shadow/libmisc/salt.c
Björn Esser 14b108728a
libmisc/salt.c: Sanitize code.
* Move all pre-processor defines to the top of the file.
* Unify the gensalt() function to be useable for all supported
  hash methods.
* Drop the gensalt_{b,yes}crypt() functions in favor of the
  previous change.
* Refactor the functions converting the rounds number into
  a string for use with the crypt() function, to not require
  any static buffer anymore.
* Clarify the comment about how crypt_make_salt() chooses the used
  hash method from the settings in the login.defs file.
* Use memset() to fill static buffers with zero before using them.
* Use a fixed amount of 16 random base64-chars for the
  sha{256,512}crypt hash methods, which is effectively still less
  than the recommendation from NIST (>= 128 bits), but the maximum
  those methods can effectively use (approx. 90 bits).
* Rename ROUNDS_{MIN,MAX} to SHA_ROUNDS_{MIN,MAX}.
* Bugfixes in the logic of setting rounds in BCRYPT_salt_rounds().
* Likewise for YESCRYPT_salt_cost().
* Fix formatting and white-space errors.

Signed-off-by: Björn Esser <besser82@fedoraproject.org>
2021-06-22 22:03:21 +02:00

424 lines
11 KiB
C

/*
* 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.
*
* l64a was Written by J.T. Conklin <jtc@netbsd.org>. Public domain.
*/
#include <config.h>
#ident "$Id$"
#include <sys/time.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#include "prototypes.h"
#include "defines.h"
#include "getdef.h"
/* 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 void seedRNG (void);
static /*@observer@*/const char *gensalt (size_t salt_size);
#if defined(USE_SHA_CRYPT) || defined(USE_BCRYPT)
static long shadow_random (long min, long max);
#endif /* USE_SHA_CRYPT || USE_BCRYPT */
#ifdef USE_SHA_CRYPT
static /*@observer@*/void SHA_salt_rounds_to_buf (char *buf, /*@null@*/int *prefered_rounds);
#endif /* USE_SHA_CRYPT */
#ifdef USE_BCRYPT
static /*@observer@*/void BCRYPT_salt_rounds_to_buf (char *buf, /*@null@*/int *prefered_rounds);
#endif /* USE_BCRYPT */
#ifdef USE_YESCRYPT
static /*@observer@*/void YESCRYPT_salt_cost_to_buf (char *buf, /*@null@*/int *prefered_cost);
#endif /* USE_YESCRYPT */
#ifndef HAVE_L64A
static /*@observer@*/char *l64a (long value)
{
static char buf[8];
char *s = buf;
int digit;
int i;
if (value < 0) {
errno = EINVAL;
return(NULL);
}
for (i = 0; value != 0 && i < 6; i++) {
digit = value & 0x3f;
if (digit < 2) {
*s = digit + '.';
} else if (digit < 12) {
*s = digit + '0' - 2;
} else if (digit < 38) {
*s = digit + 'A' - 12;
} else {
*s = digit + 'a' - 38;
}
value >>= 6;
s++;
}
*s = '\0';
return buf;
}
#endif /* !HAVE_L64A */
static void seedRNG (void)
{
struct timeval tv;
static int seeded = 0;
if (0 == seeded) {
(void) gettimeofday (&tv, NULL);
srandom (tv.tv_sec ^ tv.tv_usec ^ getpid ());
seeded = 1;
}
}
#if defined(USE_SHA_CRYPT) || defined(USE_BCRYPT)
/* It is not clear what is the maximum value of random().
* We assume 2^31-1.*/
#define RANDOM_MAX 0x7FFFFFFF
/*
* Return a random number between min and max (both included).
*
* It favors slightly the higher numbers.
*/
static long shadow_random (long min, long max)
{
double drand;
long ret;
seedRNG ();
drand = (double) (max - min + 1) * random () / RANDOM_MAX;
/* 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;
}
#endif /* USE_SHA_CRYPT || USE_BCRYPT */
#ifdef USE_SHA_CRYPT
/*
* 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, /*@null@*/int *prefered_rounds)
{
unsigned long rounds;
const size_t buf_begin = strlen (buf);
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;
}
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) shadow_random (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;
