memset_explicit(3) - NetBSD Manual Pages

Command:
Section:
Arch:
Collection:
>>>
EXPLICIT_MEMSET(3)      NetBSD Library Functions Manual     EXPLICIT_MEMSET(3)


NAME

     explicit_memset memset_explicit -- guarantee writing a byte to a byte
     string


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <string.h>

     void *
     explicit_memset(void *b, int c, size_t len);

     void *
     memset_explicit(void *b, int c, size_t len);


DESCRIPTION

     The explicit_memset() and memset_explicit() functions write len bytes of
     value c (converted to an unsigned char) to the string b.  They are guar-
     anteed not to be optimized away by the compiler even if b is no longer
     used and is about to be freed or go out of scope.


RETURN VALUES

     The explicit_memset() function returns the original value of b.


EXAMPLES

     Create a buffer on the stack for a secret key, use it, and then zero it
     in memory before throwing it away.

           void
           f(void)
           {
                   uint8_t key[32];

                   crypto_random(key, sizeof(key));
                   do_crypto_stuff(key, sizeof(key));
                   ...

                   explicit_memset(key, 0, sizeof(key));
           }


SEE ALSO

     consttime_memequal(3), memset(3)


STANDARDS

     The memset_explicit() function conforms to ISO/IEC 9899:2023
     (``ISO C23'').


HISTORY

     The explicit_memset() function appeared in NetBSD 7.0.  The
     memset_explicit() alias was added in NetBSD 11.0.

NetBSD 10.99                   November 1, 2024                   NetBSD 10.99