[pacman-dev] Package checking options (was: Changed all references to signature verification level in libalpm symbols to 'verifysig'.)

[Dan McGee]

On Tue, Jun 14, 2011 at 12:47 AM, Kerrick Staley <mail at kerrickstaley.com> wrote:
> On Mon, Jun 13, 2011 at 6:13 PM, Dan McGee <dpmcgee at gmail.com> wrote:
>> I have objections on your way of going about business here. I present
>> what i thought was a reasonable approach, got some feedback by Allan,
>> and then you attempt to throw something completely different at us
>> without really responding to what is wrong with my proposal.
>>
>> I'm trying my hardest to not get seen as a stick in the mud and
>> impediment to progress here, but it is damn hard to keep my cool when
>> my years of experience with this codebase gets shoved aside without so
>> much as a "I don't think you considered this" bit of feedback. My
>> ideas tend to be backed by those years of experience, and adding
>> config options is not something we like to do willy-nilly, nor do we
>> want a complicated config file.
>
> Sorry. I often prefer to write in a very direct way (e.g. less
> instances of "I think...", "I feel...", etc.), even when I really mean
> to make a suggestion, because it is terser. I thought it was
> appropriate in this situation because it's a feature I really want to
> see implemented, and while "We should..." tends to generate a response
> along the lines of either "yes" or "no, do this", "Should we..." tends
> to generate a 20+ message thread. While this isn't a bad thing, I
> thought it'd be better to just propose a fully-thought-out, workable
> scheme from the start, so that it could be built off of. I spent
> several hours devising this scheme and ensuring that it covers all
> functionality that I thought would be useful, without requiring too
> much configuration.
>
> Anyway, I think my writing style is somewhat in poor taste; I'll try
> to tone it down.
I'll eat some of my aggressive words as well, I'm sorry. I just come
back from taking a break over the weekend and see my own time spent
thinking, analyzing the situation, and coding seemingly get tossed
aside so I responded with some attitude.

> I feel like the config file syntax is mostly a trivial issue anyway;
> it should fall into place once we have decided (a) which situations we
> should handle specially, and (b) which actions can be taken in those
> situations. I feel that having separate directives for each case would
> be cleaner, but the "CheckLevel" syntax works as well, and since it's
> a question of conventions, it's squarely your call (as is, ultimately,
> everything else I suggest).
>
>> > No marginal signatures should come up, because I don't think we should
>> > use such signatures during the interim when not all developers have
>> > fully validated keys; a developer's key can just be excluded from
>> > pacman-keyring until it is fully validated.
>> That is a pretty bold assumption. You do realize there are more repos
>> out there that are not provided by a distro that people might want to
>> use and have signatures involved, right?
>
> OK, you're right.
>
>> SigPreviouslySigned- an interesting thought, but definitely not
>> something we need on first pass- there are also a multitude of issues
>> here considering everyone starts from a different point.
>
> Yeah, I wasn't even planning on implementing it at first; I just
> thought it'd be something we wanted in the long term, so I put it in
> among the rest.
>
> On Wed, Jun 1, 2011 at 3:46 PM, Dan McGee <dpmcgee at gmail.com> wrote:
>> I also think
>> we may need to be a bit more granular than our current
>> Always/Optional/Never trifecta. We have a multitude of possibilities
>> when checking a signature:
>>
>> * Valid signature, fully trusted (or ultimate,
>> (GPGME_VALIDITY_{ULTIMATE, FULL}).
>>
>> * Valid signature, unknown trust/unknown key (GPGME_VALIDITY_UNKNOWN,
>> GPGME_SIGSUM_KEY_MISSING).
>> * Valid signature, trust somewhere in between (marginal,
>> GPGME_VALIDITY_MARGINAL).
>>
>> * Valid signature, user is never valid (GPGME_VALIDITY_NEVER)
>> * Valid signature, signature is however expired (GPGME_SIGSUM_SIG_EXPIRED)
>> * Valid signature, key is however expired (GPGME_SIGSUM_KEY_EXPIRED)
>> * Bad signature, trust level is irrelevant (GPGME_VALIDITY_RED)
>
> It seems that the first 3 in the last group are corner cases (I could
> not, for the life of me, find a real example of when
> GPGME_VALIDITY_NEVER would come up).
TRUST_NEVER seems to only come up if you do a gpg --edit-key, "trust",
and then choose "never" as your level of trust for a given key, from
what I can see (option 2).

Please decide how far you trust this user to correctly verify other users' keys
(by looking at passports, checking fingerprints from different sources, etc.)

  1 = I don't know or won't say
  2 = I do NOT trust
  3 = I trust marginally
  4 = I trust fully
  5 = I trust ultimately
  m = back to the main menu

> For the middle two, having a
> signature with an unknown or nonexistent key doesn't really say
> anything about the validity of the package, so I think that outcome
> should just lumped in among the last 4. So, then, this boils down to
> "the signature is good", "the signature is bad", or "the signature is
> marginally trusted", but I think there are other cases (hashed,
> database unsigned) that should be considered.

Looking at this last night, I came up with something like the
following. Basically the first enum is what we have now, but moving
toward a more standard name. The real change comes with the second
enum, which unlike the first, will be bitflags (I just didn't assign
values there yet).

checklevel works more or less as it does currently. unknown falls back
to the globally set default, never/optional/always are as expected.

checkoptions basically controls where we perform checks and what we
consider valid. Potential API example:
    alpm_db_set_checklevel(PM_CHECK_LEVEL_ALWAYS,
PM_CHECK_PACKAGE_SIGNATURES | PM_CHECK_DATABASE_SIGNATURES |
PM_CHECK_MARGINAL_SIGNATURES_OK);
This particular call would enforce that signatures are present for
packages AND databases. We would however allow marginally trusted sigs
(but not unknown ones).

For simplicity, the following rules would also apply, at least initially:
* VALID_NEVER, VALIDITY_RED are always failures.
* SIG_EXPIRED, KEY_EXPIRED are always failures (we could add a
PM_CHECK_EXPIRED_SIGNATURES_OK flag).
* Even if PM_CHECK_PACKAGE_SIGNATURES is not provided, we would still
check it if present and level is at least OPTIONAL.

typedef enum _pmchecklevel_t {
       PM_CHECK_LEVEL_UNKNOWN = 0,
       PM_CHECK_LEVEL_NEVER = 1,
       PM_CHECK_LEVEL_OPTIONAL,
       PM_CHECK_LEVEL_ALWAYS
} pmchecklevel_t;

typedef enum _pmcheckoptions_t {
       PM_CHECK_PACKAGE_SIGNATURES,
       PM_CHECK_DATABASE_SIGNATURES,
       PM_CHECK_UNKNOWN_SIGNATURES_OK,
       PM_CHECK_MARGINAL_SIGNATURES_OK
} pmcheckoptions_t;

I think this API covers most of the bases we are looking to address.
The biggest place we differ is in the accept/warn/abort stuff you
proposed. For me I am not a fan of this, only because I know users
don't actually read. :/

Feedback welcome, let's work to a reasonable consensus and I should be
able to knock this out real quick.

Oh, and Kerrick, I don't know if you've figured it out by now but my
hacks are usually available in my repo, right now they are on my
working branch.
http://code.toofishes.net/cgit/dan/pacman.git/log/?h=working. We
should probably make a wiki page of our development repo URLs so
people can find them.

-Dan