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   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;
 161   octet buf[RAND_POOLSZ];
 162   ssize_t len;
 163   size_t n = 0;
 164   int ret = 0;
 165
 166   /* --- Be nice to other clients of the random device --- *
 167    *
 168    * Attempt to open the device nonblockingly.  If that works, take up to
 169    * one bufferful and then close again.  If there's no data to be read,
 170    * then that's tough and we go away again, on the grounds that the device
 171    * needs to get some more entropy from somewhere.
 172    */
 173
 174   if ((fd = open("/dev/urandom", O_RDONLY | O_NONBLOCK)) >= 0 ||
 175       (fd = open("/dev/arandom", O_RDONLY | O_NONBLOCK)) >= 0 ||
 176       (fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) >= 0) {
 177     while (n < sizeof(buf)) {
 178       if ((len = read(fd, buf + n, sizeof(buf) - n)) <= 0) break;
 179       n += len;
 180     }
 181     rand_add(r, buf, n, n * 8);
 182     BURN(buf);
 183     if (n == sizeof(buf)) ret = 1;
 184     close(fd);
 185   }
 186   noise_timer(r);
 187   return (ret);
 188 }
 189
 190 /* --- @noise_setid@ --- *
 191  *
 192  * Arguments:   @uid_t uid@ = uid to set
 193  *              @gid_t gid@ = gid to set
 194  *
 195  * Returns:     ---
 196  *
 197  * Use:         Sets the user and group ids to be used by @noise_filter@
 198  *              when running child processes.  This is useful to avoid
 199  *              giving shell commands (even carefully written ones) undue
 200  *              privileges.  This interface is Unix-specific
 201  */
 202
 203 void noise_setid(uid_t uid, gid_t gid)
 204 {
 205   noise_uid = uid;
 206   noise_gid = gid;
 207 }
 208
 209 /* --- @noise_filter@ --- *
 210  *
 211  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 212  *              @int good@ = number of good bits per 1024 bits
 213  *              @const char *c@ = shell command to run
 214  *
 215  * Returns:     Nonzero if some randomness was contributed.
 216  *
 217  * Use:         Attempts to execute a shell command, and dump it into the
 218  *              randomness pool.  A very rough estimate of the number of
 219  *              good bits is made, based on the size of the command's output.
 220  *              This function calls @waitpid@, so be careful.  Before execing
 221  *              the command, the process uid and gid are set to the values
 222  *              given to @noise_setid@, and an attempt is made to reset the
 223  *              list of supplementary groups.  The environment passed to
 224  *              the command has been severly lobotimized.  If the command
 225  *              fails to complete within a short time period, it is killed.
 226  *              Paranoid use of close-on-exec flags for file descriptors is
 227  *              recommended.
 228  *
 229  *              This interface is Unix-specific.
 230  */
 231
 232 struct noisekid {
 233   rand_pool *r;
 234   int good;
 235   char buf[4096];
 236   int donep;
 237   int ret;
 238 };
 239
 240 static void kid_read(int fd, unsigned mode, void *p)
 241 {
 242   struct noisekid *nk = p;
 243   ssize_t sz;
 244   int goodbits;
 245
 246   noise_timer(nk->r);
 247   if ((sz = read(fd, nk->buf, sizeof(nk->buf))) <= 0)
 248     nk->donep = 1;
 249   else {
 250     goodbits = (sz * nk->good) / 128;
 251     rand_add(nk->r, nk->buf, sz, goodbits);
 252     nk->ret = 1;
 253   }
 254 }
 255
 256 static void kid_dead(struct timeval *tv, void *p)
 257   { struct noisekid *nk = p; nk->donep = 1; }
 258
 259 int noise_filter(rand_pool *r, int good, const char *c)
 260 {
 261   pid_t kid;
 262   int fd[2];
 263   struct timeval dead;
 264   int ret = 0;
 265   struct noisekid nk = { 0 };
 266   sel_state sel;
 267   sel_file sf;
 268   sel_timer st;
 269   const char *env[] = {
 270     "PATH=/bin:/usr/bin:/sbin:/usr/sbin:/etc",
 271     0
 272   };
 273
 274   /* --- Remember when this business started --- */
 275
 276   gettimeofday(&dead, 0);
 277   timer(r, &dead);
 278
 279   /* --- Create a pipe --- */
 280
 281   if (pipe(fd))
 282     return (ret);
 283
 284   /* --- Fork a child off --- */
 285
 286   fflush(0);
 287   kid = fork();
 288   if (kid < 0) {
 289     close(fd[0]);
 290     close(fd[1]);
 291     return (ret);
 292   }
 293
 294   /* --- Handle the child end of the deal --- */
 295
 296   if (kid == 0) {
 297     mdup_fd mfd[3];
 298     int f, i = 0;
 299
 300     /* --- Set the pipe as standard output, close standard input --- */
 301
 302     if ((f = open("/dev/null", O_RDONLY)) < 0) _exit(127);
 303     mfd[i].cur = f; mfd[i].want = 0; i++;
 304     mfd[i].cur = fd[1]; mfd[i].want = 1; i++;
 305     mfd[i].cur = f; mfd[i].want = 2; i++;
 306     if (mdup(mfd, i)) _exit(127);
 307
 308     /* --- Play games with uids --- */
 309
 310     if (noise_gid != NOISE_NOSETGID) {
 311       setgid(noise_gid);
 312       setegid(noise_gid);
 313 #ifdef HAVE_SETGROUPS
 314       setgroups(1, &noise_gid);
 315 #endif
 316     }
 317
 318     if (noise_uid != NOISE_NOSETUID) {
 319       setuid(noise_uid);
 320       seteuid(noise_uid);
 321     }
 322
 323     /* --- Start the process up --- */
 324
 325     execle("/bin/sh", "sh", "-c", c, (char *)0, env);
 326     _exit(127);
 327   }
 328
 329   /* --- Sort out my end of the deal --- */
 330
 331   close(fd[1]);
 332   sel_init(&sel);
 333   nk.r = r; nk.good = good;
 334   TV_ADDL(&dead, &dead, 0, NOISE_KIDLIFE);
 335   sel_initfile(&sel, &sf, fd[0], SEL_READ, kid_read, &nk);
 336   sel_addfile(&sf);
 337   sel_addtimer(&sel, &st, &dead, kid_dead, &nk);
 338   while (!nk.donep && !sel_select(&sel));
 339
 340   /* --- We've finished with it: kill the child process --- *
 341    *
 342    * This is morally questionable.  On the other hand, I don't want to be
 343    * held up in the @waitpid@ call if I can possibly help it.  Maybe a
 344    * double-fork is worth doing here.
