fix(iast): add code to filter out ddtrace stuff from dir() on patched modules [backport 2.17] (#11504)

Backport a9a6ad7 from #11490 to 2.17.

Signed-off-by: Juanjo Alvarez <[email protected]>

## Description

While testing on dd-source CI we found an issue where a module was doing
a `dir(other_module)` and the changed results from the patched module
were breaking stuff (because our patching would add `ddtrace_aspects`,
`ddtrace_sink_points`, et cetera to the results and the original module
was expecting all `other_module` symbols to have some members like
`id`).

This PRs fixes this problem by:

- Creating a custom `__dir__` function (that will override any
pre-existing ones) removing from the results all the symbols that we add
ourselves while patching.
- Renaming all added `ddtrace` symbols to `__ddtrace`.

Also:
- Adds a `_DD_IAST_NO_DIR_PATCH` config var to disable the wrapping of
the patched module `__dir__` functions in case the user have some
side-effect problem.
- The return type of `visit_ast` has been fixed (it wrongly was `str`
while is in fact a `ast.Module` type).

## Checklist
- [X] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Co-authored-by: Juanjo Alvarez Martinez <[email protected]>

Author: github-actions[bot]

ddtrace/appsec/_constants.py

@@ -134,8 +134,10 @@ class IAST(metaclass=Constant_Class):
     JSON: Literal["_dd.iast.json"] = "_dd.iast.json"
     ENABLED: Literal["_dd.iast.enabled"] = "_dd.iast.enabled"
     PATCH_MODULES: Literal["_DD_IAST_PATCH_MODULES"] = "_DD_IAST_PATCH_MODULES"
+    ENV_NO_DIR_PATCH: Literal["_DD_IAST_NO_DIR_PATCH"] = "_DD_IAST_NO_DIR_PATCH"
     DENY_MODULES: Literal["_DD_IAST_DENY_MODULES"] = "_DD_IAST_DENY_MODULES"
     SEP_MODULES: Literal[","] = ","
+    PATCH_ADDED_SYMBOL_PREFIX: Literal["_ddtrace_"] = "_ddtrace_"
 
     METRICS_REPORT_LVLS = (
         (TELEMETRY_DEBUG_VERBOSITY, TELEMETRY_DEBUG_NAME),

ddtrace/appsec/_iast/_ast/ast_patching.py

@@ -5,6 +5,8 @@
 import os
 import re
 from sys import builtin_module_names
+from sys import version_info
+import textwrap
 from types import ModuleType
 from typing import Optional
 from typing import Text
@@ -14,12 +16,14 @@
 from ddtrace.appsec._python_info.stdlib import _stdlib_for_python_version
 from ddtrace.internal.logger import get_logger
 from ddtrace.internal.module import origin
+from ddtrace.internal.utils.formats import asbool
 
 from .visitor import AstVisitor
 
 
 _VISITOR = AstVisitor()
 
+_PREFIX = IAST.PATCH_ADDED_SYMBOL_PREFIX
 
 # Prefixes for modules where IAST patching is allowed
 IAST_ALLOWLIST: Tuple[Text, ...] = ("tests.appsec.iast.",)
@@ -278,6 +282,7 @@
     "protobuf.",
     "pycparser.",  # this package is called when a module is imported, propagation is not needed
     "pytest.",  # Testing framework
+    "_pytest.",
     "setuptools.",
     "sklearn.",  # Machine learning library
     "sqlalchemy.orm.interfaces.",  # Performance optimization
@@ -368,7 +373,7 @@ def visit_ast(
     source_text: Text,
     module_path: Text,
     module_name: Text = "",
-) -> Optional[str]:
+) -> Optional[ast.Module]:
     parsed_ast = ast.parse(source_text, module_path)
     _VISITOR.update_location(filename=module_path, module_name=module_name)
     modified_ast = _VISITOR.visit(parsed_ast)
@@ -401,23 +406,56 @@ def _remove_flask_run(text: Text) -> Text:
     return new_text
 
