Runtime realpath backstop:
- Guard the low-level posix / nt module mutators (os re-exports from them, so
posix.open / posix.rename / ... stayed reachable with the originals).
- Guard io.FileIO / _io.FileIO constructors for write modes (a C constructor that
opens a file without routing through open()).
- Add os.mkfifo / os.utime / os.setxattr / os.removexattr (and lchflags) to the
guarded single-path mutators.
- Materialize fspath ONCE per call so a stateful __fspath__ cannot return a workdir
path for the check and an outside path for the syscall (TOCTOU).
- Coerce open() mode through the base str and os.open flags through the base int, so
a str-subclass __contains__ or an int-subclass __and__ cannot lie to the guard.
Constant-folder allocation DoS:
- Refuse str.format templates with a nested width field ({:{}}) driven by an
oversized numeric argument before format() allocates.
Static classifier:
- Reconstruct the full pathlib receiver path (all constructor args, joined) and
accept module-qualified pathlib.Path so Path('/etc', 'passwd').read_text() and
pathlib.Path(...) reads are inspected, not just single-arg bare Path(...).
- Treat builtins.__import__ / __builtins__.__import__ as a dynamic import.
- Count alias single-assignment per function scope instead of tree-wide, so two
functions binding the same local name no longer cancel out and miss a real sink.
Adds regression tests across the runtime-backstop, const-fold, aliasing and
classifier suites for every item above.
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