From 2c3866dee4c235c37c609c72e6049d3ed75df596 Mon Sep 17 00:00:00 2001
From: Simon Fayer <sf105@ic.ac.uk>
Date: Mon, 18 May 2026 16:36:26 +0100
Subject: [PATCH] feat: Add a new eval helper function

---
 src/DIRAC/Core/Utilities/SaferEval.py         |  32 ++++
 .../Core/Utilities/test/Test_SaferEval.py     | 145 ++++++++++++++++++
 2 files changed, 177 insertions(+)
 create mode 100644 src/DIRAC/Core/Utilities/SaferEval.py
 create mode 100644 src/DIRAC/Core/Utilities/test/Test_SaferEval.py

diff --git a/src/DIRAC/Core/Utilities/SaferEval.py b/src/DIRAC/Core/Utilities/SaferEval.py
new file mode 100644
index 00000000000..7c53ae1a623
--- /dev/null
+++ b/src/DIRAC/Core/Utilities/SaferEval.py
@@ -0,0 +1,32 @@
+#!/usr/bin/env python3
+
+import ast
+
+
+def saferEval(obj_str, max_len=2048):
+    """This function adds an extra length check around literal_eval.
+    On python3.11 and above (which has a recursion guard), this should
+    be safe enough for use on general authenticated user input.
+
+    Note: This doesn't handle all of the cases of eval, such as
+          datetime as those are technically executing code to
+          instantiate the non-base objects.
+    """
+    # Ensure input is a string
+    obj_str = str(obj_str)
+    if len(obj_str) > max_len:
+        raise ValueError(f"Object string is too long (>{max_len} bytes)")
+    try:
+        return ast.literal_eval(obj_str)
+    except (ValueError, TypeError, SyntaxError):
+        # This covers all of the cases where the string is wrong (unclosed brackets...)
+        # or contains disallowed items like function calls or non-expression.
+        raise ValueError("Syntax error processing object expression")
+    except (MemoryError, RecursionError):
+        # This is encountered if the object is nested too deeply and other structures
+        # that are probably malicious.
+        raise ValueError("Object expression too large")
+    except Exception:
+        # There are no other possible exceptions at the time of writing,
+        # this is to catch any added in future python versions.
+        raise ValueError("Unknown error processing object expression")
diff --git a/src/DIRAC/Core/Utilities/test/Test_SaferEval.py b/src/DIRAC/Core/Utilities/test/Test_SaferEval.py
new file mode 100644
index 00000000000..798cd741b67
--- /dev/null
+++ b/src/DIRAC/Core/Utilities/test/Test_SaferEval.py
@@ -0,0 +1,145 @@
+"""Tests for saferEval – uses pytest parametrize for conciseness."""
+
+import time
+
+import pytest
+
+from DIRAC.Core.Utilities.SaferEval import saferEval
+
+
+@pytest.mark.parametrize(
+    "value",
+    [
+        None,
+        True,
+        False,
+        0,
+        42,
+        -17,
+        0xFF,
+        0o77,
+        0b1010,
+        3.14,
+        1e10,
+        1j,
+        [],
+        [1, "two", True, None],
+        (),
+        (1,),
+        (1, 2, 3),
+        {},
+        {"a": 1, "b": 2},
+        {1, 2, 3},
+        [[1, 2], [3, 4]],
+        {"a": {"b": {"c": [1, 2]}}},
+    ],
+)
+def test_literal(value):
+    assert saferEval(str(value)) == value
+
+
+@pytest.mark.parametrize(
+    "input_str,expected",
+    [
+        ('"hello"', "hello"),
+        ("'hello'", "hello"),
+        ("'a\\nb'", "a\nb"),
+        (r"r'\n'", r"\n"),
+        ('"hello 🌍"', "hello 🌍"),
+        ("b'bytes'", b"bytes"),
+        ("b'\\xff'", b"\xff"),
+    ],
+)
+def test_string_literal(input_str, expected):
+    assert saferEval(input_str) == expected
+
+
+@pytest.mark.parametrize(
+    "input_str",
+    [
+        "__import__('os').system('id')",
+        "open('/etc/passwd').read()",
+        "list()",
+        "foo",
+        "datetime.datetime.now()",
+        "lambda x: x",
+        "{k: v for k, v in []}",
+        "(x for x in [])",
+        "x == y",
+        "1 + 2",
+        "().__class__",
+        "x[0]",
+        "[1,2][1:]",
+        "*1",
+        "builtins.open",
+        "object()",
+        "MyList()",
+        "f'{1+2}'",
+        "@decorator",
+        "assert True",
+        "return 42",
+        "x += 1",
+        "with open('x') as f: pass",
+        "for x in []: pass",
+        "try: pass\nexcept: pass",
+        "import os",
+        "from os import path",
+        "del x",
+        "raise ValueError('x')",
+        "yield 1",
+        "await something",
+        "(x := 1)",
+        "(lambda x, /: x)(1)",
+        "10**200",
+    ],
+)
+def test_rejected_inputs(input_str):
+    with pytest.raises(ValueError):
+        saferEval(input_str)
+
+
+def test_max_len_exceeded():
+    with pytest.raises(ValueError):
+        saferEval("1" * 2049, 2048)
+
+
+def test_max_len_custom_exceeded():
+    with pytest.raises(ValueError):
+        saferEval("[1, 2, 3]", 5)
+
+
+def test_max_len_custom_ok():
+    assert saferEval("[1, 2, 3]", 10) == [1, 2, 3]
+
+
+def test_max_len_boundary_default():
+    assert saferEval("42") == 42
+
+
+@pytest.mark.parametrize("depth", [2000, 500])
+def test_deep_nesting(depth):
+    with pytest.raises((ValueError, RecursionError)):
+        saferEval("[" * depth + "1" + "]" * depth)
+
+
+def test_large_string_literal():
+    with pytest.raises(ValueError):
+        saferEval("'" + "a" * 3000 + "'", 2048)
+
+
+def test_large_list():
+    with pytest.raises(ValueError):
+        saferEval(str([1] * 3000), 2048)
+
+
+@pytest.mark.parametrize(
+    "s",
+    [
+        "{" + ", ".join(f'"k{i}": {i}' for i in range(50)) + "}",
+        "[" + ",".join(str(i) for i in range(50)) + "]",
+    ],
+)
+def test_performance(s):
+    start = time.time()
+    saferEval(s, 2048)
+    assert time.time() - start < 0.1