mdw@git.distorted.org.uk Git - become/blob - src/noise.c

   1 /* -*-c-*-
   2  *
   3  * $Id: noise.c,v 1.6 1998/06/18 15:08:14 mdw Exp $
   4  *
   5  * Collection of environmental noise
   6  *
   7  * (c) 1998 EBI
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of `become'
  13  *
  14  * `Become' is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU General Public License as published by
  16  * the Free Software Foundation; either version 2 of the License, or
  17  * (at your option) any later version.
  18  *
  19  * `Become' 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 General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU General Public License
  25  * along with `become'; if not, write to the Free Software Foundation,
  26  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  27  */
  28
  29 /*----- Revision history --------------------------------------------------*
  30  *
  31  * $Log: noise.c,v $
  32  * Revision 1.6  1998/06/18 15:08:14  mdw
  33  * Improve signal handling when accumulating noise from child processes.
  34  *
  35  * Revision 1.5  1998/04/23 13:25:23  mdw
  36  * Try to reduce the amount of `ps'ing done under OSF/1, because /dev/kmem
  37  * seems very slow.
  38  *
  39  * Revision 1.4  1998/02/20 17:52:32  mdw
  40  * Don't use `df' for noise gathering, because it gets upset when NFS
  41  * servers aren't responding.
  42  *
  43  * Revision 1.3  1998/01/12 16:46:19  mdw
  44  * Fix copyright date.
  45  *
  46  * Revision 1.2  1997/08/20  16:19:57  mdw
  47  * Fix test for `/dev/random' so that it doesn't close `stdin' if it fails!
  48  *
  49  * Revision 1.1  1997/08/07 09:45:26  mdw
  50  * New source file added to acquire environmental noise and add it to the
  51  * randomness pool (see `rand.c').
  52  *
  53  */
  54
  55 /*----- Header files ------------------------------------------------------*/
  56
  57 /* --- ANSI headers --- */
  58
  59 #include <ctype.h>
  60 #include <errno.h>
  61 #include <signal.h>
  62 #include <stdio.h>
  63 #include <stdlib.h>
  64 #include <string.h>
  65 #include <time.h>
  66
  67 /* --- Unix headers --- */
  68
  69 #include <sys/types.h>
  70 #include <sys/time.h>
  71
  72 #include "config.h"
  73 #if defined(HAVE_GETRUSAGE)
  74 #  include <sys/resource.h>
  75 #elif defined(HAVE_VTIMES)
  76 #  include <sys/vtimes.h>
  77 #endif
  78
  79 #include <sys/wait.h>
  80
  81 #include <fcntl.h>
  82 #include <unistd.h>
  83
  84 /* --- Local headers --- */
  85
  86 #include "noise.h"
  87 #include "rand.h"
  88 #include "utils.h"
  89
  90 /*----- Main code ---------------------------------------------------------*/
  91
  92 /* --- @noise__shell@ --- *
  93  *
  94  * Arguments:   @const char *cmd@ = pointer to a shell command
  95  *
  96  * Returns:     ---
  97  *
  98  * Use:         Adds the output of the shell command to the randomness pool.
  99  *              Some care is taken to do the Right Thing when running setuid.
 100  */
 101
 102 static void noise__shell(const char *cmd)
 103 {
 104   int pfd[2];
 105   pid_t pid;
 106
 107 #ifdef HAVE_SIGPROCMASK
 108   sigset_t ob, nb;
 109 #endif
 110
 111   /* --- Create a pipe for talking to the child --- */
 112
 113   if (pipe(pfd))
 114     return;
 115
 116   /* --- Sort out the signal handling for the parent --- *
 117    *
 118    * Block @SIGCHLD@ while this is going on.  Unlike the standard @system@
 119    * function, I won't disable @SIGINT@ and @SIGQUIT@.  Then, if the user
 120    * stops the child with a terminal signal, the parent (i.e., me) gets
 121    * killed too, and I don't end up with a tiny dribble of entropy when I'm
 122    * expecting quite a lot.
 123    */
 124
 125 #ifdef HAVE_SIGPROCMASK
 126   sigemptyset(&nb);
 127   sigaddset(&nb, SIGCHLD);
 128   if (sigprocmask(SIG_BLOCK, &nb, &ob))
 129     goto fail_0;
 130 #endif
 131
 132   /* --- Create the child process --- */
 133
 134   pid = fork();
 135   if (pid < 0)
 136     goto fail_1;
 137
 138   if (pid == 0) {
 139     int fd;
 140     char *argv[] = { "/bin/sh", "-c", 0, 0 };
 141     char *env[] = {
 142       "PATH=/bin:/usr/bin:/usr/ucb:/usr/etc:/sbin:/usr/sbin",
 143       0
 144     };
 145
 146     /* --- Restore signal handling things --- */
 147
 148 #ifdef HAVE_SIGPROCMASK
 149     sigprocmask(SIG_SETMASK, &nb, 0);
 150 #endif
 151
 152     /* --- Become nobody --- *
 153      *
 154      * This assumes that @-2@ is a safe user to be.  It shouldn't be root,
 155      * because it doesn't need to be, and nothing should be done as root
 156      * which could be done as someone else.  It shouldn't be the user who
 157      * invoked me, because that would enable her to kill the children before
 158      * I've read enough entropy from them, and that wouldn't be good.
