lib/genrand.c

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/* 
   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 2 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, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#include "includes.h"

static unsigned char smb_arc4_state[258];
static uint32 counter;

static BOOL done_reseed = False;
static void (*reseed_callback)(int *newseed);

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

void set_rand_reseed_callback(void (*fn)(int *))
{
        reseed_callback = fn;
        set_need_random_reseed();
}

void set_need_random_reseed(void)
{
        done_reseed = False;
}

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

/****************************************************************
 Get a 16 byte hash from the contents of a file.
 Note that the hash is not initialised.
*****************************************************************/

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;

        fd = sys_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 v1, v2; struct timeval tval; pid_t mypid;
        struct passwd *pw;
        int reseed_data = 0;

        if (use_fd) {
                if (fd != -1)
                        return fd;

                fd = sys_open( "/dev/urandom", O_RDONLY,0);
                if(fd >= 0)
                        return fd;
        }

        /* Add in some secret file contents */

        do_filehash("/etc/shadow", &seed_inbuf[0]);
        do_filehash(lp_smb_passwd_file(), &seed_inbuf[16]);

        /*
         * Add in the root encrypted password.
         * On any system where security is taken
         * seriously this will be secret.
         */

        pw = getpwnam_alloc(NULL, "root");
        if (pw && pw->pw_passwd) {
                size_t i;
                unsigned char md4_tmp[16];
                mdfour(md4_tmp, (unsigned char *)pw->pw_passwd, strlen(pw->pw_passwd));
                for (i=0;i<16;i++)
                        seed_inbuf[8+i] ^= md4_tmp[i];
                TALLOC_FREE(pw);
        }

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

        GetTimeOfDay(&tval);
        mypid = sys_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)];
        }

        smb_arc4_init(smb_arc4_state, seed_inbuf, sizeof(seed_inbuf));

        return -1;
}

/*******************************************************************
 Interface to the (hopefully) good crypto random number generator.
********************************************************************/

void generate_random_buffer( unsigned char *out, int len)
{
        static int urand_fd = -1;
        unsigned char md4_buf[64];
        unsigned char tmp_buf[16];
        unsigned char *p;

        if(!done_reseed) {
                urand_fd = do_reseed(True, urand_fd);
                done_reseed = True;
        }

        if (urand_fd != -1 && len > 0) {

                if (read(urand_fd, out, len) == len)
                        return; /* len bytes of random data read from urandom. */

                /* Read of urand error, drop back to non urand method. */
                close(urand_fd);
                urand_fd = -1;
                do_reseed(False, -1);
                done_reseed = True;
        }

        /*
         * 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;

                smb_arc4_crypt(smb_arc4_state, md4_buf, sizeof(md4_buf));
                mdfour(tmp_buf, md4_buf, sizeof(md4_buf));
                memcpy(p, tmp_buf, copy_len);
                p += copy_len;
                len -= copy_len;
        }
}

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

static char c_list[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+_-#.,";

char *generate_random_str(size_t len)
{
        static unsigned char retstr[256];
        size_t i;

        memset(retstr, '\0', sizeof(retstr));

        if (len > sizeof(retstr)-1)
                len = sizeof(retstr) -1;
        generate_random_buffer( retstr, len);
        for (i = 0; i < len; i++)
                retstr[i] = c_list[ retstr[i] % (sizeof(c_list)-1) ];

        retstr[i] = '\0';

        return (char *)retstr;
}

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