shadow/libmisc/salt.c

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/*
* SPDX-FileCopyrightText: Marek Michalkiewicz <marekm@i17linuxb.ists.pwr.wroc.pl>
* SPDX-FileCopyrightText: J.T. Conklin <jtc@netbsd.org>
*
* SPDX-License-Identifier: Unlicense
*/
/*
* salt.c - generate a random salt string for crypt()
*
* Written by Marek Michalkiewicz <marekm@i17linuxb.ists.pwr.wroc.pl>,
* it is in the public domain.
*/
#include <config.h>
#ident "$Id$"
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#if HAVE_SYS_RANDOM_H
#include <sys/random.h>
#endif
#include "prototypes.h"
#include "defines.h"
#include "getdef.h"
#include "shadowlog.h"
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#if (defined CRYPT_GENSALT_IMPLEMENTS_AUTO_ENTROPY && \
CRYPT_GENSALT_IMPLEMENTS_AUTO_ENTROPY)
#define USE_XCRYPT_GENSALT 1
#else
#define USE_XCRYPT_GENSALT 0
#endif
/* Add the salt prefix. */
#define MAGNUM(array,ch) (array)[0]=(array)[2]='$',(array)[1]=(ch),(array)[3]='\0'
#ifdef USE_BCRYPT
/* Use $2b$ as prefix for compatibility with OpenBSD's bcrypt. */
#define BCRYPTMAGNUM(array) (array)[0]=(array)[3]='$',(array)[1]='2',(array)[2]='b',(array)[4]='\0'
#define BCRYPT_SALT_SIZE 22
/* Default number of rounds if not explicitly specified. */
#define B_ROUNDS_DEFAULT 13
/* Minimum number of rounds. */
#define B_ROUNDS_MIN 4
/* Maximum number of rounds. */
#define B_ROUNDS_MAX 31
#endif /* USE_BCRYPT */
#ifdef USE_SHA_CRYPT
/* Fixed salt len for sha{256,512}crypt. */
#define SHA_CRYPT_SALT_SIZE 16
/* Default number of rounds if not explicitly specified. */
#define SHA_ROUNDS_DEFAULT 5000
/* Minimum number of rounds. */
#define SHA_ROUNDS_MIN 1000
/* Maximum number of rounds. */
#define SHA_ROUNDS_MAX 999999999
#endif
#ifdef USE_YESCRYPT
/*
* Default number of base64 characters used for the salt.
* 24 characters gives a 144 bits (18 bytes) salt. Unlike the more
* traditional 128 bits (16 bytes) salt, this 144 bits salt is always
* represented by the same number of base64 characters without padding
* issue, even with a non-standard base64 encoding scheme.
*/
#define YESCRYPT_SALT_SIZE 24
/* Default cost if not explicitly specified. */
#define Y_COST_DEFAULT 5
/* Minimum cost. */
#define Y_COST_MIN 1
/* Maximum cost. */
#define Y_COST_MAX 11
#endif
/* Fixed salt len for md5crypt. */
#define MD5_CRYPT_SALT_SIZE 8
/* Generate salt of size salt_size. */
#define MAX_SALT_SIZE 44
#define MIN_SALT_SIZE 8
/* Maximum size of the generated salt string. */
#define GENSALT_SETTING_SIZE 100
/* local function prototypes */
static long read_random_bytes (void);
#if !USE_XCRYPT_GENSALT
static /*@observer@*/const char *gensalt (size_t salt_size);
#endif /* !USE_XCRYPT_GENSALT */
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#if defined(USE_SHA_CRYPT) || defined(USE_BCRYPT)
static long csrand_interval (long min, long max);
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#endif /* USE_SHA_CRYPT || USE_BCRYPT */
#ifdef USE_SHA_CRYPT
static /*@observer@*/unsigned long SHA_get_salt_rounds (/*@null@*/const int *prefered_rounds);
static /*@observer@*/void SHA_salt_rounds_to_buf (char *buf, unsigned long rounds);
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#endif /* USE_SHA_CRYPT */
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#ifdef USE_BCRYPT
static /*@observer@*/unsigned long BCRYPT_get_salt_rounds (/*@null@*/const int *prefered_rounds);
static /*@observer@*/void BCRYPT_salt_rounds_to_buf (char *buf, unsigned long rounds);
