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

   1 /* -*-c-*-
   2  *
   3  * Acquisition of environmental noise (Unix-specific)
   4  *
   5  * (c) 1998 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Catacomb.
  11  *
  12  * Catacomb is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * Catacomb is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with Catacomb; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 /*----- Header files ------------------------------------------------------*/
  29
  30 #include "config.h"
  31
  32 #include <setjmp.h>
  33 #include <stdio.h>
  34 #include <string.h>
  35 #include <signal.h>
  36
  37 #include <sys/types.h>
  38 #include <sys/time.h>
  39 #include <sys/wait.h>
  40
  41 #include <fcntl.h>
  42 #include <unistd.h>
  43
  44 #ifdef HAVE_SETGROUPS
  45 #  include <grp.h>
  46 #endif
  47
  48 #include <mLib/bits.h>
  49 #include <mLib/tv.h>
  50
  51 #include "noise.h"
  52 #include "paranoia.h"
  53 #include "rand.h"
  54
  55 /*----- Magical numbers ---------------------------------------------------*/
  56
  57 #define NOISE_KIDLIFE 100000            /* @noise_filter@ child lifetime */
  58 #define MILLION 1000000                 /* One million */
  59
  60 /*----- Noise source definition -------------------------------------------*/
  61
  62 const rand_source noise_source = { noise_acquire, noise_timer };
  63
  64 /*----- Static variables --------------------------------------------------*/
  65
  66 /* --- Timer differences --- */
  67
  68 static unsigned long noise_last;        /* Last time recorded */
  69 static unsigned long noise_diff;        /* Last first order difference */
  70
  71 /* --- Setuid program handling --- */
  72
  73 static uid_t noise_uid = NOISE_NOSETUID; /* Uid to set to spawn processes */
  74 static gid_t noise_gid = NOISE_NOSETGID; /* Gid to set to spawn processes */
  75
  76 /*----- Main code ---------------------------------------------------------*/
  77
  78 /* --- @bitcount@ --- *
  79  *
  80  * Arguments:   @unsigned long x@ = a word containing bits
  81  *
  82  * Returns:     The number of bits set in the word.
  83  */
  84
  85 static int bitcount(unsigned long x)
  86 {
  87   char ctab[] = { 0, 1, 1, 2, 1, 2, 2, 3,
  88                   1, 2, 2, 3, 2, 3, 3, 4 };
  89   int count = 0;
  90   while (x) {
  91     count += ctab[x & 0xfu];
  92     x >>= 4;
  93   }
  94   return (count);
  95 }
  96
  97 /* --- @timer@ --- *
  98  *
  99  * Arguments:   @rand_pool *r@ = pointer to randomness pool
 100  *              @struct timeval *tv@ = pointer to time block
 101  *
 102  * Returns:     Nonzero if some randomness was contributed.
 103  *
 104  * Use:         Low-level timer contributor.
 105  */
 106
 107 static int timer(rand_pool *r, struct timeval *tv)
 108 {
 109   unsigned long x, d, dd;
 110   int de, dde;
 111   int ret;
 112
 113   x = tv->tv_usec + MILLION * tv->tv_sec;
 114   d = x ^ noise_last;
 115   dd = d ^ noise_diff;
 116   noise_diff = d;
 117   de = bitcount(d);
 118   dde = bitcount(dd);
 119   rand_add(r, tv, sizeof(*tv), de <= dde ? de : dde);
 120   ret = (de || dde);
 121   BURN(tv); x = d = dd = de = dde = 0;
 122   return (ret);
 123 }
 124
 125 /* --- @noise_timer@ --- *
 126  *
 127  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 128  *
 129  * Returns:     Nonzero if some randomness was contributed.
 130  *
 131  * Use:         Contributes the current time to the randomness pool.
 132  *              A guess at the number of useful bits contributed is made,
 133  *              based on first and second order bit differences.  This isn't
 134  *              ever-so reliable, but it's better than nothing.
 135  */
 136
 137 int noise_timer(rand_pool *r)
 138 {
 139   struct timeval tv;
 140   gettimeofday(&tv, 0);
 141   return (timer(r, &tv));
 142 }
 143
 144 /* --- @noise_devrandom@ --- *
 145  *
 146  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 147  *
 148  * Returns:     Nonzero if some randomness was contributed.
 149  *
 150  * Use:         Attempts to obtain some randomness from the system entropy
 151  *              pool.  All bits from the device are assumed to be good.
 152  */
 153
 154 int noise_devrandom(rand_pool *r)
 155 {
 156   int fd;
 157   octet buf[RAND_POOLSZ];
 158   ssize_t len;
 159   int ret = 0;
 160
 161   /* --- Be nice to other clients of the random device --- *
 162    *
 163    * Attempt to open the device nonblockingly.  If that works, take up to
 164    * one bufferful and then close again.  If there's no data to be read,
 165    * then that's tough and we go away again, on the grounds that the device
 166    * needs to get some more entropy from somewhere.
