sysdeps/unix/sysv/linux/gethostid.c

   1 /* Copyright (C) 1995-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <fcntl.h>
  20 #include <unistd.h>
  21 #include <netdb.h>
  22 #include <not-cancel.h>
  23 #include <stdbool.h>
  24
  25 #define HOSTIDFILE "/etc/hostid"
  26
  27 #ifdef SET_PROCEDURE
  28 int
  29 sethostid (long int id)
  30 {
  31   int fd;
  32   ssize_t written;
  33   int32_t id32 = id;
  34
  35   /* Test for appropriate rights to set host ID.  */
  36   if (__libc_enable_secure)
  37     {
  38       __set_errno (EPERM);
  39       return -1;
  40     }
  41
  42   /* Make sure the ID is not too large.  Needed for bi-arch support.   */
  43   if (id32 != id)
  44     {
  45       __set_errno (EOVERFLOW);
  46       return -1;
  47     }
  48
  49   /* Open file for writing.  Everybody is allowed to read this file.  */
  50   fd = __open_nocancel (HOSTIDFILE, O_CREAT|O_WRONLY|O_TRUNC, 0644);
  51   if (fd < 0)
  52     return -1;
  53
  54   written = __write_nocancel (fd, &id32, sizeof (id32));
  55
  56   __close_nocancel_nostatus (fd);
  57
  58   return written != sizeof (id32) ? -1 : 0;
  59 }
  60
  61 #else
  62 # include <string.h>
  63 # include <sys/param.h>
  64 # include <resolv/netdb.h>
  65 # include <netinet/in.h>
  66 # include <scratch_buffer.h>
  67
  68 long int
  69 gethostid (void)
  70 {
  71   char hostname[MAXHOSTNAMELEN + 1];
  72   struct hostent hostbuf, *hp;
  73   int32_t id;
  74   struct in_addr in;
  75   int herr;
  76   int fd;
  77
  78   /* First try to get the ID from a former invocation of sethostid.  */
  79   fd = __open_nocancel (HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);
  80   if (fd >= 0)
  81     {
  82       ssize_t n = __read_nocancel (fd, &id, sizeof (id));
  83
  84       __close_nocancel_nostatus (fd);
  85
  86       if (n == sizeof (id))
  87         return id;
  88     }
  89
  90   /* Getting from the file was not successful.  An intelligent guess
  91      for a unique number of a host is its IP address.  To get the IP
  92      address we need to know the host name.  */
  93   if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')
  94     /* This also fails.  Return and arbitrary value.  */
  95     return 0;
  96
  97   /* Determine the IP address of the host name.  */
  98   struct scratch_buffer tmpbuf;
  99   scratch_buffer_init (&tmpbuf);
 100   while (true)
 101     {
 102       int ret = __gethostbyname_r (hostname, &hostbuf,
 103                                    tmpbuf.data, tmpbuf.length, &hp, &herr);
 104       if (ret == 0 && hp != NULL)
 105         break;
 106       else
 107         {
 108           /* Enlarge the buffer on ERANGE.  */
 109           if (ret != 0 && herr == NETDB_INTERNAL && errno == ERANGE)
 110             {
 111               if (!scratch_buffer_grow (&tmpbuf))
 112                 return 0;
 113             }
 114           /* Other errors are a failure.  Return an arbitrary value.  */
 115           else
 116             {
 117               scratch_buffer_free (&tmpbuf);
 118               return 0;
 119             }
 120         }
 121     }
 122
 123   in.s_addr = 0;
 124   memcpy (&in, hp->h_addr,
 125           (int) sizeof (in) < hp->h_length ? (int) sizeof (in) : hp->h_length);
 126   scratch_buffer_free (&tmpbuf);
 127   /* For the return value to be not exactly the IP address we do some
 128      bit fiddling.  */
 129   return (int32_t) (in.s_addr << 16 | in.s_addr >> 16);
 130 }
 131 #endif