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#endif /* USE_BCRYPT */
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#ifdef USE_YESCRYPT
static /*@observer@*/unsigned long YESCRYPT_get_salt_cost (/*@null@*/const int *prefered_cost);
static /*@observer@*/void YESCRYPT_salt_cost_to_buf (char *buf, unsigned long cost);
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#endif /* USE_YESCRYPT */
/* Read sizeof (long) random bytes from /dev/urandom. */
static long read_random_bytes (void)
{
long randval = 0;
#ifdef HAVE_GETENTROPY
/* getentropy may exist but lack kernel support. */
if (getentropy (&randval, sizeof (randval)) == 0) {
goto end;
}
#endif
#ifdef HAVE_GETRANDOM
/* Likewise getrandom. */
if ((size_t) getrandom (&randval, sizeof (randval), 0) == sizeof (randval)) {
goto end;
}
#endif
#ifdef HAVE_ARC4RANDOM_BUF
/* arc4random_buf, if it exists, can never fail. */
arc4random_buf (&randval, sizeof (randval));
goto end;
#endif
/* Use /dev/urandom as a last resort. */
FILE *f = fopen ("/dev/urandom", "r");
if (NULL == f) {
goto fail;
}
if (fread (&randval, sizeof (randval), 1, f) != 1) {
fclose(f);
goto fail;
}
fclose(f);
goto end;
fail:
fprintf (log_get_logfd(),
_("Unable to obtain random bytes.\n"));
exit (1);
end:
return randval;
}
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#if defined(USE_SHA_CRYPT) || defined(USE_BCRYPT)
/*
* Return a random number between min and max (both included).
*
* It favors slightly the higher numbers.
*/
static long csrand_interval (long min, long max)
{
double drand;
long ret;
drand = (double) (read_random_bytes () & RAND_MAX) / (double) RAND_MAX;
drand *= (double) (max - min + 1);
/* On systems were this is not random() range is lower, we favor
* higher numbers of salt. */
ret = (long) (max + 1 - drand);
/* And we catch limits, and use the highest number */
if ((ret < min) || (ret > max)) {
ret = max;
}
return ret;
}
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#endif /* USE_SHA_CRYPT || USE_BCRYPT */
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#ifdef USE_SHA_CRYPT
/* Return the the rounds number for the SHA crypt methods. */
static /*@observer@*/unsigned long SHA_get_salt_rounds (/*@null@*/const int *prefered_rounds)
{
unsigned long rounds;
if (NULL == prefered_rounds) {
long min_rounds = getdef_long ("SHA_CRYPT_MIN_ROUNDS", -1);
long max_rounds = getdef_long ("SHA_CRYPT_MAX_ROUNDS", -1);
if ((-1 == min_rounds) && (-1 == max_rounds)) {
rounds = SHA_ROUNDS_DEFAULT;
}
else {
if (-1 == min_rounds) {
min_rounds = max_rounds;
}
if (-1 == max_rounds) {
max_rounds = min_rounds;
}
if (min_rounds > max_rounds) {
max_rounds = min_rounds;
}
rounds = (unsigned long) csrand_interval (min_rounds, max_rounds);
}
} else if (0 == *prefered_rounds) {
rounds = SHA_ROUNDS_DEFAULT;
} else {
rounds = (unsigned long) *prefered_rounds;
}
/* Sanity checks. The libc should also check this, but this
* protects against a rounds_prefix overflow. */
if (rounds < SHA_ROUNDS_MIN) {
rounds = SHA_ROUNDS_MIN;
}
if (rounds > SHA_ROUNDS_MAX) {
rounds = SHA_ROUNDS_MAX;
}
return rounds;
}
/*
* Fill a salt prefix specifying the rounds number for the SHA crypt methods
* to a buffer.
*/
static /*@observer@*/void SHA_salt_rounds_to_buf (char *buf, unsigned long rounds)
{
const size_t buf_begin = strlen (buf);
/* Nothing to do here if SHA_ROUNDS_DEFAULT is used. */
if (rounds == SHA_ROUNDS_DEFAULT) {
return;
}
/*
* Check if the result buffer is long enough.
* We are going to write a maximum of 17 bytes,
* plus one byte for the terminator.
