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 <errno.h>
  23 #include <fcntl.h>
  24 #include <string.h>
  25 #include <sys/stat.h>
  26 #include <unistd.h>
  27
  28 #include "log.h"
  29 #include "mkdir.h"
  30 #include "string-util.h"
  31 #include "util.h"
  32
  33 #define POOL_SIZE_MIN 512
  34
  35 int main(int argc, char *argv[]) {
  36         _cleanup_close_ int seed_fd = -1, random_fd = -1;
  37         _cleanup_free_ void* buf = NULL;
  38         size_t buf_size = 0;
  39         ssize_t k;
  40         int r;
  41         FILE *f;
  42         bool refresh_seed_file = true;
  43
  44         if (argc != 2) {
  45                 log_error("This program requires one argument.");
  46                 return EXIT_FAILURE;
  47         }
  48
  49         log_set_target(LOG_TARGET_AUTO);
  50         log_parse_environment();
  51         log_open();
  52
  53         umask(0022);
  54
  55         /* Read pool size, if possible */
  56         f = fopen("/proc/sys/kernel/random/poolsize", "re");
  57         if (f) {
  58                 if (fscanf(f, "%zu", &buf_size) > 0)
  59                         /* poolsize is in bits on 2.6, but we want bytes */
  60                         buf_size /= 8;
  61
  62                 fclose(f);
  63         }
  64
  65         if (buf_size <= POOL_SIZE_MIN)
  66                 buf_size = POOL_SIZE_MIN;
  67
  68         buf = malloc(buf_size);
  69         if (!buf) {
  70                 r = log_oom();
  71                 goto finish;
  72         }
  73
  74         r = mkdir_parents_label(RANDOM_SEED, 0755);
  75         if (r < 0) {
  76                 log_error_errno(r, "Failed to create directory " RANDOM_SEED_DIR ": %m");
  77                 goto finish;
  78         }
  79
  80         /* When we load the seed we read it and write it to the device
  81          * and then immediately update the saved seed with new data,
  82          * to make sure the next boot gets seeded differently. */
  83
  84         if (streq(argv[1], "load")) {
  85
  86                 seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
  87                 if (seed_fd < 0) {
  88                         seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY);
  89                         if (seed_fd < 0) {
  90                                 r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
  91                                 goto finish;
  92                         }
  93
  94                         refresh_seed_file = false;
  95                 }
  96
  97                 random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600);
  98                 if (random_fd < 0) {
  99                         random_fd = open("/dev/urandom", O_WRONLY|O_CLOEXEC|O_NOCTTY, 0600);
 100                         if (random_fd < 0) {
 101                                 r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
 102                                 goto finish;
 103                         }
 104                 }
 105
 106                 k = loop_read(seed_fd, buf, buf_size, false);
 107                 if (k < 0)
 108                         r = log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m");
 109                 else if (k == 0)
 110                         log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding.");
 111                 else {
 112                         (void) lseek(seed_fd, 0, SEEK_SET);
 113
 114                         r = loop_write(random_fd, buf, (size_t) k, false);
 115                         if (r < 0)
 116                                 log_error_errno(r, "Failed to write seed to /dev/urandom: %m");
 117                 }
 118
 119         } else if (streq(argv[1], "save")) {
 120
 121                 seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
 122                 if (seed_fd < 0) {
 123                         r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
 124                         goto finish;
 125                 }
 126
 127                 random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
 128                 if (random_fd < 0) {
 129                         r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
 130                         goto finish;
 131                 }
 132
 133         } else {
 134                 log_error("Unknown verb '%s'.", argv[1]);
 135                 r = -EINVAL;
 136                 goto finish;
 137         }
 138
 139         if (refresh_seed_file) {
 140
 141                 /* This is just a safety measure. Given that we are root and
 142                  * most likely created the file ourselves the mode and owner
 143                  * should be correct anyway. */
 144                 (void) fchmod(seed_fd, 0600);
 145                 (void) fchown(seed_fd, 0, 0);
 146
 147                 k = loop_read(random_fd, buf, buf_size, false);
 148                 if (k < 0) {
 149                         r = log_error_errno(k, "Failed to read new seed from /dev/urandom: %m");
 150                         goto finish;
 151                 }
 152                 if (k == 0) {
 153                         log_error("Got EOF while reading from /dev/urandom.");
 154                         r = -EIO;
 155                         goto finish;
 156                 }
 157
 158                 r = loop_write(seed_fd, buf, (size_t) k, false);
 159                 if (r < 0)
 160                         log_error_errno(r, "Failed to write new random seed file: %m");
 161         }
 162
 163 finish:
 164         return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 165 }