source: trunk/server/lib/util/genrand.c

/* 
   Unix SMB/CIFS implementation.

   Functions to create reasonable random numbers for crypto use.

   Copyright (C) Jeremy Allison 2001
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "system/filesys.h"
#include "../lib/crypto/crypto.h"
#include "system/locale.h"

/**
 * @file
 * @brief Random number generation
 */

static unsigned char hash[258];
static uint32_t counter;

static bool done_reseed = false;
static unsigned int bytes_since_reseed = 0;

static int urand_fd = -1;

static void (*reseed_callback)(void *userdata, int *newseed);
static void *reseed_callback_userdata = NULL;

/**
 Copy any user given reseed data.
**/

_PUBLIC_ void set_rand_reseed_callback(void (*fn)(void *, int *), void *userdata)
{
        reseed_callback = fn;
        reseed_callback_userdata = userdata;
        set_need_random_reseed();
}

/**
 * Tell the random number generator it needs to reseed.
 */
_PUBLIC_ void set_need_random_reseed(void)
{
        done_reseed = false;
        bytes_since_reseed = 0;
}

static void get_rand_reseed_data(int *reseed_data)
{
        if (reseed_callback) {
                reseed_callback(reseed_callback_userdata, reseed_data);
        } else {
                *reseed_data = 0;
        }
}

/**************************************************************** 
 Setup the seed.
*****************************************************************/

static void seed_random_stream(unsigned char *seedval, size_t seedlen)
{
        unsigned char j = 0;
        size_t ind;

        for (ind = 0; ind < 256; ind++)
                hash[ind] = (unsigned char)ind;

        for( ind = 0; ind < 256; ind++) {
                unsigned char tc;

                j += (hash[ind] + seedval[ind%seedlen]);

                tc = hash[ind];
                hash[ind] = hash[j];
                hash[j] = tc;
        }

        hash[256] = 0;
        hash[257] = 0;
}

/**************************************************************** 
 Get datasize bytes worth of random data.
*****************************************************************/

static void get_random_stream(unsigned char *data, size_t datasize)
{
        unsigned char index_i = hash[256];
        unsigned char index_j = hash[257];
        size_t ind;

        for( ind = 0; ind < datasize; ind++) {
                unsigned char tc;
                unsigned char t;

                index_i++;
                index_j += hash[index_i];

                tc = hash[index_i];
                hash[index_i] = hash[index_j];
                hash[index_j] = tc;

                t = hash[index_i] + hash[index_j];
                data[ind] = hash[t];
        }

        hash[256] = index_i;
        hash[257] = index_j;
}

/****************************************************************
 Get a 16 byte hash from the contents of a file.  

 Note that the hash is initialised, because the extra entropy is not
 worth the valgrind pain.
*****************************************************************/

static void do_filehash(const char *fname, unsigned char *the_hash)
{
        unsigned char buf[1011]; /* deliberate weird size */
        unsigned char tmp_md4[16];
        int fd, n;

        ZERO_STRUCT(tmp_md4);

        fd = open(fname,O_RDONLY,0);
        if (fd == -1)
                return;

        while ((n = read(fd, (char *)buf, sizeof(buf))) > 0) {
                mdfour(tmp_md4, buf, n);
                for (n=0;n<16;n++)
                        the_hash[n] ^= tmp_md4[n];
        }
        close(fd);
}

/**************************************************************
 Try and get a good random number seed. Try a number of
 different factors. Firstly, try /dev/urandom - use if exists.

 We use /dev/urandom as a read of /dev/random can block if
 the entropy pool dries up. This leads clients to timeout
 or be very slow on connect.

