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 3 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, see <http://www.gnu.org/licenses/>.
  20 */
  21
  22 #include "includes.h"
  23
  24 static unsigned char smb_arc4_state[258];
  25 static uint32 counter;
  26
  27 static bool done_reseed = False;
  28 static void (*reseed_callback)(int *newseed);
  29
  30 /****************************************************************
  31  Copy any user given reseed data.
  32 *****************************************************************/
  33
  34 void set_rand_reseed_callback(void (*fn)(int *))
  35 {
  36         reseed_callback = fn;
  37         set_need_random_reseed();
  38 }
  39
  40 void set_need_random_reseed(void)
  41 {
  42         done_reseed = False;
  43 }
  44
  45 static void get_rand_reseed_data(int *reseed_data)
  46 {
  47         if (reseed_callback) {
  48                 reseed_callback(reseed_data);
  49         } else {
  50                 *reseed_data = 0;
  51         }
  52 }
  53
  54 /****************************************************************
  55  Get a 16 byte hash from the contents of a file.
  56  Note that the hash is not initialised.
  57 *****************************************************************/
  58
  59 static void do_filehash(const char *fname, unsigned char *the_hash)
  60 {
  61         unsigned char buf[1011]; /* deliberate weird size */
  62         unsigned char tmp_md4[16];
  63         int fd, n;
  64
  65         fd = sys_open(fname,O_RDONLY,0);
  66         if (fd == -1)
  67                 return;
  68
  69         while ((n = read(fd, (char *)buf, sizeof(buf))) > 0) {
  70                 mdfour(tmp_md4, buf, n);
  71                 for (n=0;n<16;n++)
  72                         the_hash[n] ^= tmp_md4[n];
  73         }
  74         close(fd);
  75 }
  76
  77 /**************************************************************
  78  Try and get a good random number seed. Try a number of
  79  different factors. Firstly, try /dev/urandom - use if exists.
  80
  81  We use /dev/urandom as a read of /dev/random can block if
  82  the entropy pool dries up. This leads clients to timeout
  83  or be very slow on connect.
  84
  85  If we can't use /dev/urandom then seed the stream random generator
  86  above...
  87 **************************************************************/
  88
  89 static int do_reseed(bool use_fd, int fd)
  90 {
  91         unsigned char seed_inbuf[40];
  92         uint32 v1, v2; struct timeval tval; pid_t mypid;
  93         struct passwd *pw;
  94         int reseed_data = 0;
  95
  96         if (use_fd) {
  97                 if (fd != -1)
  98                         return fd;
  99
 100                 fd = sys_open( "/dev/urandom", O_RDONLY,0);
 101                 if(fd >= 0)
 102                         return fd;
 103         }
 104
 105         /* Add in some secret file contents */
 106
 107         do_filehash("/etc/shadow", &seed_inbuf[0]);
 108         do_filehash(lp_smb_passwd_file(), &seed_inbuf[16]);
 109
 110         /*
 111          * Add in the root encrypted password.
 112          * On any system where security is taken
 113          * seriously this will be secret.
 114          */
 115
 116         pw = getpwnam_alloc(talloc_autofree_context(), "root");
 117         if (pw && pw->pw_passwd) {
 118                 size_t i;
 119                 unsigned char md4_tmp[16];
 120                 mdfour(md4_tmp, (unsigned char *)pw->pw_passwd, strlen(pw->pw_passwd));
 121                 for (i=0;i<16;i++)
 122                         seed_inbuf[8+i] ^= md4_tmp[i];
 123                 TALLOC_FREE(pw);
 124         }
 125
 126         /*
 127          * Add the counter, time of day, and pid.
 128          */
 129
 130         GetTimeOfDay(&tval);
 131         mypid = sys_getpid();
 132         v1 = (counter++) + mypid + tval.tv_sec;
 133         v2 = (counter++) * mypid + tval.tv_usec;
 134
 135         SIVAL(seed_inbuf, 32, v1 ^ IVAL(seed_inbuf, 32));
 136         SIVAL(seed_inbuf, 36, v2 ^ IVAL(seed_inbuf, 36));
 137
 138         /*
 139          * Add any user-given reseed data.
 140          */
 141
 142         get_rand_reseed_data(&reseed_data);
 143         if (reseed_data) {
 144                 size_t i;
 145                 for (i = 0; i < sizeof(seed_inbuf); i++)
 146                         seed_inbuf[i] ^= ((char *)(&reseed_data))[i % sizeof(reseed_data)];
 147         }
 148
 149         smb_arc4_init(smb_arc4_state, seed_inbuf, sizeof(seed_inbuf));
 150
 151         return -1;
 152 }
 153
 154 /*******************************************************************
 155  Interface to the (hopefully) good crypto random number generator.
 156 ********************************************************************/
 157
 158 void generate_random_buffer( unsigned char *out, int len)
 159 {
 160         static int urand_fd = -1;
 161         unsigned char md4_buf[64];
 162         unsigned char tmp_buf[16];
 163         unsigned char *p;
 164
 165         if(!done_reseed) {
 166                 urand_fd = do_reseed(True, urand_fd);
 167                 done_reseed = True;
 168         }
 169
 170         if (urand_fd != -1 && len > 0) {
 171
 172                 if (read(urand_fd, out, len) == len)
 173                         return; /* len bytes of random data read from urandom. */
 174
 175                 /* Read of urand error, drop back to non urand method. */
 176                 close(urand_fd);
 177                 urand_fd = -1;
 178                 do_reseed(False, -1);
 179                 done_reseed = True;
 180         }
 181
 182         /*
 183          * Generate random numbers in chunks of 64 bytes,
 184          * then md4 them & copy to the output buffer.
 185          * This way the raw state of the stream is never externally
 186          * seen.
 187          */
 188
 189         p = out;
 190         while(len > 0) {
 191                 int copy_len = len > 16 ? 16 : len;
 192
 193                 smb_arc4_crypt(smb_arc4_state, md4_buf, sizeof(md4_buf));
 194                 mdfour(tmp_buf, md4_buf, sizeof(md4_buf));
 195                 memcpy(p, tmp_buf, copy_len);
 196                 p += copy_len;
 197                 len -= copy_len;
 198         }
 199 }
 200
 201 /*******************************************************************
 202  Use the random number generator to generate a random string.
 203 ********************************************************************/
 204
 205 static char c_list[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+_-#.,";
 206
 207 char *generate_random_str(size_t len)
 208 {
 209         static unsigned char retstr[256];
 210         size_t i;
 211
 212         memset(retstr, '\0', sizeof(retstr));
 213
 214         if (len > sizeof(retstr)-1)
 215                 len = sizeof(retstr) -1;
 216         generate_random_buffer( retstr, len);
 217         for (i = 0; i < len; i++)
 218                 retstr[i] = c_list[ retstr[i] % (sizeof(c_list)-1) ];
 219
 220         retstr[i] = '\0';
 221
 222         return (char *)retstr;
 223 }