mdw@git.distorted.org.uk Git - 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 <signal.h>
  34 #include <stdio.h>
  35 #include <stdlib.h>
  36 #include <string.h>
  37
  38 #include <sys/types.h>
  39 #include <sys/time.h>
  40 #include <sys/wait.h>
  41
  42 #include <fcntl.h>
  43 #include <unistd.h>
  44
  45 #ifdef HAVE_SETGROUPS
  46 #  include <grp.h>
  47 #endif
  48
  49 #include <mLib/bits.h>
  50 #include <mLib/mdup.h>
  51 #include <mLib/sel.h>
  52 #include <mLib/tv.h>
  53
  54 #include "noise.h"
  55 #include "paranoia.h"
  56 #include "rand.h"
  57
  58 /*----- Magical numbers ---------------------------------------------------*/
  59
  60 #define NOISE_KIDLIFE 100000            /* @noise_filter@ child lifetime */
  61 #define MILLION 1000000                 /* One million */
  62
  63 /*----- Noise source definition -------------------------------------------*/
  64
  65 const rand_source noise_source = { noise_acquire, noise_timer };
  66
  67 /*----- Static variables --------------------------------------------------*/
  68
  69 /* --- Timer differences --- */
  70
  71 static unsigned long noise_last;        /* Last time recorded */
  72 static unsigned long noise_diff;        /* Last first order difference */
  73
  74 /* --- Setuid program handling --- */
  75
  76 static uid_t noise_uid = NOISE_NOSETUID; /* Uid to set to spawn processes */
  77 static gid_t noise_gid = NOISE_NOSETGID; /* Gid to set to spawn processes */
  78
  79 /*----- Main code ---------------------------------------------------------*/
  80
  81 /* --- @bitcount@ --- *
  82  *
  83  * Arguments:   @unsigned long x@ = a word containing bits
  84  *
  85  * Returns:     The number of bits set in the word.
  86  */
  87
  88 static int bitcount(unsigned long x)
  89 {
  90   static const char ctab[] = { 0, 1, 1, 2, 1, 2, 2, 3,
  91                                1, 2, 2, 3, 2, 3, 3, 4 };
  92   int count = 0;
  93   while (x) {
  94     count += ctab[x & 0xfu];
  95     x >>= 4;
  96   }
  97   return (count);
  98 }
  99
 100 /* --- @timer@ --- *
 101  *
 102  * Arguments:   @rand_pool *r@ = pointer to randomness pool
 103  *              @struct timeval *tv@ = pointer to time block
 104  *
 105  * Returns:     Nonzero if some randomness was contributed.
 106  *
 107  * Use:         Low-level timer contributor.
 108  */
 109
 110 static int timer(rand_pool *r, struct timeval *tv)
 111 {
 112   unsigned long x, d, dd;
 113   int de, dde;
 114   int ret;
 115
 116   x = tv->tv_usec + MILLION * tv->tv_sec;
 117   d = x ^ noise_last;
 118   dd = d ^ noise_diff;
 119   noise_last = x;
 120   noise_diff = d;
 121   de = bitcount(d);
 122   dde = bitcount(dd);
 123   rand_add(r, tv, sizeof(*tv), de <= dde ? de : dde);
 124   ret = (de || dde);
 125   BURN(tv); x = d = dd = de = dde = 0;
 126   return (ret);
 127 }
 128
 129 /* --- @noise_timer@ --- *
 130  *
 131  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 132  *
 133  * Returns:     Nonzero if some randomness was contributed.
 134  *
 135  * Use:         Contributes the current time to the randomness pool.
 136  *              A guess at the number of useful bits contributed is made,
 137  *              based on first and second order bit differences.  This isn't
 138  *              ever-so reliable, but it's better than nothing.
