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Resync arc4random with OpenBSD.
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This brings us up to current, including djm's random-reseeding change,
as prompted by logan at cyberstorm.mu in bz#3467.  It brings the
platform-specific hooks from LibreSSL Portable, simplified to match our
use case.  ok djm@.
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@daztucker
daztucker committed Sep 2, 2022
1 parent beaddde commit ce39e7d
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Showing 3 changed files with 175 additions and 108 deletions.
191 changes: 90 additions & 101 deletions openbsd-compat/arc4random.c
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@@ -1,11 +1,10 @@
/* OPENBSD ORIGINAL: lib/libc/crypto/arc4random.c */

/* $OpenBSD: arc4random.c,v 1.25 2013/10/01 18:34:57 markus Exp $ */
/* $OpenBSD: arc4random.c,v 1.58 2022/07/31 13:41:45 tb Exp $ */

/*
* Copyright (c) 1996, David Mazieres <dm@uun.org>
* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
* Copyright (c) 2013, Markus Friedl <markus@openbsd.org>
* Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
Expand All @@ -24,14 +23,23 @@
* ChaCha based random number generator for OpenBSD.
*/

/* OPENBSD ORIGINAL: lib/libc/crypt/arc4random.c */

#include "includes.h"

#include <sys/types.h>

#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#ifdef HAVE_STDINT_H
#include <stdint.h>
#endif
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/time.h>

#ifndef HAVE_ARC4RANDOM

Expand All @@ -44,33 +52,43 @@
# define getentropy(x, y) (_ssh_compat_getentropy((x), (y)))
#endif

#define MINIMUM(a, b) (((a) < (b)) ? (a) : (b))
#define DEF_WEAK(x)

#include "log.h"

#define KEYSTREAM_ONLY
#include "chacha_private.h"

#ifdef __GNUC__
#define minimum(a, b) ((a) < (b) ? (a) : (b))

#if defined(__GNUC__) || defined(_MSC_VER)
#define inline __inline
#else /* !__GNUC__ */
#else /* __GNUC__ || _MSC_VER */
#define inline
#endif /* !__GNUC__ */

/* OpenSSH isn't multithreaded */
#define _ARC4_LOCK()
#define _ARC4_UNLOCK()
#endif /* !__GNUC__ && !_MSC_VER */

#define KEYSZ 32
#define IVSZ 8
#define BLOCKSZ 64
#define RSBUFSZ (16*BLOCKSZ)
static int rs_initialized;
static pid_t rs_stir_pid;
static chacha_ctx rs; /* chacha context for random keystream */
static u_char rs_buf[RSBUFSZ]; /* keystream blocks */
static size_t rs_have; /* valid bytes at end of rs_buf */
static size_t rs_count; /* bytes till reseed */

#define REKEY_BASE (1024*1024) /* NB. should be a power of 2 */

/* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
static struct _rs {
size_t rs_have; /* valid bytes at end of rs_buf */
size_t rs_count; /* bytes till reseed */
} *rs;

/* Maybe be preserved in fork children, if _rs_allocate() decides. */
static struct _rsx {
chacha_ctx rs_chacha; /* chacha context for random keystream */
u_char rs_buf[RSBUFSZ]; /* keystream blocks */
} *rsx;

static inline int _rs_allocate(struct _rs **, struct _rsx **);
static inline void _rs_forkdetect(void);
#include "arc4random.h"

static inline void _rs_rekey(u_char *dat, size_t datlen);

Expand All @@ -79,137 +97,128 @@ _rs_init(u_char *buf, size_t n)
{
if (n < KEYSZ + IVSZ)
return;
chacha_keysetup(&rs, buf, KEYSZ * 8);
chacha_ivsetup(&rs, buf + KEYSZ);

if (rs == NULL) {
if (_rs_allocate(&rs, &rsx) == -1)
_exit(1);
}

chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8);
chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
}

static void
_rs_stir(void)
{
u_char rnd[KEYSZ + IVSZ];
uint32_t rekey_fuzz = 0;

if (getentropy(rnd, sizeof rnd) == -1)
fatal("getentropy failed");
_getentropy_fail();

if (!rs_initialized) {
rs_initialized = 1;
if (!rs)
_rs_init(rnd, sizeof(rnd));
} else
else
_rs_rekey(rnd, sizeof(rnd));
explicit_bzero(rnd, sizeof(rnd));
explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */

