bigbrother/tests/test_presence_parsers.py

#!/usr/bin/env python3
"""
Test suite for presence_daemon parsers — netlink and DHCP bounds checking.
Tests minimal reproductions of bounds checking issues.
"""

import struct
import sys
from pathlib import Path

# We'll test by importing just the functions directly
# by reading the source and executing key portions


def parse_netlink_current(data: bytes) -> None:
    """Current implementation from presence_daemon.py."""
    try:
        offset = 0
        while offset < len(data):
            if offset + 16 > len(data):
                break

            nlmsg_len, nlmsg_type, _, _, _ = struct.unpack_from('=IHHII', data, offset)
            if nlmsg_len < 16:
                break

            payload = data[offset + 16:offset + nlmsg_len]
            # This is the issue: if nlmsg_len > len(data), we silently get a short payload
            # No guard that offset + nlmsg_len <= len(data)

            offset += (nlmsg_len + 3) & ~3
    except Exception as e:
        pass


def parse_ndmsg_current(data: bytes, msg_type: int) -> None:
    """Current implementation from presence_daemon.py."""
    try:
        if len(data) < 12:
            return

        state = struct.unpack_from('=H', data, 8)[0]

        mac = None
        ip = None
        offset = 12

        while offset + 4 <= len(data):
            rta_len, rta_type = struct.unpack_from('=HH', data, offset)
            if rta_len < 4:
                break

            val = data[offset + 4:offset + rta_len]

            if rta_type == 1 and len(val) == 6:  # NDA_LLADDR
                mac = ':'.join(f'{b:02x}' for b in val)
            elif rta_type == 2:  # NDA_DST
                if len(val) == 4:
                    pass  # would parse IP

            offset += (rta_len + 3) & ~3

        # If we had extracted a MAC, we'd proceed
        # The issue: rta_len might claim more bytes than available

    except Exception as e:
        pass


def parse_dhcp_current(data: bytes) -> None:
    """Current implementation from presence_daemon.py."""
    try:
        if len(data) < 14:
            return

        eth_type = struct.unpack('!H', data[12:14])[0]
        if eth_type != 0x0800:
            return

        if len(data) < 23:
            return
        proto = data[23]
        if proto != 17:
            return

        if len(data) < 38:
            return
        src_port = struct.unpack('!H', data[34:36])[0]
        dst_port = struct.unpack('!H', data[36:38])[0]
        if not (src_port in (67, 68) and dst_port in (67, 68)):
            return

        if len(data) < 42:
            return
        dhcp = data[42:]
        if len(dhcp) < 236:
            return

        # MAC extraction — offset 28-34
        mac_bytes = dhcp[28:34]
        mac = ':'.join(f'{b:02x}' for b in mac_bytes)
        if mac in ('00:00:00:00:00:00', 'ff:ff:ff:ff:ff:ff'):
            return

        if len(dhcp) < 240:
            return

        msg_type = None
        i = 240
        while i < len(dhcp):
            opt = dhcp[i]
            if opt == 255:
                break
            if opt == 0:
                i += 1
                continue
            if i + 1 >= len(dhcp):
                break

            length = dhcp[i + 1]
            if i + 2 + length > len(dhcp):
                break

            val = dhcp[i + 2:i + 2 + length]

            if opt == 53 and length == 1:
                msg_type = val[0]

            i += 2 + length

    except Exception as e:
        pass


# Test cases

def test_parse_netlink_truncated_header():
    """Netlink parser should handle buffer shorter than header gracefully."""
    truncated = b'\x01\x02\x03'
    # Should not raise
    parse_netlink_current(truncated)
    print("✓ test_parse_netlink_truncated_header passed")


def test_parse_netlink_header_claims_more_than_available():
    """Netlink parser should handle nlmsg_len > buffer length."""
    # Build a netlink header that claims 100 bytes but only provide 16
    nlmsg_len = 100
    nlmsg_type = 20
    flags = 0
    seq = 0
    pid = 0
    data = struct.pack('=IHHII', nlmsg_len, nlmsg_type, flags, seq, pid)
    assert len(data) == 16
    # Should not raise
    parse_netlink_current(data)
    print("✓ test_parse_netlink_header_claims_more_than_available passed")