 139  */
 140
 141 int noise_timer(rand_pool *r)
 142 {
 143   struct timeval tv;
 144   gettimeofday(&tv, 0);
 145   return (timer(r, &tv));
 146 }
 147
 148 /* --- @noise_devrandom@ --- *
 149  *
 150  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 151  *
 152  * Returns:     Nonzero if some randomness was contributed.
 153  *
 154  * Use:         Attempts to obtain some randomness from the system entropy
 155  *              pool.  All bits from the device are assumed to be good.
 156  */
 157
 158 int noise_devrandom(rand_pool *r)
 159 {
 160   int fd = -1;
 161   octet buf[RAND_POOLSZ];
 162   ssize_t len;
 163   size_t n = 0;
 164   int ret = 0;
 165 #ifdef __linux__
 166   fd_set infd;
 167   struct timeval tv = { 0, 0 };
 168 #endif
 169
 170 #ifdef __linux__
 171   /* --- Don't take from `/dev/urandom' if `/dev/random' would block --- */
 172
 173   if ((fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) < 0) goto done;
 174   FD_ZERO(&infd);
 175   FD_SET(fd, &infd);
 176   if (select(fd + 1, &infd, 0, 0, &tv) < 0 || !FD_ISSET(fd, &infd))
 177     goto done;
 178   close(fd); fd = -1;
 179 #endif
 180
 181   /* --- Be nice to other clients of the random device --- *
 182    *
 183    * Attempt to open the device nonblockingly.  If that works, take up to
 184    * one bufferful and then close again.  If there's no data to be read,
 185    * then that's tough and we go away again, on the grounds that the device
 186    * needs to get some more entropy from somewhere.
 187    */
 188
 189   if (fd >= 0 ||
 190       (fd = open("/dev/urandom", O_RDONLY | O_NONBLOCK)) >= 0 ||
 191       (fd = open("/dev/arandom", O_RDONLY | O_NONBLOCK)) >= 0 ||
 192       (fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) >= 0) {
 193     while (n < sizeof(buf)) {
 194       if ((len = read(fd, buf + n, sizeof(buf) - n)) <= 0) break;
 195       n += len;
 196     }
 197     if (n == sizeof(buf)) goto win;
 198   }
 199   goto done;
 200
 201 win:
 202   ret = 1;
 203 done:
 204   if (fd >= 0) close(fd);
 205   rand_add(r, buf, n, 8*n);
 206   BURN(buf);
 207   noise_timer(r);
 208   return (ret);
 209 }
 210
 211 /* --- @noise_setid@ --- *
 212  *
 213  * Arguments:   @uid_t uid@ = uid to set
 214  *              @gid_t gid@ = gid to set
 215  *
 216  * Returns:     ---
 217  *
 218  * Use:         Sets the user and group ids to be used by @noise_filter@
 219  *              when running child processes.  This is useful to avoid
 220  *              giving shell commands (even carefully written ones) undue
 221  *              privileges.  This interface is Unix-specific
 222  */
 223
 224 void noise_setid(uid_t uid, gid_t gid)
 225 {
 226   noise_uid = uid;
 227   noise_gid = gid;
 228 }
 229
 230 /* --- @noise_filter@ --- *
 231  *
 232  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 233  *              @int good@ = number of good bits per 1024 bits
 234  *              @const char *c@ = shell command to run
 235  *
 236  * Returns:     Nonzero if some randomness was contributed.
 237  *
 238  * Use:         Attempts to execute a shell command, and dump it into the
 239  *              randomness pool.  A very rough estimate of the number of
 240  *              good bits is made, based on the size of the command's output.
 241  *              This function calls @waitpid@, so be careful.  Before execing
 242  *              the command, the process uid and gid are set to the values
 243  *              given to @noise_setid@, and an attempt is made to reset the
 244  *              list of supplementary groups.  The environment passed to
 245  *              the command has been severly lobotimized.  If the command
 246  *              fails to complete within a short time period, it is killed.
 247  *              Paranoid use of close-on-exec flags for file descriptors is
 248  *              recommended.