 345    */
 346
 347   close(fd[0]);
 348   BURN(nk.buf);
 349   noise_timer(r);
 350   kill(kid, SIGKILL);
 351   waitpid(kid, 0, 0);
 352   return (nk.ret);
 353 }
 354
 355 /* --- @noise_freewheel@ --- *
 356  *
 357  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 358  *
 359  * Returns:     Nonzero if some randomness was contributed.
 360  *
 361  * Use:         Runs a free counter for a short while as a desparate attempt
 362  *              to get randomness from somewhere.  This is actually quite
 363  *              effective.
 364  */
 365
 366 #ifdef USE_FREEWHEEL
 367
 368 static jmp_buf fwjmp;
 369
 370 static void fwalarm(int sig)
 371 {
 372   siglongjmp(fwjmp, 1);
 373 }
 374
 375 int noise_freewheel(rand_pool *r)
 376 {
 377   void (*sigal)(int) = 0;
 378   struct itimerval oitv, itv = { { 0, 0 }, { 0, 5000 } };
 379   int rc = 0;
 380   volatile uint32 fwcount = 0;
 381
 382   if (!sigsetjmp(fwjmp, 1)) {
 383     if ((sigal = signal(SIGALRM, fwalarm)) == SIG_ERR)
 384       return (0);
 385     if (setitimer(ITIMER_REAL, &itv, &oitv))
 386       goto done;
 387     for (;;)
 388       fwcount++;
 389   } else {
 390     octet buf[4];
 391     STORE32(buf, fwcount);
 392     rand_add(r, buf, sizeof(buf), 16);
 393     rc = 1;
 394   }
 395
 396 done:
 397   signal(SIGALRM, sigal);
 398   if (oitv.it_value.tv_sec || oitv.it_value.tv_usec)
 399     TV_SUB(&oitv.it_value, &oitv.it_value, &itv.it_value);
 400   setitimer(ITIMER_REAL, &oitv, 0);
 401   return (rc);
 402 }
 403
 404 #else
 405
 406 int noise_freewheel(rand_pool *r)
 407 {
 408   return (0);
 409 }
 410
 411 #endif
 412
 413 /* --- @noise_enquire@ --- *
 414  *
 415  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 416  *
 417  * Returns:     Nonzero if some randomness was contributed.
 418  *
 419  * Use:         Runs some shell commands to enquire about the prevailing
 420  *              environment.  This can gather quite a lot of low-quality
 421  *              entropy.
 422  */
 423
 424 int noise_enquire(rand_pool *r)
 425 {
 426   struct tab {
 427     const char *cmd;
 428     unsigned rate;
 429   } tab[] = {
 430     { "ps alxww || ps -elf",    16 },
 431     { "netstat -n",              6 },
 432     { "ifconfig -a",             8 },
 433     { "df",                     20 },
 434     { "w",                       6 },
 435     { "ls -align /tmp/.",       10 },
 436     { 0,                         0 }
 437   };
 438   int i;
 439
 440   for (i = 0; tab[i].cmd; i++)
 441     noise_filter(r, tab[i].rate, tab[i].cmd);
 442   return (1);
 443 }
 444
 445 /* --- @noise_acquire@ --- *
 446  *
 447  * Arguments:   @rand_pool *r@ = pointer to a randomness pool
 448  *
 449  * Returns:     ---
 450  *
 451  * Use:         Acquires some randomness from somewhere.
 452  */
 453
 454 void noise_acquire(rand_pool *r)
 455 {
 456   unsigned i;
 457   for (i = 0; i < 8; i++)
 458     noise_freewheel(r);
 459   if (!noise_devrandom(r) || getenv("CATACOMB_FORCE_ESOTERIC_SOURCES")) {
 460     noise_enquire(r);
 461     for (i = 0; i < 8; i++)
 462       noise_freewheel(r);
 463   }
 464 }
 465
 466 /*----- That's all, folks -------------------------------------------------*/