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                 IN_SET(c, '-', '_', '.');
  94 }
  95
  96 /**
  97  * Check if s looks like a valid host name or FQDN. This does not do
  98  * full DNS validation, but only checks if the name is composed of
  99  * allowed characters and the length is not above the maximum allowed
 100  * by Linux (c.f. dns_name_is_valid()). Trailing dot is allowed if
 101  * allow_trailing_dot is true and at least two components are present
 102  * in the name. Note that due to the restricted charset and length
 103  * this call is substantially more conservative than
 104  * dns_name_is_valid().
 105  */
 106 bool hostname_is_valid(const char *s, bool allow_trailing_dot) {
 107         unsigned n_dots = 0;
 108         const char *p;
 109         bool dot;
 110
 111         if (isempty(s))
 112                 return false;
 113
 114         /* Doesn't accept empty hostnames, hostnames with
 115          * leading dots, and hostnames with multiple dots in a
 116          * sequence. Also ensures that the length stays below
 117          * HOST_NAME_MAX. */
 118
 119         for (p = s, dot = true; *p; p++) {
 120                 if (*p == '.') {
 121                         if (dot)
 122                                 return false;
 123
 124                         dot = true;
 125                         n_dots++;
 126                 } else {
 127                         if (!hostname_valid_char(*p))
 128                                 return false;
 129
 130                         dot = false;
 131                 }
 132         }
 133
 134         if (dot && (n_dots < 2 || !allow_trailing_dot))
 135                 return false;
 136
 137         if (p-s > HOST_NAME_MAX) /* Note that HOST_NAME_MAX is 64 on
 138                                   * Linux, but DNS allows domain names
 139                                   * up to 255 characters */
 140                 return false;
 141
 142         return true;
 143 }
 144
 145 char* hostname_cleanup(char *s) {
 146         char *p, *d;
 147         bool dot;
 148
 149         assert(s);
 150
 151         strshorten(s, HOST_NAME_MAX);
 152
 153         for (p = s, d = s, dot = true; *p; p++) {
 154                 if (*p == '.') {
 155                         if (dot)
 156                                 continue;
 157
 158                         *(d++) = '.';
 159                         dot = true;
 160                 } else if (hostname_valid_char(*p)) {
 161                         *(d++) = *p;
 162                         dot = false;
 163                 }
 164         }
 165
 166         if (dot && d > s)
 167                 d[-1] = 0;
 168         else
 169                 *d = 0;
 170
 171         return s;
 172 }
 173
 174 bool is_localhost(const char *hostname) {
 175         assert(hostname);
 176
 177         /* This tries to identify local host and domain names
 178          * described in RFC6761 plus the redhatism of localdomain */
 179
 180         return strcaseeq(hostname, "localhost") ||
 181                strcaseeq(hostname, "localhost.") ||
 182                strcaseeq(hostname, "localhost.localdomain") ||
 183                strcaseeq(hostname, "localhost.localdomain.") ||
 184                endswith_no_case(hostname, ".localhost") ||
 185                endswith_no_case(hostname, ".localhost.") ||
 186                endswith_no_case(hostname, ".localhost.localdomain") ||
 187                endswith_no_case(hostname, ".localhost.localdomain.");
 188 }
 189
 190 bool is_gateway_hostname(const char *hostname) {
 191         assert(hostname);
 192
 193         /* This tries to identify the valid syntaxes for the our
 194          * synthetic "gateway" host. */
 195
 196         return
 197                 strcaseeq(hostname, "_gateway") || strcaseeq(hostname, "_gateway.")
 198 #if ENABLE_COMPAT_GATEWAY_HOSTNAME
 199                 || strcaseeq(hostname, "gateway") || strcaseeq(hostname, "gateway.")
 200 #endif
 201                 ;
 202 }
 203
 204 int sethostname_idempotent(const char *s) {
 205         char buf[HOST_NAME_MAX + 1] = {};
 206
 207         assert(s);
 208
 209         if (gethostname(buf, sizeof(buf)) < 0)
 210                 return -errno;
 211
 212         if (streq(buf, s))
 213                 return 0;
 214
 215         if (sethostname(s, strlen(s)) < 0)
 216                 return -errno;
 217
 218         return 1;
 219 }
 220
 221 int read_hostname_config(const char *path, char **hostname) {
 222         _cleanup_fclose_ FILE *f = NULL;
 223         char l[LINE_MAX];
 224         char *name = NULL;
 225
 226         assert(path);
 227         assert(hostname);
 228
 229         f = fopen(path, "re");
 230         if (!f)
 231                 return -errno;
 232
 233         /* may have comments, ignore them */
 234         FOREACH_LINE(l, f, return -errno) {
 235                 truncate_nl(l);
 236                 if (!IN_SET(l[0], '\0', '#')) {
 237                         /* found line with value */
 238                         name = hostname_cleanup(l);
 239                         name = strdup(name);
 240                         if (!name)
 241                                 return -ENOMEM;
 242                         break;
 243                 }
 244         }
 245
 246         if (!name)
 247                 /* no non-empty line found */
 248                 return -ENOENT;
 249
 250         *hostname = name;
 251         return 0;
 252 }