[New-bugs-announce] [issue17405] Add _Py_memset_s() to securely clear memory

[Christian Heimes]

New submission from Christian Heimes:

Compilers like GCC optimize away code like memset(var, 0, sizeof(var)) if the code occurs at the end of a function and var is not used anymore [1]. But security relevant code like hash and encryption use this to overwrite sensitive data with zeros.

The code in _sha3module.c uses memset() to clear its internal state. The other hash modules don't clear their internal states yet.


There exists a couple of solutions for the problem:

 * C11 [ISO/IEC 9899:2011] has a memset_s() function
 * MSVC has SecureZeroMemory()
 * GCC can disable the optimization with #pragma GCC optimize ("O0") since GCC 4.4
 * [2] contains an example for a custom implementation of memset_s() with volatile.

[1] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8537

[2] https://www.securecoding.cert.org/confluence/display/seccode/MSC06-C.+Be+aware+of+compiler+optimization+when+dealing+with+sensitive+data

----------
assignee: christian.heimes
messages: 184032
nosy: christian.heimes
priority: normal
severity: normal
stage: needs patch
status: open
title: Add _Py_memset_s() to securely clear memory
type: security
versions: Python 3.4

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<http://bugs.python.org/issue17405>
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