Improve hooks tests by EliahKagan · Pull Request #1777

Improve hooks tests by EliahKagan · Pull Request #1777 · gitpython-developers/GitPython

added 2 commits

December 21, 2023 00:58

Precise xfail marks were added to commit hook tests in gitpython-developers#1745, but
in a few tests I didn't get it right for WinBashStatus.Absent. That
is, on a Windows system that has no bash.exe at all:

- More of the tests are unable to pass than have xfail marks.

- One of the tests, test_commit_msg_hook_success, which does have
  an xfail mark for that, wrongly combines it with the xfail mark
  for WinBashStatus.Wsl. That test is the only one where the WSL
  bash.exe, even when a working WSL distribution is installed, is
  unable to pass. But using a single mark there is wrong, in part
  because the "reason" is not correct for both, but even more so
  because the exceptions they raise are different: AssertionError
  is raised when the WSL bash.exe is used in that test, but when
  bash.exe is altogether absent, HookExecutionError is raised.

This fixes that by adding xfail marks for WinBashStatus.Absent
where missing, and splitting test_commit_msg_hook_success's xfail
mark that unsuccessfully tried to cover two conditions into two
separate marks, each of which gives a correct reason and exception.

This commit also rewords the xfail reason given for WslNoDistro,
which was somewhat unclear and potentially ambiguous, to make it
clearer.

This has three benefits:

- run_commit_hook is public, being listed in git.index.fun.__all__,
  so it makes sense for it to have its own test.

- When investigating (future, or current xfail-covered) failure of
  functions that use run_commit_hook, it will be useful to compare
  the results of other tests that already do exist to that of a
  direct test of run_commit_hook.

- When changing which bash.exe run_commit_hook selects to use on
  Windows (including to ameliorate the limitation covered by the
  WinBashStatus.WslNoDistro xfail marks, or to attempt other
  possible changes suggested in gitpython-developers#1745), or even just to investigate
  the possibility of doing so, it will make sense to add tests like
  this test but for more specific conditions or edge cases. Having
  this typical-case test to compare to should be helpful both for
  writing such tests and for efficiently verifying that the
  conditions they test are really the triggers for any failures.

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [GitPython](https://togithub.com/gitpython-developers/GitPython) |
`==3.1.40` -> `==3.1.41` |
[![age](https://developer.mend.io/api/mc/badges/age/pypi/GitPython/3.1.41?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/pypi/GitPython/3.1.41?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/pypi/GitPython/3.1.40/3.1.41?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/GitPython/3.1.40/3.1.41?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

> [!WARNING]
> Some dependencies could not be looked up. Check the Dependency
Dashboard for more information.

### GitHub Vulnerability Alerts

####
[CVE-2024-22190](https://togithub.com/gitpython-developers/GitPython/security/advisories/GHSA-2mqj-m65w-jghx)

### Summary

This issue exists because of an incomplete fix for CVE-2023-40590. On
Windows, GitPython uses an untrusted search path if it uses a shell to
run `git`, as well as when it runs `bash.exe` to interpret hooks. If
either of those features are used on Windows, a malicious `git.exe` or
`bash.exe` may be run from an untrusted repository.

### Details

Although GitPython often avoids executing programs found in an untrusted
search path since 3.1.33, two situations remain where this still occurs.
Either can allow arbitrary code execution under some circumstances.

#### When a shell is used

GitPython can be told to run `git` commands through a shell rather than
as direct subprocesses, by passing `shell=True` to any method that
accepts it, or by both setting `Git.USE_SHELL = True` and not passing
`shell=False`. Then the Windows `cmd.exe` shell process performs the
path search, and GitPython does not prevent that shell from finding and
running `git` in the current directory.

When GitPython runs `git` directly rather than through a shell, the
GitPython process performs the path search, and currently omits the
current directory by setting `NoDefaultCurrentDirectoryInExePath` in its
own environment during the `Popen` call. Although the `cmd.exe` shell
will honor this environment variable when present, GitPython does not
currently pass it into the shell subprocess's environment.

