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 "alloc-util.h"
  29 #include "fd-util.h"
  30 #include "io-util.h"
  31 #include "log.h"
  32 #include "mkdir.h"
  33 #include "string-util.h"
  34 #include "util.h"
  35
  36 #define POOL_SIZE_MIN 512
  37
  38 int main(int argc, char *argv[]) {
  39         _cleanup_close_ int seed_fd = -1, random_fd = -1;
  40         _cleanup_free_ void* buf = NULL;
  41         size_t buf_size = 0;
  42         ssize_t k;
  43         int r;
  44         FILE *f;
  45         bool refresh_seed_file = true;
  46
  47         if (argc != 2) {
  48                 log_error("This program requires one argument.");
  49                 return EXIT_FAILURE;
  50         }
  51
  52         log_set_target(LOG_TARGET_AUTO);
  53         log_parse_environment();
  54         log_open();
  55
  56         umask(0022);
  57
  58         /* Read pool size, if possible */
  59         f = fopen("/proc/sys/kernel/random/poolsize", "re");
  60         if (f) {
  61                 if (fscanf(f, "%zu", &buf_size) > 0)
  62                         /* poolsize is in bits on 2.6, but we want bytes */
  63                         buf_size /= 8;
  64
  65                 fclose(f);
  66         }
  67
  68         if (buf_size <= POOL_SIZE_MIN)
  69                 buf_size = POOL_SIZE_MIN;
  70
  71         buf = malloc(buf_size);
  72         if (!buf) {
  73                 r = log_oom();
  74                 goto finish;
  75         }
  76
  77         r = mkdir_parents_label(RANDOM_SEED, 0755);
  78         if (r < 0) {
  79                 log_error_errno(r, "Failed to create directory " RANDOM_SEED_DIR ": %m");
  80                 goto finish;
  81         }
  82
  83         /* When we load the seed we read it and write it to the device
  84          * and then immediately update the saved seed with new data,
  85          * to make sure the next boot gets seeded differently. */
  86
  87         if (streq(argv[1], "load")) {
  88
  89                 seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
  90                 if (seed_fd < 0) {
  91                         seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY);
  92                         if (seed_fd < 0) {
  93                                 r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
  94                                 goto finish;
  95                         }
  96
  97                         refresh_seed_file = false;
  98                 }
  99
 100                 random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600);
 101                 if (random_fd < 0) {
 102                         random_fd = open("/dev/urandom", O_WRONLY|O_CLOEXEC|O_NOCTTY, 0600);
 103                         if (random_fd < 0) {
 104                                 r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
 105                                 goto finish;
 106                         }
 107                 }
 108
 109                 k = loop_read(seed_fd, buf, buf_size, false);
 110                 if (k < 0)
 111                         r = log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m");
 112                 else if (k == 0)
 113                         log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding.");
 114                 else {
 115                         (void) lseek(seed_fd, 0, SEEK_SET);
 116
 117                         r = loop_write(random_fd, buf, (size_t) k, false);
 118                         if (r < 0)
 119                                 log_error_errno(r, "Failed to write seed to /dev/urandom: %m");
 120                 }
 121
 122         } else if (streq(argv[1], "save")) {
 123
 124                 seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
 125                 if (seed_fd < 0) {
 126                         r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
 127                         goto finish;
 128                 }
 129
 130                 random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
 131                 if (random_fd < 0) {
 132                         r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
 133                         goto finish;
 134                 }
 135
 136         } else {
 137                 log_error("Unknown verb '%s'.", argv[1]);
 138                 r = -EINVAL;
 139                 goto finish;
 140         }
 141
 142         if (refresh_seed_file) {
 143
 144                 /* This is just a safety measure. Given that we are root and
 145                  * most likely created the file ourselves the mode and owner
 146                  * should be correct anyway. */
 147                 (void) fchmod(seed_fd, 0600);
 148                 (void) fchown(seed_fd, 0, 0);
 149
 150                 k = loop_read(random_fd, buf, buf_size, false);
 151                 if (k < 0) {
 152                         r = log_error_errno(k, "Failed to read new seed from /dev/urandom: %m");
 153                         goto finish;
 154                 }
 155                 if (k == 0) {
 156                         log_error("Got EOF while reading from /dev/urandom.");
 157                         r = -EIO;
 158                         goto finish;
 159                 }
 160
 161                 r = loop_write(seed_fd, buf, (size_t) k, false);
 162                 if (r < 0)
 163                         log_error_errno(r, "Failed to write new random seed file: %m");
 164         }
 165
 166 finish:
 167         return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 168 }