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eddieran wants to merge 1 commit into from
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Validate log_file paths to prevent arbitrary file writes #3656

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18 changes: 17 additions & 1 deletion pre_commit/clientlib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,22 @@

check_string_regex = cfgv.check_and(cfgv.check_string, cfgv.check_regex)


def _check_log_file(val: str) -> None:
if val == '':
return
if os.path.isabs(val):
raise cfgv.ValidationError(
f'log_file must be a relative path, got absolute path: {val!r}',
)
if os.path.normpath(val).startswith('..'):
raise cfgv.ValidationError(
f'log_file must not reference a parent directory: {val!r}',
)


check_log_file = cfgv.check_and(cfgv.check_string, _check_log_file)

HOOK_TYPES = (
'commit-msg',
'post-checkout',
Expand Down Expand Up @@ -258,7 +274,7 @@ def check(self, dct: dict[str, Any]) -> None:
cfgv.Optional('pass_filenames', cfgv.check_bool, True),
cfgv.Optional('description', cfgv.check_string, ''),
cfgv.Optional('language_version', cfgv.check_string, C.DEFAULT),
cfgv.Optional('log_file', cfgv.check_string, ''),
cfgv.Optional('log_file', check_log_file, ''),
cfgv.Optional('require_serial', cfgv.check_bool, False),
StagesMigration('stages', []),
cfgv.Optional('verbose', cfgv.check_bool, False),
Expand Down
20 changes: 20 additions & 0 deletions tests/clientlib_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
import pytest

import pre_commit.constants as C
from pre_commit.clientlib import _check_log_file
from pre_commit.clientlib import check_type_tag
from pre_commit.clientlib import CONFIG_HOOK_DICT
from pre_commit.clientlib import CONFIG_REPO_DICT
Expand Down Expand Up @@ -605,3 +606,22 @@ def test_manifest_v5_forward_compat(tmp_path):
f'=====> pre-commit version 5 is required but version {C.VERSION} '
f'is installed. Perhaps run `pip install --upgrade pre-commit`.'
)


@pytest.mark.parametrize('value', ('output.log', 'logs/hook.log', ''))
def test_check_log_file_valid(value):
_check_log_file(value)


@pytest.mark.parametrize(
'value',
(
'/tmp/evil.log',
'/etc/cron.d/malicious',
'../../../etc/passwd',
'../outside.log',
),
)
def test_check_log_file_invalid(value):
with pytest.raises(cfgv.ValidationError):
_check_log_file(value)
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