 If we can't use /dev/urandom then seed the stream random generator
 above...
**************************************************************/

static int do_reseed(bool use_fd, int fd)
{
        unsigned char seed_inbuf[40];
        uint32_t v1, v2; struct timeval tval; pid_t mypid;
        int reseed_data = 0;

        if (use_fd) {
                if (fd == -1) {
                        fd = open( "/dev/urandom", O_RDONLY,0);
                }
                if (fd != -1
                    && (read(fd, seed_inbuf, sizeof(seed_inbuf)) == sizeof(seed_inbuf))) {
                        seed_random_stream(seed_inbuf, sizeof(seed_inbuf));
                        return fd;
                }
        }

        /* Add in some secret file contents */

        do_filehash("/etc/shadow", &seed_inbuf[0]);

        /*
         * Add the counter, time of day, and pid.
         */

        GetTimeOfDay(&tval);
        mypid = getpid();
        v1 = (counter++) + mypid + tval.tv_sec;
        v2 = (counter++) * mypid + tval.tv_usec;

        SIVAL(seed_inbuf, 32, v1 ^ IVAL(seed_inbuf, 32));
        SIVAL(seed_inbuf, 36, v2 ^ IVAL(seed_inbuf, 36));

        /*
         * Add any user-given reseed data.
         */

        get_rand_reseed_data(&reseed_data);
        if (reseed_data) {
                size_t i;
                for (i = 0; i < sizeof(seed_inbuf); i++)
                        seed_inbuf[i] ^= ((char *)(&reseed_data))[i % sizeof(reseed_data)];
        }

        seed_random_stream(seed_inbuf, sizeof(seed_inbuf));

        return -1;
}

/**
 Interface to the (hopefully) good crypto random number generator.
 Will use our internal PRNG if more than 40 bytes of random generation
 has been requested, otherwise tries to read from /dev/random
**/
_PUBLIC_ void generate_random_buffer(uint8_t *out, int len)
{
        unsigned char md4_buf[64];
        unsigned char tmp_buf[16];
        unsigned char *p;

#ifndef __OS2__
        if(!done_reseed) {
                bytes_since_reseed += len;
                
                /* Magic constant to try and avoid reading 40 bytes
                 * and setting up the PRNG if the app only ever wants
                 * a few bytes */
                if (bytes_since_reseed < 40) {
                        if (urand_fd == -1) {
                                urand_fd = open( "/dev/urandom", O_RDONLY,0);
                        }
                        if(urand_fd != -1 && (read(urand_fd, out, len) == len)) {
                                return;
                        }
                }

                urand_fd = do_reseed(true, urand_fd);
                done_reseed = true;
        }
#endif

        /*
         * Generate random numbers in chunks of 64 bytes,
         * then md4 them & copy to the output buffer.
         * This way the raw state of the stream is never externally
         * seen.
         */

        p = out;
        while(len > 0) {
                int copy_len = len > 16 ? 16 : len;

#ifdef __OS2__
                os2_randget(md4_buf, sizeof(md4_buf));
#else
                get_random_stream(md4_buf, sizeof(md4_buf));
#endif
                mdfour(tmp_buf, md4_buf, sizeof(md4_buf));
                memcpy(p, tmp_buf, copy_len);
                p += copy_len;
                len -= copy_len;
        }
}

/**
 Interface to the (hopefully) good crypto random number generator.
 Will always use /dev/urandom if available.
**/
_PUBLIC_ void generate_secret_buffer(uint8_t *out, int len)
{
        if (urand_fd == -1) {
                urand_fd = open( "/dev/urandom", O_RDONLY,0);
        }
        if(urand_fd != -1 && (read(urand_fd, out, len) == len)) {
                return;
        }
        
        generate_random_buffer(out, len);
}

/**
  generate a single random uint32_t
**/
_PUBLIC_ uint32_t generate_random(void)
{
        uint8_t v[4];
        generate_random_buffer(v, 4);
        return IVAL(v, 0);
}


/**
  very basic password quality checker
**/
_PUBLIC_ bool check_password_quality(const char *s)
{
        int has_digit=0, has_capital=0, has_lower=0, has_special=0, has_high=0;
        const char* reals = s;
        while (*s) {
                if (isdigit((unsigned char)*s)) {
                        has_digit |= 1;
                } else if (isupper((unsigned char)*s)) {
                        has_capital |= 1;
                } else if (islower((unsigned char)*s)) {
                        has_lower |= 1;
                } else if (isascii((unsigned char)*s)) {
                        has_special |= 1;
                } else {
                        has_high++;
                }
                s++;
        }

        return ((has_digit + has_lower + has_capital + has_special) >= 3
                || (has_high > strlen(reals)/2));
}

