[loop-cycle-3] fix: replace eval() with AST-walking safe evaluator (#52) #60

Rockachopa · 2026-03-14T19:55:28Z

Rockachopa commented

2026-03-14 19:55:28 +00:00

Why

The calculator tool used eval() with a sandboxed namespace. While the sandbox blocked __builtins__, eval() is inherently dangerous — sandbox escapes exist, and it is a code smell that static analyzers rightfully flag.

What

Replaced eval() with a custom AST-walking evaluator (_safe_eval) that:

Parses expressions into an AST tree using ast.parse()
Walks each node, only allowing: numeric literals, arithmetic operators, math.* functions/constants, and whitelisted builtins (abs, round, min, max)
Rejects everything else: imports, arbitrary attribute access, subscripts, comparisons, lambdas, comprehensions, string operations, keyword arguments

Uses only stdlib (ast + operator). Zero new dependencies.

Testing

Expanded test coverage from 18 → 33 tests. New security tests verify rejection of:

exec(), __import__(), open()
Arbitrary attribute chains (str.__class__.__bases__)
Lambdas, list comprehensions, boolean ops
String operations, keyword arguments, subscripts

All 1249 tests pass, 75.26% coverage maintained.

Closes #52

## Why The calculator tool used `eval()` with a sandboxed namespace. While the sandbox blocked `__builtins__`, `eval()` is inherently dangerous — sandbox escapes exist, and it is a code smell that static analyzers rightfully flag. ## What Replaced `eval()` with a custom AST-walking evaluator (`_safe_eval`) that: - Parses expressions into an AST tree using `ast.parse()` - Walks each node, only allowing: numeric literals, arithmetic operators, `math.*` functions/constants, and whitelisted builtins (`abs`, `round`, `min`, `max`) - **Rejects** everything else: imports, arbitrary attribute access, subscripts, comparisons, lambdas, comprehensions, string operations, keyword arguments Uses only stdlib (`ast` + `operator`). Zero new dependencies. ## Testing Expanded test coverage from 18 → 33 tests. New security tests verify rejection of: - `exec()`, `__import__()`, `open()` - Arbitrary attribute chains (`str.__class__.__bases__`) - Lambdas, list comprehensions, boolean ops - String operations, keyword arguments, subscripts All 1249 tests pass, 75.26% coverage maintained. Closes #52

Rockachopa added 1 commit 2026-03-14 19:55:28 +00:00

fix: replace eval() with AST-walking safe evaluator in calculator (#52 )

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Details

6bc1ce4723

Replace eval() in the calculator tool with a safe AST-walking evaluator
that only allows arithmetic operations, math module functions, and a
whitelist of builtins (abs, round, min, max).

The new _safe_eval() function:
- Parses the expression into an AST tree
- Walks each node, only allowing:
  - Numeric literals (int, float, complex)
  - Binary ops (+, -, *, /, //, %, **)
  - Unary ops (+, -)
  - math.* attribute access
  - Whitelisted function calls
- Rejects: imports, attribute chains, subscripts, comparisons,
  lambdas, comprehensions, string operations, keyword args

No new dependencies — uses stdlib ast + operator modules.

Test coverage expanded from 18 to 33 tests, including security tests
for exec(), arbitrary attributes, lambdas, list comprehensions,
boolean ops, keyword args, and subscripts.

Rockachopa closed this pull request

2026-03-14 20:35:07 +00:00

Pull request closed

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Reference: Rockachopa/Timmy-time-dashboard#60