Furthermore, because GitPython sets the subprocess CWD to the root of a
repository's working tree, using a shell will run a malicious `git.exe`
in an untrusted repository even if GitPython itself is run from a
trusted location.

This also applies if `Git.execute` is called directly with `shell=True`
(or after `Git.USE_SHELL = True`) to run any command.

#### When hook scripts are run

On Windows, GitPython uses `bash.exe` to run hooks that appear to be
scripts. However, unlike when running `git`, no steps are taken to avoid
finding and running `bash.exe` in the current directory.

This allows the author of an untrusted fork or branch to cause a
malicious `bash.exe` to be run in some otherwise safe workflows. An
example of such a scenario is if the user installs a trusted hook while
on a trusted branch, then switches to an untrusted feature branch
(possibly from a fork) to review proposed changes. If the untrusted
feature branch contains a malicious `bash.exe` and the user's current
working directory is the working tree, and the user performs an action
that runs the hook, then although the hook itself is uncorrupted, it
runs with the malicious `bash.exe`.

Note that, while `bash.exe` is a shell, this is a separate scenario from
when `git` is run using the unrelated Windows `cmd.exe` shell.

### PoC

On Windows, create a `git.exe` file in a repository. Then create a
`Repo` object, and call any method through it (directly or indirectly)
that supports the `shell` keyword argument with `shell=True`:

```powershell
mkdir testrepo
git init testrepo
cp ... testrepo git.exe # Replace "..." with any executable of choice.
python -c "import git; print(git.Repo('testrepo').git.version(shell=True))"
```

The `git.exe` executable in the repository directory will be run.

Or use no `Repo` object, but do it from the location with the `git.exe`:

```powershell
cd testrepo
python -c "import git; print(git.Git().version(shell=True))"
```

The `git.exe` executable in the current directory will be run.

For the scenario with hooks, install a hook in a repository, create a
`bash.exe` file in the current directory, and perform an operation that
causes GitPython to attempt to run the hook:

```powershell
mkdir testrepo
cd testrepo
git init
mv .git/hooks/pre-commit.sample .git/hooks/pre-commit
cp ... bash.exe # Replace "..." with any executable of choice.
echo "Some text" >file.txt
git add file.txt
python -c "import git; git.Repo().index.commit('Some message')"
```

The `bash.exe` executable in the current directory will be run.

### Impact

The greatest impact is probably in applications that set `Git.USE_SHELL
= True` for historical reasons. (Undesired console windows had, in the
past, been created in some kinds of applications, when it was not used.)
Such an application may be vulnerable to arbitrary code execution from a
malicious repository, even with no other exacerbating conditions. This
is to say that, if a shell is used to run `git`, the full effect of
CVE-2023-40590 is still present. Furthermore, as noted above, running
the application itself from a trusted directory is not a sufficient
mitigation.

An application that does not direct GitPython to use a shell to run
`git` subprocesses thus avoids most of the risk. However, there is no
such straightforward way to prevent GitPython from running `bash.exe` to
interpret hooks. So while the conditions needed for that to be exploited
are more involved, it may be harder to mitigate decisively prior to
patching.

### Possible solutions

A straightforward approach would be to address each bug directly:

- When a shell is used, pass `NoDefaultCurrentDirectoryInExePath` into
the subprocess environment, because in that scenario the subprocess is
the `cmd.exe` shell that itself performs the path search.
- Set `NoDefaultCurrentDirectoryInExePath` in the GitPython process
environment during the `Popen` call made to run hooks with a `bash.exe`
subprocess.

These need only be done on Windows.

---

### Release Notes

<details>
<summary>gitpython-developers/GitPython (GitPython)</summary>

###
[`v3.1.41`](https://togithub.com/gitpython-developers/GitPython/releases/tag/3.1.41):
- fix Windows security issue

[Compare
Source](https://togithub.com/gitpython-developers/GitPython/compare/3.1.40...3.1.41)

The details about the Windows security issue [can be found in this
advisory](https://togithub.com/gitpython-developers/GitPython/security/advisories/GHSA-2mqj-m65w-jghx).

