seed.c

   1 /*
   2  * Routines to get/set seeds.
   3  */
   4 #include <syslog.h>
   5 #include <unistd.h>
   6 #include <stdlib.h>
   7 #include <sys/stat.h>
   8 #include <fcntl.h>
   9 #include <limits.h>
  10 #include "shm.h"
  11 #include "params.h"     // 'user_set_seed'
  12 #include "pids.h"
  13 #include "log.h"
  14 #include "random.h"
  15
  16 /* The actual seed lives in the shm. This variable is used
  17  * to store what gets passed in from the command line -s argument */
  18 unsigned int seed = 0;
  19
  20 static void syslog_seed(int seedparam)
  21 {
  22         outputerr("Randomness reseeded to %u\n", seedparam);
  23         openlog("trinity", LOG_CONS|LOG_PERROR, LOG_USER);
  24         syslog(LOG_CRIT, "Randomness reseeded to %u\n", seedparam);
  25         closelog();
  26 }
  27
  28 unsigned int new_seed(void)
  29 {
  30         int fd;
  31         struct timeval t;
  32         unsigned int r;
  33
  34         if ((fd = open("/dev/urandom", O_RDONLY)) < 0 ||
  35             read(fd, &r, sizeof(r)) != sizeof(r)) {
  36                 r = rand();
  37                 if (!(rand_bool())) {
  38                         gettimeofday(&t, NULL);
  39                         r |= t.tv_usec;
  40                 }
  41         }
  42         if (fd >= 0)
  43                 close(fd);
  44         return r;
  45 }
  46
  47 /*
  48  * If we passed in a seed with -s, use that. Otherwise make one up from time of day.
  49  */
  50 unsigned int init_seed(unsigned int seedparam)
  51 {
  52         if (user_set_seed == TRUE)
  53                 output(0, "Using user passed random seed: %u\n", seedparam);
  54         else {
  55                 seedparam = new_seed();
  56
  57                 output(0, "Initial random seed: %u\n", seedparam);
  58         }
  59
  60         if (do_syslog == TRUE)
  61                 syslog_seed(seedparam);
  62
  63         return seedparam;
  64 }
  65
  66 /* Mix in the pidslot so that all children get different randomness.
  67  * we can't use the actual pid or anything else 'random' because otherwise reproducing
  68  * seeds with -s would be much harder to replicate.
  69  */
  70 void set_seed(unsigned int pidslot)
  71 {
  72         srand(shm->seed + (pidslot + 1));
  73         shm->seeds[pidslot] = shm->seed;
  74 }
  75
  76 /*
  77  * Set a new seed in the parent.
  78  * Called when a new child starts, so we don't repeat runs across different pids.
  79  * We only reseed in the main pid, all the children are expected to periodically
  80  * check if the seed changed, and reseed accordingly.
  81  *
  82  * Caveat: Not used if we passed in our own seed with -s
  83  */
  84 void reseed(void)
  85 {
  86         if (getpid() != shm->mainpid) {
  87                 outputerr("Reseeding should only happen from parent!\n");
  88                 exit(EXIT_FAILURE);
  89         }
  90
  91         /* don't change the seed if we passed -s */
  92         if (user_set_seed == TRUE)
  93                 return;
  94
  95         /* We are reseeding. */
  96         shm->seed = new_seed();
  97
  98         output(0, "Random reseed: %u\n", shm->seed);
  99
 100         if (do_syslog == TRUE)
 101                 syslog_seed(shm->seed);
 102 }