src/basic/hostname-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <limits.h>
   5 #include <stdio.h>
   6 #include <string.h>
   7 #include <sys/utsname.h>
   8 #include <unistd.h>
   9
  10 #include "alloc-util.h"
  11 #include "fd-util.h"
  12 #include "fileio.h"
  13 #include "hostname-util.h"
  14 #include "macro.h"
  15 #include "string-util.h"
  16
  17 bool hostname_is_set(void) {
  18         struct utsname u;
  19
  20         assert_se(uname(&u) >= 0);
  21
  22         if (isempty(u.nodename))
  23                 return false;
  24
  25         /* This is the built-in kernel default host name */
  26         if (streq(u.nodename, "(none)"))
  27                 return false;
  28
  29         return true;
  30 }
  31
  32 char* gethostname_malloc(void) {
  33         struct utsname u;
  34
  35         /* This call tries to return something useful, either the actual hostname
  36          * or it makes something up. The only reason it might fail is OOM.
  37          * It might even return "localhost" if that's set. */
  38
  39         assert_se(uname(&u) >= 0);
  40
  41         if (isempty(u.nodename) || streq(u.nodename, "(none)"))
  42                 return strdup(FALLBACK_HOSTNAME);
  43
  44         return strdup(u.nodename);
  45 }
  46
  47 int gethostname_strict(char **ret) {
  48         struct utsname u;
  49         char *k;
  50
  51         /* This call will rather fail than make up a name. It will not return "localhost" either. */
  52
  53         assert_se(uname(&u) >= 0);
  54
  55         if (isempty(u.nodename))
  56                 return -ENXIO;
  57
  58         if (streq(u.nodename, "(none)"))
  59                 return -ENXIO;
  60
  61         if (is_localhost(u.nodename))
  62                 return -ENXIO;
  63
  64         k = strdup(u.nodename);
  65         if (!k)
  66                 return -ENOMEM;
  67
  68         *ret = k;
  69         return 0;
  70 }
  71
  72 static bool hostname_valid_char(char c) {
  73         return
  74                 (c >= 'a' && c <= 'z') ||
  75                 (c >= 'A' && c <= 'Z') ||
  76                 (c >= '0' && c <= '9') ||
  77                 IN_SET(c, '-', '_', '.');
  78 }
  79
  80 /**
  81  * Check if s looks like a valid host name or FQDN. This does not do
  82  * full DNS validation, but only checks if the name is composed of
  83  * allowed characters and the length is not above the maximum allowed
  84  * by Linux (c.f. dns_name_is_valid()). Trailing dot is allowed if
  85  * allow_trailing_dot is true and at least two components are present
  86  * in the name. Note that due to the restricted charset and length
  87  * this call is substantially more conservative than
  88  * dns_name_is_valid().
  89  */
  90 bool hostname_is_valid(const char *s, bool allow_trailing_dot) {
  91         unsigned n_dots = 0;
  92         const char *p;
  93         bool dot;
  94
  95         if (isempty(s))
  96                 return false;
  97
  98         /* Doesn't accept empty hostnames, hostnames with
  99          * leading dots, and hostnames with multiple dots in a
 100          * sequence. Also ensures that the length stays below
 101          * HOST_NAME_MAX. */
 102
 103         for (p = s, dot = true; *p; p++) {
 104                 if (*p == '.') {
 105                         if (dot)
 106                                 return false;
 107
 108                         dot = true;
 109                         n_dots++;
 110                 } else {
 111                         if (!hostname_valid_char(*p))
 112                                 return false;
 113
 114                         dot = false;
 115                 }
 116         }
 117
 118         if (dot && (n_dots < 2 || !allow_trailing_dot))
 119                 return false;
 120
 121         if (p-s > HOST_NAME_MAX) /* Note that HOST_NAME_MAX is 64 on
 122                                   * Linux, but DNS allows domain names
 123                                   * up to 255 characters */
 124                 return false;
 125
 126         return true;
 127 }
 128
 129 char* hostname_cleanup(char *s) {
 130         char *p, *d;
 131         bool dot;
 132
 133         assert(s);
 134
 135         strshorten(s, HOST_NAME_MAX);
 136
 137         for (p = s, d = s, dot = true; *p; p++) {
 138                 if (*p == '.') {
 139                         if (dot)
 140                                 continue;
 141
 142                         *(d++) = '.';
 143                         dot = true;