 
-def astpatch_module(module: ModuleType, remove_flask_run: bool = False) -> Tuple[str, str]:
+_DIR_WRAPPER = textwrap.dedent(
+    f"""
+
+
+def {_PREFIX}dir():
+    orig_dir = globals().get("{_PREFIX}orig_dir__")
+
+    if orig_dir:
+        # Use the original __dir__ method and filter the results
+        results = [name for name in orig_dir() if not name.startswith("{_PREFIX}")]
+    else:
+        # List names from the module's __dict__ and filter out the unwanted names
+        results = [
+            name for name in globals()
+            if not (name.startswith("{_PREFIX}") or name == "__dir__")
+        ]
+
+    return results
+
+def {_PREFIX}set_dir_filter():
+    if "__dir__" in globals():
+        # Store the original __dir__ method
+        globals()["{_PREFIX}orig_dir__"] = __dir__
+
+    # Replace the module's __dir__ with the custom one
+    globals()["__dir__"] = {_PREFIX}dir
+
+{_PREFIX}set_dir_filter()
+
+    """
+)
+
+
+def astpatch_module(module: ModuleType, remove_flask_run: bool = False) -> Tuple[str, Optional[ast.Module]]:
     module_name = module.__name__
 
     module_origin = origin(module)
     if module_origin is None:
         log.debug("astpatch_source couldn't find the module: %s", module_name)
-        return "", ""
+        return "", None
 
     module_path = str(module_origin)
     try:
         if module_origin.stat().st_size == 0:
             # Don't patch empty files like __init__.py
             log.debug("empty file: %s", module_path)
-            return "", ""
+            return "", None
     except OSError:
         log.debug("astpatch_source couldn't find the file: %s", module_path, exc_info=True)
-        return "", ""
+        return "", None
 
     # Get the file extension, if it's dll, os, pyd, dyn, dynlib: return
     # If its pyc or pyo, change to .py and check that the file exists. If not,
@@ -427,30 +465,35 @@ def astpatch_module(module: ModuleType, remove_flask_run: bool = False) -> Tuple
     if module_ext.lower() not in {".pyo", ".pyc", ".pyw", ".py"}:
         # Probably native or built-in module
         log.debug("extension not supported: %s for: %s", module_ext, module_path)
-        return "", ""
+        return "", None
 
     with open(module_path, "r", encoding=get_encoding(module_path)) as source_file:
         try:
             source_text = source_file.read()
         except UnicodeDecodeError:
             log.debug("unicode decode error for file: %s", module_path, exc_info=True)
-            return "", ""
+            return "", None
 
     if len(source_text.strip()) == 0:
         # Don't patch empty files like __init__.py
         log.debug("empty file: %s", module_path)
-        return "", ""
+        return "", None
 
     if remove_flask_run:
         source_text = _remove_flask_run(source_text)
 
-    new_source = visit_ast(
+    if not asbool(os.environ.get(IAST.ENV_NO_DIR_PATCH, "false")) and version_info > (3, 7):
+        # Add the dir filter so __ddtrace stuff is not returned by dir(module)
+        # does not work in 3.7 because it enters into infinite recursion
+        source_text += _DIR_WRAPPER
+
+    new_ast = visit_ast(
         source_text,
         module_path,
         module_name=module_name,
     )
-    if new_source is None:
+    if new_ast is None:
         log.debug("file not ast patched: %s", module_path)
-        return "", ""
+        return "", None
 
-    return module_path, new_source
+    return module_path, new_ast

ddtrace/appsec/_iast/_ast/visitor.py

@@ -12,6 +12,7 @@
 from typing import Text
 from typing import Tuple  # noqa:F401
 
+from ..._constants import IAST
 from .._metrics import _set_metric_iast_instrumented_propagation
 from ..constants import DEFAULT_PATH_TRAVERSAL_FUNCTIONS
 from ..constants import DEFAULT_WEAK_RANDOMNESS_FUNCTIONS
@@ -22,11 +23,12 @@
 PY38_PLUS = sys.version_info >= (3, 8, 0)
 PY39_PLUS = sys.version_info >= (3, 9, 0)
 
