src/random-seed/random-seed.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   This file is part of systemd.
   4
   5   Copyright 2010 Lennart Poettering
   6
   7   systemd is free software; you can redistribute it and/or modify it
   8   under the terms of the GNU Lesser General Public License as published by
   9   the Free Software Foundation; either version 2.1 of the License, or
  10   (at your option) any later version.
  11
  12   systemd is distributed in the hope that it will be useful, but
  13   WITHOUT ANY WARRANTY; without even the implied warranty of
  14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15   Lesser General Public License for more details.
  16
  17   You should have received a copy of the GNU Lesser General Public License
  18   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  19 ***/
  20
  21 #include <errno.h>
  22 #include <fcntl.h>
  23 #include <string.h>
  24 #include <sys/stat.h>
  25 #include <unistd.h>
  26
  27 #include "alloc-util.h"
  28 #include "fd-util.h"
  29 #include "io-util.h"
  30 #include "log.h"
  31 #include "mkdir.h"
  32 #include "string-util.h"
  33 #include "util.h"
  34
  35 #define POOL_SIZE_MIN 512
  36
  37 int main(int argc, char *argv[]) {
  38         _cleanup_close_ int seed_fd = -1, random_fd = -1;
  39         _cleanup_free_ void* buf = NULL;
  40         size_t buf_size = 0;
  41         ssize_t k;
  42         int r, open_rw_error;
  43         FILE *f;
  44         bool refresh_seed_file = true;
  45
  46         if (argc != 2) {
  47                 log_error("This program requires one argument.");
  48                 return EXIT_FAILURE;
  49         }
  50
  51         log_set_target(LOG_TARGET_AUTO);
  52         log_parse_environment();
  53         log_open();
  54
  55         umask(0022);
  56
  57         /* Read pool size, if possible */
  58         f = fopen("/proc/sys/kernel/random/poolsize", "re");
  59         if (f) {
  60                 if (fscanf(f, "%zu", &buf_size) > 0)
  61                         /* poolsize is in bits on 2.6, but we want bytes */
  62                         buf_size /= 8;
  63
  64                 fclose(f);
  65         }
  66
  67         if (buf_size <= POOL_SIZE_MIN)
  68                 buf_size = POOL_SIZE_MIN;
  69
  70         buf = malloc(buf_size);
  71         if (!buf) {
  72                 r = log_oom();
  73                 goto finish;
  74         }
  75
  76         r = mkdir_parents_label(RANDOM_SEED, 0755);
  77         if (r < 0) {
  78                 log_error_errno(r, "Failed to create directory " RANDOM_SEED_DIR ": %m");
  79                 goto finish;
  80         }
  81
  82         /* When we load the seed we read it and write it to the device
  83          * and then immediately update the saved seed with new data,
  84          * to make sure the next boot gets seeded differently. */
  85
  86         if (streq(argv[1], "load")) {
  87
  88                 seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
  89                 open_rw_error = -errno;
  90                 if (seed_fd < 0) {
  91                         refresh_seed_file = false;
  92
  93                         seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY);
  94                         if (seed_fd < 0) {
  95                                 bool missing = errno == ENOENT;
  96
  97                                 log_full_errno(missing ? LOG_DEBUG : LOG_ERR,
  98                                                open_rw_error, "Failed to open " RANDOM_SEED " for writing: %m");
  99                                 r = log_full_errno(missing ? LOG_DEBUG : LOG_ERR,
 100                                                    errno, "Failed to open " RANDOM_SEED " for reading: %m");
 101                                 if (missing)
 102                                         r = 0;
 103
 104                                 goto finish;
 105                         }
 106                 }
 107
 108                 random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600);
 109                 if (random_fd < 0) {
 110                         random_fd = open("/dev/urandom", O_WRONLY|O_CLOEXEC|O_NOCTTY, 0600);
 111                         if (random_fd < 0) {
 112                                 r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
 113                                 goto finish;
 114                         }
 115                 }
 116
 117                 k = loop_read(seed_fd, buf, buf_size, false);
 118                 if (k < 0)
 119                         r = log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m");
 120                 else if (k == 0) {
 121                         r = 0;
 122                         log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding.");
 123                 } else {
 124                         (void) lseek(seed_fd, 0, SEEK_SET);
 125
 126                         r = loop_write(random_fd, buf, (size_t) k, false);
 127                         if (r < 0)
 128                                 log_error_errno(r, "Failed to write seed to /dev/urandom: %m");
 129                 }
 130
 131         } else if (streq(argv[1], "save")) {
 132
 133                 seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
 134                 if (seed_fd < 0) {
 135                         r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
 136                         goto finish;
 137                 }
 138
 139                 random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
 140                 if (random_fd < 0) {
 141                         r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
 142                         goto finish;
 143                 }
 144
 145         } else {
 146                 log_error("Unknown verb '%s'.", argv[1]);
 147                 r = -EINVAL;
 148                 goto finish;
 149         }
 150
 151         if (refresh_seed_file) {
 152
 153                 /* This is just a safety measure. Given that we are root and
 154                  * most likely created the file ourselves the mode and owner
 155                  * should be correct anyway. */
 156                 (void) fchmod(seed_fd, 0600);
 157                 (void) fchown(seed_fd, 0, 0);
 158
 159                 k = loop_read(random_fd, buf, buf_size, false);
 160                 if (k < 0) {
 161                         r = log_error_errno(k, "Failed to read new seed from /dev/urandom: %m");
 162                         goto finish;
 163                 }
 164                 if (k == 0) {
 165                         log_error("Got EOF while reading from /dev/urandom.");
 166                         r = -EIO;
 167                         goto finish;
 168                 }
 169
 170                 r = loop_write(seed_fd, buf, (size_t) k, false);
 171                 if (r < 0)
 172                         log_error_errno(r, "Failed to write new random seed file: %m");
 173         }
 174
 175 finish:
 176         return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 177 }