Re: [PoC] Federated Authn/z with OAUTHBEARER

On Wed, Nov 27, 2024 at 9:27 AM Daniel Gustafsson <daniel(at)yesql(dot)se> wrote:
> Thanks for the updated version, it's really starting to take good shape. A few
> small comments on v37 from a a first quick skim-through:

Applied in v38, thanks!

> fail_validator.c seems to have the #include list copied from validator.c and
> pulls in unnecessarily many headers.

Oops, thanks for the cleanup.

> In validate() I wonder if we should doublecheck that have a a proper set of
> validator callbacks loaded just to make even more sure that we don't introduce
> anything terrible in this codepath.

Seems good. I think this part of the API is going to need an
ABI-compatibility pass, too. For example, do we want a module to
allocate the result struct itself (which locks in the struct length)?
And should we have a MAGIC_NUMBER of some sort in the static callback
list, maybe?

--

Now that our JSON API can be put into "leakproof" mode [1], I can fuzz
the parser implementations. libfuzzer has been able to find one known
issue, plus two more that I was unaware of:

1. Duplicate fields caused the previous field values to leak. (This
was the documented FIXME; we now error out in this case.)
2. The array-of-strings parsing had a subtle logic bug: if field "a"
was expected to be an array of strings, we would also accept the
construction `"a": "1"` as if it were equivalent to `"a": ["1"]`. This
messed up the internal tracking and tripped assertions.
3. handle_oauth_sasl_error() was leaking all of its parsed fields if
they didn't get hooked into the PGconn struct before a failure.

All three are fixed in v38; I will keep working on expanding the
amount of code covered by my fuzzers.

Additionally, the following pieces of feedback has been addressed:
- We now validate the incoming JSON as UTF-8 before lexing it, to
prevent invalid multibyte sequences from sneaking through in the
strings [2]. Still need to determine how \uXXXX sequences will
interact with the more punishing client encodings in error messages.
- --with-builtin-oauth/-Dwith_builtin_oauth has been renamed
--with-libcurl/-Dlibcurl, and the Autoconf side uses PKG_CHECK_MODULES
exclusively.
- markPQExpBufferBroken has been replaced with termPQExpBuffer in
append_urlencoded()
- the anonymous union has been named
- pg_be_oauth_mech uses a designated initializer

Next up, the many-many documentation requests, now that the fuzzers
can run while I write.

Thanks,
--Jacob

[1] https://postgr.es/c/5c32c21afe6
[2] https://postgr.es/m/ZjmjPyA29dIJjmjI%40paquier.xyz