MCPTap v2.0.0

[pczerkas]

Changelog

[2.0.0]

Added

• openat2 interception (Linux 5.6+) — the LD_PRELOAD file-block library
  now intercepts openat2 via a raw syscall wrapper (glibc has no openat2
  wrapper) and exports the openat2() symbol for direct-link compatibility.
• exec* interceptors to close the setuid escape vector — execve,
  execv, execvp, execvpe, posix_spawn, and posix_spawnp are now
  intercepted in the parent process. The library scans argv before the child
  is spawned, blocking arguments that resolve to a blocked path. This closes the
  escape vector where glibc drops LD_PRELOAD for setuid binaries (sudo,
  su, doas, pkexec, …), so sudo cat <blocked> is refused while
  unrelated sudo calls are still allowed.
• Surgical escalator + interpreter + payload detection — when argv[0] is
  a privilege-escalator and a later argument is an interpreter (bash, sh,
  python3, perl, xargs, dd, …), the concatenated payload is searched
  for a blocklist path as a substring (with ~ expanded anywhere). This blocks
  sudo bash -c 'cat ~/.fzf-history' without affecting legitimate uses like
  sudo bash -c 'systemctl restart nginx'. Configurable via:
  • MCPTAP_FB_ESCALATORS — override the default escalator list
  • MCPTAP_FB_INTERPRETERS — override the default interpreter list
  • MCPTAP_FB_DISABLE_ESCALATOR_CHECK=1 — disable the layer entirely
• Realpath normalization — candidate paths and blocklist entries are
  resolved via realpath, so ./, ../, and symlink aliases can no longer
  bypass the blocklist.
• Comprehensive file-block test coverage — 41 new tests covering C-level
  interceptors (openat, openat2, open64, fopen64, statx, faccessat,
  …), Python-level interceptors (access, lstat, readlink, realpath,
  shutil.copy2), blocklist parsing, dynamic blocklist updates, and
  tool-level blocking (cp, mv, dd, directory blocking).
• ANSI color output in setup.sh — the "Installation complete" section is
  shown in green; errors (die(), unknown options, diagnostic heredocs) are
  shown in red. Colors are gated on TTY detection (no color when piped).
• hook= status in per-request log — the INFO log line now includes
  hook=True/False alongside intercept=....

Changed

• Tool-call hook works without MCP intercept config — the intercept/hook
  loop now runs when either MCP tool interception or the tool-call hook
  (MCP_TAP_USE_TOOL_HOOK) is enabled. Previously the hook was silently
  disabled when MCP_TAP_INTERCEPT_YAML was empty. The two features are
  independent: the hook can gate client tool calls and write blocked_files
  for the LD_PRELOAD library even without any MCP intercept config.
• --with-file-block wires both settings — wire_file_block_in_proxy_env
  now enables both MCP_TAP_USE_TOOL_HOOK and MCP_TAP_FILE_BLOCK_LIB in
  proxy.env (previously only the library path was wired). The wiring runs on
  every --with-file-block invocation, not only on new installations.
• Per-session directory path — changed from /tmp/mcptap/per_session_id
  to /tmp/mcptap/per_session to match the directory actually created by the
  proxy.
• File-block library no longer wired through proxy env — LD_PRELOAD is
  applied at command launch (LD_PRELOAD=… codex …) rather than through
  proxy.env. The example proxy.env no longer contains
  MCP_TAP_FILE_BLOCK_LIB.
• Example use_tool_hook.py simplified — the hook now consistently
  returns an allow action while preserving the sensitive-file block list,
  instead of reading stdin and applying resource-based blocking.
• /home/user/ placeholder substitution — during installation, sed
  replaces all /home/user/ occurrences in copied example config files with
  the real $HOME path.
• README expanded — added documentation for file-block limitations
  (stdin/heredoc payloads, obfuscated paths, path-normalization aliases),
  the setuid escape vector, and the escalator/interpreter configuration
  environment variables.

Fixed

• Electron/Node.js deadlock — the generic syscall() interceptor
  forwarded all non-openat2 syscalls through va_arg with 6 arguments,
  corrupting argument passing for syscalls with fewer arguments. This caused
  Electron/Node.js (used by code --locate-extension in the Codex wrapper) to
  deadlock on getrandom/futex/thread synchronization. The syscall()
  interceptor has been removed entirely; the exported openat2() wrapper
  symbol is retained.
• Test failures on Polish-locale systems — LC_ALL=C is now set in the
  test environment to ensure English error messages.

Removed

• Generic syscall() interceptor — removed because it broke
  Electron/Node.js (see Fixed above). Raw syscall(__NR_openat2, …) is no
  longer intercepted; programs linking against the openat2() wrapper symbol
  are still intercepted.

Full Changelog

v1.3.0...v2.0.0

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This discussion was created from the release MCPTap v2.0.0.