Check the .fc files for common typos
Writing .fc files without any mistake is quite hard. Sometimes a regular
expression pattern compiles fine but it does not match what is intended.
Add a script that detects some issues in .fc files. When this script is
used directly ("./testing/check_fc_files.py"), it checks the content of
policy/. The path to policy/ can also be provided by option -p.
Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
This commit is contained in:
Nicolas Iooss
parent
6b11dcef89
commit
f9deb94ba4
3
INSTALL
3
INSTALL
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@ -6,6 +6,9 @@ Reference Policy has the following build requirements:
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* Python >= 3.4
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* GCC
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When developing a policy, running scripts from directory testing/ requires:
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* Python >= 3.6
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To install Reference Policy sources into /etc/selinux/refpolicy/src/policy:
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make install-src
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@ -0,0 +1,307 @@
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#!/usr/bin/env python3
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# -*- coding:UTF-8 -*-
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# Copyright (C) 2019 Nicolas Iooss
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, version 2.
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#
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# This program is distributed in the hope that it will be useful, but WITHOUT
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# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
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# details.
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"""Check the .fc files for some common errors
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@author: Nicolas Iooss
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@license: GPLv2
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"""
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import argparse
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from pathlib import Path
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import re
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# Common patterns for ending a file pattern, associated with something to
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# replace the pattern with, during the checks.
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# Order matters as the first ones are tried before the last ones
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#
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# Use the infinity symbol to replace "any character", in order to keep a meaning
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# of any possible character in the pattern after the reduction operations.
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COMMON_FILE_END_PATTERNS = (
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('/.+', ''), # Match the children of a directory
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('/.*', ''), # Like /.+, but it could be empty
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('(/.*)', ''), # Like /.*, but with useless parentheses
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('/[^/]+', ''), # Match any filename
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('/[^/]*', ''), # Match any filename, but it could be empty
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('(/[^/]*)', ''), # Like /[^/]*, but with useless parentheses
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('(/[^/]*)?', ''), # Match a directory and its direct children
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('(/.+)?', ''), # Match a directory and its children
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('(/.*)?', ''), # Match a directory and its children
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('/(sbin/)?.*', ''), # Weird pattern for postfix, which would better be (/sbin)?(/.*)?
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('\\.so(\\.[^/]*)*', '\\.so'), # Match a .so extension, which is really weird because [^/] matches a dot too, so the final star can be replaced with '?' # noqa
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('\\.db(\\.[^/]*)*', '\\.db'), # Match a .db extension, which is really weird because [^/] matches a dot too, so the final star can be replaced with '?' # noqa
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('(\\.[^/]+)?', ''), # Match a possible file extension
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('(\\..+)', '\\.∞'), # Match a dot and anything after
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('(\\..*)?', '\\.∞'), # Match a dot and anything after or nothing, or nothing at all
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('\\..*', '\\.'), # Match a dot and anything after or nothing
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('.*', ''), # Match anything after
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('.+', '∞'), # Match anything after, but at least one character
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('[^/]+', '∞'), # Match anything after which does not create a new directory level
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('[^/]*', ''), # Like [^/]+, but may be empty
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('[^/-]*', ''), # Like [^/]*, but do not match files with dashes in their names
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('[a-z]?', ''), # Match a possible letter
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('[a-z]*', ''), # Match some letters
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('[0-9]?', ''), # Match a possible digit
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('[0-9]*', ''), # Match some digits
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('[0-9]+', '0'), # Match at least one digit
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('(\\.bin)?', ''), # Match an optional extension
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('(-.*)?', ''), # Match an optional suffix with a minus sign
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)
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# File types in a .fc file
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FILE_TYPES = (None, '--', '-b', '-c', '-d', '-l', '-p', '-s')
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NONE_CONTEXT = '<<none>>'
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MLS_LEVELS = ('s0', 'mls_systemhigh', 's0-mls_systemhigh')
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def analyze_fc_file(fc_path):
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"""Analyze a .fc file
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Return False if a warning has been generated
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"""
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retval = True
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with fc_path.open('r') as fd:
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for lineno, line in enumerate(fd, start=1):
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line = line.strip()
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# Ignore lines that cannot contain a file context
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if not line or line.startswith(('#', "'", 'ifdef(', 'ifndef(')):
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continue
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prefix = f"{fc_path}:{lineno}: "
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matches = re.match(r'^(?P<path>\S+)\s+(?P<ftype>-.)?\s*(?P<context>.+)$', line)
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if matches is None:
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print(f"{prefix}unable to parse a file context file: {repr(line)}")
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retval = False
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continue
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path, ftype, context = matches.group('path', 'ftype', 'context')
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# Check the file type of the pattern
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if ftype not in FILE_TYPES:
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print(f"{prefix}unexpected file type for {path}: {repr(ftype)}")
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retval = False
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# Check the SELinux context
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if context != NONE_CONTEXT:
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matches = re.match(r'^gen_context\((\S*), ?(\S*)\)$', context)
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if not matches:
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print(f"{prefix}unknown SELinux context format for {path}: {context}")
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retval = False
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else:
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context_label, context_mls = matches.groups()
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if not context_label.startswith('system_u:object_r:'):
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print(f"{prefix}SELinux context does not begin with 'system_u:object_r:' for {path}: {context}") # noqa
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retval = False
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elif not re.match(r'^system_u:object_r:[0-9A-Za-z_]+$', context_label):
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print(f"{prefix}SELinux context type uses unexpected characters for {path}: {context}") # noqa
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retval = False
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elif context_mls not in MLS_LEVELS:
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print(f"{prefix}SELinux context uses an unexpected MLS label for {path}: {context_mls} (in {context})") # noqa
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retval = False
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# Find obviously-wrong patterns
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if '(.*)?' in path:
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# As (.*) can match the empty string, the question mark is redundant
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print(f"{prefix}pattern (.*)? is very likely to be a misspelling for .* or (/.*)?, for {path}")
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retval = False
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if '\\d' in path:
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# In the past, "resource.\d" has already been introduced instead of "resource\.d".
