workflows: add some os things to sandbox whitelist, only restrict callables

src/vercel/_internal/workflow/py_sandbox.py

@@ -26,6 +26,8 @@ class SandboxRestrictionError(RuntimeError):
     """Raised when workflow code calls a non-deterministic function."""
 
 
+# TODO: We should have a more proper proxy that blocks __call__ and
+# returns proxied members but otherwise looks the same.
 def _restricted(name: str) -> Callable[..., NoReturn]:
     def _raise(*_args: Any, **_kwargs: Any) -> NoReturn:
         raise SandboxRestrictionError(
@@ -288,7 +290,12 @@ def _current_task(loop: Any = None) -> Any:
         "fsdecode",
         "fsencode",
         "fspath",
+        # These are deterministic enough if the functions that change
+        # them are blocked...
+        "getenv",
+        "getcwd",
         "_get_exports_list",
+        "PathLike",
         environ=os.environ.copy(),
         allow_if=str.isupper,
         drops=["fork", "register_at_fork"],
@@ -488,6 +495,8 @@ def __getattr__(self, name: str) -> Any:
             and name not in policy.allowed
             and not (name.startswith("__") and name.endswith("__"))
             and not (policy.allow_if is not None and policy.allow_if(name))
+            # Only restrict callables (which will include classes).
+            and callable(policy.resolve_attr(name, real))
         ):
             # Return a restricted callable instead of raising immediately.
             # This allows module init code like ``from os import urandom``

tests/unit/test_py_sandbox.py

@@ -136,8 +136,9 @@ def test_os_fspath_allowed(self):
     def test_os_constants_allowed(self):
         _run_in_sandbox("import os; _ = os.O_RDONLY")
 
-    def test_os_getcwd_blocked(self):
-        _raises_in_sandbox("import os; os.getcwd()")
+    def test_os_getcwd_allowed(self):
+        ns = _run_in_sandbox("import os; result = os.getcwd()")
+        assert isinstance(ns["result"], str)
 
     def test_os_listdir_blocked(self):
         _raises_in_sandbox("import os; os.listdir('.')")
@@ -874,6 +875,14 @@ def test_math_works(self):
         ns = _run_in_sandbox("import math; result = math.sqrt(16)")
         assert ns["result"] == 4.0
 
+    def test_shutil_works(self):
+        _run_in_sandbox("import os; lurr = os.supports_dir_fd")
+        _run_in_sandbox("import shutil")
+
+    def test_pathlib_works(self):
+        ns = _run_in_sandbox("import pathlib; result = isinstance(0, pathlib.Path)")
+        assert not ns["result"]
+
     def test_collections_counter(self):
         ns = _run_in_sandbox("from collections import Counter; result = dict(Counter('aabbc'))")
         assert ns["result"] == {"a": 2, "b": 2, "c": 1}