* rounds=XXXXXXXXX$
* 00000000011111111
* 12345678901234567
*/
assert (GENSALT_SETTING_SIZE > buf_begin + 17);
(void) snprintf (buf + buf_begin, 18, "rounds=%lu$", rounds);
}
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#endif /* USE_SHA_CRYPT */
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#ifdef USE_BCRYPT
/* Return the the rounds number for the BCRYPT method. */
static /*@observer@*/unsigned long BCRYPT_get_salt_rounds (/*@null@*/const int *prefered_rounds)
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{
unsigned long rounds;
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if (NULL == prefered_rounds) {
long min_rounds = getdef_long ("BCRYPT_MIN_ROUNDS", -1);
long max_rounds = getdef_long ("BCRYPT_MAX_ROUNDS", -1);
if ((-1 == min_rounds) && (-1 == max_rounds)) {
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rounds = B_ROUNDS_DEFAULT;
} else {
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if (-1 == min_rounds) {
min_rounds = max_rounds;
}
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if (-1 == max_rounds) {
max_rounds = min_rounds;
}
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if (min_rounds > max_rounds) {
max_rounds = min_rounds;
}
rounds = (unsigned long) csrand_interval (min_rounds, max_rounds);
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}
} else if (0 == *prefered_rounds) {
rounds = B_ROUNDS_DEFAULT;
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} else {
rounds = (unsigned long) *prefered_rounds;
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}
/* Sanity checks. */
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if (rounds < B_ROUNDS_MIN) {
rounds = B_ROUNDS_MIN;
}
#if USE_XCRYPT_GENSALT
if (rounds > B_ROUNDS_MAX) {
rounds = B_ROUNDS_MAX;
}
#else /* USE_XCRYPT_GENSALT */
/*
* Use 19 as an upper bound for now,
* because musl doesn't allow rounds >= 20.
* If musl ever supports > 20 rounds,
* rounds should be set to B_ROUNDS_MAX.
*/
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if (rounds > 19) {
rounds = 19;
}
#endif /* USE_XCRYPT_GENSALT */
return rounds;
}
/*
* Fill a salt prefix specifying the rounds number for the BCRYPT method
* to a buffer.
*/
static /*@observer@*/void BCRYPT_salt_rounds_to_buf (char *buf, unsigned long rounds)
{
const size_t buf_begin = strlen (buf);
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/*
* Check if the result buffer is long enough.
* We are going to write three bytes,
* plus one byte for the terminator.
* XX$
* 000
* 123
*/
assert (GENSALT_SETTING_SIZE > buf_begin + 3);
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(void) snprintf (buf + buf_begin, 4, "%2.2lu$", rounds);
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}
#endif /* USE_BCRYPT */
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#ifdef USE_YESCRYPT
/* Return the the cost number for the YESCRYPT method. */
static /*@observer@*/unsigned long YESCRYPT_get_salt_cost (/*@null@*/const int *prefered_cost)
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{
unsigned long cost;
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if (NULL == prefered_cost) {
cost = getdef_num ("YESCRYPT_COST_FACTOR", Y_COST_DEFAULT);
} else if (0 == *prefered_cost) {
cost = Y_COST_DEFAULT;
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} else {
cost = (unsigned long) *prefered_cost;
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}
/* Sanity checks. */
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if (cost < Y_COST_MIN) {
cost = Y_COST_MIN;
}
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if (cost > Y_COST_MAX) {
cost = Y_COST_MAX;
}
return cost;
}
/*
* Fill a salt prefix specifying the cost for the YESCRYPT method
* to a buffer.
*/
static /*@observer@*/void YESCRYPT_salt_cost_to_buf (char *buf, unsigned long cost)
{
const size_t buf_begin = strlen (buf);
/*
* Check if the result buffer is long enough.
* We are going to write four bytes,
* plus one byte for the terminator.
* jXX$
* 0000
* 1234
*/
assert (GENSALT_SETTING_SIZE > buf_begin + 4);
buf[buf_begin + 0] = 'j';
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if (cost < 3) {
buf[buf_begin + 1] = 0x36 + cost;
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} else if (cost < 6) {
buf[buf_begin + 1] = 0x34 + cost;
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} else {
buf[buf_begin + 1] = 0x3b + cost;
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}
buf[buf_begin + 2] = cost >= 3 ? 'T' : '5';
buf[buf_begin + 3] = '$';
buf[buf_begin + 4] = '\0';
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}
#endif /* USE_YESCRYPT */
#if !USE_XCRYPT_GENSALT
static /*@observer@*/const char *gensalt (size_t salt_size)
{
static char salt[MAX_SALT_SIZE + 6];
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memset (salt, '\0', MAX_SALT_SIZE + 6);
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assert (salt_size >= MIN_SALT_SIZE &&
salt_size <= MAX_SALT_SIZE);
strcat (salt, l64a (read_random_bytes ()));
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do {
strcat (salt, l64a (read_random_bytes ()));
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} while (strlen (salt) < salt_size);
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salt[salt_size] = '\0';
return salt;
}
#endif /* !USE_XCRYPT_GENSALT */
/*
* Generate 8 base64 ASCII characters of random salt. If MD5_CRYPT_ENAB
* in /etc/login.defs is "yes", the salt string will be prefixed by "$1$"
* (magic) and pw_encrypt() will execute the MD5-based FreeBSD-compatible
* version of crypt() instead of the standard one.