Special thanks go to
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) who reported the
issue and fixed it in a single stroke, while being responsible for an
incredible amount of improvements that he contributed over the last
couple of months ❤️.

#### What's Changed

- Add `__all__` in git.exc by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1719](https://togithub.com/gitpython-developers/GitPython/pull/1719)
- Set submodule update cadence to weekly by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1721](https://togithub.com/gitpython-developers/GitPython/pull/1721)
- Never modify sys.path by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1720](https://togithub.com/gitpython-developers/GitPython/pull/1720)
- Bump git/ext/gitdb from `8ec2390` to `ec58b7e` by
[@&#8203;dependabot](https://togithub.com/dependabot) in
[https://github.com/gitpython-developers/GitPython/pull/1722](https://togithub.com/gitpython-developers/GitPython/pull/1722)
- Revise comments, docstrings, some messages, and a bit of code by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1725](https://togithub.com/gitpython-developers/GitPython/pull/1725)
- Use zero-argument super() by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1726](https://togithub.com/gitpython-developers/GitPython/pull/1726)
- Remove obsolete note in \_iter_packed_refs by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1727](https://togithub.com/gitpython-developers/GitPython/pull/1727)
- Reorganize test_util and make xfail marks precise by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1729](https://togithub.com/gitpython-developers/GitPython/pull/1729)
- Clarify license and make module top comments more consistent by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1730](https://togithub.com/gitpython-developers/GitPython/pull/1730)
- Deprecate compat.is\_<platform>, rewriting all uses by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1732](https://togithub.com/gitpython-developers/GitPython/pull/1732)
- Revise and restore some module docstrings by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1735](https://togithub.com/gitpython-developers/GitPython/pull/1735)
- Make the rmtree callback Windows-only by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1739](https://togithub.com/gitpython-developers/GitPython/pull/1739)
- List all non-passing tests in test summaries by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1740](https://togithub.com/gitpython-developers/GitPython/pull/1740)
- Document some minor subtleties in test_util.py by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1749](https://togithub.com/gitpython-developers/GitPython/pull/1749)
- Always read metadata files as UTF-8 in setup.py by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1748](https://togithub.com/gitpython-developers/GitPython/pull/1748)
- Test native Windows on CI by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1745](https://togithub.com/gitpython-developers/GitPython/pull/1745)
- Test macOS on CI by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1752](https://togithub.com/gitpython-developers/GitPython/pull/1752)
- Let close_fds be True on all platforms by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1753](https://togithub.com/gitpython-developers/GitPython/pull/1753)
- Fix IndexFile.from_tree on Windows by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1751](https://togithub.com/gitpython-developers/GitPython/pull/1751)
- Remove unused TASKKILL fallback in AutoInterrupt by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1754](https://togithub.com/gitpython-developers/GitPython/pull/1754)
- Don't return with operand when conceptually void by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1755](https://togithub.com/gitpython-developers/GitPython/pull/1755)
- Group .gitignore entries by purpose by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1758](https://togithub.com/gitpython-developers/GitPython/pull/1758)
- Adding dubious ownership handling by
[@&#8203;marioaag](https://togithub.com/marioaag) in
[https://github.com/gitpython-developers/GitPython/pull/1746](https://togithub.com/gitpython-developers/GitPython/pull/1746)
- Avoid brittle assumptions about preexisting temporary files in tests
by [@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1759](https://togithub.com/gitpython-developers/GitPython/pull/1759)
- Overhaul noqa directives by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1760](https://togithub.com/gitpython-developers/GitPython/pull/1760)
- Clarify some Git.execute kill_after_timeout limitations by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1761](https://togithub.com/gitpython-developers/GitPython/pull/1761)