/* invalidate rs_buf */
rs_have = 0;
memset(rs_buf, 0, RSBUFSZ);
rs->rs_have = 0;
memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));

rs_count = 1600000;
/* rekey interval should not be predictable */
chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz,
(uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz));
rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE);
}

static inline void
_rs_stir_if_needed(size_t len)
{
pid_t pid = getpid();

if (rs_count <= len || !rs_initialized || rs_stir_pid != pid) {
rs_stir_pid = pid;
_rs_forkdetect();
if (!rs || rs->rs_count <= len)
_rs_stir();
} else
rs_count -= len;
if (rs->rs_count <= len)
rs->rs_count = 0;
else
rs->rs_count -= len;
}

static inline void
_rs_rekey(u_char *dat, size_t datlen)
{
#ifndef KEYSTREAM_ONLY
memset(rs_buf, 0,RSBUFSZ);
memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
#endif
/* fill rs_buf with the keystream */
chacha_encrypt_bytes(&rs, rs_buf, rs_buf, RSBUFSZ);
chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
rsx->rs_buf, sizeof(rsx->rs_buf));
/* mix in optional user provided data */
if (dat) {
size_t i, m;

m = MINIMUM(datlen, KEYSZ + IVSZ);
m = minimum(datlen, KEYSZ + IVSZ);
for (i = 0; i < m; i++)
rs_buf[i] ^= dat[i];
rsx->rs_buf[i] ^= dat[i];
}
/* immediately reinit for backtracking resistance */
_rs_init(rs_buf, KEYSZ + IVSZ);
memset(rs_buf, 0, KEYSZ + IVSZ);
rs_have = RSBUFSZ - KEYSZ - IVSZ;
_rs_init(rsx->rs_buf, KEYSZ + IVSZ);
memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
}

static inline void
_rs_random_buf(void *_buf, size_t n)
{
u_char *buf = (u_char *)_buf;
u_char *keystream;
size_t m;

_rs_stir_if_needed(n);
while (n > 0) {
if (rs_have > 0) {
m = MINIMUM(n, rs_have);
memcpy(buf, rs_buf + RSBUFSZ - rs_have, m);
memset(rs_buf + RSBUFSZ - rs_have, 0, m);
if (rs->rs_have > 0) {
m = minimum(n, rs->rs_have);
keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
- rs->rs_have;
memcpy(buf, keystream, m);
memset(keystream, 0, m);
buf += m;
n -= m;
rs_have -= m;
rs->rs_have -= m;
}
if (rs_have == 0)
if (rs->rs_have == 0)
_rs_rekey(NULL, 0);
}
}

static inline void
_rs_random_u32(u_int32_t *val)
_rs_random_u32(uint32_t *val)
{
u_char *keystream;

_rs_stir_if_needed(sizeof(*val));
if (rs_have < sizeof(*val))
if (rs->rs_have < sizeof(*val))
_rs_rekey(NULL, 0);
memcpy(val, rs_buf + RSBUFSZ - rs_have, sizeof(*val));
memset(rs_buf + RSBUFSZ - rs_have, 0, sizeof(*val));
rs_have -= sizeof(*val);
return;
keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
memcpy(val, keystream, sizeof(*val));
memset(keystream, 0, sizeof(*val));
rs->rs_have -= sizeof(*val);
}

void
arc4random_stir(void)
{
_ARC4_LOCK();
_rs_stir();
_ARC4_UNLOCK();
}

void
arc4random_addrandom(u_char *dat, int datlen)
{
int m;

_ARC4_LOCK();
if (!rs_initialized)
_rs_stir();
while (datlen > 0) {
m = MINIMUM(datlen, KEYSZ + IVSZ);
_rs_rekey(dat, m);
dat += m;
datlen -= m;
}
_ARC4_UNLOCK();
}

u_int32_t
uint32_t
arc4random(void)
{
u_int32_t val;
uint32_t val;

_ARC4_LOCK();
_rs_random_u32(&val);
_ARC4_UNLOCK();
return val;
}
DEF_WEAK(arc4random);

/*
* If we are providing arc4random, then we can provide a more efficient
* If we are providing arc4random, then we can provide a more efficient
* arc4random_buf().
*/
# ifndef HAVE_ARC4RANDOM_BUF
Expand All @@ -220,6 +229,7 @@ arc4random_buf(void *buf, size_t n)
_rs_random_buf(buf, n);
_ARC4_UNLOCK();
}
DEF_WEAK(arc4random_buf);
# endif /* !HAVE_ARC4RANDOM_BUF */
#endif /* !HAVE_ARC4RANDOM */

Expand All @@ -242,24 +252,3 @@ arc4random_buf(void *_buf, size_t n)
}
#endif /* !defined(HAVE_ARC4RANDOM_BUF) && defined(HAVE_ARC4RANDOM) */

#if 0
/*-------- Test code for i386 --------*/
#include <stdio.h>
#include <machine/pctr.h>
int
main(int argc, char **argv)
{
const int iter = 1000000;
int i;
pctrval v;

v = rdtsc();
for (i = 0; i < iter; i++)
arc4random();
v = rdtsc() - v;
v /= iter;

printf("%qd cycles\n", v);
exit(0);
}
#endif

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