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

   1 /* -*-c-*-
   2  *
   3  * $Id$
   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 /*----- Header files ------------------------------------------------------*/
  31
  32 #include "config.h"
  33
  34 #include <setjmp.h>
  35 #include <stdio.h>
  36 #include <string.h>
  37 #include <signal.h>
  38
  39 #include <sys/types.h>
  40 #include <sys/time.h>
  41 #include <sys/wait.h>
  42
  43 #include <fcntl.h>
  44 #include <unistd.h>
  45
  46 #ifdef HAVE_SETGROUPS
  47 #  include <grp.h>
  48 #endif
  49
  50 #include <mLib/bits.h>
  51 #include <mLib/tv.h>
  52
  53 #include "noise.h"
  54 #include "paranoia.h"
  55 #include "rand.h"
  56
  57 /*----- Magical numbers ---------------------------------------------------*/
  58
  59 #define NOISE_KIDLIFE 100000            /* @noise_filter@ child lifetime */
  60 #define MILLION 1000000                 /* One million */
  61
  62 /*----- Noise source definition -------------------------------------------*/
  63
  64 const rand_source noise_source = { noise_acquire, noise_timer };
  65
  66 /*----- Static variables --------------------------------------------------*/
  67
  68 /* --- Timer differences --- */
  69
  70 static unsigned long noise_last;        /* Last time recorded */
  71 static unsigned long noise_diff;        /* Last first order difference */
  72
  73 /* --- Setuid program handling --- */
  74
  75 static uid_t noise_uid = NOISE_NOSETUID; /* Uid to set to spawn processes */
  76 static gid_t noise_gid = NOISE_NOSETGID; /* Gid to set to spawn processes */
  77
  78 /*----- Main code ---------------------------------------------------------*/
  79
  80 /* --- @bitcount@ --- *
  81  *
  82  * Arguments:   @unsigned long x@ = a word containing bits
  83  *
  84  * Returns:     The number of bits set in the word.
  85  */
  86
  87 static int bitcount(unsigned long x)
  88 {
  89   char ctab[] = { 0, 1, 1, 2, 1, 2, 2, 3,
  90                   1, 2, 2, 3, 2, 3, 3, 4 };
  91   int count = 0;
  92   while (x) {
  93     count += ctab[x & 0xfu];
  94     x >>= 4;
  95   }
  96   return (count);
  97 }
  98
  99 /* --- @timer@ --- *
 100  *
 101  * Arguments:   @rand_pool *r@ = pointer to randomness pool
 102  *              @struct timeval *tv@ = pointer to time block
 103  *
 104  * Returns:     Nonzero if some randomness was contributed.
 105  *
 106  * Use:         Low-level timer contributor.
 107  */
 108
 109 static int timer(rand_pool *r, struct timeval *tv)
 110 {
 111   unsigned long x, d, dd;
 112   int de, dde;
 113   int ret;
 114
 115   x = tv->tv_usec + MILLION * tv->tv_sec;
 116   d = x ^ noise_last;
 117   dd = d ^ noise_diff;
 118   noise_diff = d;
 119   de = bitcount(d);
 120   dde = bitcount(dd);
 121   rand_add(r, tv, sizeof(*tv), de <= dde ? de : dde);
 122   ret = (de || dde);
 123   BURN(tv); x = d = dd = de = dde = 0;
 124   return (ret);
 125 }
 126
 127 /* --- @noise_timer@ --- *
 128  *
 129  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 130  *
 131  * Returns:     Nonzero if some randomness was contributed.
 132  *
 133  * Use:         Contributes the current time to the randomness pool.
 134  *              A guess at the number of useful bits contributed is made,
 135  *              based on first and second order bit differences.  This isn't
 136  *              ever-so reliable, but it's better than nothing.
 137  */
 138
 139 int noise_timer(rand_pool *r)
 140 {
 141   struct timeval tv;
 142   gettimeofday(&tv, 0);
 143   return (timer(r, &tv));
 144 }
 145
 146 /* --- @noise_devrandom@ --- *
 147  *
 148  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 149  *
 150  * Returns:     Nonzero if some randomness was contributed.
 151  *
 152  * Use:         Attempts to obtain some randomness from the system entropy
 153  *              pool.  All bits from the device are assumed to be good.
 154  */
 155
 156 int noise_devrandom(rand_pool *r)
 157 {
 158   int fd;
 159   octet buf[RAND_POOLSZ];
 160   ssize_t len;
 161   int ret = 0;
 162
 163   /* --- Be nice to other clients of the random device --- *
 164    *
 165    * Attempt to open the device nonblockingly.  If that works, take up to
 166    * one bufferful and then close again.  If there's no data to be read,
 167    * then that's tough and we go away again, on the grounds that the device
 168    * needs to get some more entropy from somewhere.
