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         _cleanup_close_ int seed_fd = -1, random_fd = -1;
  36         _cleanup_free_ void* buf = NULL;
  37         size_t buf_size = 0;
  38         ssize_t k;
  39         int 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         f = fopen("/proc/sys/kernel/random/poolsize", "re");
  55         if (f) {
  56                 if (fscanf(f, "%zu", &buf_size) > 0) {
  57                         /* poolsize is in bits on 2.6, but we want bytes */
  58                         buf_size /= 8;
  59                 }
  60
  61                 fclose(f);
  62         }
  63
  64         if (buf_size <= POOL_SIZE_MIN)
  65                 buf_size = POOL_SIZE_MIN;
  66
  67         buf = malloc(buf_size);
  68         if (!buf) {
  69                 r = log_oom();
  70                 goto finish;
  71         }
  72
  73         r = mkdir_parents_label(RANDOM_SEED, 0755);
  74         if (r < 0) {
  75                 log_error_errno(r, "Failed to create directory " RANDOM_SEED_DIR ": %m");
  76                 goto finish;
  77         }
  78
  79         /* When we load the seed we read it and write it to the device
  80          * and then immediately update the saved seed with new data,
  81          * to make sure the next boot gets seeded differently. */
  82
  83         if (streq(argv[1], "load")) {
  84
  85                 seed_fd = open(RANDOM_SEED, O_RDWR|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
  86                 if (seed_fd < 0) {
  87                         seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY);
  88                         if (seed_fd < 0) {
  89                                 log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
  90                                 r = -errno;
  91                                 goto finish;
  92                         }
  93                 }
  94
  95                 random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600);
  96                 if (random_fd < 0) {
  97                         random_fd = open("/dev/urandom", O_WRONLY|O_CLOEXEC|O_NOCTTY, 0600);
  98                         if (random_fd < 0) {
  99                                 log_error_errno(errno, "Failed to open /dev/urandom: %m");
 100                                 r = -errno;
 101                                 goto finish;
 102                         }
 103                 }
 104
 105                 k = loop_read(seed_fd, buf, buf_size, false);
 106                 if (k <= 0) {
 107
 108                         if (r != 0)
 109                                 log_error_errno(errno, "Failed to read seed from " RANDOM_SEED ": %m");
 110
 111                         r = k == 0 ? -EIO : (int) k;
 112
 113                 } else {
 114                         lseek(seed_fd, 0, SEEK_SET);
 115
 116                         r = loop_write(random_fd, buf, (size_t) k, false);
 117                         if (r < 0)
 118                                 log_error_errno(r, "Failed to write seed to /dev/urandom: %m");
 119                 }
 120
 121         } else if (streq(argv[1], "save")) {
 122
 123                 seed_fd = open(RANDOM_SEED, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_CREAT, 0600);
 124                 if (seed_fd < 0) {
 125                         log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
 126                         r = -errno;
 127                         goto finish;
 128                 }
 129
 130                 random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
 131                 if (random_fd < 0) {
 132                         log_error_errno(errno, "Failed to open /dev/urandom: %m");
 133                         r = -errno;
 134                         goto finish;
 135                 }
 136
 137         } else {
 138                 log_error("Unknown verb %s.", argv[1]);
 139                 r = -EINVAL;
 140                 goto finish;
 141         }
 142
 143         /* This is just a safety measure. Given that we are root and
 144          * most likely created the file ourselves the mode and owner
 145          * should be correct anyway. */
 146         fchmod(seed_fd, 0600);
 147         fchown(seed_fd, 0, 0);
 148
 149         k = loop_read(random_fd, buf, buf_size, false);
 150         if (k <= 0) {
 151                 log_error("Failed to read new seed from /dev/urandom: %s", r < 0 ? strerror(-r) : "EOF");
 152                 r = k == 0 ? -EIO : (int) k;
 153         } else {
 154                 r = loop_write(seed_fd, buf, (size_t) k, false);
 155                 if (r < 0)
 156                         log_error_errno(r, "Failed to write new random seed file: %m");
 157         }
 158
 159 finish:
 160         return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 161 }