 249  *
 250  *              This interface is Unix-specific.
 251  */
 252
 253 struct noisekid {
 254   rand_pool *r;
 255   int good;
 256   char buf[4096];
 257   int donep;
 258   int ret;
 259 };
 260
 261 static void kid_read(int fd, unsigned mode, void *p)
 262 {
 263   struct noisekid *nk = p;
 264   ssize_t sz;
 265   int goodbits;
 266
 267   noise_timer(nk->r);
 268   if ((sz = read(fd, nk->buf, sizeof(nk->buf))) <= 0)
 269     nk->donep = 1;
 270   else {
 271     goodbits = (sz * nk->good) / 128;
 272     rand_add(nk->r, nk->buf, sz, goodbits);
 273     nk->ret = 1;
 274   }
 275 }
 276
 277 static void kid_dead(struct timeval *tv, void *p)
 278   { struct noisekid *nk = p; nk->donep = 1; }
 279
 280 int noise_filter(rand_pool *r, int good, const char *c)
 281 {
 282   pid_t kid;
 283   int fd[2];
 284   struct timeval dead;
 285   int ret = 0;
 286   struct noisekid nk = { 0 };
 287   sel_state sel;
 288   sel_file sf;
 289   sel_timer st;
 290   const char *env[] = {
 291     "PATH=/bin:/usr/bin:/sbin:/usr/sbin:/etc",
 292     0
 293   };
 294
 295   /* --- Remember when this business started --- */
 296
 297   gettimeofday(&dead, 0);
 298   timer(r, &dead);
 299
 300   /* --- Create a pipe --- */
 301
 302   if (pipe(fd))
 303     return (ret);
 304
 305   /* --- Fork a child off --- */
 306
 307   fflush(0);
 308   kid = fork();
 309   if (kid < 0) {
 310     close(fd[0]);
 311     close(fd[1]);
 312     return (ret);
 313   }
 314
 315   /* --- Handle the child end of the deal --- */
 316
 317   if (kid == 0) {
 318     mdup_fd mfd[3];
 319     int f, i = 0;
 320
 321     /* --- Set the pipe as standard output, close standard input --- */
 322
 323     if ((f = open("/dev/null", O_RDONLY)) < 0) _exit(127);
 324     mfd[i].cur = f; mfd[i].want = 0; i++;
 325     mfd[i].cur = fd[1]; mfd[i].want = 1; i++;
 326     mfd[i].cur = f; mfd[i].want = 2; i++;
 327     if (mdup(mfd, i)) _exit(127);
 328
 329     /* --- Play games with uids --- */
 330
 331     if (noise_gid != NOISE_NOSETGID) {
 332       setgid(noise_gid);
 333       setegid(noise_gid);
 334 #ifdef HAVE_SETGROUPS
 335       setgroups(1, &noise_gid);
 336 #endif
 337     }
 338
 339     if (noise_uid != NOISE_NOSETUID) {
 340       setuid(noise_uid);
 341       seteuid(noise_uid);
 342     }
 343
 344     /* --- Start the process up --- */
 345
 346     execle("/bin/sh", "sh", "-c", c, (char *)0, env);
 347     _exit(127);
 348   }
 349
 350   /* --- Sort out my end of the deal --- */
 351
 352   close(fd[1]);
 353   sel_init(&sel);
 354   nk.r = r; nk.good = good;
 355   TV_ADDL(&dead, &dead, 0, NOISE_KIDLIFE);
 356   sel_initfile(&sel, &sf, fd[0], SEL_READ, kid_read, &nk);
 357   sel_addfile(&sf);
 358   sel_addtimer(&sel, &st, &dead, kid_dead, &nk);
 359   while (!nk.donep && !sel_select(&sel));
 360
 361   /* --- We've finished with it: kill the child process --- *
 362    *
 363    * This is morally questionable.  On the other hand, I don't want to be
 364    * held up in the @waitpid@ call if I can possibly help it.  Maybe a
 365    * double-fork is worth doing here.
