source/lib/genrand.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3
   4    Functions to create reasonable random numbers for crypto use.
   5
   6    Copyright (C) Jeremy Allison 2001
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 2 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  21 */
  22
  23 #include "includes.h"
  24
  25 static unsigned char smb_arc4_state[258];
  26 static uint32 counter;
  27
  28 static BOOL done_reseed = False;
  29 static void (*reseed_callback)(int *newseed);
  30
  31 /****************************************************************
  32  Copy any user given reseed data.
  33 *****************************************************************/
  34
  35 void set_rand_reseed_callback(void (*fn)(int *))
  36 {
  37         reseed_callback = fn;
  38         set_need_random_reseed();
  39 }
  40
  41 void set_need_random_reseed(void)
  42 {
  43         done_reseed = False;
  44 }
  45
  46 static void get_rand_reseed_data(int *reseed_data)
  47 {
  48         if (reseed_callback) {
  49                 reseed_callback(reseed_data);
  50         } else {
  51                 *reseed_data = 0;
  52         }
  53 }
  54
  55 /****************************************************************
  56  Get a 16 byte hash from the contents of a file.
  57  Note that the hash is not initialised.
  58 *****************************************************************/
  59
  60 static void do_filehash(const char *fname, unsigned char *the_hash)
  61 {
  62         unsigned char buf[1011]; /* deliberate weird size */
  63         unsigned char tmp_md4[16];
  64         int fd, n;
  65
  66         fd = sys_open(fname,O_RDONLY,0);
  67         if (fd == -1)
  68                 return;
  69
  70         while ((n = read(fd, (char *)buf, sizeof(buf))) > 0) {
  71                 mdfour(tmp_md4, buf, n);
  72                 for (n=0;n<16;n++)
  73                         the_hash[n] ^= tmp_md4[n];
  74         }
  75         close(fd);
  76 }
  77
  78 /**************************************************************
  79  Try and get a good random number seed. Try a number of
  80  different factors. Firstly, try /dev/urandom - use if exists.
  81
  82  We use /dev/urandom as a read of /dev/random can block if
  83  the entropy pool dries up. This leads clients to timeout
  84  or be very slow on connect.
  85
  86  If we can't use /dev/urandom then seed the stream random generator
  87  above...
  88 **************************************************************/
  89
  90 static int do_reseed(BOOL use_fd, int fd)
  91 {
  92         unsigned char seed_inbuf[40];
  93         uint32 v1, v2; struct timeval tval; pid_t mypid;
  94         struct passwd *pw;
  95         int reseed_data = 0;
  96
  97         if (use_fd) {
  98                 if (fd != -1)
  99                         return fd;
 100
 101                 fd = sys_open( "/dev/urandom", O_RDONLY,0);
 102                 if(fd >= 0)
 103                         return fd;
 104         }
 105
 106         /* Add in some secret file contents */
 107
 108         do_filehash("/etc/shadow", &seed_inbuf[0]);
 109         do_filehash(lp_smb_passwd_file(), &seed_inbuf[16]);
 110
 111         /*
 112          * Add in the root encrypted password.
 113          * On any system where security is taken
 114          * seriously this will be secret.
 115          */
 116
 117         pw = getpwnam_alloc(NULL, "root");
 118         if (pw && pw->pw_passwd) {
 119                 size_t i;
 120                 unsigned char md4_tmp[16];
 121                 mdfour(md4_tmp, (unsigned char *)pw->pw_passwd, strlen(pw->pw_passwd));
 122                 for (i=0;i<16;i++)
 123                         seed_inbuf[8+i] ^= md4_tmp[i];
 124                 TALLOC_FREE(pw);
 125         }
 126
 127         /*
 128          * Add the counter, time of day, and pid.
 129          */
 130
 131         GetTimeOfDay(&tval);
 132         mypid = sys_getpid();
 133         v1 = (counter++) + mypid + tval.tv_sec;
 134         v2 = (counter++) * mypid + tval.tv_usec;
 135
 136         SIVAL(seed_inbuf, 32, v1 ^ IVAL(seed_inbuf, 32));
 137         SIVAL(seed_inbuf, 36, v2 ^ IVAL(seed_inbuf, 36));
 138
 139         /*
 140          * Add any user-given reseed data.
 141          */
 142
 143         get_rand_reseed_data(&reseed_data);
 144         if (reseed_data) {
 145                 size_t i;
 146                 for (i = 0; i < sizeof(seed_inbuf); i++)
 147                         seed_inbuf[i] ^= ((char *)(&reseed_data))[i % sizeof(reseed_data)];
 148         }
 149
 150         smb_arc4_init(smb_arc4_state, seed_inbuf, sizeof(seed_inbuf));
 151
 152         return -1;
 153 }
 154
 155 /*******************************************************************
 156  Interface to the (hopefully) good crypto random number generator.
 157 ********************************************************************/
 158
 159 void generate_random_buffer( unsigned char *out, int len)
 160 {
 161         static int urand_fd = -1;
 162         unsigned char md4_buf[64];
 163         unsigned char tmp_buf[16];
 164         unsigned char *p;
 165
 166         if(!done_reseed) {
 167                 urand_fd = do_reseed(True, urand_fd);
 168                 done_reseed = True;
 169         }
 170
 171         if (urand_fd != -1 && len > 0) {
 172
 173                 if (read(urand_fd, out, len) == len)
 174                         return; /* len bytes of random data read from urandom. */
 175
 176                 /* Read of urand error, drop back to non urand method. */
 177                 close(urand_fd);
 178                 urand_fd = -1;
 179                 do_reseed(False, -1);
 180                 done_reseed = True;
 181         }
 182
 183         /*
 184          * Generate random numbers in chunks of 64 bytes,
 185          * then md4 them & copy to the output buffer.
 186          * This way the raw state of the stream is never externally
 187          * seen.
 188          */
 189
 190         p = out;
 191         while(len > 0) {
 192                 int copy_len = len > 16 ? 16 : len;
 193
 194                 smb_arc4_crypt(smb_arc4_state, md4_buf, sizeof(md4_buf));
 195                 mdfour(tmp_buf, md4_buf, sizeof(md4_buf));
 196                 memcpy(p, tmp_buf, copy_len);
 197                 p += copy_len;
 198                 len -= copy_len;
 199         }
 200 }
 201
 202 /*******************************************************************
 203  Use the random number generator to generate a random string.
 204 ********************************************************************/
 205
 206 static char c_list[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+_-#.,";
 207
 208 char *generate_random_str(size_t len)
 209 {
 210         static unsigned char retstr[256];
 211         size_t i;
 212
 213         memset(retstr, '\0', sizeof(retstr));
 214
 215         if (len > sizeof(retstr)-1)
 216                 len = sizeof(retstr) -1;
 217         generate_random_buffer( retstr, len);
 218         for (i = 0; i < len; i++)
 219                 retstr[i] = c_list[ retstr[i] % (sizeof(c_list)-1) ];
 220
 221         retstr[i] = '\0';
 222
 223         return (char *)retstr;
 224 }