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# Detect such bugs by forbidding the use of \d
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print(f"{prefix}escaping d could be a bug in {path}, please use [0-9] instead")
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retval = False
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if re.search(r'[^/]\(\.\*/\)\?', path):
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print(f"{prefix}using (.*/)? without a previous slash could be a bug in {path} as it can match the empty string, please use /(.*/)? instead") # noqa
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retval = False
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if re.search(r'[^/]\(\.\*/\)\*', path):
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print(f"{prefix}using (.*/)* without a previous slash could be a bug in {path} as it can match the empty string, please use /(.*/)* instead") # noqa
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retval = False
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if re.search(r'\(\.\*/\)[^?*+]', path):
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print(f"{prefix}using (.*/) without a ?, * or + symbol could be a bug in {path} as it misleads readers into thinking that this part is optional, please use .*/ instead") # noqa
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retval = False
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reduced_path = path
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# Using "index`'(...)" is a way to prevent an error message from m4:
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# https://github.com/SELinuxProject/refpolicy/commit/cc1eee120263523c7b79ac16acc698c537a4d25e
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# Let's replace the symbols in the path, for the checks,
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# while keeping "path" untouched in the warning messages
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reduced_path = reduced_path.replace("index`'(", 'index(')
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reduced_path = reduced_path.replace("inde(x)(", 'index(')
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reduced_path = reduced_path.replace("include`'(", 'include(')
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# Check the character set of the path
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invalid_characters = set(re.findall(r'[^-0-9A-Za-z_./()?+*%{}\[\]^|:~\\]', reduced_path))
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if invalid_characters:
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print(f"{prefix}unexpected characters {' '.join(sorted(invalid_characters))} in {path}")
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retval = False
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# Check the start of the path
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if not path.startswith(('/', 'HOME_DIR/', 'HOME_ROOT/')) and path not in ('HOME_DIR', 'HOME_ROOT'):
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print(f"{prefix}unexpected start of file pattern for {path}")
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retval = False
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# Reduce the path in order to check its sanity (like using a non-buggy end pattern):
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# * Truncating common endings
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while True:
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has_truncated = False
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for (common_end, substitute) in COMMON_FILE_END_PATTERNS:
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if reduced_path.endswith(common_end):
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reduced_path = f"{reduced_path[:-len(common_end)]}{substitute}"
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has_truncated = True
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break
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if not has_truncated:
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break
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# * Replace back-slashed characters with special ones
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while '\\' in reduced_path:
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backslash_index = reduced_path.index('\\')
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esc_sequence = reduced_path[backslash_index:backslash_index + 2]
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if esc_sequence == '\\.':
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# Replace \. with U+00B7 middle dot
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reduced_path = f"{reduced_path[:backslash_index]}\u00b7{reduced_path[backslash_index + 2:]}"
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elif esc_sequence == '\\+':
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# Replace \+ with U+2020 dagger
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reduced_path = f"{reduced_path[:backslash_index]}\u2020{reduced_path[backslash_index + 2:]}"
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elif esc_sequence == '\\d':
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# Replace \d with U+03B4 delta
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reduced_path = f"{reduced_path[:backslash_index]}\u03b4{reduced_path[backslash_index + 2:]}"
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else:
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print(f"{prefix}unexpected escape sequence {esc_sequence} in {path} (reduced to {reduced_path})")
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retval = False
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break
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# * Replace variables with place-holders
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if '%' in reduced_path:
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reduced_path = reduced_path.replace('%{USERID}', '_USERID_')
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reduced_path = reduced_path.replace('%{USERNAME}', '_USERNAME_')
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if '%{' in reduced_path:
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print(f"{prefix}unexpected '%{{' in {path} after reduction to {reduced_path}")
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retval = False
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# * Detect "??", "**", etc. before more reductions occur
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for bad_pattern in sorted(set(re.findall(r'[?*+][?*+]', reduced_path))):
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print(f"{prefix}unexpected pattern {repr(bad_pattern)} in {path} after reduction to {reduced_path}")
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retval = False
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# Remove optional directories and filename parts
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reduced_path = reduced_path.replace('[^/]*', '')
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reduced_path = reduced_path.replace('[^/]+', '∞')
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reduced_path = reduced_path.replace('[^/-]+', '∞')
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reduced_path = reduced_path.replace('/(.*/)?', '/')
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reduced_path = reduced_path.replace('(/.*)?', '')
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reduced_path = reduced_path.replace('/.*/', '/')
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# * Remove parenthesese around choices options: ((www)|(web)|(public_html)) -> (www|web|public_html)
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while True:
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new_reduced_path = re.sub(r'([|(])\(([-0-9A-Za-z_]+)\)([|)])', r'\1\2\3', reduced_path)
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if new_reduced_path == reduced_path:
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break
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reduced_path = new_reduced_path
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# * Detect a pipe directly inside a parenthesis, which is wrong (use symbol ? instead)
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if '|)' in reduced_path or '(|' in reduced_path:
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print(f"{prefix}unexpected pipe-parenthesis pattern in {path} after reduction to {reduced_path}")
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retval = False
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# * Remove optional choices (...|...)?