+_PREFIX = IAST.PATCH_ADDED_SYMBOL_PREFIX
 CODE_TYPE_FIRST_PARTY = "first_party"
 CODE_TYPE_DD = "datadog"
 CODE_TYPE_SITE_PACKAGES = "site_packages"
 CODE_TYPE_STDLIB = "stdlib"
-TAINT_SINK_FUNCTION_REPLACEMENT = "ddtrace_taint_sinks.ast_function"
+TAINT_SINK_FUNCTION_REPLACEMENT = _PREFIX + "taint_sinks.ast_function"
 
 
 def _mark_avoid_convert_recursively(node):
@@ -38,71 +40,71 @@ def _mark_avoid_convert_recursively(node):
 
 _ASPECTS_SPEC: Dict[Text, Any] = {
     "definitions_module": "ddtrace.appsec._iast._taint_tracking.aspects",
-    "alias_module": "ddtrace_aspects",
+    "alias_module": _PREFIX + "aspects",
     "functions": {
-        "StringIO": "ddtrace_aspects.stringio_aspect",
-        "BytesIO": "ddtrace_aspects.bytesio_aspect",
-        "str": "ddtrace_aspects.str_aspect",
-        "bytes": "ddtrace_aspects.bytes_aspect",
-        "bytearray": "ddtrace_aspects.bytearray_aspect",
-        "ddtrace_iast_flask_patch": "ddtrace_aspects.empty_func",  # To avoid recursion
+        "StringIO": _PREFIX + "aspects.stringio_aspect",
+        "BytesIO": _PREFIX + "aspects.bytesio_aspect",
+        "str": _PREFIX + "aspects.str_aspect",
+        "bytes": _PREFIX + "aspects.bytes_aspect",
+        "bytearray": _PREFIX + "aspects.bytearray_aspect",
+        "ddtrace_iast_flask_patch": _PREFIX + "aspects.empty_func",  # To avoid recursion
     },
     "stringalike_methods": {
-        "StringIO": "ddtrace_aspects.stringio_aspect",
-        "BytesIO": "ddtrace_aspects.bytesio_aspect",
-        "decode": "ddtrace_aspects.decode_aspect",
-        "join": "ddtrace_aspects.join_aspect",
-        "encode": "ddtrace_aspects.encode_aspect",
-        "extend": "ddtrace_aspects.bytearray_extend_aspect",
-        "upper": "ddtrace_aspects.upper_aspect",
-        "lower": "ddtrace_aspects.lower_aspect",
-        "replace": "ddtrace_aspects.replace_aspect",
-        "swapcase": "ddtrace_aspects.swapcase_aspect",
-        "title": "ddtrace_aspects.title_aspect",
-        "capitalize": "ddtrace_aspects.capitalize_aspect",
-        "casefold": "ddtrace_aspects.casefold_aspect",
-        "translate": "ddtrace_aspects.translate_aspect",
-        "format": "ddtrace_aspects.format_aspect",
-        "format_map": "ddtrace_aspects.format_map_aspect",
-        "zfill": "ddtrace_aspects.zfill_aspect",
-        "ljust": "ddtrace_aspects.ljust_aspect",
-        "split": "ddtrace_aspects.split_aspect",  # Both regular split and re.split
-        "rsplit": "ddtrace_aspects.rsplit_aspect",
-        "splitlines": "ddtrace_aspects.splitlines_aspect",
+        "StringIO": _PREFIX + "aspects.stringio_aspect",
+        "BytesIO": _PREFIX + "aspects.bytesio_aspect",
+        "decode": _PREFIX + "aspects.decode_aspect",
+        "join": _PREFIX + "aspects.join_aspect",
+        "encode": _PREFIX + "aspects.encode_aspect",
+        "extend": _PREFIX + "aspects.bytearray_extend_aspect",
+        "upper": _PREFIX + "aspects.upper_aspect",
+        "lower": _PREFIX + "aspects.lower_aspect",
+        "replace": _PREFIX + "aspects.replace_aspect",
+        "swapcase": _PREFIX + "aspects.swapcase_aspect",
+        "title": _PREFIX + "aspects.title_aspect",
+        "capitalize": _PREFIX + "aspects.capitalize_aspect",
+        "casefold": _PREFIX + "aspects.casefold_aspect",
+        "translate": _PREFIX + "aspects.translate_aspect",
+        "format": _PREFIX + "aspects.format_aspect",
+        "format_map": _PREFIX + "aspects.format_map_aspect",
+        "zfill": _PREFIX + "aspects.zfill_aspect",
+        "ljust": _PREFIX + "aspects.ljust_aspect",
+        "split": _PREFIX + "aspects.split_aspect",  # Both regular split and re.split
