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 "fd-util.h"
  29 #include "log.h"
  30 #include "mkdir.h"
  31 #include "string-util.h"
  32 #include "util.h"
  33
  34 #define POOL_SIZE_MIN 512
  35
  36 int main(int argc, char *argv[]) {
  37         _cleanup_close_ int seed_fd = -1, random_fd = -1;
  38         _cleanup_free_ void* buf = NULL;
  39         size_t buf_size = 0;
  40         ssize_t k;
  41         int r;
  42         FILE *f;
  43         bool refresh_seed_file = true;
  44
  45         if (argc != 2) {
  46                 log_error("This program requires one argument.");
  47                 return EXIT_FAILURE;
  48         }
  49
  50         log_set_target(LOG_TARGET_AUTO);
  51         log_parse_environment();
  52         log_open();
  53
  54         umask(0022);
  55
  56         /* Read pool size, if possible */
  57         f = fopen("/proc/sys/kernel/random/poolsize", "re");
  58         if (f) {
  59                 if (fscanf(f, "%zu", &buf_size) > 0)
  60                         /* poolsize is in bits on 2.6, but we want bytes */
  61                         buf_size /= 8;
  62
  63                 fclose(f);
  64         }
  65
  66         if (buf_size <= POOL_SIZE_MIN)
  67                 buf_size = POOL_SIZE_MIN;
  68
  69         buf = malloc(buf_size);
  70         if (!buf) {
  71                 r = log_oom();
  72                 goto finish;
  73         }
  74
  75         r = mkdir_parents_label(RANDOM_SEED, 0755);
  76         if (r < 0) {
  77                 log_error_errno(r, "Failed to create directory " RANDOM_SEED_DIR ": %m");
  78                 goto finish;
  79         }
  80
  81         /* When we load the seed we read it and write it to the device
  82          * and then immediately update the saved seed with new data,
  83          * to make sure the next boot gets seeded differently. */
  84
  85         if (streq(argv[1], "load")) {
  86
  87                 seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
  88                 if (seed_fd < 0) {
  89                         seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY);
  90                         if (seed_fd < 0) {
  91                                 r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
  92                                 goto finish;
  93                         }
  94
  95                         refresh_seed_file = false;
  96                 }
  97
  98                 random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600);
  99                 if (random_fd < 0) {
 100                         random_fd = open("/dev/urandom", O_WRONLY|O_CLOEXEC|O_NOCTTY, 0600);
 101                         if (random_fd < 0) {
 102                                 r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
 103                                 goto finish;
 104                         }
 105                 }
 106
 107                 k = loop_read(seed_fd, buf, buf_size, false);
 108                 if (k < 0)
 109                         r = log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m");
 110                 else if (k == 0)
 111                         log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding.");
 112                 else {
 113                         (void) lseek(seed_fd, 0, SEEK_SET);
 114
 115                         r = loop_write(random_fd, buf, (size_t) k, false);
 116                         if (r < 0)
 117                                 log_error_errno(r, "Failed to write seed to /dev/urandom: %m");
 118                 }
 119
 120         } else if (streq(argv[1], "save")) {
 121
 122                 seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
 123                 if (seed_fd < 0) {
 124                         r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
 125                         goto finish;
 126                 }
 127
 128                 random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
 129                 if (random_fd < 0) {
 130                         r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
 131                         goto finish;
 132                 }
 133
 134         } else {
 135                 log_error("Unknown verb '%s'.", argv[1]);
 136                 r = -EINVAL;
 137                 goto finish;
 138         }
 139
 140         if (refresh_seed_file) {
 141
 142                 /* This is just a safety measure. Given that we are root and
 143                  * most likely created the file ourselves the mode and owner
 144                  * should be correct anyway. */
 145                 (void) fchmod(seed_fd, 0600);
 146                 (void) fchown(seed_fd, 0, 0);
 147
 148                 k = loop_read(random_fd, buf, buf_size, false);
 149                 if (k < 0) {
 150                         r = log_error_errno(k, "Failed to read new seed from /dev/urandom: %m");
 151                         goto finish;
 152                 }
 153                 if (k == 0) {
 154                         log_error("Got EOF while reading from /dev/urandom.");
 155                         r = -EIO;
 156                         goto finish;
 157                 }
 158
 159                 r = loop_write(seed_fd, buf, (size_t) k, false);
 160                 if (r < 0)
 161                         log_error_errno(r, "Failed to write new random seed file: %m");
 162         }
 163
 164 finish:
 165         return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 166 }