src/basic/hostname-util.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2015 Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <limits.h>
  22 #include <stdio.h>
  23 #include <string.h>
  24 #include <sys/utsname.h>
  25 #include <unistd.h>
  26
  27 #include "fd-util.h"
  28 #include "fileio.h"
  29 #include "hostname-util.h"
  30 #include "macro.h"
  31 #include "string-util.h"
  32
  33 bool hostname_is_set(void) {
  34         struct utsname u;
  35
  36         assert_se(uname(&u) >= 0);
  37
  38         if (isempty(u.nodename))
  39                 return false;
  40
  41         /* This is the built-in kernel default host name */
  42         if (streq(u.nodename, "(none)"))
  43                 return false;
  44
  45         return true;
  46 }
  47
  48 char* gethostname_malloc(void) {
  49         struct utsname u;
  50
  51         /* This call tries to return something useful, either the actual hostname
  52          * or it makes something up. The only reason it might fail is OOM.
  53          * It might even return "localhost" if that's set. */
  54
  55         assert_se(uname(&u) >= 0);
  56
  57         if (isempty(u.nodename) || streq(u.nodename, "(none)"))
  58                 return strdup(FALLBACK_HOSTNAME);
  59
  60         return strdup(u.nodename);
  61 }
  62
  63 int gethostname_strict(char **ret) {
  64         struct utsname u;
  65         char *k;
  66
  67         /* This call will rather fail than make up a name. It will not return "localhost" either. */
  68
  69         assert_se(uname(&u) >= 0);
  70
  71         if (isempty(u.nodename))
  72                 return -ENXIO;
  73
  74         if (streq(u.nodename, "(none)"))
  75                 return -ENXIO;
  76
  77         if (is_localhost(u.nodename))
  78                 return -ENXIO;
  79
  80         k = strdup(u.nodename);
  81         if (!k)
  82                 return -ENOMEM;
  83
  84         *ret = k;
  85         return 0;
  86 }
  87
  88 static bool hostname_valid_char(char c) {
  89         return
  90                 (c >= 'a' && c <= 'z') ||
  91                 (c >= 'A' && c <= 'Z') ||
  92                 (c >= '0' && c <= '9') ||
  93                 c == '-' ||
  94                 c == '_' ||
  95                 c == '.';
  96 }
  97
  98 /**
  99  * Check if s looks like a valid host name or FQDN. This does not do
 100  * full DNS validation, but only checks if the name is composed of
 101  * allowed characters and the length is not above the maximum allowed
 102  * by Linux (c.f. dns_name_is_valid()). Trailing dot is allowed if
 103  * allow_trailing_dot is true and at least two components are present
 104  * in the name. Note that due to the restricted charset and length
 105  * this call is substantially more conservative than
 106  * dns_name_is_valid().
 107  */
 108 bool hostname_is_valid(const char *s, bool allow_trailing_dot) {
 109         unsigned n_dots = 0;
 110         const char *p;
 111         bool dot;
 112
 113         if (isempty(s))
 114                 return false;
 115
 116         /* Doesn't accept empty hostnames, hostnames with
 117          * leading dots, and hostnames with multiple dots in a
 118          * sequence. Also ensures that the length stays below
 119          * HOST_NAME_MAX. */
 120
 121         for (p = s, dot = true; *p; p++) {
 122                 if (*p == '.') {
 123                         if (dot)
 124                                 return false;
 125
 126                         dot = true;
 127                         n_dots++;
 128                 } else {
 129                         if (!hostname_valid_char(*p))
 130                                 return false;
 131
 132                         dot = false;
 133                 }
 134         }
 135
 136         if (dot && (n_dots < 2 || !allow_trailing_dot))
 137                 return false;
 138
 139         if (p-s > HOST_NAME_MAX) /* Note that HOST_NAME_MAX is 64 on
 140                                   * Linux, but DNS allows domain names
 141                                   * up to 255 characters */
 142                 return false;
 143
 144         return true;
 145 }
 146
 147 char* hostname_cleanup(char *s) {
 148         char *p, *d;
 149         bool dot;
 150
 151         assert(s);
 152
 153         strshorten(s, HOST_NAME_MAX);
 154
 155         for (p = s, d = s, dot = true; *p; p++) {
 156                 if (*p == '.') {
 157                         if (dot)
 158                                 continue;
 159
 160                         *(d++) = '.';
 161                         dot = true;
 162                 } else if (hostname_valid_char(*p)) {
 163                         *(d++) = *p;
 164                         dot = false;
 165                 }
 166         }
 167
 168         if (dot && d > s)
 169                 d[-1] = 0;
 170         else
 171                 *d = 0;
 172
 173         return s;
 174 }
 175
 176 bool is_localhost(const char *hostname) {
 177         assert(hostname);
 178
 179         /* This tries to identify local host and domain names
 180          * described in RFC6761 plus the redhatism of localdomain */
 181
 182         return strcaseeq(hostname, "localhost") ||
 183                strcaseeq(hostname, "localhost.") ||
 184                strcaseeq(hostname, "localhost.localdomain") ||
 185                strcaseeq(hostname, "localhost.localdomain.") ||
 186                endswith_no_case(hostname, ".localhost") ||
 187                endswith_no_case(hostname, ".localhost.") ||
 188                endswith_no_case(hostname, ".localhost.localdomain") ||
 189                endswith_no_case(hostname, ".localhost.localdomain.");
 190 }
 191
 192 bool is_gateway_hostname(const char *hostname) {
 193         assert(hostname);
 194
 195         /* This tries to identify the valid syntaxes for the our
 196          * synthetic "gateway" host. */
 197
 198         return
 199                 strcaseeq(hostname, "gateway") ||
 200                 strcaseeq(hostname, "gateway.");
 201 }
 202
 203 int sethostname_idempotent(const char *s) {
 204         char buf[HOST_NAME_MAX + 1] = {};
 205
 206         assert(s);
 207
 208         if (gethostname(buf, sizeof(buf)) < 0)
 209                 return -errno;
 210
 211         if (streq(buf, s))
 212                 return 0;
 213
 214         if (sethostname(s, strlen(s)) < 0)
 215                 return -errno;
 216
 217         return 1;
 218 }
 219
 220 int read_hostname_config(const char *path, char **hostname) {
 221         _cleanup_fclose_ FILE *f = NULL;
 222         char l[LINE_MAX];
 223         char *name = NULL;
 224
 225         assert(path);
 226         assert(hostname);
 227
 228         f = fopen(path, "re");
 229         if (!f)
 230                 return -errno;
 231
 232         /* may have comments, ignore them */
 233         FOREACH_LINE(l, f, return -errno) {
 234                 truncate_nl(l);
 235                 if (l[0] != '\0' && l[0] != '#') {
 236                         /* found line with value */
 237                         name = hostname_cleanup(l);
 238                         name = strdup(name);
 239                         if (!name)
 240                                 return -ENOMEM;
 241                         break;
 242                 }
 243         }
 244
 245         if (!name)
 246                 /* no non-empty line found */
 247                 return -ENOENT;
 248
 249         *hostname = name;
 250         return 0;
 251 }