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| 1 | +#!/usr/bin/env python3 |
| 2 | +# |
| 3 | +# Copyright The Mbed TLS Contributors |
| 4 | +# SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later |
| 5 | +# |
| 6 | + |
| 7 | +""" |
| 8 | +Make fuzz like testing for pkcs7 tests |
| 9 | +Given a valid DER pkcs7 file add tests to the test_suite_pkcs7.data file |
| 10 | + - It is expected that the pkcs7_asn1_fail( data_t *pkcs7_buf ) |
| 11 | + function is defined in test_suite_pkcs7.function |
| 12 | + - This is not meant to be portable code, if anything it is meant to serve as |
| 13 | + documentation for showing how those ugly tests in test_suite_pkcs7.data were created |
| 14 | +""" |
| 15 | + |
| 16 | + |
| 17 | +import sys |
| 18 | +from os.path import exists |
| 19 | + |
| 20 | +PKCS7_TEST_FILE = "../suites/test_suite_pkcs7.data" |
| 21 | + |
| 22 | +class Test: # pylint: disable=too-few-public-methods |
| 23 | + """ |
| 24 | + A instance of a test in test_suite_pkcs7.data |
| 25 | + """ |
| 26 | + def __init__(self, name, depends, func_call): |
| 27 | + self.name = name |
| 28 | + self.depends = depends |
| 29 | + self.func_call = func_call |
| 30 | + |
| 31 | + # pylint: disable=no-self-use |
| 32 | + def to_string(self): |
| 33 | + return "\n" + self.name + "\n" + self.depends + "\n" + self.func_call + "\n" |
| 34 | + |
| 35 | +class TestData: |
| 36 | + """ |
| 37 | + Take in test_suite_pkcs7.data file. |
| 38 | + Allow for new tests to be added. |
| 39 | + """ |
| 40 | + mandatory_dep = "MBEDTLS_MD_CAN_SHA256" |
| 41 | + test_name = "PKCS7 Parse Failure Invalid ASN1" |
| 42 | + test_function = "pkcs7_asn1_fail:" |
| 43 | + def __init__(self, file_name): |
| 44 | + self.file_name = file_name |
| 45 | + self.last_test_num, self.old_tests = self.read_test_file(file_name) |
| 46 | + self.new_tests = [] |
| 47 | + |
| 48 | + # pylint: disable=no-self-use |
| 49 | + def read_test_file(self, file): |
| 50 | + """ |
| 51 | + Parse the test_suite_pkcs7.data file. |
| 52 | + """ |
| 53 | + tests = [] |
| 54 | + if not exists(file): |
| 55 | + print(file + " Does not exist") |
| 56 | + sys.exit() |
| 57 | + with open(file, "r", encoding='UTF-8') as fp: |
| 58 | + data = fp.read() |
| 59 | + lines = [line.strip() for line in data.split('\n') if len(line.strip()) > 1] |
| 60 | + i = 0 |
| 61 | + while i < len(lines): |
| 62 | + if "depends" in lines[i+1]: |
| 63 | + tests.append(Test(lines[i], lines[i+1], lines[i+2])) |
| 64 | + i += 3 |
| 65 | + else: |
| 66 | + tests.append(Test(lines[i], None, lines[i+1])) |
| 67 | + i += 2 |
| 68 | + latest_test_num = float(tests[-1].name.split('#')[1]) |
| 69 | + return latest_test_num, tests |
| 70 | + |
| 71 | + def add(self, name, func_call): |
| 72 | + self.last_test_num += 1 |
| 73 | + self.new_tests.append(Test(self.test_name + ": " + name + " #" + \ |
| 74 | + str(self.last_test_num), "depends_on:" + self.mandatory_dep, \ |
| 75 | + self.test_function + '"' + func_call + '"')) |
| 76 | + |
| 77 | + def write_changes(self): |
| 78 | + with open(self.file_name, 'a', encoding='UTF-8') as fw: |
| 79 | + fw.write("\n") |
| 80 | + for t in self.new_tests: |
| 81 | + fw.write(t.to_string()) |
| 82 | + |
| 83 | + |
| 84 | +def asn1_mutate(data): |
| 85 | + """ |
| 86 | + We have been given an asn1 structure representing a pkcs7. |
| 87 | + We want to return an array of slightly modified versions of this data |
| 88 | + they should be modified in a way which makes the structure invalid |
| 89 | +
|
| 90 | + We know that asn1 structures are: |
| 91 | + |---1 byte showing data type---|----byte(s) for length of data---|---data content--| |
| 92 | + We know that some data types can contain other data types. |
| 93 | + Return a dictionary of reasons and mutated data types. |
| 94 | + """ |
| 95 | + |
| 96 | + # off the bat just add bytes to start and end of the buffer |
| 97 | + mutations = [] |
| 98 | + reasons = [] |