}
/* Nothing to do here if SHA_ROUNDS_DEFAULT is used. */
if (rounds == SHA_ROUNDS_DEFAULT) {
return;
}
/* Check if the result buffer is long enough. */
assert (GENSALT_SETTING_SIZE > buf_begin + 17);
(void) snprintf (buf + buf_begin, 18, "rounds=%lu$", rounds);
}
#endif /* USE_SHA_CRYPT */
#ifdef USE_BCRYPT
/*
* 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, /*@null@*/int *prefered_rounds)
{
unsigned long rounds;
const size_t buf_begin = strlen (buf);
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)) {
rounds = B_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) shadow_random (min_rounds, max_rounds);
}
} else if (0 == *prefered_rounds) {
rounds = B_ROUNDS_DEFAULT;
} else {
rounds = (unsigned long) *prefered_rounds;
}
/* Sanity checks. */
if (rounds < B_ROUNDS_MIN) {
rounds = B_ROUNDS_MIN;
}
/*
* Use 19 as an upper bound for now,
* because musl doesn't allow rounds >= 20.
*/
if (rounds > 19) {
/* rounds = B_ROUNDS_MAX; */
rounds = 19;
}
/* Check if the result buffer is long enough. */
assert (GENSALT_SETTING_SIZE > buf_begin + 3);
(void) snprintf (buf + buf_begin, 4, "%2.2lu$", rounds);
}
#endif /* USE_BCRYPT */
#ifdef USE_YESCRYPT
/*
* Fill a salt prefix specifying the cost for the YESCRYPT method
* to a buffer.
*/
static /*@observer@*/void YESCRYPT_salt_cost_to_buf (char *buf, /*@null@*/int *prefered_cost)
{
unsigned long cost;
const size_t buf_begin = strlen (buf);
if (NULL == prefered_cost) {
cost = getdef_num ("YESCRYPT_COST_FACTOR", Y_COST_DEFAULT);
} else if (0 == *prefered_cost) {
cost = Y_COST_DEFAULT;
} else {
cost = (unsigned long) *prefered_cost;
}
/* Sanity checks. */
if (cost < Y_COST_MIN) {
cost = Y_COST_MIN;
}
if (cost > Y_COST_MAX) {
cost = Y_COST_MAX;
}
/* Check if the result buffer is long enough. */
assert (GENSALT_SETTING_SIZE > buf_begin + 3);
buf[buf_begin + 0] = 'j';
if (cost < 3) {
buf[buf_begin + 1] = 0x36 + cost;
} else if (cost < 6) {
buf[buf_begin + 1] = 0x34 + cost;
} else {
buf[buf_begin + 1] = 0x3b + cost;
}
buf[buf_begin + 2] = cost >= 3 ? 'T' : '5';
buf[buf_begin + 3] = '$';
buf[buf_begin + 4] = '\0';
}
#endif /* USE_YESCRYPT */
static /*@observer@*/const char *gensalt (size_t salt_size)
{
static char salt[MAX_SALT_SIZE + 6];
memset (salt, '\0', MAX_SALT_SIZE + 6);
assert (salt_size >= MIN_SALT_SIZE &&
salt_size <= MAX_SALT_SIZE);
seedRNG ();
strcat (salt, l64a (random()));
do {
strcat (salt, l64a (random()));
} while (strlen (salt) < salt_size);
salt[salt_size] = '\0';
return salt;
}
/*
* 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).
* * 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;
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;
#ifdef USE_BCRYPT
} else if (0 == strcmp (method, "BCRYPT")) {
BCRYPTMAGNUM(result);
salt_len = BCRYPT_SALT_SIZE;
BCRYPT_salt_rounds_to_buf (result, (int *) arg);
#endif /* USE_BCRYPT */
#ifdef USE_YESCRYPT
} else if (0 == strcmp (method, "YESCRYPT")) {
MAGNUM(result, 'y');
salt_len = YESCRYPT_SALT_SIZE;
YESCRYPT_salt_cost_to_buf (result, (int *) arg);
#endif /* USE_YESCRYPT */
#ifdef USE_SHA_CRYPT
} else if (0 == strcmp (method, "SHA256")) {
MAGNUM(result, '5');
salt_len = SHA_CRYPT_SALT_SIZE;
SHA_salt_rounds_to_buf (result, (int *) arg);
} else if (0 == strcmp (method, "SHA512")) {
MAGNUM(result, '6');
salt_len = SHA_CRYPT_SALT_SIZE;
SHA_salt_rounds_to_buf (result, (int *) arg);
#endif /* USE_SHA_CRYPT */
} else if (0 != strcmp (method, "DES")) {
fprintf (shadow_logfd,
_("Invalid ENCRYPT_METHOD value: '%s'.\n"
"Defaulting to DES.\n"),
method);
salt_len = MAX_SALT_SIZE;
memset (result, '\0', GENSALT_SETTING_SIZE);
}
/* 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;
}