195 lines
7.3 KiB
Python
Executable file
195 lines
7.3 KiB
Python
Executable file
#!/usr/bin/env python3
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#
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# Copyright The Mbed TLS Contributors
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# SPDX-License-Identifier: Apache-2.0
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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#
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"""
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Make fuzz like testing for pkcs7 tests
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Given a valid DER pkcs7 file add tests to the test_suite_pkcs7.data file
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- It is expected that the pkcs7_asn1_fail( data_t *pkcs7_buf )
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function is defined in test_suite_pkcs7.function
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- This is not meant to be portable code, if anything it is meant to serve as
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documentation for showing how those ugly tests in test_suite_pkcs7.data were created
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"""
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import sys
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from os.path import exists
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PKCS7_TEST_FILE = "../suites/test_suite_pkcs7.data"
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class Test: # pylint: disable=too-few-public-methods
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"""
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A instance of a test in test_suite_pkcs7.data
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"""
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def __init__(self, name, depends, func_call):
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self.name = name
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self.depends = depends
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self.func_call = func_call
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# pylint: disable=no-self-use
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def to_string(self):
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return "\n" + self.name + "\n" + self.depends + "\n" + self.func_call + "\n"
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class TestData:
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"""
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Take in test_suite_pkcs7.data file.
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Allow for new tests to be added.
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"""
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mandatory_dep = "MBEDTLS_SHA256_C"
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test_name = "PKCS7 Parse Failure Invalid ASN1"
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test_function = "pkcs7_asn1_fail:"
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def __init__(self, file_name):
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self.file_name = file_name
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self.last_test_num, self.old_tests = self.read_test_file(file_name)
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self.new_tests = []
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# pylint: disable=no-self-use
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def read_test_file(self, file):
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"""
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Parse the test_suite_pkcs7.data file.
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"""
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tests = []
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if not exists(file):
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print(file + " Does not exist")
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sys.exit()
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with open(file, "r", encoding='UTF-8') as fp:
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data = fp.read()
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lines = [line.strip() for line in data.split('\n') if len(line.strip()) > 1]
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i = 0
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while i < len(lines):
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if "depends" in lines[i+1]:
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tests.append(Test(lines[i], lines[i+1], lines[i+2]))
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i += 3
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else:
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tests.append(Test(lines[i], None, lines[i+1]))
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i += 2
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latest_test_num = float(tests[-1].name.split('#')[1])
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return latest_test_num, tests
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def add(self, name, func_call):
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self.last_test_num += 1
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self.new_tests.append(Test(self.test_name + ": " + name + " #" + \
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str(self.last_test_num), "depends_on:" + self.mandatory_dep, \
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self.test_function + '"' + func_call + '"'))
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def write_changes(self):
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with open(self.file_name, 'a', encoding='UTF-8') as fw:
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fw.write("\n")
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for t in self.new_tests:
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fw.write(t.to_string())
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def asn1_mutate(data):
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"""
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We have been given an asn1 structure representing a pkcs7.
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We want to return an array of slightly modified versions of this data
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they should be modified in a way which makes the structure invalid
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We know that asn1 structures are:
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|---1 byte showing data type---|----byte(s) for length of data---|---data content--|
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We know that some data types can contain other data types.
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Return a dictionary of reasons and mutated data types.
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"""
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# off the bat just add bytes to start and end of the buffer
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mutations = []
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reasons = []
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mutations.append(["00"] + data)
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reasons.append("Add null byte to start")
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mutations.append(data + ["00"])
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reasons.append("Add null byte to end")
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# for every asn1 entry we should attempt to:
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# - change the data type tag
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# - make the length longer than actual
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# - make the length shorter than actual
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i = 0
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while i < len(data):
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tag_i = i
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leng_i = tag_i + 1
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data_i = leng_i + 1 + (int(data[leng_i][1], 16) if data[leng_i][0] == '8' else 0)
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if data[leng_i][0] == '8':
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length = int(''.join(data[leng_i + 1: data_i]), 16)
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else:
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length = int(data[leng_i], 16)
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tag = data[tag_i]
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print("Looking at ans1: offset " + str(i) + " tag = " + tag + \
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", length = " + str(length)+ ":")
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print(''.join(data[data_i:data_i+length]))
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# change tag to something else
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if tag == "02":
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# turn integers into octet strings
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new_tag = "04"
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else:
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# turn everything else into an integer
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new_tag = "02"
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mutations.append(data[:tag_i] + [new_tag] + data[leng_i:])
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reasons.append("Change tag " + tag + " to " + new_tag)
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# change lengths to too big
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# skip any edge cases which would cause carry over
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if int(data[data_i - 1], 16) < 255:
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new_length = str(hex(int(data[data_i - 1], 16) + 1))[2:]
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if len(new_length) == 1:
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new_length = "0"+new_length
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mutations.append(data[:data_i -1] + [new_length] + data[data_i:])
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reasons.append("Change length from " + str(length) + " to " \
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+ str(length + 1))
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# we can add another test here for tags that contain other tags \
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# where they have more data than there containing tags account for
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if tag in ["30", "a0", "31"]:
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mutations.append(data[:data_i -1] + [new_length] + \
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data[data_i:data_i + length] + ["00"] + \
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data[data_i + length:])
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reasons.append("Change contents of tag " + tag + " to contain \
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one unaccounted extra byte")
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# change lengths to too small
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if int(data[data_i - 1], 16) > 0:
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new_length = str(hex(int(data[data_i - 1], 16) - 1))[2:]
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if len(new_length) == 1:
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new_length = "0"+new_length
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mutations.append(data[:data_i -1] + [new_length] + data[data_i:])
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reasons.append("Change length from " + str(length) + " to " + str(length - 1))
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# some tag types contain other tag types so we should iterate into the data
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if tag in ["30", "a0", "31"]:
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i = data_i
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else:
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i = data_i + length
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return list(zip(reasons, mutations))
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if __name__ == "__main__":
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if len(sys.argv) < 2:
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print("USAGE: " + sys.argv[0] + " <pkcs7_der_file>")
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sys.exit()
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DATA_FILE = sys.argv[1]
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TEST_DATA = TestData(PKCS7_TEST_FILE)
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with open(DATA_FILE, 'rb') as f:
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DATA_STR = f.read().hex()
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# make data an array of byte strings eg ['de','ad','be','ef']
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HEX_DATA = list(map(''.join, [[DATA_STR[i], DATA_STR[i+1]] for i in range(0, len(DATA_STR), \
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2)]))
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# returns tuples of test_names and modified data buffers
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MUT_ARR = asn1_mutate(HEX_DATA)
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print("made " + str(len(MUT_ARR)) + " new tests")
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for new_test in MUT_ARR:
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TEST_DATA.add(new_test[0], ''.join(new_test[1]))
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TEST_DATA.write_changes()
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