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1//
2// printf_count_output.cpp
3//
4// Copyright (c) Microsoft Corporation. All rights reserved.
5//
6// Defines the functions that control the enable state of %n.
7//
8#include <corecrt_internal_stdio.h>
9
10
11
12static UINT_PTR enable_percent_n = 0;
13
14
15
16// Enables or disables the %n format specifier for the printf family of functions.
17// Note the use of the __security_cookie: if the static variable was set to a
18// known value, an attacker could potentially modify that value and then provide
19// a malicious %n specifier. The cookie is or'ed with 1 becuase a cookie with a
20// value of zero is possible.
21extern "C" int __cdecl _set_printf_count_output(int const value)
22{
23 int const old = (enable_percent_n == (__security_cookie | 1));
24 enable_percent_n = (value ? (__security_cookie | 1) : 0);
25 return old;
26}
27
28
29
30// Tests whether the %n format specifier for the printf family of functions is
31// enabled.
32extern "C" int __cdecl _get_printf_count_output()
33{
34 return enable_percent_n == (__security_cookie | 1);
35}