 144                 } else if (hostname_valid_char(*p)) {
 145                         *(d++) = *p;
 146                         dot = false;
 147                 }
 148         }
 149
 150         if (dot && d > s)
 151                 d[-1] = 0;
 152         else
 153                 *d = 0;
 154
 155         return s;
 156 }
 157
 158 bool is_localhost(const char *hostname) {
 159         assert(hostname);
 160
 161         /* This tries to identify local host and domain names
 162          * described in RFC6761 plus the redhatism of localdomain */
 163
 164         return strcaseeq(hostname, "localhost") ||
 165                strcaseeq(hostname, "localhost.") ||
 166                strcaseeq(hostname, "localhost.localdomain") ||
 167                strcaseeq(hostname, "localhost.localdomain.") ||
 168                endswith_no_case(hostname, ".localhost") ||
 169                endswith_no_case(hostname, ".localhost.") ||
 170                endswith_no_case(hostname, ".localhost.localdomain") ||
 171                endswith_no_case(hostname, ".localhost.localdomain.");
 172 }
 173
 174 bool is_gateway_hostname(const char *hostname) {
 175         assert(hostname);
 176
 177         /* This tries to identify the valid syntaxes for the our
 178          * synthetic "gateway" host. */
 179
 180         return
 181                 strcaseeq(hostname, "_gateway") || strcaseeq(hostname, "_gateway.")
 182 #if ENABLE_COMPAT_GATEWAY_HOSTNAME
 183                 || strcaseeq(hostname, "gateway") || strcaseeq(hostname, "gateway.")
 184 #endif
 185                 ;
 186 }
 187
 188 int sethostname_idempotent(const char *s) {
 189         char buf[HOST_NAME_MAX + 1] = {};
 190
 191         assert(s);
 192
 193         if (gethostname(buf, sizeof(buf)) < 0)
 194                 return -errno;
 195
 196         if (streq(buf, s))
 197                 return 0;
 198
 199         if (sethostname(s, strlen(s)) < 0)
 200                 return -errno;
 201
 202         return 1;
 203 }
 204
 205 int shorten_overlong(const char *s, char **ret) {
 206         char *h, *p;
 207
 208         /* Shorten an overlong name to HOST_NAME_MAX or to the first dot,
 209          * whatever comes earlier. */
 210
 211         assert(s);
 212
 213         h = strdup(s);
 214         if (!h)
 215                 return -ENOMEM;
 216
 217         if (hostname_is_valid(h, false)) {
 218                 *ret = h;
 219                 return 0;
 220         }
 221
 222         p = strchr(h, '.');
 223         if (p)
 224                 *p = 0;
 225
 226         strshorten(h, HOST_NAME_MAX);
 227
 228         if (!hostname_is_valid(h, false)) {
 229                 free(h);
 230                 return -EDOM;
 231         }
 232
 233         *ret = h;
 234         return 1;
 235 }
 236
 237 int read_etc_hostname_stream(FILE *f, char **ret) {
 238         int r;
 239
 240         assert(f);
 241         assert(ret);
 242
 243         for (;;) {
 244                 _cleanup_free_ char *line = NULL;
 245                 char *p;
 246
 247                 r = read_line(f, LONG_LINE_MAX, &line);
 248                 if (r < 0)
 249                         return r;
 250                 if (r == 0) /* EOF without any hostname? the file is empty, let's treat that exactly like no file at all: ENOENT */
 251                         return -ENOENT;
 252
 253                 p = strstrip(line);
 254
 255                 /* File may have empty lines or comments, ignore them */
 256                 if (!IN_SET(*p, '\0', '#')) {
 257                         char *copy;
 258
 259                         hostname_cleanup(p); /* normalize the hostname */
 260
 261                         if (!hostname_is_valid(p, true)) /* check that the hostname we return is valid */
 262                                 return -EBADMSG;
 263
 264                         copy = strdup(p);
 265                         if (!copy)
 266                                 return -ENOMEM;
 267
 268                         *ret = copy;
 269                         return 0;
 270                 }
 271         }
 272 }
 273
 274 int read_etc_hostname(const char *path, char **ret) {
 275         _cleanup_fclose_ FILE *f = NULL;
 276
 277         assert(ret);
 278
 279         if (!path)
 280                 path = "/etc/hostname";
 281
 282         f = fopen(path, "re");
 283         if (!f)
 284                 return -errno;
 285
 286         return read_etc_hostname_stream(f, ret);
 287
 288 }