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