git.distorted.org.uk Git - u/mdw/catacomb/blob - noise.c

   1 /* -*-c-*-
   2  *
   3  * $Id: noise.c,v 1.3 1999/12/10 23:24:11 mdw Exp $
   4  *
   5  * Acquisition of environmental noise (Unix specific)
   6  *
   7  * (c) 1998 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of Catacomb.
  13  *
  14  * Catacomb is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU Library General Public License as
  16  * published by the Free Software Foundation; either version 2 of the
  17  * License, or (at your option) any later version.
  18  *
  19  * Catacomb is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU Library General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU Library General Public
  25  * License along with Catacomb; if not, write to the Free
  26  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  27  * MA 02111-1307, USA.
  28  */
  29
  30 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: noise.c,v $
  33  * Revision 1.3  1999/12/10 23:24:11  mdw
  34  * Bug fix: flush buffers before forking.
  35  *
  36  * Revision 1.2  1999/11/11 00:59:08  mdw
  37  * A bit of reformatting.  Initialize the uid and gid correctly.
  38  *
  39  * Revision 1.1  1999/09/03 08:41:12  mdw
  40  * Initial import.
  41  *
  42  */
  43
  44 /*----- Header files ------------------------------------------------------*/
  45
  46 #include "config.h"
  47
  48 #include <stdio.h>
  49 #include <string.h>
  50 #include <signal.h>
  51
  52 #include <sys/types.h>
  53 #include <sys/time.h>
  54 #include <sys/wait.h>
  55
  56 #include <fcntl.h>
  57 #include <unistd.h>
  58
  59 #ifdef HAVE_SETGROUPS
  60 #  include <grp.h>
  61 #endif
  62
  63 #include <mLib/bits.h>
  64 #include <mLib/tv.h>
  65
  66 #include "noise.h"
  67 #include "paranoia.h"
  68 #include "rand.h"
  69
  70 /*----- Magical numbers ---------------------------------------------------*/
  71
  72 #define NOISE_KIDLIFE 100000            /* @noise_filter@ child lifetime */
  73 #define MILLION 1000000                 /* One million */
  74
  75 /*----- Noise source definition -------------------------------------------*/
  76
  77 rand_source noise_source = { noise_acquire, noise_timer };
  78
  79 /*----- Static variables --------------------------------------------------*/
  80
  81 /* --- Timer differences --- */
  82
  83 static unsigned long noise_last;        /* Last time recorded */
  84 static unsigned long noise_diff;        /* Last first order difference */
  85
  86 /* --- Setuid program handling --- */
  87
  88 static uid_t noise_uid = NOISE_NOSETUID; /* Uid to set to spawn processes */
  89 static gid_t noise_gid = NOISE_NOSETGID; /* Gid to set to spawn processes */
  90
  91 /*----- Main code ---------------------------------------------------------*/
  92
  93 /* --- @bitcount@ --- *
  94  *
  95  * Arguments:   @unsigned long x@ = a word containing bits
  96  *
  97  * Returns:     The number of bits set in the word.
  98  */
  99
 100 static int bitcount(unsigned long x)
 101 {
 102   char ctab[] = { 0, 1, 1, 2, 1, 2, 2, 3,
 103                   1, 2, 2, 3, 2, 3, 3, 4 };
 104   int count = 0;
 105   while (x) {
 106     count += ctab[x & 0xfu];
 107     x >>= 4;
 108   }
 109   return (count);
 110 }
 111
 112 /* --- @timer@ --- *
 113  *
 114  * Arguments:   @rand_pool *r@ = pointer to randomness pool
 115  *              @struct timeval *tv@ = pointer to time block
 116  *
 117  * Returns:     Nonzer if some randomness was contributed.
 118  *
 119  * Use:         Low-level timer contributor.
 120  */
 121
 122 static int timer(rand_pool *r, struct timeval *tv)
 123 {
 124   unsigned long x, d, dd;
 125   int de, dde;
 126   int ret;
 127
 128   x = tv->tv_usec + MILLION * tv->tv_sec;
 129   d = x ^ noise_last;
 130   dd = d ^ noise_diff;
 131   noise_diff = d;
 132   de = bitcount(d);
 133   dde = bitcount(dd);
 134   rand_add(r, tv, sizeof(*tv), de <= dde ? de : dde);
 135   ret = (de || dde);
 136   BURN(tv); x = d = dd = de = dde = 0;
 137   return (ret);
 138 }
 139
 140 /* --- @noise_timer@ --- *
 141  *
 142  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 143  *
 144  * Returns:     Nonzero if some randomness was contributed.