 167    */
 168
 169   if ((fd = open("/dev/urandom", O_RDONLY | O_NONBLOCK)) >= 0 ||
 170       (fd = open("/dev/arandom", O_RDONLY | O_NONBLOCK)) >= 0 ||
 171       (fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) >= 0) {
 172     if ((len = read(fd, buf, sizeof(buf))) > 0) {
 173       rand_add(r, buf, len, len * 8);
 174       BURN(buf);
 175       ret = 1;
 176     }
 177     close(fd);
 178   }
 179   noise_timer(r);
 180   return (ret);
 181 }
 182
 183 /* --- @noise_setid@ --- *
 184  *
 185  * Arguments:   @uid_t uid@ = uid to set
 186  *              @gid_t gid@ = gid to set
 187  *
 188  * Returns:     ---
 189  *
 190  * Use:         Sets the user and group ids to be used by @noise_filter@
 191  *              when running child processes.  This is useful to avoid
 192  *              giving shell commands (even carefully written ones) undue
 193  *              privileges.  This interface is Unix-specific
 194  */
 195
 196 void noise_setid(uid_t uid, gid_t gid)
 197 {
 198   noise_uid = uid;
 199   noise_gid = gid;
 200 }
 201
 202 /* --- @noise_filter@ --- *
 203  *
 204  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 205  *              @int good@ = number of good bits per 1024 bits
 206  *              @const char *c@ = shell command to run
 207  *
 208  * Returns:     Nonzero if some randomness was contributed.
 209  *
 210  * Use:         Attempts to execute a shell command, and dump it into the
 211  *              randomness pool.  A very rough estimate of the number of
 212  *              good bits is made, based on the size of the command's output.
 213  *              This function calls @waitpid@, so be careful.  Before execing
 214  *              the command, the process uid and gid are set to the values
 215  *              given to @noise_setid@, and an attempt is made to reset the
 216  *              list of supplementary groups.  The environment passed to
 217  *              the command has been severly lobotimized.  If the command
 218  *              fails to complete within a short time period, it is killed.
 219  *              Paranoid use of close-on-exec flags for file descriptors is
 220  *              recommended.
 221  *
 222  *              This interface is Unix-specific.
 223  */
 224
 225 int noise_filter(rand_pool *r, int good, const char *c)
 226 {
 227   char buf[4096];
 228   pid_t kid;
 229   int fd[2];
 230   struct timeval dead;
 231   int ret = 0;
 232   const char *env[] = {
 233     "PATH=/bin:/usr/bin:/sbin:/usr/sbin:/etc",
 234     0
 235   };
 236
 237   /* --- Remember when this business started --- */
 238
 239   gettimeofday(&dead, 0);
 240   timer(r, &dead);
 241
 242   /* --- Create a pipe --- */
 243
 244   if (pipe(fd))
 245     return (ret);
 246
 247   /* --- Fork a child off --- */
 248
 249   fflush(0);
 250   kid = fork();
 251   if (kid < 0) {
 252     close(fd[0]);
 253     close(fd[1]);
 254     return (ret);
 255   }
 256
 257   /* --- Handle the child end of the deal --- */
 258
 259   if (kid == 0) {
 260     int f;
 261
 262     /* --- Set the pipe as standard output, close standard input --- */
 263
 264     close(0); close(1); close(2);
 265
 266     if (fd[1] != 1) {
 267       if (dup2(fd[1], 1) < 0) _exit(127);
 268       close(fd[1]);
 269     }
 270
 271     if ((f = open("/dev/null", O_RDONLY)) != 0 ||
 272         (f = open("/dev/null", O_WRONLY)) != 2)
 273       _exit(127);
 274
 275     /* --- Play games with uids --- */
 276
 277     if (noise_gid != NOISE_NOSETGID) {
 278       setgid(noise_gid);
 279       setegid(noise_gid);
 280 #ifdef HAVE_SETGROUPS
 281       setgroups(1, &noise_gid);
 282 #endif
 283     }
 284
 285     if (noise_uid != NOISE_NOSETUID) {
 286       setuid(noise_uid);
 287       seteuid(noise_uid);
 288     }
 289
 290     /* --- Start the process up --- */
 291
 292     execle("/bin/sh", "-c", c, (char *)0, env);
 293     _exit(127);
 294   }
 295
 296   /* --- Sort out my end of the deal --- */
 297
 298   close(fd[1]);
 299
 300   /* --- Decide on the deadline --- */
 301
 302   TV_ADDL(&dead, &dead, 0, NOISE_KIDLIFE);
 303
 304   /* --- Now read, and think --- */
 305
 306   for (;;) {
 307     struct timeval now, diff;
 308     fd_set rd;
 309
 310     gettimeofday(&now, 0);
 311     timer(r, &now);
 312     if (TV_CMP(&now, >, &dead))
 313       break;
 314     TV_SUB(&diff, &dead, &now);
 315
 316     FD_ZERO(&rd);
 317     FD_SET(fd[0], &rd);
 318
 319     if (select(fd[0] + 1, &rd, 0, 0, &diff) < 0)
 320       break;
 321     if (FD_ISSET(fd[0], &rd)) {
 322       ssize_t sz;
 323       int goodbits;
 324
 325       if ((sz = read(fd[0], buf, sizeof(buf))) <= 0)
 326         break;
 327       goodbits = (sz * good) / 128;
 328       rand_add(r, buf, sz, goodbits);
 329       ret = 1;
 330     }
 331   }
 332
 333   /* --- We've finished with it: kill the child process --- *
 334    *
 335    * This is morally questionable.  On the other hand, I don't want to be
 336    * held up in the @waitpid@ call if I can possibly help it.  Maybe a
 337    * double-fork is worth doing here.
