Git Bug Report: git credential 'url' parsing clear other fields

Hi,

I encountered what seems to be a small bug in git credential parsing. Just want to confirm it's not expected behavior. I'm willing to work on a patch.

First time submitting a bug to git (and a potential patch), so let me know if I do anything wrong!

What did you do before the bug happened? (Steps to reproduce your issue)

Run git credential approve with the 'url' field of the form NOT as first entry.

example: git -c credential.helper= -c "credential.helper=store --file=.git-credentials" credential approve

input: ``` username=user password=s3cret url=https://example.com/repository.git ```

This next input works as intended. input: ``` url=https://example.com/repository.git username=user password=s3cret ```

This was reproduced on both master and next branches.

What did you expect to happen? (Expected behavior)

Credentials should be saved with `username` and `password` provided. `url` parsing should not clear the `credential` struct.

What happened instead? (Actual behavior)

`username` and `password` are correctly parsed and stored in the struct. `url` parsing then clear the fields.

Culprit would be this `credential_clear` in `credential_from_url_1`. On branch `next`, commit `2a3ae87e7f8e9585d7565a8b5d6a6c9c28d6d943`.

Thanks, Thomas Desveaux

On Fri, Apr 26, 2024 at 09:27:03PM +0200, Thomas Desveaux wrote:

Thanks for a clear report and example.

However, what you're seeing is the intended behavior. When the "url" feature was added, it came with these docs in git-credential.txt:

  When this special attribute is read by `git credential`, the value is
  parsed as a URL and treated as if its constituent parts were read
  (e.g., `url=https://example.com` would behave as if `protocol=https`
  and `host=example.com` had been provided). This can help callers avoid
  parsing URLs themselves.  Note that any components which are missing
  from the URL (e.g., there is no username in the example above) will be
  set to empty; if you want to provide a URL and override some
  attributes, provide the URL attribute first, followed by any
  overrides.

That last "Note that..." part was lost in 1aed817f99 (credential: document protocol updates, 2020-05-06). Between digging around in the thread[1] and my recollection, I think the point was that we might drop the "override" behavior as a defense-in-depth against injection attacks (like "path=evil/\nhost=github.com"). I.e., make it an error to specify "host=" more than once. But we didn't actually make that code change yet.

However, even if we did so, I think we'd keep the "clear" half of the behavior (we parsed a URL with no password in it, so the result is a credential with no password in it). In which case your first example still wouldn't behave as you expected.

So I think 1aed817f99 may have gone a bit too far and caused the documentation to be misleading. It should probably keep the "any components which are missing will be set to empty" part.

-Peff

[1] https://lore.kernel.org/git/20200505013908.4596-1-carenas@gmail.com/