 145  *
 146  * Use:         Contributes the current time to the randomness pool.
 147  *              A guess at the number of useful bits contributed is made,
 148  *              based on first and second order bit differences.  This isn't
 149  *              ever-so reliable, but it's better than nothing.
 150  */
 151
 152 int noise_timer(rand_pool *r)
 153 {
 154   struct timeval tv;
 155   gettimeofday(&tv, 0);
 156   return (timer(r, &tv));
 157 }
 158
 159 /* --- @noise_devrandom@ --- *
 160  *
 161  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 162  *
 163  * Returns:     Nonzero if some randomness was contributed.
 164  *
 165  * Use:         Attempts to obtain some randomness from the system entropy
 166  *              pool.  All bits from the device are assumed to be good.
 167  */
 168
 169 int noise_devrandom(rand_pool *r)
 170 {
 171   int fd;
 172   octet buf[RAND_POOLSZ];
 173   ssize_t len;
 174   int ret = 0;
 175
 176   /* --- Be nice to other clients of the random device --- *
 177    *
 178    * Attempt to open the device nonblockingly.  If that works, take up to
 179    * one bufferful and then close again.  If there's no data to be read,
 180    * then that's tough and we go away again, on the grounds that the device
 181    * needs to get some more entropy from somewhere.
 182    */
 183
 184   if ((fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) >= 0) {
 185     if ((len = read(fd, buf, sizeof(buf))) > 0) {
 186       rand_add(r, buf, len, len * 8);
 187       BURN(buf);
 188       ret = 1;
 189     }
 190     close(fd);
 191   }
 192   noise_timer(r);
 193   return (ret);
 194 }
 195
 196 /* --- @noise_setid@ --- *
 197  *
 198  * Arguments:   @uid_t uid@ = uid to set
 199  *              @gid_t gid@ = gid to set
 200  *
 201  * Returns:     ---
 202  *
 203  * Use:         Sets the user and group ids to be used by @noise_filter@
 204  *              when running child processes.  This is useful to avoid
 205  *              giving shell commands (even carefully written ones) undue
 206  *              privileges.
 207  */
 208
 209 void noise_setid(uid_t uid, gid_t gid)
 210 {
 211   noise_uid = uid;
 212   noise_gid = gid;
 213 }
 214
 215 /* --- @noise_filter@ --- *
 216  *
 217  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 218  *              @int good@ = number of good bits per 1024 bits
 219  *              @const char *c@ = shell command to run
 220  *
 221  * Returns:     Nonzero if some randomness was contributed.
 222  *
 223  * Use:         Attempts to execute a shell command, and dump it into the
 224  *              randomness pool.  A very rough estimate of the number of
 225  *              good bits is made, based on the size of the command's output.
 226  *              This function calls @waitpid@, so be careful.  Before execing
 227  *              the command, the process uid and gid are set to the values
 228  *              given to @noise_setid@, and an attempt is made to reset the
 229  *              list of supplementary groups.  The environment passed to
 230  *              the command has been severly lobotimized.  If the command
 231  *              fails to complete within a short time period, it is killed.
 232  *              Paranoid use of close-on-exec flags for file descriptors is
 233  *              recommended.