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while True:
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new_reduced_path = re.sub(r'\([-0-9A-Za-z_|/·]+\)\?', '', reduced_path)
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if new_reduced_path == reduced_path:
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break
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reduced_path = new_reduced_path
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# * Replace mandatory choices (...|...) with the first option
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while True:
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new_reduced_path = re.sub(r'\(([-0-9A-Za-z_/]+)\|[-0-9A-Za-z_|/]+\)', r'\1', reduced_path)
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if new_reduced_path == reduced_path:
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break
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reduced_path = new_reduced_path
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# * Remove optional characters like c?
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reduced_path = re.sub(r'[-0-9A-Za-z_·]\?', '', reduced_path)
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# If the reduced path still ends with a special character, something went wrong.
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# Instead of guessing the possible buggy characters, list the allowed ones.
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if reduced_path and not re.match(r'[-0-9A-Za-z_\]~ᠰ]', reduced_path[-1]):
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if path != '/':
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if reduced_path == path:
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print(f"{prefix}unexpected end of file pattern for {path}")
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else:
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print(f"{prefix}unexpected end of file pattern for {path} after being reduced to {reduced_path}") # noqa
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retval = False
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# Now remove and replace some matching patterns from the path, in order to catch invalid characters
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reduced_path = reduced_path.replace('(-.*)?', '')
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reduced_path = reduced_path.replace('(.*-)?', '')
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reduced_path = reduced_path.replace('(-[0-9])?', '')
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reduced_path = reduced_path.replace('(.*)', '')
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reduced_path = reduced_path.replace('.*', '')
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reduced_path = reduced_path.replace('.+', '∞')
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reduced_path = re.sub(r'\[[-0-9A-Za-z_.^]+\][?*]', '', reduced_path)
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reduced_path = re.sub(r'\[[-0-9A-Za-z_.^]+\](\+)?', '∞', reduced_path)
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reduced_path = reduced_path.replace('/[^/]+/', '/∞/')
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if '.' in reduced_path:
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print(f"{prefix}unescaped dot still present {path} after being reduced to {reduced_path} (suggestion: use \\. to match a dot, or a charset like [^/])") # noqa
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retval = False
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# Check the remaining symbols in the reduced path.
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# Only show a warning if no other ones were reported, in order to reduce the probability of false-positive.
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invalid_symbols = set(re.findall(r'[^-0-9A-Za-z_~:ᠰ/]', reduced_path))
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if retval and invalid_symbols:
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print(f"{prefix}unexpected symbols {' '.join(sorted(invalid_symbols))} in {path} after being reduced to {reduced_path}. This could be due to an error in the pattern or a missing reduction rule in the checker") # noqa
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retval = False
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return retval
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def analyze_all_fc(policy_dirpath):
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"""Analyze all .fc files in the specified directory"""
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retval = True
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for file_path in sorted(policy_dirpath.glob('**/*.fc')):
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if not analyze_fc_file(file_path):
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retval = False
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return retval
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def main(argv=None):
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policy_dir = (Path(__file__).parent / '..' / 'policy').resolve()
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parser = argparse.ArgumentParser(description="Find missing file contexts")
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parser.add_argument('fc_files', metavar='FC_FILES', nargs='*', type=Path,
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help=".fc files to analyze (by default: all in the policy)")
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parser.add_argument('-p', '--policy', metavar='POLICY_DIR', type=Path, default=policy_dir,
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help="path to the policy directory [{0}]".format(policy_dir))
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args = parser.parse_args(argv)
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if args.fc_files:
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retval = True
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for file_path in args.fc_files:
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if not analyze_fc_file(file_path):
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retval = False
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return retval
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return 0 if analyze_all_fc(args.policy) else 1
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if __name__ == '__main__':
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import sys
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sys.exit(main())
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Reference in New Issue