+        "rsplit": _PREFIX + "aspects.rsplit_aspect",
+        "splitlines": _PREFIX + "aspects.splitlines_aspect",
         # re module and re.Match methods
-        "findall": "ddtrace_aspects.re_findall_aspect",
-        "finditer": "ddtrace_aspects.re_finditer_aspect",
-        "fullmatch": "ddtrace_aspects.re_fullmatch_aspect",
-        "expand": "ddtrace_aspects.re_expand_aspect",
-        "group": "ddtrace_aspects.re_group_aspect",
-        "groups": "ddtrace_aspects.re_groups_aspect",
-        "match": "ddtrace_aspects.re_match_aspect",
-        "search": "ddtrace_aspects.re_search_aspect",
-        "sub": "ddtrace_aspects.re_sub_aspect",
-        "subn": "ddtrace_aspects.re_subn_aspect",
+        "findall": _PREFIX + "aspects.re_findall_aspect",
+        "finditer": _PREFIX + "aspects.re_finditer_aspect",
+        "fullmatch": _PREFIX + "aspects.re_fullmatch_aspect",
+        "expand": _PREFIX + "aspects.re_expand_aspect",
+        "group": _PREFIX + "aspects.re_group_aspect",
+        "groups": _PREFIX + "aspects.re_groups_aspect",
+        "match": _PREFIX + "aspects.re_match_aspect",
+        "search": _PREFIX + "aspects.re_search_aspect",
+        "sub": _PREFIX + "aspects.re_sub_aspect",
+        "subn": _PREFIX + "aspects.re_subn_aspect",
     },
     # Replacement function for indexes and ranges
     "slices": {
-        "index": "ddtrace_aspects.index_aspect",
-        "slice": "ddtrace_aspects.slice_aspect",
+        "index": _PREFIX + "aspects.index_aspect",
+        "slice": _PREFIX + "aspects.slice_aspect",
     },
     # Replacement functions for modules
     "module_functions": {
         "os.path": {
-            "basename": "ddtrace_aspects.ospathbasename_aspect",
-            "dirname": "ddtrace_aspects.ospathdirname_aspect",
-            "join": "ddtrace_aspects.ospathjoin_aspect",
-            "normcase": "ddtrace_aspects.ospathnormcase_aspect",
-            "split": "ddtrace_aspects.ospathsplit_aspect",
-            "splitext": "ddtrace_aspects.ospathsplitext_aspect",
+            "basename": _PREFIX + "aspects.ospathbasename_aspect",
+            "dirname": _PREFIX + "aspects.ospathdirname_aspect",
+            "join": _PREFIX + "aspects.ospathjoin_aspect",
+            "normcase": _PREFIX + "aspects.ospathnormcase_aspect",
+            "split": _PREFIX + "aspects.ospathsplit_aspect",
+            "splitext": _PREFIX + "aspects.ospathsplitext_aspect",
         }
     },
     "operators": {
-        ast.Add: "ddtrace_aspects.add_aspect",
-        "INPLACE_ADD": "ddtrace_aspects.add_inplace_aspect",
-        "FORMAT_VALUE": "ddtrace_aspects.format_value_aspect",
-        ast.Mod: "ddtrace_aspects.modulo_aspect",
-        "BUILD_STRING": "ddtrace_aspects.build_string_aspect",
+        ast.Add: _PREFIX + "aspects.add_aspect",
+        "INPLACE_ADD": _PREFIX + "aspects.add_inplace_aspect",
+        "FORMAT_VALUE": _PREFIX + "aspects.format_value_aspect",
+        ast.Mod: _PREFIX + "aspects.modulo_aspect",
+        "BUILD_STRING": _PREFIX + "aspects.build_string_aspect",
     },
     "excluded_from_patching": {
         # Key: module being patched
@@ -123,6 +125,8 @@ def _mark_avoid_convert_recursively(node):
         },
         "django.utils.html": {"": ("format_html", "format_html_join")},
         "sqlalchemy.sql.compiler": {"": ("_requires_quotes",)},
+        # Our added functions
+        "": {"": (f"{_PREFIX}dir", f"{_PREFIX}set_dir_filter")},
     },
     # This is a set since all functions will be replaced by taint_sink_functions
     "taint_sinks": {
@@ -149,10 +153,10 @@ def _mark_avoid_convert_recursively(node):
 
