdo and the tree, I think it's important to add this. Especially
>>> >> since we can do it in dim without overhead.
>>> >>
>>> >>>> Signed-off-by: Sean Paul <seanpaul at chromium.org>
>>> >>>> ---
>>> >>>>
>>> >>>> This has been lightly tested with dim apply-branch/dim push-branch.
>>> >>>>
>>> >>>> Sean
>>> >>>>
>>> >>>>  dim | 78 +++++++++++++++++++++++++++++++++++++++++++++------------------------
>>> >>>>  1 file changed, 51 insertions(+), 27 deletions(-)
>>> >>>>
>>> >>>> diff --git a/dim b/dim
>>> >>>> index 527989aff9ad..cd5e41f89a3a 100755
>>> >>>> --- a/dim
>>> >>>> +++ b/dim
>>> >>>> @@ -67,9 +67,6 @@ DIM_TEMPLATE_SIGNATURE=${DIM_TEMPLATE_SIGNATURE:-$HOME/.dim.template.signature}
>>> >>>>  # dim pull-request tag summary template
>>> >>>>  DIM_TEMPLATE_TAG_SUMMARY=${DIM_TEMPLATE_TAG_SUMMARY:-$HOME/.dim.template.tagsummary}
>>> >>>>
>>> >>>> -# GPG key id for signing tags. If unset, don't sign.
>>> >>>> -DIM_GPG_KEYID=${DIM_GPG_KEYID:+-u $DIM_GPG_KEYID}
>>> >>>> -
>>> >>>>  #
>>> >>>>  # Internal configuration.
>>> >>>>  #
>>> >>>> @@ -104,6 +101,20 @@ test_request_recipients=(
>>> >>>>  # integration configuration
>>> >>>>  integration_config=nightly.conf
>>> >>>>
>>> >>>> +# GPG key id for signing tags. If unset, don't sign.
>>> >>>> +function gpg_keyid_for_tag
>>> >>>> +{
>>> >>>> +     echo "${DIM_GPG_KEYID:+-u $DIM_GPG_KEYID}"
>>> >>>> +     return 0
>>> >>>> +}
>>> >>>> +
>>> >>>> +# GPG key id for committing (git commit/am). If unset, don't sign.
>>> >>>> +function gpg_keyid_for_commit
>>> >>>> +{
>>> >>>> +     echo "${DIM_GPG_KEYID:+-S$DIM_GPG_KEYID}"
>>> >>>> +     return 0
>>> >>>> +}
>>> >>>
>>> >>> This seems like an overly complicated way to achieve what you want.
>>> >>>
>>> >>> Just put these under "Internal configuration." instead:
>>> >>>
>>> >>> dim_gpg_sign_tag=${DIM_GPG_KEYID:+-u $DIM_GPG_KEYID}
>>> >>> dim_gpg_sign_commit=${DIM_GPG_KEYID:+-S$DIM_GPG_KEYID}
>>> >>>
>>> >>> And use directly in git tag and commit, respectively?
>>> >>>
>>> >>
>>> >> Yep, sounds good.
>>> >>
>>> >>> Although... perhaps starting to sign tags should not force signing
>>> >>> commits?
>>> >>>
>>> >>
>>> >> Why would it be desirable to *not* sign tags?
>>> >
>>> > Again, what's the threat model you're trying to defend against? Atm
>>> > anyone with commit rights to fd.o can push whatever they want to. If
>>> > they want to be evil, they can also push whatever kind of garbage they
>>> > want to, including commit signature and and fake Link: and review
>>> > tags. With pull requests/tags signing them prevents a
>>> > man-in-the-midddle attack of the unprotected pull request in the mail,
>>> > but I still don't see what signing commits protects against.
>>>
>>> This is protecting against a bad actor (either through a committer's
>>> account, or some other fdo account) gaining access to the tree on fdo
>>> and either adding a malicious commit, or altering an existing commit.
>>
>> Yeah, but then we need to enforce it for all committer
>
> My hope is that dim makes it easy enough to get everyone on board
> eventually. In the interim, the people with signing commits will be
> able to attest that those commits were applied by them.
>
>> and we also need
>> a signing party to sign each others keys.
>
> I feel like most of us see each other often enough to make this
> possible. Even without a signing party, we still get *some* amount of
> coverage by virtue of TOFU [1].
>
> Is anyone against the idea of signing commits? Is there a reason that
> we shouldn't?

We've used GPG a bunch in fdo infrastructure, and my experience is that
it gets you basically no assurance, in exchange for a bunch of admin
overhead (since people lose keys and need to be able to say "Yes, this
is really me, here with a new key").

I've been signing email for years, but I'm not a fan of tying
participation in open source development to using GPG.  It's just not
useful enough for its costs, particularly discouraging new developers.
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