.. title:: clang-tidy - bugprone-random-generator-seed

bugprone-random-generator-seed
==============================

Flags all pseudo-random number engines, engine adaptor
instantiations and ``srand()`` when initialized or seeded with default
argument, constant expression or any user-configurable type. Pseudo-random
number engines seeded with a predictable value may cause vulnerabilities
e.g. in security protocols.

Examples:

.. code-block:: c++

  void foo() {
    std::mt19937 engine1; // Diagnose, always generate the same sequence
    std::mt19937 engine2(1); // Diagnose
    engine1.seed(); // Diagnose
    engine2.seed(1); // Diagnose

    std::time_t t;
    engine1.seed(std::time(&t)); // Diagnose, system time might be controlled by user

    int x = atoi(argv[1]);
    std::mt19937 engine3(x);  // Will not warn
  }

Options
-------

.. option:: DisallowedSeedTypes

   A comma-separated list of the type names which are disallowed.
   Default value is `time_t,std::time_t`.

References
----------

This check corresponds to the CERT C++ Coding Standard rules
`MSC51-CPP. Ensure your random number generator is properly seeded
<https://cmu-sei.github.io/secure-coding-standards/sei-cert-cpp-coding-standard/rules/miscellaneous-msc/msc51-cpp/>`_ and
`MSC32-C. Properly seed pseudorandom number generators
<https://cmu-sei.github.io/secure-coding-standards/sei-cert-c-coding-standard/rules/miscellaneous-msc/msc32-c/>`_.
