src/random-seed/random-seed.c

   1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
   2
   3 /***
   4   This file is part of systemd.
   5
   6   Copyright 2010 Lennart Poettering
   7
   8   systemd is free software; you can redistribute it and/or modify it
   9   under the terms of the GNU Lesser General Public License as published by
  10   the Free Software Foundation; either version 2.1 of the License, or
  11   (at your option) any later version.
  12
  13   systemd is distributed in the hope that it will be useful, but
  14   WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16   Lesser General Public License for more details.
  17
  18   You should have received a copy of the GNU Lesser General Public License
  19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  20 ***/
  21
  22 #include <unistd.h>
  23 #include <fcntl.h>
  24 #include <errno.h>
  25 #include <string.h>
  26 #include <sys/stat.h>
  27
  28 #include "log.h"
  29 #include "util.h"
  30 #include "mkdir.h"
  31
  32 #define POOL_SIZE_MIN 512
  33
  34 int main(int argc, char *argv[]) {
  35         int seed_fd = -1, random_fd = -1;
  36         int ret = EXIT_FAILURE;
  37         void* buf;
  38         size_t buf_size = 0;
  39         ssize_t r;
  40         FILE *f;
  41
  42         if (argc != 2) {
  43                 log_error("This program requires one argument.");
  44                 return EXIT_FAILURE;
  45         }
  46
  47         log_set_target(LOG_TARGET_AUTO);
  48         log_parse_environment();
  49         log_open();
  50
  51         umask(0022);
  52
  53         /* Read pool size, if possible */
  54         if ((f = fopen("/proc/sys/kernel/random/poolsize", "re"))) {
  55                 if (fscanf(f, "%zu", &buf_size) > 0) {
  56                         /* poolsize is in bits on 2.6, but we want bytes */
  57                         buf_size /= 8;
  58                 }
  59
  60                 fclose(f);
  61         }
  62
  63         if (buf_size <= POOL_SIZE_MIN)
  64                 buf_size = POOL_SIZE_MIN;
  65
  66         if (!(buf = malloc(buf_size))) {
  67                 log_error("Failed to allocate buffer.");
  68                 goto finish;
  69         }
  70
  71         if (mkdir_parents_label(RANDOM_SEED, 0755) < 0) {
  72                 log_error("Failed to create directories parents of %s: %m", RANDOM_SEED);
  73                 goto finish;
  74         }
  75
  76         /* When we load the seed we read it and write it to the device
  77          * and then immediately update the saved seed with new data,
  78          * to make sure the next boot gets seeded differently. */
  79
  80         if (streq(argv[1], "load")) {
  81
  82                 if ((seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600)) < 0) {
  83                         if ((seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY)) < 0) {
  84                                 log_error("Failed to open random seed: %m");
  85                                 goto finish;
  86                         }
  87                 }
  88
  89                 if ((random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600)) < 0) {
  90                         if ((random_fd = open("/dev/urandom", O_WRONLY|O_CLOEXEC|O_NOCTTY, 0600)) < 0) {
  91                                 log_error("Failed to open /dev/urandom: %m");
  92                                 goto finish;
  93                         }
  94                 }
  95
  96                 if ((r = loop_read(seed_fd, buf, buf_size, false)) <= 0) {
  97
  98                         if (r != 0)
  99                                 log_error("Failed to read seed file: %m");
 100                 } else {
 101                         lseek(seed_fd, 0, SEEK_SET);
 102
 103                         if ((r = loop_write(random_fd, buf, (size_t) r, false)) <= 0)
 104                                 log_error("Failed to write seed to /dev/random: %s", r < 0 ? strerror(errno) : "short write");
 105                 }
 106
 107         } else if (streq(argv[1], "save")) {
 108
 109                 if ((seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600)) < 0) {
 110                         log_error("Failed to open random seed: %m");
 111                         goto finish;
 112                 }
 113
 114                 if ((random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY)) < 0) {
 115                         log_error("Failed to open /dev/urandom: %m");
 116                         goto finish;
 117                 }
 118         } else {
 119                 log_error("Unknown verb %s.", argv[1]);
 120                 goto finish;
 121         }
 122
 123         /* This is just a safety measure. Given that we are root and
 124          * most likely created the file ourselves the mode and owner
 125          * should be correct anyway. */
 126         fchmod(seed_fd, 0600);
 127         fchown(seed_fd, 0, 0);
 128
 129         if ((r = loop_read(random_fd, buf, buf_size, false)) <= 0)
 130                 log_error("Failed to read new seed from /dev/urandom: %s", r < 0 ? strerror(errno) : "EOF");
 131         else {
 132                 if ((r = loop_write(seed_fd, buf, (size_t) r, false)) <= 0)
 133                         log_error("Failed to write new random seed file: %s", r < 0 ? strerror(errno) : "short write");
 134         }
 135
 136         ret = EXIT_SUCCESS;
 137
 138 finish:
 139         if (random_fd >= 0)
 140                 close_nointr_nofail(random_fd);
 141
 142         if (seed_fd >= 0)
 143                 close_nointr_nofail(seed_fd);
 144
 145         free(buf);
 146
 147         return ret;
 148 }