 169    */
 170
 171   if ((fd = open("/dev/urandom", O_RDONLY | O_NONBLOCK)) >= 0 ||
 172       (fd = open("/dev/arandom", O_RDONLY | O_NONBLOCK)) >= 0 ||
 173       (fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) >= 0) {
 174     if ((len = read(fd, buf, sizeof(buf))) > 0) {
 175       rand_add(r, buf, len, len * 8);
 176       BURN(buf);
 177       ret = 1;
 178     }
 179     close(fd);
 180   }
 181   noise_timer(r);
 182   return (ret);
 183 }
 184
 185 /* --- @noise_setid@ --- *
 186  *
 187  * Arguments:   @uid_t uid@ = uid to set
 188  *              @gid_t gid@ = gid to set
 189  *
 190  * Returns:     ---
 191  *
 192  * Use:         Sets the user and group ids to be used by @noise_filter@
 193  *              when running child processes.  This is useful to avoid
 194  *              giving shell commands (even carefully written ones) undue
 195  *              privileges.  This interface is Unix-specific
 196  */
 197
 198 void noise_setid(uid_t uid, gid_t gid)
 199 {
 200   noise_uid = uid;
 201   noise_gid = gid;
 202 }
 203
 204 /* --- @noise_filter@ --- *
 205  *
 206  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 207  *              @int good@ = number of good bits per 1024 bits
 208  *              @const char *c@ = shell command to run
 209  *
 210  * Returns:     Nonzero if some randomness was contributed.
 211  *
 212  * Use:         Attempts to execute a shell command, and dump it into the
 213  *              randomness pool.  A very rough estimate of the number of
 214  *              good bits is made, based on the size of the command's output.
 215  *              This function calls @waitpid@, so be careful.  Before execing
 216  *              the command, the process uid and gid are set to the values
 217  *              given to @noise_setid@, and an attempt is made to reset the
 218  *              list of supplementary groups.  The environment passed to
 219  *              the command has been severly lobotimized.  If the command
 220  *              fails to complete within a short time period, it is killed.
 221  *              Paranoid use of close-on-exec flags for file descriptors is
 222  *              recommended.
 223  *
 224  *              This interface is Unix-specific.
 225  */
 226
 227 int noise_filter(rand_pool *r, int good, const char *c)
 228 {
 229   char buf[4096];
 230   pid_t kid;
 231   int fd[2];
 232   struct timeval dead;
 233   int ret = 0;
 234   const char *env[] = {
 235     "PATH=/bin:/usr/bin:/sbin:/usr/sbin:/etc",
 236     0
 237   };
 238
 239   /* --- Remember when this business started --- */
 240
 241   gettimeofday(&dead, 0);
 242   timer(r, &dead);
 243
 244   /* --- Create a pipe --- */
 245
 246   if (pipe(fd))
 247     return (ret);
 248
 249   /* --- Fork a child off --- */
 250
 251   fflush(0);
 252   kid = fork();
 253   if (kid < 0) {
 254     close(fd[0]);
 255     close(fd[1]);
 256     return (ret);
 257   }
 258
 259   /* --- Handle the child end of the deal --- */
 260
 261   if (kid == 0) {
 262     int f;
 263
 264     /* --- Set the pipe as standard output, close standard input --- */
 265
 266     close(0); close(1); close(2);
 267
 268     if (fd[1] != 1) {
 269       if (dup2(fd[1], 1) < 0) _exit(127);
 270       close(fd[1]);
 271     }
 272
 273     if ((f = open("/dev/null", O_RDONLY)) != 0 ||
 274         (f = open("/dev/null", O_WRONLY)) != 2)
 275       _exit(127);
 276
 277     /* --- Play games with uids --- */
 278
 279     if (noise_gid != NOISE_NOSETGID) {
 280       setgid(noise_gid);
 281       setegid(noise_gid);
 282 #ifdef HAVE_SETGROUPS
 283       setgroups(1, &noise_gid);
 284 #endif
 285     }
 286
 287     if (noise_uid != NOISE_NOSETUID) {
 288       setuid(noise_uid);
 289       seteuid(noise_uid);
 290     }
 291
 292     /* --- Start the process up --- */
 293
 294     execle("/bin/sh", "-c", c, (char *)0, env);
 295     _exit(127);
 296   }
 297
 298   /* --- Sort out my end of the deal --- */
 299
 300   close(fd[1]);
 301
 302   /* --- Decide on the deadline --- */
 303
 304   TV_ADDL(&dead, &dead, 0, NOISE_KIDLIFE);
 305
 306   /* --- Now read, and think --- */
 307
 308   for (;;) {
 309     struct timeval now, diff;
 310     fd_set rd;
 311
 312     gettimeofday(&now, 0);
 313     timer(r, &now);
 314     if (TV_CMP(&now, >, &dead))
 315       break;
 316     TV_SUB(&diff, &dead, &now);
 317
 318     FD_ZERO(&rd);
 319     FD_SET(fd[0], &rd);
 320
 321     if (select(fd[0] + 1, &rd, 0, 0, &diff) < 0)
 322       break;
 323     if (FD_ISSET(fd[0], &rd)) {
 324       ssize_t sz;
 325       int goodbits;
 326
 327       if ((sz = read(fd[0], buf, sizeof(buf))) <= 0)
 328         break;
 329       goodbits = (sz * good) / 128;
 330       rand_add(r, buf, sz, goodbits);
 331       ret = 1;
 332     }
 333   }
 334
 335   /* --- We've finished with it: kill the child process --- *
 336    *
 337    * This is morally questionable.  On the other hand, I don't want to be
 338    * held up in the @waitpid@ call if I can possibly help it.  Maybe a
 339    * double-fork is worth doing here.