 
 if sys.version_info >= (3, 12):
-    _ASPECTS_SPEC["module_functions"]["os.path"]["splitroot"] = "ddtrace_aspects.ospathsplitroot_aspect"
+    _ASPECTS_SPEC["module_functions"]["os.path"]["splitroot"] = _PREFIX + "aspects.ospathsplitroot_aspect"
 
 if sys.version_info >= (3, 12) or os.name == "nt":
-    _ASPECTS_SPEC["module_functions"]["os.path"]["splitdrive"] = "ddtrace_aspects.ospathsplitdrive_aspect"
+    _ASPECTS_SPEC["module_functions"]["os.path"]["splitdrive"] = _PREFIX + "aspects.ospathsplitdrive_aspect"
 
 
 class AstVisitor(ast.NodeTransformer):
@@ -163,7 +167,7 @@ def __init__(
     ):
         self._sinkpoints_spec = {
             "definitions_module": "ddtrace.appsec._iast.taint_sinks",
-            "alias_module": "ddtrace_taint_sinks",
+            "alias_module": _PREFIX + "taint_sinks",
             "functions": {},
         }
         self._sinkpoints_functions = self._sinkpoints_spec["functions"]
@@ -458,6 +462,9 @@ def visit_FunctionDef(self, def_node: ast.FunctionDef) -> Any:
         Special case for some tests which would enter in a patching
         loop otherwise when visiting the check functions
         """
+        if f"{_PREFIX}dir" in def_node.name or f"{_PREFIX}set_dir_filter" in def_node.name:
+            return def_node
+
         self.replacements_disabled_for_functiondef = def_node.name in self.dont_patch_these_functionsdefs
 
         if hasattr(def_node.args, "vararg") and def_node.args.vararg:

ddtrace/appsec/_iast/_loader.py

@@ -12,19 +12,19 @@
 
 
 def _exec_iast_patched_module(module_watchdog, module):
-    patched_source = None
+    patched_ast = None
     compiled_code = None
     if IS_IAST_ENABLED:
         try:
-            module_path, patched_source = astpatch_module(module)
+            module_path, patched_ast = astpatch_module(module)
         except Exception:
             log.debug("Unexpected exception while AST patching", exc_info=True)
-            patched_source = None
+            patched_ast = None
 
-    if patched_source:
+    if patched_ast:
         try:
             # Patched source is compiled in order to execute it
-            compiled_code = compile(patched_source, module_path, "exec")
+            compiled_code = compile(patched_ast, module_path, "exec")
         except Exception:
             log.debug("Unexpected exception while compiling patched code", exc_info=True)
             compiled_code = None

releasenotes/notes/code-security-patch-dir-54cc85f18e31f45c.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Code Security: patch the module dir function so original pre-patch results are not changed.

tests/appsec/appsec_utils.py

@@ -100,6 +100,7 @@ def appsec_application_server(
         env[IAST.ENV] = iast_enabled
         env[IAST.ENV_REQUEST_SAMPLING] = "100"
         env["_DD_APPSEC_DEDUPLICATION_ENABLED"] = "false"
+        env[IAST.ENV_NO_DIR_PATCH] = "false"
         if assert_debug:
             env["_" + IAST.ENV_DEBUG] = iast_enabled
             env["_" + IAST.ENV_PROPAGATION_DEBUG] = iast_enabled