[pacman-dev] Could makepkg verify .dsc file?

[Eli Schwartz]

On 12/16/2016 05:08 PM, Bruno Pagani wrote:
> Le 16/12/2016 à 20:52, Eli Schwartz a écrit :
>> Not really true in the general case. :p There are several somewhat
>> famous Debian bugs regarding software they shipped that did what was to
>> them very offensive things, and the maintainer got thoroughly scolded
>> for having failed to catch it.
> 
> Indeed, never thought of “Debian OpenSSL keys” from that perspective. :p

Um, actually, I've never thought about it from that perspective either,
I think...

The openssl fiasco wasn't really a case of the source code doing things
that violate Debian standards (and hence is offensive *to Debian*
specifically). It was *because* of their tampering that it did the wrong
thing, but not necessarily an "offensive" thing.

I was actually thinking about xscreensaver.[1]

> I’ll switch bs1770gain to that then. But I have the impression you’re
> seing that even before I should have used upstream source despite their
> ugly/shadowy build system, is that the case? Maybe while carrying Debian
> patch to build correctly aside?

Correct. I agree that things should build against system libraries
(except in cases like FS#43382 in which case the appropriate response is
to work with upstream to make the software work properly with system
libraries).

Patching the build system is okay (but dirty) in that case, as long as
upstream is notified in due course (so it can stop being dirty).

However, I strongly believe that should only be done as patches applied
to the unmodified and verifiable upstream source code. If the patches
are from Debian, I am not suggesting we hate on Debian and reject it. ;)
I am simply saying, use their patches and upstream's release tarball,
rather than using Debian's modified tarball.

>>>> What does authenticating Debian's checksums get us, that we couldn't
>>>> have gotten out of verifying the AUR maintainer's checksums?
>>> Not sure to understand that one: what’s the point of PGP at all in
>>> makepkg then? Like I’ve said in my other emails responding to Allan, how
>>> is this different from a signed source verified by the maintainer while
>>> having just the checksum pasted in the PKGBUILD?
>> PGP in makepkg does whatever you tell it to, which unlike checksums is
>> *capable* of supplying authority in addition to integrity.
> 
> Yes, but signed sums are just one more step away from this setup.

True, and signed sums generated by a "real upstream" is something I
wouldn't mind having. But authenticating Debian's checksums is no better
or worse than having an AUR maintainer ship a signature generated from
the AUR maintainer's *own* GPG key!

I disapprove of that in the AUR, so I won't hold us to a higher standard
than I hold Debian. :)

> I’m not familiar with makepkg code, but would it really be that hard to
> allow such things to work? I’m not sure why makepkg can’t see the
> downloaded file the first time but can the second, is that because the
> commands in sha256sums are executed before downloading?

Correct. Towards the beginning of makepkg's runtime, it sources the
PKGBUILD and at that time the grep magic occurs, because a PKGBUILD can
contain any kind of bash hacks.

However, ultimately the job of a PKGBUILD is to define certain variables
and functions (at the time it is sourced), which makepkg will then use.

Later on, makepkg does its "download all the sources" thing, looping
through the source array and calling appropriate download agents to
retrieve those sources.
And later on yet, makepkg loops through the sources again and verifies
them via the *sums array(s) and PGP signatures if available

What you can do since you are after all relying on hacks ;) is to
pre-download the dsc. You can always depend on curl to exist since
pacman relies on it, and essentially it can be treated like a local source.

>> The other problem is formats for checksum files. ;) Theoretically, the
>> reusable output of sha*sum is a standard, but in practice some use the
>> BSD-style type, and as witnessed in the Firefox checksum manifest, there
>> may be many files listed in one checksum file using complex paths, so
>> that would have to be filtered.
> 
> Or just allow the above setup and let the parsing of the checksum file
> at maintainer responsibility?
> 
>> As for attached signatures, that is hardly a Debian-specific idea, but I
>> confess I don't usually see file resources with attached signatures
>> floating around. The thing about them is that you need to have gpg in
>> order to transform the file into something usable -- that's why the
>> detached signature exists.
> 
> Yes indeed, file resources with attached signature are not likely to
> exist. But this is really about signed checksums.
> 
>> So I think it is, in practice, more or less limited to inline signing of
>> *messages*, and makepkg doesn't usually need to worry about those. But
>> in theory we could fix that and teach makepkg how to recognize sources
>> with builtin signatures. (Actually the case with git, and I had to
>> special-case it to add signed commit/tag support.)
> 
> Yes indeed, it’s all about inline signing of messages, those messages
> being sha*sums of the resource file. ;)

All this ^^ is really about "what is likely enough that we should build
special handling into libmakepkg, rather than requiring each maintainer
to reinvent the wheel/do more busywork".

-- 
Eli Schwartz

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=819703

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