 340    */
 341
 342   close(fd[0]);
 343   BURN(buf);
 344   noise_timer(r);
 345   kill(kid, SIGKILL);
 346   waitpid(kid, 0, 0);
 347   return (ret);
 348 }
 349
 350 /* --- @noise_freewheel@ --- *
 351  *
 352  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 353  *
 354  * Returns:     Nonzero if some randomness was contributed.
 355  *
 356  * Use:         Runs a free counter for a short while as a desparate attempt
 357  *              to get randomness from somewhere.  This is actually quite
 358  *              effective.
 359  */
 360
 361 #ifdef USE_FREEWHEEL
 362
 363 static jmp_buf fwjmp;
 364
 365 static void fwalarm(int sig)
 366 {
 367   siglongjmp(fwjmp, 1);
 368 }
 369
 370 int noise_freewheel(rand_pool *r)
 371 {
 372   void (*sigal)(int) = 0;
 373   struct itimerval oitv, itv = { { 0, 0 }, { 0, 5000 } };
 374   int rc = 0;
 375   volatile uint32 fwcount = 0;
 376
 377   if (!sigsetjmp(fwjmp, 1)) {
 378     if ((sigal = signal(SIGALRM, fwalarm)) == SIG_ERR)
 379       return (0);
 380     if (setitimer(ITIMER_REAL, &itv, &oitv))
 381       goto done;
 382     for (;;)
 383       fwcount++;
 384   } else {
 385     octet buf[4];
 386     STORE32(buf, fwcount);
 387     rand_add(r, buf, sizeof(buf), 16);
 388     rc = 1;
 389   }
 390
 391 done:
 392   signal(SIGALRM, sigal);
 393   if (oitv.it_value.tv_sec || oitv.it_value.tv_usec)
 394     TV_SUB(&oitv.it_value, &oitv.it_value, &itv.it_value);
 395   setitimer(ITIMER_REAL, &oitv, 0);
 396   return (rc);
 397 }
 398
 399 #else
 400
 401 int noise_freewheel(rand_pool *r)
 402 {
 403   return (0);
 404 }
 405
 406 #endif
 407
 408 /* --- @noise_enquire@ --- *
 409  *
 410  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 411  *
 412  * Returns:     Nonzero if some randomness was contributed.
 413  *
 414  * Use:         Runs some shell commands to enquire about the prevailing
 415  *              environment.  This can gather quite a lot of low-quality
 416  *              entropy.
 417  */
 418
 419 int noise_enquire(rand_pool *r)
 420 {
 421   struct tab {
 422     const char *cmd;
 423     unsigned rate;
 424   } tab[] = {
 425     { "ps alxww || ps -elf",    16 },
 426     { "netstat -n",              6 },
 427     { "ifconfig -a",             8 },
 428     { "df",                     20 },
 429     { "w",                       6 },
 430     { "ls -align /tmp/.",       10 },
 431     { 0,                         0 }
 432   };
 433   int i;
 434
 435   for (i = 0; tab[i].cmd; i++)
 436     noise_filter(r, tab[i].rate, tab[i].cmd);
 437   return (1);
 438 }
 439
 440 /* --- @noise_acquire@ --- *
 441  *
 442  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 443  *
 444  * Returns:     ---
 445  *
 446  * Use:         Acquires some randomness from somewhere.
 447  */
 448
 449 void noise_acquire(rand_pool *r)
 450 {
 451   unsigned i;
 452   for (i = 0; i < 8; i++)
 453     noise_freewheel(r);
 454   if (!noise_devrandom(r)) {
 455     noise_enquire(r);
 456     for (i = 0; i < 8; i++)
 457       noise_freewheel(r);
 458   }
 459 }
 460
 461 /*----- That's all, folks -------------------------------------------------*/