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 or it makes something up. The only
  52          * reason it might mail is OOM. It might even return "localhost" if that's set. */
  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 int gethostname_strict(char **ret) {
  63         struct utsname u;
  64         char *k;
  65
  66         /* This call will rather fail than make up a name. It will not return "localhost" either. */
  67
  68         assert_se(uname(&u) >= 0);
  69
  70         if (isempty(u.nodename))
  71                 return -ENXIO;
  72
  73         if (streq(u.nodename, "(none)"))
  74                 return -ENXIO;
  75
  76         if (is_localhost(u.nodename))
  77                 return -ENXIO;
  78
  79         k = strdup(u.nodename);
  80         if (!k)
  81                 return -ENOMEM;
  82
  83         *ret = k;
  84         return 0;
  85 }
  86
  87 static bool hostname_valid_char(char c) {
  88         return
  89                 (c >= 'a' && c <= 'z') ||
  90                 (c >= 'A' && c <= 'Z') ||
  91                 (c >= '0' && c <= '9') ||
  92                 c == '-' ||
  93                 c == '_' ||
  94                 c == '.';
  95 }
  96
  97 /**
  98  * Check if s looks like a valid host name or FQDN. This does not do
  99  * full DNS validation, but only checks if the name is composed of
 100  * allowed characters and the length is not above the maximum allowed
 101  * by Linux (c.f. dns_name_is_valid()). Trailing dot is allowed if
 102  * allow_trailing_dot is true and at least two components are present
 103  * in the name. Note that due to the restricted charset and length
 104  * this call is substantially more conservative than
 105  * dns_name_is_valid().
 106  */
 107 bool hostname_is_valid(const char *s, bool allow_trailing_dot) {
 108         unsigned n_dots = 0;
 109         const char *p;
 110         bool dot;
 111
 112         if (isempty(s))
 113                 return false;
 114
 115         /* Doesn't accept empty hostnames, hostnames with
 116          * leading dots, and hostnames with multiple dots in a
 117          * sequence. Also ensures that the length stays below
 118          * HOST_NAME_MAX. */
 119
 120         for (p = s, dot = true; *p; p++) {
 121                 if (*p == '.') {
 122                         if (dot)
 123                                 return false;
 124
 125                         dot = true;
 126                         n_dots++;
 127                 } else {
 128                         if (!hostname_valid_char(*p))
 129                                 return false;
 130
 131                         dot = false;
 132                 }
 133         }
 134
 135         if (dot && (n_dots < 2 || !allow_trailing_dot))
 136                 return false;
 137
 138         if (p-s > HOST_NAME_MAX) /* Note that HOST_NAME_MAX is 64 on
 139                                   * Linux, but DNS allows domain names
 140                                   * up to 255 characters */
 141                 return false;
 142
 143         return true;
 144 }
 145
 146 char* hostname_cleanup(char *s) {
 147         char *p, *d;
 148         bool dot;
 149
 150         assert(s);
 151
 152         for (p = s, d = s, dot = true; *p; p++) {
 153                 if (*p == '.') {
 154                         if (dot)
 155                                 continue;
 156
 157                         *(d++) = '.';
 158                         dot = true;
 159                 } else if (hostname_valid_char(*p)) {
 160                         *(d++) = *p;
 161                         dot = false;
 162                 }
 163
 164         }
 165
 166         if (dot && d > s)
 167                 d[-1] = 0;
 168         else
 169                 *d = 0;
 170
 171         strshorten(s, HOST_NAME_MAX);
 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, "localdomain.") ||
 185                strcaseeq(hostname, "localdomain") ||
 186                endswith_no_case(hostname, ".localhost") ||
 187                endswith_no_case(hostname, ".localhost.") ||
 188                endswith_no_case(hostname, ".localdomain") ||
 189                endswith_no_case(hostname, ".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 }