test/pkcs7: Add more tests for better coverage
Add test calls to raw asn1 data with slight syntatical errors
Increases %branches covered from 70.4% to 87.7%.
Add a script which serves as documentation for how these new test
cases were generated:
./generate_pkcs7_tests.py ../data_files/pkcs7_data_cert_signed_sha256.der
./generate_pkcs7_tests.py ../data_files/pkcs7_data_multiple_signed.der
Signed-off-by: Nick Child <nick.child@ibm.com>
diff --git a/tests/scripts/generate_pkcs7_tests.py b/tests/scripts/generate_pkcs7_tests.py
new file mode 100755
index 0000000..ffc5343
--- /dev/null
+++ b/tests/scripts/generate_pkcs7_tests.py
@@ -0,0 +1,175 @@
+#!/usr/bin/env python3
+#
+# Copyright The Mbed TLS Contributors
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+"""
+Make fuzz like testing for pkcs7 tests
+Given a valid DER pkcs7 file add tests to the test_suite_pkcs7.data file
+ - It is expected that the pkcs7_asn1_fail( data_t *pkcs7_buf )
+ function is defined in test_suite_pkcs7.function
+ - This is not meant to be portable code, if anything it is meant to serve as
+ documentation for showing how those ugly tests in test_suite_pkcs7.data were created
+"""
+
+
+import sys
+from os.path import exists
+
+pkcs7_test_file = "../suites/test_suite_pkcs7.data"
+
+class Test:
+ def __init__(self, name, depends, func_call):
+ self.name = name
+ self.depends = depends
+ self.func_call = func_call
+
+ def to_string(self):
+ return f"\n{self.name}\n{self.depends}\n{self.func_call}\n"
+
+class TestData:
+ mandatory_dep = "MBEDTLS_SHA256_C"
+ test_name = "PKCS7 Parse Failure Invalid ASN1"
+ test_function = "pkcs7_asn1_fail:"
+ def __init__(self, file_name):
+ self.file_name = file_name
+ self.last_test_num, self.old_tests = self.read_test_file(file_name)
+ self.new_tests = []
+
+ def read_test_file(self, file):
+ tests = []
+ if not exists(file):
+ print(f"{file} Does not exist")
+ quit(1)
+ f = open(file, "r")
+ data = f.read()
+ f.close()
+ lines = [line.strip() for line in data.split('\n') if len(line.strip()) > 1]
+ i = 0
+ while i < len(lines):
+ if "depends" in lines[i+1]:
+ tests.append(Test(lines[i],lines[i+1], lines[i+2]))
+ i += 3
+ else:
+ tests.append(Test(lines[i], None, lines[i+1]))
+ i += 2
+ latest_test_num = float(tests[-1].name.split('#')[1])
+ return latest_test_num, tests
+
+ def add(self, name, func_call):
+ self.last_test_num += 1
+ self.new_tests.append(Test(f"{self.test_name}: {name} #{self.last_test_num}", f"depends_on:{self.mandatory_dep}", f'{self.test_function}"{func_call}"'))
+
+ def write_changes(self):
+ f = open(self.file_name, 'a')
+ f.write("\n")
+ for t in self.new_tests:
+ f.write(t.to_string())
+ f.close()
+
+
+def asn1_mutate(data):
+ mutations = []
+ reasons = []
+ # we have been given an asn1 structure representing a pkcs7
+ # we want to return an array of slightly modified versions of this data
+ # they should be modified in a way which makes the structure invalid
+
+ # we know that asn1 structures are:
+ # |---1 byte showing data type---|----byte(s) for length of data---|---data content--|
+ # we know that some data types can contain other data types
+
+ # off the bat just add bytes to start and end of the buffer
+ mutations.append(["00"] + data)
+ reasons.append("Add null byte to start")
+ mutations.append(data + ["00"])
+ reasons.append("Add null byte to end")
+ # for every asn1 entry we should attempt to:
+ # - change the data type tag
+ # - make the length longer than actual
+ # - make the length shorter than actual
+ i = 0
+ while i < len(data):
+ tag_i = i
+ leng_i = tag_i + 1
+ data_i = leng_i + 1 + (int(data[leng_i][1], 16) if data[leng_i][0] == '8' else 0)
+ if data[leng_i][0] == '8':
+ length = int(''.join(data[leng_i + 1: data_i]), 16)
+ else:
+ length = int(data[leng_i], 16)
+
+ tag = data[tag_i]
+ print(f"Looking at ans1: offset {i}, tag = {tag}, length = {length}:")
+ print(f"{''.join(data[data_i:data_i+length])}")
+ # change tag to something else
+ if tag == "02":
+ # turn integers into octet strings
+ new_tag = "04"
+ else:
+ # turn everything else into an integer
+ new_tag = "02"
+ mutations.append(data[:tag_i] + [new_tag] + data[leng_i:])
+ reasons.append(f"Change tag {tag} to {new_tag}")
+
+ # change lengths to too big
+ # skip any edge cases which would cause carry over
+ if int(data[data_i - 1], 16) < 255:
+ new_length = str(hex(int(data[data_i - 1], 16) + 1))[2:]
+ if len(new_length) == 1:
+ new_length = "0"+new_length
+ mutations.append(data[:data_i -1] + [new_length] + data[data_i:])
+ reasons.append(f"Change length from {length} to {length + 1}")
+ # we can add another test here for tags that contain other tags where they have more data than there containing tags account for
+ if tag in ["30", "a0", "31"]:
+ mutations.append(data[:data_i -1] + [new_length] + data[data_i:data_i + length] + ["00"] + data[data_i + length:])
+ reasons.append(f"Change contents of tag {tag} to contain one unaccounted extra byte")
+ # change lengths to too small
+ if int(data[data_i - 1], 16) > 0:
+ new_length = str(hex(int(data[data_i - 1], 16) - 1))[2:]
+ if len(new_length) == 1:
+ new_length = "0"+new_length
+ mutations.append(data[:data_i -1] + [new_length] + data[data_i:])
+ reasons.append(f"Change length from {length} to {length - 1}")
+
+ # some tag types contain other tag types so we should iterate into the data
+ if tag in ["30", "a0", "31"]:
+ i = data_i
+ else:
+ i = data_i + length
+
+ return list(zip(reasons, mutations))
+
+if len(sys.argv) < 2:
+ print(f"USAGE: {sys.argv[0]} <pkcs7_der_file>")
+ quit(1)
+
+data_file = sys.argv[1]
+test_data = TestData(pkcs7_test_file)
+f = open(data_file, 'rb')
+data = f.read().hex()
+f.close()
+# make data an array of byte strings eg ['de','ad','be','ef']
+data = list(map(''.join, [[data[i], data[i+1]] for i in range(0,len(data),2)]))
+# returns tuples of test_names and modified data buffers
+mutations = asn1_mutate(data)
+
+print(f"made {len(mutations)} new tests")
+for new_test in mutations:
+ test_data.add(new_test[0], ''.join(new_test[1]))
+
+
+test_data.write_changes()
+