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 "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;
  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                 if (seed_fd < 0) {
  90                         seed_fd = open(RANDOM_SEED, O_RDONLY|O_CLOEXEC|O_NOCTTY);
  91                         if (seed_fd < 0) {
  92                                 r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
  93                                 goto finish;
  94                         }
  95
  96                         refresh_seed_file = false;
  97                 }
  98
  99                 random_fd = open("/dev/urandom", O_RDWR|O_CLOEXEC|O_NOCTTY, 0600);
 100                 if (random_fd < 0) {
 101                         random_fd = open("/dev/urandom", O_WRONLY|O_CLOEXEC|O_NOCTTY, 0600);
 102                         if (random_fd < 0) {
 103                                 r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
 104                                 goto finish;
 105                         }
 106                 }
 107
 108                 k = loop_read(seed_fd, buf, buf_size, false);
 109                 if (k < 0)
 110                         r = log_error_errno(k, "Failed to read seed from " RANDOM_SEED ": %m");
 111                 else if (k == 0)
 112                         log_debug("Seed file " RANDOM_SEED " not yet initialized, proceeding.");
 113                 else {
 114                         (void) 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                         r = log_error_errno(errno, "Failed to open " RANDOM_SEED ": %m");
 126                         goto finish;
 127                 }
 128
 129                 random_fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
 130                 if (random_fd < 0) {
 131                         r = log_error_errno(errno, "Failed to open /dev/urandom: %m");
 132                         goto finish;
 133                 }
 134
 135         } else {
 136                 log_error("Unknown verb '%s'.", argv[1]);
 137                 r = -EINVAL;
 138                 goto finish;
 139         }
 140
 141         if (refresh_seed_file) {
 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                 (void) fchmod(seed_fd, 0600);
 147                 (void) fchown(seed_fd, 0, 0);
 148
 149                 k = loop_read(random_fd, buf, buf_size, false);
 150                 if (k < 0) {
 151                         r = log_error_errno(k, "Failed to read new seed from /dev/urandom: %m");
 152                         goto finish;
 153                 }
 154                 if (k == 0) {
 155                         log_error("Got EOF while reading from /dev/urandom.");
 156                         r = -EIO;
 157                         goto finish;
 158                 }
 159
 160                 r = loop_write(seed_fd, buf, (size_t) k, false);
 161                 if (r < 0)
 162                         log_error_errno(r, "Failed to write new random seed file: %m");
 163         }
 164
 165 finish:
 166         return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 167 }