Generate handshake defragmentation test cases

The output is identical to the manually written tests in
`tests/opt-testcases/handshake-manual.sh`, except that the script doesn't
generate explanatory comments (they're in the generator script instead).

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

scripts/generate_tls_handshake_tests.py

@@ -13,6 +13,137 @@ from typing import Optional
 
 from mbedtls_framework import tls_test_case
 from mbedtls_framework import typing_util
+
+from mbedtls_framework.tls_test_case import Side, Version
+
+
+# Assume that a TLS 1.2 ClientHello used in these tests will be at most
+# this many bytes long.
+TLS12_CLIENT_HELLO_ASSUMED_MAX_LENGTH = 255
+
+# Minimum handshake fragment length that Mbed TLS supports.
+TLS_HANDSHAKE_FRAGMENT_MIN_LENGTH = 4
+
+def write_tls_handshake_defragmentation_test(
+        out: typing_util.Writable,
+        side: Side,
+        length: Optional[int],
+        version: Optional[Version] = None
+) -> None:
+    """Generate one TLS handshake defragmentation test.
+
+    :param out: file to write to.
+    :param side: which side is Mbed TLS.
+    :param length: fragment length, or None to not fragment.
+    :param version: protocol version, if forced.
+    """
+    #pylint: disable=chained-comparison,too-many-branches,too-many-statements
+
+    our_args = ''
+    their_args = ''
+
+    if length is None:
+        description = 'no fragmentation, for reference'
+    else:
+        description = 'len=' + str(length)
+    if version is not None:
+        description += ', TLS 1.' + str(version.value)
+    description = f'Handshake defragmentation on {side.name.lower()}: {description}'
+    tc = tls_test_case.TestCase(description)
+
+    if version == Version.TLS12 and \
+       length is not None and \
+       length >= TLS_HANDSHAKE_FRAGMENT_MIN_LENGTH and \
+       length < 16 and \
+       side == side.CLIENT:
+        # Skip test cases where the Finished message is fragmented in TLS 1.2.
+        # This is currently buggy when the symmetric encryption used an
+        # explicit IV (CBC, GCM or CCM; Chachapoly and null work, as does
+        # TLS 1.3, because they use a purely implicit IV).
+        tc.requirements.append('skip_next_test')
+
+    if version is not None:
+        their_args += ' -tls1_' + str(version.value)
+        # Emit a version requirement, because we're forcing the version via
+        # OpenSSL, not via Mbed TLS, and the automatic depdendencies in
+        # ssl-opt.sh only handle forcing the version via Mbed TLS.
+        tc.requirements.append('requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_' +
+                               str(version.value))
+        if side == Side.SERVER and version == Version.TLS12 and \
+           length is not None and \
+           length <= TLS12_CLIENT_HELLO_ASSUMED_MAX_LENGTH:
+            # Server-side ClientHello defragmentation is only supported in
+            # the TLS 1.3 message parser. When that parser sees an 1.2-only
+            # ClientHello, it forwards the reassembled record to the
+            # TLS 1.2 ClientHello parser so the ClientHello can be fragmented.
+            # When TLS 1.3 support is disabled in the server (at compile-time
+            # or at runtime), the TLS 1.2 ClientHello parser only sees
+            # the first fragment of the ClientHello.
+            tc.requirements.append('requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_3')
+            tc.description += '  TLS 1.3 ClientHello -> 1.2 Handshake'
+
+    # To guarantee that the handhake messages are large enough and need to be
+    # split into fragments, the tests require certificate authentication.
+    # The party in control of the fragmentation operations is OpenSSL and
+    # will always use server5.crt (548 Bytes).
+    if length is not None and \
+       length >= TLS_HANDSHAKE_FRAGMENT_MIN_LENGTH:
+        tc.requirements.append('requires_certificate_authentication')
+        if version == Version.TLS12 and side == Side.CLIENT:
+            #The server uses an ECDSA cert, so make sure we have a compatible key exchange
+            tc.requirements.append(
+                'requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED')
+
+    if length is None:
+        forbidden_patterns = [
+            'reassembled record',
+            'waiting for more fragments',
+        ]
+        wanted_patterns = []
+    elif length < TLS_HANDSHAKE_FRAGMENT_MIN_LENGTH:
+        their_args += ' -split_send_frag ' + str(length)
+        tc.exit_code = 1
+        forbidden_patterns = []
+        wanted_patterns = [
+            'handshake message too short: ' + str(length),
+            'SSL - An invalid SSL record was received',
+        ]
+        if side == Side.SERVER:
+            wanted_patterns[0:0] = ['<= parse client hello']
+        elif version == Version.TLS13:
+            wanted_patterns[0:0] = ['=> ssl_tls13_process_server_hello']
+    else:
+        their_args += ' -split_send_frag ' + str(length)
+        forbidden_patterns = []
+        wanted_patterns = [
+            'reassembled record',
+            fr'handshake fragment: 0 \.\. {length} of [0-9]\+ msglen {length}',
+            fr'waiting for more fragments ({length} of',
+        ]
+
+    if side == Side.CLIENT:
+        tc.client = '$P_CLI debug_level=4' + our_args
+        tc.server = '$O_NEXT_SRV' + their_args
+        tc.wanted_client_patterns = wanted_patterns
+        tc.forbidden_client_patterns = forbidden_patterns
+    else:
+        their_args += ' -cert $DATA_FILES_PATH/server5.crt -key $DATA_FILES_PATH/server5.key'
+        our_args += ' auth_mode=required'
+        tc.client = '$O_NEXT_CLI' + their_args
+        tc.server = '$P_SRV debug_level=4' + our_args
+        tc.wanted_server_patterns = wanted_patterns
+        tc.forbidden_server_patterns = forbidden_patterns
+    tc.write(out)
+
+def write_tls_handshake_defragmentation_tests(out: typing_util.Writable) -> None:
+    """Generate TLS handshake defragmentation tests."""
+    for side in Side.CLIENT, Side.SERVER:
+        write_tls_handshake_defragmentation_test(out, side, None)
+        for length in [512, 513, 256, 128, 64, 36, 32, 16, 13, 5, 4, 3]:
+            write_tls_handshake_defragmentation_test(out, side, length, Version.TLS13)
+            write_tls_handshake_defragmentation_test(out, side, length, Version.TLS12)
+
+
 def write_handshake_tests(out: typing_util.Writable) -> None:
     """Generate handshake tests."""
     out.write(f"""\
@@ -24,6 +155,7 @@ def write_handshake_tests(out: typing_util.Writable) -> None:
 # SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 
 """)
+    write_tls_handshake_defragmentation_tests(out)
     out.write("""\
 # End of automatically generated file.
 """)