| 99 | + mutations.append(["00"] + data) |
| 100 | + reasons.append("Add null byte to start") |
| 101 | + mutations.append(data + ["00"]) |
| 102 | + reasons.append("Add null byte to end") |
| 103 | + # for every asn1 entry we should attempt to: |
| 104 | + # - change the data type tag |
| 105 | + # - make the length longer than actual |
| 106 | + # - make the length shorter than actual |
| 107 | + i = 0 |
| 108 | + while i < len(data): |
| 109 | + tag_i = i |
| 110 | + leng_i = tag_i + 1 |
| 111 | + data_i = leng_i + 1 + (int(data[leng_i][1], 16) if data[leng_i][0] == '8' else 0) |
| 112 | + if data[leng_i][0] == '8': |
| 113 | + length = int(''.join(data[leng_i + 1: data_i]), 16) |
| 114 | + else: |
| 115 | + length = int(data[leng_i], 16) |
| 116 | + |
| 117 | + tag = data[tag_i] |
| 118 | + print("Looking at ans1: offset " + str(i) + " tag = " + tag + \ |
| 119 | + ", length = " + str(length)+ ":") |
| 120 | + print(''.join(data[data_i:data_i+length])) |
| 121 | + # change tag to something else |
| 122 | + if tag == "02": |
| 123 | + # turn integers into octet strings |
| 124 | + new_tag = "04" |
| 125 | + else: |
| 126 | + # turn everything else into an integer |
| 127 | + new_tag = "02" |
| 128 | + mutations.append(data[:tag_i] + [new_tag] + data[leng_i:]) |
| 129 | + reasons.append("Change tag " + tag + " to " + new_tag) |
| 130 | + |
| 131 | + # change lengths to too big |
| 132 | + # skip any edge cases which would cause carry over |
| 133 | + if int(data[data_i - 1], 16) < 255: |
| 134 | + new_length = str(hex(int(data[data_i - 1], 16) + 1))[2:] |
| 135 | + if len(new_length) == 1: |
| 136 | + new_length = "0"+new_length |
| 137 | + mutations.append(data[:data_i -1] + [new_length] + data[data_i:]) |
| 138 | + reasons.append("Change length from " + str(length) + " to " \ |
| 139 | + + str(length + 1)) |
| 140 | + # we can add another test here for tags that contain other tags \ |
| 141 | + # where they have more data than there containing tags account for |
| 142 | + if tag in ["30", "a0", "31"]: |
| 143 | + mutations.append(data[:data_i -1] + [new_length] + \ |
| 144 | + data[data_i:data_i + length] + ["00"] + \ |
| 145 | + data[data_i + length:]) |
| 146 | + reasons.append("Change contents of tag " + tag + " to contain \ |
| 147 | + one unaccounted extra byte") |
| 148 | + # change lengths to too small |
| 149 | + if int(data[data_i - 1], 16) > 0: |
| 150 | + new_length = str(hex(int(data[data_i - 1], 16) - 1))[2:] |
| 151 | + if len(new_length) == 1: |
| 152 | + new_length = "0"+new_length |
| 153 | + mutations.append(data[:data_i -1] + [new_length] + data[data_i:]) |
| 154 | + reasons.append("Change length from " + str(length) + " to " + str(length - 1)) |
| 155 | + |
| 156 | + # some tag types contain other tag types so we should iterate into the data |
| 157 | + if tag in ["30", "a0", "31"]: |
| 158 | + i = data_i |
| 159 | + else: |
| 160 | + i = data_i + length |
| 161 | + |
| 162 | + return list(zip(reasons, mutations)) |
| 163 | + |
| 164 | +if __name__ == "__main__": |
| 165 | + if len(sys.argv) < 2: |
| 166 | + print("USAGE: " + sys.argv[0] + " <pkcs7_der_file>") |
| 167 | + sys.exit() |
| 168 | + |
| 169 | + DATA_FILE = sys.argv[1] |
| 170 | + TEST_DATA = TestData(PKCS7_TEST_FILE) |
| 171 | + with open(DATA_FILE, 'rb') as f: |
| 172 | + DATA_STR = f.read().hex() |
| 173 | + # make data an array of byte strings eg ['de','ad','be','ef'] |
| 174 | + HEX_DATA = list(map(''.join, [[DATA_STR[i], DATA_STR[i+1]] for i in range(0, len(DATA_STR), \ |
| 175 | + 2)])) |
| 176 | + # returns tuples of test_names and modified data buffers |
| 177 | + MUT_ARR = asn1_mutate(HEX_DATA) |
| 178 | + |
| 179 | + print("made " + str(len(MUT_ARR)) + " new tests") |
| 180 | + for new_test in MUT_ARR: |
| 181 | + TEST_DATA.add(new_test[0], ''.join(new_test[1])) |
| 182 | + |
| 183 | + TEST_DATA.write_changes() |
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