🔒 fix: Replace unsafe eval() for key deserialization

[Periecle]

This PR addresses a security vulnerability where eval() was used for deserializing keys and cost functions in pybandits/quantitative_model.py. This could allow an attacker to execute arbitrary code by providing a malicious string.

The fix involves:

1. Using ast.literal_eval() for parsing literal structures like tuples and lists, which is safe as it doesn't execute any code.
2. Using a globals() dictionary lookup for retrieving functions by name, ensuring that only existing objects in the global namespace can be accessed.

These changes effectively eliminate the code injection vector while maintaining the original functionality for valid inputs.

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PR created automatically by Jules for task 1835057178953127085 started by @Periecle

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the security posture of the pybandits library by addressing a critical vulnerability. The changes eliminate the use of eval() for deserializing keys and cost functions, which previously posed a risk of arbitrary code execution. By adopting safer alternatives like ast.literal_eval() and direct globals() lookups, the system now maintains its original functionality for valid inputs while preventing malicious code injection.

Highlights

• Security Fix: Replaced the unsafe eval() function with ast.literal_eval() for deserializing literal structures like tuples and lists, eliminating a potential code injection vulnerability.
• Function Deserialization: Changed function deserialization to use a globals() dictionary lookup by name instead of eval(), ensuring only existing global objects can be accessed securely.

Changelog

• pybandits/quantitative_model.py
  • Imported the ast module to enable safe evaluation of literal structures.
  • Modified _deserialize_function to replace eval(func_name) with globals()[func_name] for secure function retrieval.
  • Updated deserialize_cost to use ast.literal_eval(args_str) instead of eval(args_str) for parsing function arguments.
  • Changed _deserialize_sub_action_key to utilize ast.literal_eval(key) instead of eval(key) for deserializing sub-action keys.

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Code Review

This pull request successfully addresses the identified security vulnerability by replacing unsafe eval() calls with ast.literal_eval() for literal structure parsing and globals() dictionary lookups for function retrieval. These changes effectively eliminate the code injection vector while maintaining the intended functionality.