 366    */
 367
 368   close(fd[0]);
 369   BURN(nk.buf);
 370   noise_timer(r);
 371   kill(kid, SIGKILL);
 372   waitpid(kid, 0, 0);
 373   return (nk.ret);
 374 }
 375
 376 /* --- @noise_freewheel@ --- *
 377  *
 378  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 379  *
 380  * Returns:     Nonzero if some randomness was contributed.
 381  *
 382  * Use:         Runs a free counter for a short while as a desparate attempt
 383  *              to get randomness from somewhere.  This is actually quite
 384  *              effective.
 385  */
 386
 387 #ifdef USE_FREEWHEEL
 388
 389 static sigjmp_buf fwjmp;
 390
 391 static void fwalarm(int sig)
 392 {
 393   siglongjmp(fwjmp, 1);
 394 }
 395
 396 int noise_freewheel(rand_pool *r)
 397 {
 398   void (*sigal)(int) = 0;
 399   struct itimerval oitv, itv = { { 0, 0 }, { 0, 5000 } };
 400   int rc = 0;
 401   volatile uint32 fwcount = 0;
 402
 403   if (!sigsetjmp(fwjmp, 1)) {
 404     if ((sigal = signal(SIGALRM, fwalarm)) == SIG_ERR)
 405       return (0);
 406     if (setitimer(ITIMER_REAL, &itv, &oitv))
 407       goto done;
 408     for (;;)
 409       fwcount++;
 410   } else {
 411     octet buf[4];
 412     STORE32(buf, fwcount);
 413     rand_add(r, buf, sizeof(buf), 16);
 414     rc = 1;
 415   }
 416
 417 done:
 418   signal(SIGALRM, sigal);
 419   if (oitv.it_value.tv_sec || oitv.it_value.tv_usec)
 420     TV_SUB(&oitv.it_value, &oitv.it_value, &itv.it_value);
 421   setitimer(ITIMER_REAL, &oitv, 0);
 422   return (rc);
 423 }
 424
 425 #else
 426
 427 int noise_freewheel(rand_pool *r)
 428 {
 429   return (0);
 430 }
 431
 432 #endif
 433
 434 /* --- @noise_enquire@ --- *
 435  *
 436  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 437  *
 438  * Returns:     Nonzero if some randomness was contributed.
 439  *
 440  * Use:         Runs some shell commands to enquire about the prevailing
 441  *              environment.  This can gather quite a lot of low-quality
 442  *              entropy.
 443  */
 444
 445 int noise_enquire(rand_pool *r)
 446 {
 447   struct tab {
 448     const char *cmd;
 449     unsigned rate;
 450   } tab[] = {
 451     { "ps alxww || ps -elf",    16 },
 452     { "netstat -n",              6 },
 453     { "ifconfig -a",             8 },
 454     { "df",                     20 },
 455     { "w",                       6 },
 456     { "ls -align /tmp/.",       10 },
 457     { 0,                         0 }
 458   };
 459   int i;
 460
 461   for (i = 0; tab[i].cmd; i++)
 462     noise_filter(r, tab[i].rate, tab[i].cmd);
 463   return (1);
 464 }
 465
 466 /* --- @noise_acquire@ --- *
 467  *
 468  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 469  *
 470  * Returns:     ---
 471  *
 472  * Use:         Acquires some randomness from somewhere.
 473  */
 474
 475 void noise_acquire(rand_pool *r)
 476 {
 477   unsigned i;
 478   for (i = 0; i < 8; i++)
 479     noise_freewheel(r);
 480   if (!noise_devrandom(r) || getenv("CATACOMB_FORCE_ESOTERIC_SOURCES")) {
 481     noise_enquire(r);
 482     for (i = 0; i < 8; i++)
 483       noise_freewheel(r);
 484   }
 485 }
 486
 487 /*----- That's all, folks -------------------------------------------------*/