* Other methods can be set with ENCRYPT_METHOD
*
* The method can be forced with the meth parameter.
* If NULL, the method will be defined according to the ENCRYPT_METHOD
* variable, and if not set according to the MD5_CRYPT_ENAB variable,
* which can both be set inside the login.defs file.
*
* If meth is specified, an additional parameter can be provided.
* * For the SHA256 and SHA512 method, this specifies the number of rounds
* (if not NULL).
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* * For the YESCRYPT method, this specifies the cost factor (if not NULL).
*/
/*@observer@*/const char *crypt_make_salt (/*@null@*//*@observer@*/const char *meth, /*@null@*/void *arg)
{
static char result[GENSALT_SETTING_SIZE];
size_t salt_len = MAX_SALT_SIZE;
const char *method;
unsigned long rounds = 0;
memset (result, '\0', GENSALT_SETTING_SIZE);
if (NULL != meth)
method = meth;
else {
method = getdef_str ("ENCRYPT_METHOD");
if (NULL == method) {
method = getdef_bool ("MD5_CRYPT_ENAB") ? "MD5" : "DES";
}
}
if (0 == strcmp (method, "MD5")) {
MAGNUM(result, '1');
salt_len = MD5_CRYPT_SALT_SIZE;
rounds = 0;
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#ifdef USE_BCRYPT
} else if (0 == strcmp (method, "BCRYPT")) {
BCRYPTMAGNUM(result);
salt_len = BCRYPT_SALT_SIZE;
rounds = BCRYPT_get_salt_rounds ((int *) arg);
BCRYPT_salt_rounds_to_buf (result, rounds);
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#endif /* USE_BCRYPT */
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#ifdef USE_YESCRYPT
} else if (0 == strcmp (method, "YESCRYPT")) {
MAGNUM(result, 'y');
salt_len = YESCRYPT_SALT_SIZE;
rounds = YESCRYPT_get_salt_cost ((int *) arg);
YESCRYPT_salt_cost_to_buf (result, rounds);
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#endif /* USE_YESCRYPT */
#ifdef USE_SHA_CRYPT
} else if (0 == strcmp (method, "SHA256")) {
MAGNUM(result, '5');
salt_len = SHA_CRYPT_SALT_SIZE;
rounds = SHA_get_salt_rounds ((int *) arg);
SHA_salt_rounds_to_buf (result, rounds);
} else if (0 == strcmp (method, "SHA512")) {
MAGNUM(result, '6');
salt_len = SHA_CRYPT_SALT_SIZE;
rounds = SHA_get_salt_rounds ((int *) arg);
SHA_salt_rounds_to_buf (result, rounds);
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#endif /* USE_SHA_CRYPT */
} else if (0 != strcmp (method, "DES")) {
fprintf (log_get_logfd(),
_("Invalid ENCRYPT_METHOD value: '%s'.\n"
"Defaulting to DES.\n"),
method);
salt_len = MAX_SALT_SIZE;
rounds = 0;
memset (result, '\0', GENSALT_SETTING_SIZE);
}
#if USE_XCRYPT_GENSALT
/*
* Prepare DES setting for crypt_gensalt(), if result
* has not been filled with anything previously.
*/
if ('\0' == result[0]) {
/* Avoid -Wunused-but-set-variable. */
salt_len = GENSALT_SETTING_SIZE - 1;
rounds = 0;
memset (result, '.', salt_len);
result[salt_len] = '\0';
}
char *retval = crypt_gensalt (result, rounds, NULL, 0);
/* Should not happen, but... */
if (NULL == retval) {
fprintf (log_get_logfd(),
_("Unable to generate a salt from setting "
"\"%s\", check your settings in "
"ENCRYPT_METHOD and the corresponding "
"configuration for your selected hash "
"method.\n"), result);
exit (1);
}
return retval;
#else /* USE_XCRYPT_GENSALT */
/* Check if the result buffer is long enough. */
assert (GENSALT_SETTING_SIZE > strlen (result) + salt_len);
/* Concatenate a pseudo random salt. */
strncat (result, gensalt (salt_len),
GENSALT_SETTING_SIZE - strlen (result) - 1);
return result;
#endif /* USE_XCRYPT_GENSALT */
}