 159      */
 160
 161     setuid(-2);
 162
 163     /* --- Close the old standard streams --- */
 164
 165     close(0);
 166     close(1);
 167     close(2);
 168
 169     /* --- Set up stdin and stderr to be empty, and stdout as our pipe --- */
 170
 171     if (((fd = open("/dev/null", O_RDONLY)) != 0 &&
 172          (fd = dup2(fd, 0)) != 0) ||
 173         ((fd = dup2(pfd[1], 1)) != 1) ||
 174         ((fd = open("/dev/null", O_WRONLY)) != 2 &&
 175          (fd = dup2(fd, 2)) != 2))
 176       goto child_fail;
 177
 178     /* --- Close the original pipe file descriptors --- */
 179
 180     close(pfd[0]);
 181     close(pfd[1]);
 182     burn(pfd);
 183
 184     /* --- Now run the child process --- */
 185
 186     argv[2] = (char *)cmd;              /* POSIX screwed up the prototype */
 187     execve("/bin/sh", argv, env);
 188
 189     /* --- Something went horribly wrong --- */
 190
 191   child_fail:
 192     _exit(127);
 193   }
 194
 195   /* --- Now read from the child until it's all done --- */
 196
 197   {
 198     char buf[1024];
 199     ssize_t sz;
 200
 201     close(pfd[1]);
 202     for (;;) {
 203       sz = read(pfd[0], buf, sizeof(buf));
 204       if (sz == 0 || (sz < 0 && sz != EINTR))
 205         break;
 206       rand_add(buf, sz);
 207     }
 208     close(pfd[0]);
 209     rand_add(pfd, sizeof(pfd));
 210     burn(buf); burn(pfd);
 211   }
 212
 213   /* --- The child should be dead now, so wait for it --- */
 214
 215   {
 216     int st;
 217     wait(&st);
 218     rand_add(&st, sizeof(st));
 219     rand_add(&pid, sizeof(pid));
 220   }
 221
 222   /* --- Restore signals --- */
 223
 224 fail_1:
 225 #ifdef HAVE_SIGPROCMASK
 226   sigprocmask(SIG_SETMASK, &ob, 0);
 227 #endif
 228 fail_0:;
 229 }
 230
 231 /* --- @noise_acquire@ --- *
 232  *
 233  * Arguments:   ---
 234  *
 235  * Returns:     ---
 236  *
 237  * Use:         Attempts to acquire an amount of random noise from the
 238  *              environment.  A lot of it's not actually much good, but
 239  *              it's better than nothing.  There's probably a bit or two's
 240  *              worth in each item which gets added.
 241  */
 242
 243 void noise_acquire(void)
 244 {
 245   /* --- Try a real random number source --- *
 246    *
 247    * Some operating systems (notably Linux) provide a `/dev/random' which
 248    * contains distilled random numbers from the outside world.
 249    */
 250
 251   {
 252     int fd;
 253     int f;
 254     unsigned char buff[64];
 255     ssize_t sz;
 256
 257     if ((fd = open("/dev/random", O_RDONLY)) >= 0 &&
 258         (f = fcntl(fd, F_GETFL, 0)) >= 0 &&
 259         fcntl(fd, F_SETFL, f | O_NONBLOCK) >= 0 &&
 260         (sz = read(fd, buff, sizeof(buff))) > 0) {
 261       rand_add(buff, sz);
 262       burn(buff);
 263     }
 264     if (fd >= 0)
 265       close(fd);
 266   }
 267
 268   /* --- Squeeze some entropy from the current time --- */
 269
 270   {
 271     struct timeval tv;
 272     clock_t c;
 273
 274     gettimeofday(&tv, 0);
 275     c = clock();
 276     rand_add(&tv, sizeof(tv));
 277     rand_add(&c, sizeof(c));
 278     burn(tv); burn(c);
 279   }
 280
 281   /* --- Try some commands which ask the outside world some questions --- */
 282
 283   noise__shell("ps auxww || ps -ef; netstat -an");
 284
 285   /* --- Get our resource usage to see if that's at all interesting --- */
 286
 287 #if defined(HAVE_GETRUSAGE)
 288   {
 289     struct rusage ru;
 290     getrusage(RUSAGE_SELF, &ru);
 291     rand_add(&ru, sizeof(ru));
 292     getrusage(RUSAGE_CHILDREN, &ru);
 293     rand_add(&ru, sizeof(ru));
 294     burn(ru);
 295   }
 296 #elif defined(HAVE_VTIMES)
 297   {
 298     struct vtimes vt, vtc;
 299     vtimes(&vt, &vtc);
 300     rand_add(&vt, sizeof(vt));
 301     rand_add(&vtc, sizeof(vtc));
 302     burn(vt); burn(vtc);
 303   }
 304 #endif
 305
 306   /* --- Squeeze some more entropy from the current time --- */
 307
 308   {
 309     struct timeval tv;
 310     clock_t c;
 311
 312     gettimeofday(&tv, 0);
 313     c = clock();
 314     rand_add(&tv, sizeof(tv));
 315     rand_add(&c, sizeof(c));
 316     burn(tv); burn(c);
 317   }
 318
 319   /* --- Done -- churn the random pool --- */
 320
 321   rand_churn();
 322 }
 323
 324 /*----- That's all, folks -------------------------------------------------*/