- Bump actions/setup-python from 4 to 5 by
[@&#8203;dependabot](https://togithub.com/dependabot) in
[https://github.com/gitpython-developers/GitPython/pull/1763](https://togithub.com/gitpython-developers/GitPython/pull/1763)
- Don't install black on Cygwin by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1766](https://togithub.com/gitpython-developers/GitPython/pull/1766)
- Extract all "import gc" to module level by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1765](https://togithub.com/gitpython-developers/GitPython/pull/1765)
- Extract remaining local "import gc" to module level by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1768](https://togithub.com/gitpython-developers/GitPython/pull/1768)
- Replace xfail with gc.collect in TestSubmodule.test_rename by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1767](https://togithub.com/gitpython-developers/GitPython/pull/1767)
- Enable CodeQL by [@&#8203;EliahKagan](https://togithub.com/EliahKagan)
in
[https://github.com/gitpython-developers/GitPython/pull/1769](https://togithub.com/gitpython-developers/GitPython/pull/1769)
- Replace some uses of the deprecated mktemp function by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1770](https://togithub.com/gitpython-developers/GitPython/pull/1770)
- Bump github/codeql-action from 2 to 3 by
[@&#8203;dependabot](https://togithub.com/dependabot) in
[https://github.com/gitpython-developers/GitPython/pull/1773](https://togithub.com/gitpython-developers/GitPython/pull/1773)
- Run some Windows environment variable tests only on Windows by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1774](https://togithub.com/gitpython-developers/GitPython/pull/1774)
- Fix TemporaryFileSwap regression where file_path could not be Path by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1776](https://togithub.com/gitpython-developers/GitPython/pull/1776)
- Improve hooks tests by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1777](https://togithub.com/gitpython-developers/GitPython/pull/1777)
- Fix if items of Index is of type PathLike by
[@&#8203;stegm](https://togithub.com/stegm) in
[https://github.com/gitpython-developers/GitPython/pull/1778](https://togithub.com/gitpython-developers/GitPython/pull/1778)
- Better document IterableObj.iter_items and improve some subclasses by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1780](https://togithub.com/gitpython-developers/GitPython/pull/1780)
- Revert "Don't install black on Cygwin" by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1783](https://togithub.com/gitpython-developers/GitPython/pull/1783)
- Add missing pip in $PATH on Cygwin CI by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1784](https://togithub.com/gitpython-developers/GitPython/pull/1784)
- Shorten Iterable docstrings and put IterableObj first by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1785](https://togithub.com/gitpython-developers/GitPython/pull/1785)
- Fix incompletely revised Iterable/IterableObj docstrings by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1786](https://togithub.com/gitpython-developers/GitPython/pull/1786)
- Pre-deprecate setting Git.USE_SHELL by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1782](https://togithub.com/gitpython-developers/GitPython/pull/1782)
- Deprecate Git.USE_SHELL by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1787](https://togithub.com/gitpython-developers/GitPython/pull/1787)
- In handle_process_output don't forward finalizer result by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1788](https://togithub.com/gitpython-developers/GitPython/pull/1788)
- Fix mypy warning "Missing return statement" by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1789](https://togithub.com/gitpython-developers/GitPython/pull/1789)
- Fix two remaining Windows untrusted search path cases by
[@&#8203;EliahKagan](https://togithub.com/EliahKagan) in
[https://github.com/gitpython-developers/GitPython/pull/1792](https://togithub.com/gitpython-developers/GitPython/pull/1792)

#### New Contributors

- [@&#8203;marioaag](https://togithub.com/marioaag) made their first
contribution in
[https://github.com/gitpython-developers/GitPython/pull/1746](https://togithub.com/gitpython-developers/GitPython/pull/1746)
- [@&#8203;stegm](https://togithub.com/stegm) made their first
contribution in
[https://github.com/gitpython-developers/GitPython/pull/1778](https://togithub.com/gitpython-developers/GitPython/pull/1778)

**Full Changelog**:
gitpython-developers/GitPython@3.1.40...3.1.41

</details>

---

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