src/machine-id-setup.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 General Public License as published by
  10   the Free Software Foundation; either version 2 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   General Public License for more details.
  17
  18   You should have received a copy of the GNU General Public License
  19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  20 ***/
  21
  22 #include <unistd.h>
  23 #include <stdio.h>
  24 #include <errno.h>
  25 #include <string.h>
  26 #include <stdlib.h>
  27 #include <fcntl.h>
  28 #include <sys/mount.h>
  29
  30 #include <systemd/sd-id128.h>
  31
  32 #include "machine-id-setup.h"
  33 #include "macro.h"
  34 #include "util.h"
  35 #include "log.h"
  36
  37 static int generate(char id[34]) {
  38         int fd, r;
  39         unsigned char *p;
  40         sd_id128_t buf;
  41         char *q;
  42         ssize_t k;
  43
  44         assert(id);
  45
  46         /* First, try reading the D-Bus machine id, unless it is a symlink */
  47         fd = open("/var/lib/dbus/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
  48         if (fd >= 0) {
  49
  50                 k = loop_read(fd, id, 33, false);
  51                 close_nointr_nofail(fd);
  52
  53                 if (k >= 32) {
  54                         id[32] = '\n';
  55                         id[33] = 0;
  56
  57                         log_info("Initializing machine ID from D-Bus machine ID.");
  58                         return 0;
  59                 }
  60         }
  61
  62         /* If that didn't work, generate a random machine id */
  63         r = sd_id128_randomize(&buf);
  64         if (r < 0) {
  65                 log_error("Failed to open /dev/urandom: %s", strerror(-r));
  66                 return r;
  67         }
  68
  69         for (p = buf.bytes, q = id; p < buf.bytes + sizeof(buf); p++, q += 2) {
  70                 q[0] = hexchar(*p >> 4);
  71                 q[1] = hexchar(*p & 15);
  72         }
  73
  74         id[32] = '\n';
  75         id[33] = 0;
  76
  77         log_info("Initializing machine ID from random generator.");
  78
  79         return 0;
  80 }
  81
  82 int machine_id_setup(void) {
  83         int fd, r;
  84         bool writable;
  85         struct stat st;
  86         char id[34]; /* 32 + \n + \0 */
  87         mode_t m;
  88
  89         m = umask(0000);
  90
  91         /* We create this 0444, to indicate that this isn't really
  92          * something you should ever modify. Of course, since the file
  93          * will be owned by root it doesn't matter much, but maybe
  94          * people look. */
  95
  96         fd = open("/etc/machine-id", O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
  97         if (fd >= 0)
  98                 writable = true;
  99         else {
 100                 fd = open("/etc/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY);
 101                 if (fd < 0) {
 102                         umask(m);
 103                         log_error("Cannot open /etc/machine-id: %m");
 104                         return -errno;
 105                 }
 106
 107                 writable = false;
 108         }
 109
 110         umask(m);
 111
 112         if (fstat(fd, &st) < 0) {
 113                 log_error("fstat() failed: %m");
 114                 r = -errno;
 115                 goto finish;
 116         }
 117
 118         if (S_ISREG(st.st_mode)) {
 119                 if (loop_read(fd, id, 32, false) >= 32) {
 120                         r = 0;
 121                         goto finish;
 122                 }
 123         }
 124
 125         /* Hmm, so, the id currently stored is not useful, then let's
 126          * generate one */
 127
 128         r = generate(id);
 129         if (r < 0)
 130                 goto finish;
 131
 132         if (S_ISREG(st.st_mode) && writable) {
 133                 lseek(fd, 0, SEEK_SET);
 134
 135                 if (loop_write(fd, id, 33, false) == 33) {
 136                         r = 0;
 137                         goto finish;
 138                 }
 139         }
 140
 141         close_nointr_nofail(fd);
 142         fd = -1;
 143
 144         /* Hmm, we couldn't write it? So let's write it to
 145          * /run/systemd/machine-id as a replacement */
 146
 147         mkdir_p("/run/systemd", 0755);
 148
 149         m = umask(0022);
 150         r = write_one_line_file("/run/systemd/machine-id", id);
 151         umask(m);
 152
 153         if (r < 0) {
 154                 log_error("Cannot write /run/systemd/machine-id: %s", strerror(-r));
 155
 156                 unlink("/run/systemd/machine-id");
 157                 goto finish;
 158         }
 159
 160         /* And now, let's mount it over */
 161         r = mount("/run/systemd/machine-id", "/etc/machine-id", "bind", MS_BIND|MS_RDONLY, NULL) < 0 ? -errno : 0;
 162         unlink("/run/systemd/machine-id");
 163
 164         if (r < 0)
 165                 log_error("Failed to mount /etc/machine-id: %s", strerror(-r));
 166         else
 167                 log_info("Installed transient /etc/machine-id file.");
 168
 169 finish:
 170
 171         if (fd >= 0)
 172                 close_nointr_nofail(fd);
 173
 174         return r;
 175 }