Fixes a further batch of P1 bypasses and analysis-time DoS vectors found in review.
Static classifier:
- Decode exec/compile bytes payloads the way CPython does (PEP 263 coding cookie
via tokenize.detect_encoding), then analyze the real source. A bytes payload whose
UTF-8 view is pure comments but whose utf-7 decode runs hidden code no longer slips
through; a payload decoding to a blocked op blocks, a benign one stays allowed.
- Resolve exec-builtin aliases assigned in nested scopes (def f(): e = exec; e(...)),
matching the shell-sink aliasing (stored-once guard keeps it low false-positive).
- Treat deserializer modules (pickle/marshal/dill/...) as dangerous dynamic-import
targets so __import__('pickle').loads(blob) is caught.
- Flag vars(os) / vars(__builtins__) as a module-__dict__ obfuscation, like os.__dict__.
- Inspect the pathlib receiver path for read methods: Path('../../.ssh/id_rsa').read_text()
/ read_bytes() / open() now check the constructor path, not only call args.
- Fold literal os.path.join / posixpath.join so open(os.path.join('/etc','passwd')).read()
is seen by the sensitive-read scanner instead of treated as opaque.
Constant-folder allocation DoS (folding runs in-process, before subprocess rlimits):
- Reject oversized f-string / str.format / %-format widths and precisions before
format() allocates the padded string.
- Reject oversized str padding-method widths (ljust/rjust/center/zfill).
- Cap list/tuple repetition (seq * n) as str/bytes repetition already was.
Runtime realpath backstop:
- Do not publish __wrapped__ on the guard wrappers (functools.wraps would expose the
original unguarded callable, e.g. open.__wrapped__(outside, 'w')).
- Guard the low-level _io.open entry point (io.open / builtins.open originate there).
- Confine os.chdir to the workdir and deny os.fchdir so a cwd escape cannot turn a
later relative read/write into a host-path access.
- Deny fd-based metadata mutators (os.fchmod / os.fchown) that could reuse a read-only
descriptor opened on an outside file.
Adds regression tests across the const-fold, aliasing, exec-recursion and runtime-
backstop suites for every item above.
Harden the code-exec sandbox against bypasses raised in review, keeping the
static gate a pure classifier (it never executes the tool call):
- Shell scan: `timeout` duration/float args (5m, 0.5, 2h) no longer drop the
following command out of command position, and `find -exec CMD ... ;` rescans
the whole slice so a wrapped `env`/`timeout`/`sh -c` target is still caught.
- exec/eval/compile of a bytes payload that is not valid UTF-8 Python now blocks:
those sinks honor PEP 263 coding cookies (e.g. utf-7) that the static UTF-8 view
cannot see; plain ASCII bytes payloads stay allowed.
- Resolve aliased/indirect reaches to exec, dynamic import, sensitive modules and
deserialization sinks: builtins.eval / __builtins__.exec, from builtins import
exec as e, importlib aliases, sys.modules[...] (and the getattr form), os.__dict__,
posix/nt, and pickle/marshal module-and-symbol aliases plus the *.load variants.
- Shell-sink aliasing walks the whole tree, so a function-local `s = os.system`
alias is resolved (the stored-once guard keeps it low false-positive).
- Drop __mro__ / __code__ from the introspection-gadget dunders: on their own they
do not reach an execution primitive and are read by ordinary ML/debug code.
- Refuse folding oversized `bytes(n)` / `bytearray(n)` so static analysis cannot OOM.
Runtime realpath backstop:
- Fail closed on a mutating dir_fd / src_dir_fd / dst_dir_fd (an fd-relative path
cannot be confined by a string realpath) for os and shutil mutators.
- Confine Path.rename/replace/symlink_to/hardlink_to when the destination is passed
as the `target=` keyword, not only positionally.
- Splice the guard after a leading docstring and `from __future__` imports instead
of prepending it, so future-import programs no longer raise SyntaxError while the
sandbox is still established before the first real statement.
Adds regression tests for each gap across the shell, const-fold, exec-recursion,
aliasing and runtime-backstop suites.
Introduce _const_fold, a whitelist-only, bounded, side-effect-free partial
evaluator plus a single-assignment const-prop environment builder. It recomputes
pure transforms on literals only (concat, repeat, join, format, f-strings,
slice/reverse, chr/ord, base64/hex/rot13/zlib decode, pure builtins and string
methods) and never executes, imports, or reflects on user code. Depth, op, size,
and sequence caps guarantee it can only fail to recover a value, never crash or
hang. This is the foundation the later eval/exec unwrapping and filesystem path
resolver build on.