 338    */
 339
 340   close(fd[0]);
 341   BURN(buf);
 342   noise_timer(r);
 343   kill(kid, SIGKILL);
 344   waitpid(kid, 0, 0);
 345   return (ret);
 346 }
 347
 348 /* --- @noise_freewheel@ --- *
 349  *
 350  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 351  *
 352  * Returns:     Nonzero if some randomness was contributed.
 353  *
 354  * Use:         Runs a free counter for a short while as a desparate attempt
 355  *              to get randomness from somewhere.  This is actually quite
 356  *              effective.
 357  */
 358
 359 #ifdef USE_FREEWHEEL
 360
 361 static jmp_buf fwjmp;
 362
 363 static void fwalarm(int sig)
 364 {
 365   siglongjmp(fwjmp, 1);
 366 }
 367
 368 int noise_freewheel(rand_pool *r)
 369 {
 370   void (*sigal)(int) = 0;
 371   struct itimerval oitv, itv = { { 0, 0 }, { 0, 5000 } };
 372   int rc = 0;
 373   volatile uint32 fwcount = 0;
 374
 375   if (!sigsetjmp(fwjmp, 1)) {
 376     if ((sigal = signal(SIGALRM, fwalarm)) == SIG_ERR)
 377       return (0);
 378     if (setitimer(ITIMER_REAL, &itv, &oitv))
 379       goto done;
 380     for (;;)
 381       fwcount++;
 382   } else {
 383     octet buf[4];
 384     STORE32(buf, fwcount);
 385     rand_add(r, buf, sizeof(buf), 16);
 386     rc = 1;
 387   }
 388
 389 done:
 390   signal(SIGALRM, sigal);
 391   if (oitv.it_value.tv_sec || oitv.it_value.tv_usec)
 392     TV_SUB(&oitv.it_value, &oitv.it_value, &itv.it_value);
 393   setitimer(ITIMER_REAL, &oitv, 0);
 394   return (rc);
 395 }
 396
 397 #else
 398
 399 int noise_freewheel(rand_pool *r)
 400 {
 401   return (0);
 402 }
 403
 404 #endif
 405
 406 /* --- @noise_enquire@ --- *
 407  *
 408  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 409  *
 410  * Returns:     Nonzero if some randomness was contributed.
 411  *
 412  * Use:         Runs some shell commands to enquire about the prevailing
 413  *              environment.  This can gather quite a lot of low-quality
 414  *              entropy.
 415  */
 416
 417 int noise_enquire(rand_pool *r)
 418 {
 419   struct tab {
 420     const char *cmd;
 421     unsigned rate;
 422   } tab[] = {
 423     { "ps alxww || ps -elf",    16 },
 424     { "netstat -n",              6 },
 425     { "ifconfig -a",             8 },
 426     { "df",                     20 },
 427     { "w",                       6 },
 428     { "ls -align /tmp/.",       10 },
 429     { 0,                         0 }
 430   };
 431   int i;
 432
 433   for (i = 0; tab[i].cmd; i++)
 434     noise_filter(r, tab[i].rate, tab[i].cmd);
 435   return (1);
 436 }
 437
 438 /* --- @noise_acquire@ --- *
 439  *
 440  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 441  *
 442  * Returns:     ---
 443  *
 444  * Use:         Acquires some randomness from somewhere.
 445  */
 446
 447 void noise_acquire(rand_pool *r)
 448 {
 449   unsigned i;
 450   for (i = 0; i < 8; i++)
 451     noise_freewheel(r);
 452   if (!noise_devrandom(r)) {
 453     noise_enquire(r);
 454     for (i = 0; i < 8; i++)
 455       noise_freewheel(r);
 456   }
 457 }
 458
 459 /*----- That's all, folks -------------------------------------------------*/