 234  */
 235
 236 int noise_filter(rand_pool *r, int good, const char *c)
 237 {
 238   char buf[4096];
 239   pid_t kid;
 240   int fd[2];
 241   struct timeval dead;
 242   int ret = 0;
 243   const char *env[] = {
 244     "PATH=/bin:/usr/bin:/sbin:/usr/sbin:/etc",
 245     0
 246   };
 247
 248   /* --- Remember when this business started --- */
 249
 250   gettimeofday(&dead, 0);
 251   timer(r, &dead);
 252
 253   /* --- Create a pipe --- */
 254
 255   if (pipe(fd))
 256     return (ret);
 257
 258   /* --- Fork a child off --- */
 259
 260   fflush(0);
 261   kid = fork();
 262   if (kid < 0) {
 263     close(fd[0]);
 264     close(fd[1]);
 265     return (ret);
 266   }
 267
 268   /* --- Handle the child end of the deal --- */
 269
 270   fflush(0);
 271   if (kid == 0) {
 272     int f;
 273
 274     /* --- Set the pipe as standard output, close standard input --- */
 275
 276     close(0); close(1); close(2);
 277
 278     if (fd[1] != 1) {
 279       if (dup2(fd[1], 1) < 0) _exit(127);
 280       close(fd[1]);
 281     }
 282
 283     if ((f = open("/dev/null", O_RDONLY)) != 0 ||
 284         (f = open("/dev/null", O_WRONLY)) != 2)
 285       _exit(127);
 286
 287     /* --- Play games with uids --- */
 288
 289     if (noise_gid != NOISE_NOSETGID) {
 290       setgid(noise_gid);
 291       setegid(noise_gid);
 292 #ifdef HAVE_SETGROUPS
 293       setgroups(1, &noise_gid);
 294 #endif
 295     }
 296
 297     if (noise_uid != NOISE_NOSETUID) {
 298       setuid(noise_uid);
 299       seteuid(noise_uid);
 300     }
 301
 302     /* --- Start the process up --- */
 303
 304     execle("/bin/sh", "-c", c, (char *)0, env);
 305     _exit(127);
 306   }
 307
 308   /* --- Sort out my end of the deal --- */
 309
 310   close(fd[1]);
 311
 312   /* --- Decide on the deadline --- */
 313
 314   TV_ADDL(&dead, &dead, 0, NOISE_KIDLIFE);
 315
 316   /* --- Now read, and think --- */
 317
 318   for (;;) {
 319     struct timeval now, diff;
 320     fd_set rd;
 321
 322     gettimeofday(&now, 0);
 323     timer(r, &now);
 324     if (TV_CMP(&now, >, &dead))
 325       break;
 326     TV_SUB(&diff, &dead, &now);
 327
 328     FD_ZERO(&rd);
 329     FD_SET(fd[0], &rd);
 330
 331     if (select(fd[0] + 1, &rd, 0, 0, &diff) < 0)
 332       break;
 333     if (FD_ISSET(fd[0], &rd)) {
 334       ssize_t sz;
 335       int goodbits;
 336
 337       if ((sz = read(fd[0], buf, sizeof(buf))) <= 0)
 338         break;
 339       goodbits = (sz * good) / 128;
 340       rand_add(r, buf, sz, goodbits);
 341       ret = 1;
 342     }
 343   }
 344
 345   /* --- We've finished with it: kill the child process --- *
 346    *
 347    * This is morally questionable.  On the other hand, I don't want to be
 348    * held up in the @waitpid@ call if I can possibly help it.  Maybe a
 349    * double-fork is worth doing here.
 350    */
 351
 352   close(fd[0]);
 353   BURN(buf);
 354   noise_timer(r);
 355   kill(kid, SIGKILL);
 356   waitpid(kid, 0, 0);
 357   return (ret);
 358 }
 359
 360 /* --- @noise_acquire@ --- *
 361  *
 362  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 363  *
 364  * Returns:     ---
 365  *
 366  * Use:         Acquires some randomness from somewhere.
 367  */
 368
 369 void noise_acquire(rand_pool *r)
 370 {
 371   if (!noise_devrandom(r)) {
 372
 373     /* --- Output of `ps' --- *
 374      *
 375      * This is a hopefully cheap way of getting a bit of noise.  I'm guessing
 376      * the good bit ratio based on about 90 bytes per line of output, and
 377      * each line containing maybe 12 bits worth of interesting data.  (Some
 378      * quick experiments with gzip seem to bear this idea out.)  So, 12 good
 379      * bits per 90 bytes of output gives slightly more than 17 good bits per
 380      * 1024 bits of output.  So I'll be a pessimist and say 16 bits.
 381      */
 382
 383     (void)
 384       (noise_filter(r, 16, "ps alxww") ||
 385        noise_filter(r, 16, "ps -elf"));
 386
 387     /* --- Output of `netstat' --- *
 388      *
 389      * Another possibly cheap way of getting noise.  My output has about
 390      * 72 bytes per line of output.  My wild guesses are telling me that
 391      * there are probably only about four good bits per line (gzip tells
 392      * me there's six, but I want to underestimate).  Four bits per 72 bytes
 393      * is 7 good bits per 1024 bits of output.  Pessimist that I am, I'll
 394      * call it six.
 395      */
 396
 397     noise_filter(r, 6, "netstat -n");
 398   }
 399 }
 400
 401 /*----- That's all, folks -------------------------------------------------*/