/**
 Use the random number generator to generate a random string.
**/

_PUBLIC_ char *generate_random_str_list(TALLOC_CTX *mem_ctx, size_t len, const char *list)
{
        size_t i;
        size_t list_len = strlen(list);

        char *retstr = talloc_array(mem_ctx, char, len + 1);
        if (!retstr) return NULL;

        generate_random_buffer((uint8_t *)retstr, len);
        for (i = 0; i < len; i++) {
                retstr[i] = list[retstr[i] % list_len];
        }
        retstr[i] = '\0';

        return retstr;
}

/**
 * Generate a random text string consisting of the specified length.
 * The returned string will be allocated.
 *
 * Characters used are: ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+_-#.,
 */

_PUBLIC_ char *generate_random_str(TALLOC_CTX *mem_ctx, size_t len)
{
        char *retstr;
        const char *c_list = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+_-#.,";

again:
        retstr = generate_random_str_list(mem_ctx, len, c_list);
        if (!retstr) return NULL;

        /* we need to make sure the random string passes basic quality tests
           or it might be rejected by windows as a password */
        if (len >= 7 && !check_password_quality(retstr)) {
                talloc_free(retstr);
                goto again;
        }

        return retstr;
}

/**
 * Generate a random text password.
 */

_PUBLIC_ char *generate_random_password(TALLOC_CTX *mem_ctx, size_t min, size_t max)
{
        char *retstr;
        /* This list does not include { or } because they cause
         * problems for our provision (it can create a substring
         * ${...}, and for Fedora DS (which treats {...} at the start
         * of a stored password as special 
         *  -- Andrew Bartlett 2010-03-11
         */
        const char *c_list = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+_-#.,@$%&!?:;<=>()[]~";
        size_t len = max;
        size_t diff;

        if (min > max) {
                errno = EINVAL;
                return NULL;
        }

        diff = max - min;

        if (diff > 0 ) {
                size_t tmp;

                generate_random_buffer((uint8_t *)&tmp, sizeof(tmp));

                tmp %= diff;

                len = min + tmp;
        }

again:
        retstr = generate_random_str_list(mem_ctx, len, c_list);
        if (!retstr) return NULL;

        /* we need to make sure the random string passes basic quality tests
           or it might be rejected by windows as a password */
        if (len >= 7 && !check_password_quality(retstr)) {
                talloc_free(retstr);
                goto again;
        }

        return retstr;
}

/**
 * Generate an array of unique text strings all of the same length.
 * The returned string will be allocated.
 * Returns NULL if the number of unique combinations cannot be created.
 *
 * Characters used are: abcdefghijklmnopqrstuvwxyz0123456789+_-#.,
 */
_PUBLIC_ char** generate_unique_strs(TALLOC_CTX *mem_ctx, size_t len,
                                     uint32_t num)
{
        const char *c_list = "abcdefghijklmnopqrstuvwxyz0123456789+_-#.,";
        const unsigned c_size = 42;
        int i, j;
        unsigned rem;
        char ** strs = NULL;

        if (num == 0 || len == 0)
                return NULL;

        strs = talloc_array(mem_ctx, char *, num);
        if (strs == NULL) return NULL;

        for (i = 0; i < num; i++) {
                char *retstr = (char *)talloc_size(strs, len + 1);
                if (retstr == NULL) {
                        talloc_free(strs);
                        return NULL;
                }
                rem = i;
                for (j = 0; j < len; j++) {
                        retstr[j] = c_list[rem % c_size];
                        rem = rem / c_size;
                }
                retstr[j] = 0;
                strs[i] = retstr;
                if (rem != 0) {
                        /* we were not able to fit the number of
                         * combinations asked for in the length
                         * specified */
                        DEBUG(0,(__location__ ": Too many combinations %u for length %u\n",
                                 num, (unsigned)len));
                                 
                        talloc_free(strs);
                        return NULL;                     
                }
        }

        return strs;
}