[Distutils] PEP 470 discussion, part 3

Thu Jul 24 17:41:57 CEST 2014

On July 24, 2014 at 7:26:11 AM, Richard Jones (r1chardj0n3s at gmail.com) wrote:
Even ignoring the malicious possibility there is a probably greater chance of accidental mistakes:

- company sets up internal index using pip's multi-index support and hosts various modules
- someone quite innocently uploads something with the same name, never version, to pypi
- company installs now use that unknown code

devpi avoids this (I would recommend it over multi-index for companies anyway) by having a white list system for packages that might be pulled from upstream that would clash with internal packages.

As Nick's mentioned, a signing infrastructure - tied to the index registration of a name - could solve this problem.
Yes, those are two solutions, another solution is for PyPI to allow registering a namespace, like dstufft.* and companies simply name all their packages that. This isn’t a unique problem to this PEP though. This problem exists anytime a company has an internal package that they do not want on PyPI. It’s unlikely that any of those companies are using the external link feature if that package is internal.

There still remains the usability issue of unsophisticated users running into external indexes and needing to cope with that in one of a myriad of ways as evidenced by the PEP. One solution proposed and refined at the EuroPython gathering today has PyPI caching packages from external indexes *for packages registered with PyPI*. That is: a requirement of registering your package (and external index URL) with PyPI is that you grant PyPI permission to cache packages from your index in the central index - a scenario that is ideal for users. Organisations not wishing to do that understand that they're the ones causing the pain for users.
We can’t cache the packages which aren’t currently hosted on PyPI. Not in an automatic fashion anyways. We’d need to ensure that their license allows us to do so. The PyPI ToS ensures this when they upload but if they never upload then they’ve never agreed to the ToS for that artifact.

An extension of this proposal is quite elegant; to reduce the pain of migration from the current approach to the new, we implement that caching right now, using the current simple index scraping. This ensures the packages are available to all clients throughout the transition period.
As said above, we can’t legally do this automatically, we’d need to ensure that there is a license that grants us distribution rights.

The transition issue was enough for those at the meeting today to urge me to reject the PEP.
To be clear, there are really three issues at play:

1) Should we continue to support scraping external urls *at all*. This is a cause of a lot of problems in pip and it infects our architecture with things that cause confusing error messages that we cannot really get away from. It’s also super slow and grossly insecure. 

2) Should we continue to support direct links from a project’s /simple/ page to a downloadable file which isn’t hosted on PyPI. 

3) If we allow direct links to a downloadable file from a project’s /simple/ page, do we mandate that they include a hash (and thus are safe) or do we also allow ones without a checksum (and thus are unsafe).

For me, 1 is absolutely not. It is terrible and it is the cause of horrible UX issues as well as performance issues. However 1 is also the majorly useful one. Eliminating 1 eliminates PIL and that is > 90% of the /simple/ traffic for the projects which this will have any impact.

For me 2 is a question of, is the relatively small (both traffic and number of packages) worth the extra cognitive overhead of users having to understand that there are *two* ways for something to be installed from not PyPI. Additionally is it worth the removal of ability for people to legally mirror the actual *files* without manually white listing the ones that they’ve vetted and found the license to allow them to do so (and even then in the future a project could switch to a license which doesn’t allow that). For me this is again no, it’s not worth it. Additional concepts to learn with their own quirks and causing pain for people wanting to mirror their installs is not worth keeping things working for a tiny fraction of things.

For me 3 is no just because 2 is no, but assuming 2 is “yes”, I still think 3 is no because the external vs unverified split is confusing to users. Additionally the impact of this one, if I recall correctly, is almost zero.

      Richard

On 24 July 2014 12:40, Vladimir Diaz <vladimir.v.diaz at gmail.com> wrote:
In metadata 2.0 even with package signing you end up where I can have you install “django-foobar” which depends on “FakeDjango”, which provides “Django”, and then for all intents and purposes you have a “Django” package installed.

Can you go into more detail?  Particularly, the part where "FakeDjango" provides Django.

Richard Jones mentions the case where an external index provides an "updated release" and tricks the updater into installing a compromised "Django."  Is this the same thing?

On Thu, Jul 24, 2014 at 4:55 AM, Richard Jones <r1chardj0n3s at gmail.com> wrote:
Thanks for responding, even from your sick bed.

This message about users having to view and understand /simple/ indexes is repeated many times. I didn't have to do that in the case of PIL. The tool told me "use --allow-external PIL to allow" and then when that failed it told me "use --allow-unverified PIL to allow". There was no needing to understand why, nor any reading of /simple/ indexes.
Currently most users (I'm thinking of people who install PIL once or twice) don't need to edit configuration files, and with a modification we could make the above process interactive. Those ~3000 packages that have internal and external packages would be slow, yes.

This PEP proposes a potentially confusing break for both users and packagers. In particular, during the transition there will be packages which just disappear as far as users are concerned. In those cases users will indeed need to learn that there is a /simple/ page and they will need to view it in order to find the URL to add to their installation invocation in some manner. Even once install tools start supporting the new mechanism, users who lag (which as we all know are the vast majority) will run into this.

On the devpi front: indeed it doesn't use the mirroring protocol because it is not a mirror. It is a caching proxy that uses the same protocols as the install tools to obtain, and then cache the files for install. Those files are then presented in a single index for the user to use. There is no need for multi-index support, even in the case of having multiple staging indexes. There is a need for devpi to be able to behave just like an installer without needing intervention, which I believe will be possible in this proposal as it can automatically add external indexes as it needs to.

I talked to a number of people last night and I believe the package spoofing concept is also a vulnerability in the Linux multi-index model (where an external index provides an "updated release" of some core package like libssl on Linux, or perhaps requests in Python land). As I understand it, there is no protection against this. Happy to be told why I'm wrong, of course :)

      Richard

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