src/basic/hostname-util.c

   1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
   2
   3 /***
   4   This file is part of systemd.
   5
   6   Copyright 2015 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 <bits/local_lim.h>
  23 #include <errno.h>
  24 #include <limits.h>
  25 #include <stdio.h>
  26 #include <string.h>
  27 #include <sys/utsname.h>
  28 #include <unistd.h>
  29
  30 #include "fd-util.h"
  31 #include "fileio.h"
  32 #include "hostname-util.h"
  33 #include "macro.h"
  34 #include "string-util.h"
  35
  36 bool hostname_is_set(void) {
  37         struct utsname u;
  38
  39         assert_se(uname(&u) >= 0);
  40
  41         if (isempty(u.nodename))
  42                 return false;
  43
  44         /* This is the built-in kernel default host name */
  45         if (streq(u.nodename, "(none)"))
  46                 return false;
  47
  48         return true;
  49 }
  50
  51 char* gethostname_malloc(void) {
  52         struct utsname u;
  53
  54         assert_se(uname(&u) >= 0);
  55
  56         if (isempty(u.nodename) || streq(u.nodename, "(none)"))
  57                 return strdup(u.sysname);
  58
  59         return strdup(u.nodename);
  60 }
  61
  62 static bool hostname_valid_char(char c) {
  63         return
  64                 (c >= 'a' && c <= 'z') ||
  65                 (c >= 'A' && c <= 'Z') ||
  66                 (c >= '0' && c <= '9') ||
  67                 c == '-' ||
  68                 c == '_' ||
  69                 c == '.';
  70 }
  71
  72 /**
  73  * Check if s looks like a valid host name or FQDN. This does not do
  74  * full DNS validation, but only checks if the name is composed of
  75  * allowed characters and the length is not above the maximum allowed
  76  * by Linux (c.f. dns_name_is_valid()). Trailing dot is allowed if
  77  * allow_trailing_dot is true and at least two components are present
  78  * in the name. Note that due to the restricted charset and length
  79  * this call is substantially more conservative than
  80  * dns_name_is_valid().
  81  */
  82 bool hostname_is_valid(const char *s, bool allow_trailing_dot) {
  83         unsigned n_dots = 0;
  84         const char *p;
  85         bool dot;
  86
  87         if (isempty(s))
  88                 return false;
  89
  90         /* Doesn't accept empty hostnames, hostnames with
  91          * leading dots, and hostnames with multiple dots in a
  92          * sequence. Also ensures that the length stays below
  93          * HOST_NAME_MAX. */
  94
  95         for (p = s, dot = true; *p; p++) {
  96                 if (*p == '.') {
  97                         if (dot)
  98                                 return false;
  99
 100                         dot = true;
 101                         n_dots ++;
 102                 } else {
 103                         if (!hostname_valid_char(*p))
 104                                 return false;
 105
 106                         dot = false;
 107                 }
 108         }
 109
 110         if (dot && (n_dots < 2 || !allow_trailing_dot))
 111                 return false;
 112
 113         if (p-s > HOST_NAME_MAX) /* Note that HOST_NAME_MAX is 64 on
 114                                   * Linux, but DNS allows domain names
 115                                   * up to 255 characters */
 116                 return false;
 117
 118         return true;
 119 }
 120
 121 char* hostname_cleanup(char *s) {
 122         char *p, *d;
 123         bool dot;
 124
 125         assert(s);
 126
 127         for (p = s, d = s, dot = true; *p; p++) {
 128                 if (*p == '.') {
 129                         if (dot)
 130                                 continue;
 131
 132                         *(d++) = '.';
 133                         dot = true;
 134                 } else if (hostname_valid_char(*p)) {
 135                         *(d++) = *p;
 136                         dot = false;
 137                 }
 138
 139         }
 140
 141         if (dot && d > s)
 142                 d[-1] = 0;
 143         else
 144                 *d = 0;
 145
 146         strshorten(s, HOST_NAME_MAX);
 147
 148         return s;
 149 }
 150
 151 bool is_localhost(const char *hostname) {
 152         assert(hostname);
 153
 154         /* This tries to identify local host and domain names
 155          * described in RFC6761 plus the redhatism of .localdomain */
 156
 157         return strcaseeq(hostname, "localhost") ||
 158                strcaseeq(hostname, "localhost.") ||
 159                strcaseeq(hostname, "localdomain.") ||
 160                strcaseeq(hostname, "localdomain") ||
 161                endswith_no_case(hostname, ".localhost") ||
 162                endswith_no_case(hostname, ".localhost.") ||
 163                endswith_no_case(hostname, ".localdomain") ||
 164                endswith_no_case(hostname, ".localdomain.");
 165 }
 166
 167 bool is_gateway_hostname(const char *hostname) {
 168         assert(hostname);
 169
 170         /* This tries to identify the valid syntaxes for the our
 171          * synthetic "gateway" host. */
 172
 173         return
 174                 strcaseeq(hostname, "gateway") ||
 175                 strcaseeq(hostname, "gateway.");
 176 }
 177
 178 int sethostname_idempotent(const char *s) {
 179         char buf[HOST_NAME_MAX + 1] = {};
 180
 181         assert(s);
 182
 183         if (gethostname(buf, sizeof(buf)) < 0)
 184                 return -errno;
 185
 186         if (streq(buf, s))
 187                 return 0;
 188
 189         if (sethostname(s, strlen(s)) < 0)
 190                 return -errno;
 191
 192         return 1;
 193 }
 194
 195 int read_hostname_config(const char *path, char **hostname) {
 196         _cleanup_fclose_ FILE *f = NULL;
 197         char l[LINE_MAX];
 198         char *name = NULL;
 199
 200         assert(path);
 201         assert(hostname);
 202
 203         f = fopen(path, "re");
 204         if (!f)
 205                 return -errno;
 206
 207         /* may have comments, ignore them */
 208         FOREACH_LINE(l, f, return -errno) {
 209                 truncate_nl(l);
 210                 if (l[0] != '\0' && l[0] != '#') {
 211                         /* found line with value */
 212                         name = hostname_cleanup(l);
 213                         name = strdup(name);
 214                         if (!name)
 215                                 return -ENOMEM;
 216                         break;
 217                 }
 218         }
 219
 220         if (!name)
 221                 /* no non-empty line found */
 222                 return -ENOENT;
 223
 224         *hostname = name;
 225         return 0;
 226 }