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 "machine-id-setup.h"
  31 #include "macro.h"
  32 #include "util.h"
  33 #include "log.h"
  34
  35 static void make_v4_uuid(unsigned char *id) {
  36         /* Stolen from generate_random_uuid() of drivers/char/random.c
  37          * in the kernel sources */
  38
  39         /* Set UUID version to 4 --- truly random generation */
  40         id[6] = (id[6] & 0x0F) | 0x40;
  41
  42         /* Set the UUID variant to DCE */
  43         id[8] = (id[8] & 0x3F) | 0x80;
  44 }
  45
  46 static int generate(char id[34]) {
  47         int fd;
  48         unsigned char buf[16], *p;
  49         char *q;
  50         ssize_t k;
  51
  52         assert(id);
  53
  54         /* First, try reading the D-Bus machine id, unless it is a symlink */
  55         fd = open("/var/lib/dbus/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
  56         if (fd >= 0) {
  57
  58                 k = loop_read(fd, id, 33, false);
  59                 close_nointr_nofail(fd);
  60
  61                 if (k >= 32) {
  62                         id[32] = '\n';
  63                         id[33] = 0;
  64
  65                         log_info("Initializing machine ID from D-Bus machine ID.");
  66                         return 0;
  67                 }
  68         }
  69
  70         /* If that didn't work, generate a random machine id */
  71         fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
  72         if (fd < 0) {
  73                 log_error("Failed to open /dev/urandom: %m");
  74                 return -errno;
  75         }
  76
  77         k = loop_read(fd, buf, sizeof(buf), false);
  78         close_nointr_nofail(fd);
  79
  80         if (k != sizeof(buf)) {
  81                 log_error("Failed to read /dev/urandom: %s", strerror(k < 0 ? -k : EIO));
  82                 return k < 0 ? (int) k : -EIO;
  83         }
  84
  85         /* Turn this into a valid v4 UUID, to be nice. Note that we
  86          * only guarantee this for newly generated UUIDs, not for
  87          * pre-existing ones.*/
  88         make_v4_uuid(buf);
  89
  90         for (p = buf, q = id; p < buf + sizeof(buf); p++, q += 2) {
  91                 q[0] = hexchar(*p >> 4);
  92                 q[1] = hexchar(*p & 15);
  93         }
  94
  95         id[32] = '\n';
  96         id[33] = 0;
  97
  98         log_info("Initializing machine ID from random generator.");
  99
 100         return 0;
 101 }
 102
 103 int machine_id_setup(void) {
 104         int fd, r;
 105         bool writable;
 106         struct stat st;
 107         char id[34]; /* 32 + \n + \0 */
 108         mode_t m;
 109
 110         m = umask(0000);
 111
 112         /* We create this 0444, to indicate that this isn't really
 113          * something you should ever modify. Of course, since the file
 114          * will be owned by root it doesn't matter much, but maybe
 115          * people look. */
 116
 117         fd = open("/etc/machine-id", O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
 118         if (fd >= 0)
 119                 writable = true;
 120         else {
 121                 fd = open("/etc/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY);
 122                 if (fd < 0) {
 123                         umask(m);
 124                         log_error("Cannot open /etc/machine-id: %m");
 125                         return -errno;
 126                 }
 127
 128                 writable = false;
 129         }
 130
 131         umask(m);
 132
 133         if (fstat(fd, &st) < 0) {
 134                 log_error("fstat() failed: %m");
 135                 r = -errno;
 136                 goto finish;
 137         }
 138
 139         if (S_ISREG(st.st_mode)) {
 140                 if (loop_read(fd, id, 32, false) >= 32) {
 141                         r = 0;
 142                         goto finish;
 143                 }
 144         }
 145
 146         /* Hmm, so, the id currently stored is not useful, then let's
 147          * generate one */
 148
 149         r = generate(id);
 150         if (r < 0)
 151                 goto finish;
 152
 153         if (S_ISREG(st.st_mode) && writable) {
 154                 lseek(fd, 0, SEEK_SET);
 155
 156                 if (loop_write(fd, id, 33, false) == 33) {
 157                         r = 0;
 158                         goto finish;
 159                 }
 160         }
 161
 162         close_nointr_nofail(fd);
 163         fd = -1;
 164
 165         /* Hmm, we couldn't write it? So let's write it to
 166          * /run/systemd/machine-id as a replacement */
 167
 168         mkdir_p("/run/systemd", 0755);
 169
 170         m = umask(0022);
 171         r = write_one_line_file("/run/systemd/machine-id", id);
 172         umask(m);
 173
 174         if (r < 0) {
 175                 log_error("Cannot write /run/systemd/machine-id: %s", strerror(-r));
 176
 177                 unlink("/run/systemd/machine-id");
 178                 goto finish;
 179         }
 180
 181         /* And now, let's mount it over */
 182         r = mount("/run/systemd/machine-id", "/etc/machine-id", "bind", MS_BIND|MS_RDONLY, NULL) < 0 ? -errno : 0;
 183         unlink("/run/systemd/machine-id");
 184
 185         if (r < 0)
 186                 log_error("Failed to mount /etc/machine-id: %s", strerror(-r));
 187         else
 188                 log_info("Installed transient /etc/machine-id file.");
 189
 190 finish:
 191
 192         if (fd >= 0)
 193                 close_nointr_nofail(fd);
 194
 195         return r;
 196 }