minix/lib/libc/string/explicit_memset.3
Lionel Sambuc 84d9c625bf Synchronize on NetBSD-CVS (2013/12/1 12:00:00 UTC)
- Fix for possible unset uid/gid in toproto
 - Fix for default mtree style
 - Update libelf
 - Importing libexecinfo
 - Resynchronize GCC, mpc, gmp, mpfr
 - build.sh: Replace params with show-params.
     This has been done as the make target has been renamed in the same
     way, while a new target named params has been added. This new
     target generates a file containing all the parameters, instead of
     printing it on the console.
 - Update test48 with new etc/services (Fix by Ben Gras <ben@minix3.org)
     get getservbyport() out of the inner loop

Change-Id: Ie6ad5226fa2621ff9f0dee8782ea48f9443d2091
2014-07-28 17:05:06 +02:00

82 lines
2.6 KiB
Groff

.\" $NetBSD: explicit_memset.3,v 1.2 2013/08/28 15:46:23 riastradh Exp $
.\"
.\" Copyright (c) 2013 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This documentation is derived from text contributed to The NetBSD
.\" Foundation by Taylor R. Campbell.
.\"
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.\" modification, are permitted provided that the following conditions
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.Dd August 28, 2013
.Dt EXPLICIT_MEMSET 3
.Os
.Sh NAME
.Nm explicit_memset
.Nd guarantee writing a byte to a byte string
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In string.h
.Ft void *
.Fn explicit_memset "void *b" "int c" "size_t len"
.Sh DESCRIPTION
The
.Fn explicit_memset
function writes
.Fa len
bytes of value
.Fa c
(converted to an unsigned char) to the string
.Fa b .
It is guaranteed not to be optimized away by the compiler even if
.Fa b
is no longer used and is about to be freed or go out of scope.
.Sh RETURN VALUES
The
.Fn explicit_memset
function returns the original value of
.Fa b .
.Sh EXAMPLES
Create a buffer on the stack for a secret key, use it, and then zero it
in memory before throwing it away.
.Bd -literal -offset indent
void
f(void)
{
uint8_t key[32];
crypto_random(key, sizeof(key));
do_crypto_stuff(key, sizeof(key));
\&...
explicit_memset(key, 0, sizeof(key));
}
.Ed
.Sh SEE ALSO
.Xr consttime_memequal 3 ,
.Xr memset 3
.Sh HISTORY
The
.Fn explicit_memset
function appeared in
.Nx 7.0 .