def test_parse_netlink_offset_overflow():
    """Netlink parser should not overflow offset calculation."""
    # Two messages: first claims huge length, second is valid
    msg1 = struct.pack('=IHHII', 0xffffffff, 20, 0, 0, 0)  # Claims ~4GB
    msg2 = struct.pack('=IHHII', 16, 20, 0, 1, 0)  # Valid header
    data = msg1 + msg2
    # Should not raise (might infinite loop with current code)
    parse_netlink_current(data)
    print("✓ test_parse_netlink_offset_overflow passed")


def test_parse_ndmsg_rta_claims_more_data():
    """ndmsg parser should handle RTA that claims more bytes than available."""
    # ndmsg header: family, pad, type, flags, state, index (6 bytes with BBBBHH)
    ndmsg_header = struct.pack('=BBBBHH', 0, 0, 0, 0, 64, 0)

    # RTA header claiming 20 bytes total length
    rta_len = 20
    rta_type = 1  # NDA_LLADDR
    rta_header = struct.pack('=HH', rta_len, rta_type)

    # But only provide 2 bytes of actual RTA data (not 16 bytes as claimed)
    data = ndmsg_header + rta_header + b'\x01\x02'

    # Should not raise
    parse_ndmsg_current(data, 20)  # RTM_NEWNEIGH
    print("✓ test_parse_ndmsg_rta_claims_more_data passed")


def test_parse_dhcp_minimal_valid():
    """DHCP parser should accept valid minimal DHCP frame."""
    # Build minimal valid DHCP frame (Eth + IP + UDP + DHCP)
    eth_dst = b'\xff\xff\xff\xff\xff\xff'
    eth_src = b'\x00\x11\x22\x33\x44\x55'
    eth_type = struct.pack('!H', 0x0800)

    # IP header (20 bytes)
    ip_version_ihl = 0x45
    ip_dscp_ecn = 0
    ip_length = struct.pack('!H', 20 + 8 + 260)
    ip_id = struct.pack('!H', 0)
    ip_flags_frag = struct.pack('!H', 0x4000)
    ip_ttl = 64
    ip_proto = 17  # UDP
    ip_checksum = struct.pack('!H', 0)
    ip_src = b'\x00\x00\x00\x00'
    ip_dst = b'\xff\xff\xff\xff'

    ip_header = (
        bytes([ip_version_ihl, ip_dscp_ecn]) +
        ip_length + ip_id + ip_flags_frag +
        bytes([ip_ttl, ip_proto]) + ip_checksum +
        ip_src + ip_dst
    )

    # UDP header (8 bytes)
    udp_src = struct.pack('!H', 68)
    udp_dst = struct.pack('!H', 67)
    udp_length = struct.pack('!H', 8 + 260)
    udp_checksum = struct.pack('!H', 0)

    udp_header = udp_src + udp_dst + udp_length + udp_checksum

    # DHCP payload (260 bytes)
    dhcp_body = bytearray(260)
    dhcp_body[0] = 1  # BOOTREQUEST
    dhcp_body[4:10] = b'\x12\x34\x56\x78\x9a\xbc'
    dhcp_body[28:34] = b'\xaa\xbb\xcc\xdd\xee\xff'  # chaddr

    # DHCP magic + option 53
    dhcp_body[240:244] = b'\x63\x82\x53\x63'
    dhcp_body[244:247] = b'\x35\x01\x01'  # option 53, length 1, value 1 (DISCOVER)
    dhcp_body[247] = 255  # End

    frame = eth_dst + eth_src + eth_type + ip_header + udp_header + bytes(dhcp_body)
    parse_dhcp_current(frame)
    print("✓ test_parse_dhcp_minimal_valid passed")


if __name__ == '__main__':
    test_parse_netlink_truncated_header()
    test_parse_netlink_header_claims_more_than_available()
    test_parse_netlink_offset_overflow()
    test_parse_ndmsg_rta_claims_more_data()
    test_parse_dhcp_minimal_valid()
    print("\nAll tests passed!")