resolv/nss_dns/dns-canon.c

   1 /* Copyright (C) 2004 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@redhat.com>, 2004.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <errno.h>
  21 #include <netdb.h>
  22 #include <resolv.h>
  23 #include <stdlib.h>
  24 #include <arpa/nameser.h>
  25 #include <nsswitch.h>
  26
  27
  28 #if PACKETSZ > 65536
  29 # define MAXPACKET      PACKETSZ
  30 #else
  31 # define MAXPACKET      65536
  32 #endif
  33
  34
  35 /* We need this time later.  */
  36 typedef union querybuf
  37 {
  38   HEADER hdr;
  39   unsigned char buf[MAXPACKET];
  40 } querybuf;
  41
  42
  43 enum nss_status
  44 _nss_dns_getcanonname_r (const char *name, char *buffer, size_t buflen,
  45                          char **result,int *errnop, int *h_errnop)
  46 {
  47   /* Just an alibi buffer, res_nquery will allocate a real buffer for
  48      us.  */
  49   unsigned char buf[20];
  50   union
  51   {
  52     querybuf *buf;
  53     unsigned char *ptr;
  54   } ansp = { .ptr = buf };
  55   enum nss_status status = NSS_STATUS_UNAVAIL;
  56   int qtypes[] = { ns_t_a, ns_t_aaaa };
  57 #define nqtypes (sizeof (qtypes) / sizeof (qtypes[0]))
  58
  59   for (int i = 0; i < nqtypes; ++i)
  60     {
  61       int r = __libc_res_nquery (&_res, name, ns_c_in, qtypes[i],
  62                                  buf, sizeof (buf), &ansp.ptr);
  63       if (r > 0)
  64         {
  65           /* We need to decode the response.  Just one question record.
  66              And if we got no answers we bail out, too.  */
  67           if (ansp.buf->hdr.qdcount != htons (1))
  68             continue;
  69
  70           /* Number of answers.   */
  71           unsigned int ancount = ntohs (ansp.buf->hdr.ancount);
  72
  73           /* Beginning and end of the buffer with query, answer, and the
  74              rest.  */
  75           unsigned char *ptr = &ansp.buf->buf[sizeof (HEADER)];
  76           unsigned char *endptr = ansp.ptr + r;
  77
  78           /* Skip over the query.  This is the name, type, and class.  */
  79           int s = __dn_skipname (ptr, endptr);
  80           if (s < 0)
  81             {
  82             unavail:
  83               status = NSS_STATUS_UNAVAIL;
  84               break;
  85             }
  86
  87           /* Skip over the name and the two 16-bit values containing type
  88              and class.  */
  89           ptr += s + 2 * sizeof (uint16_t);
  90
  91           while (ancount-- > 0)
  92             {
  93               /* Now the reply.  First again the name from the query,
  94                  then type, class, TTL, and the length of the RDATA.
  95                  We remember the name start.  */
  96               unsigned char *namestart = ptr;
  97               s = __dn_skipname (ptr, endptr);
  98               if (s < 0)
  99                 goto unavail;
 100
 101               ptr += s;
 102
 103               /* Check whether type and class match.  */
 104               unsigned int type = ntohs (*(uint16_t *) ptr);
 105               if (type == qtypes[i])
 106                 {
 107                   /* We found the record.  */
 108                   s = __dn_expand (ansp.buf->buf, endptr, namestart,
 109                                    buffer, buflen);
 110                   if (s < 0)
 111                     {
 112                       if (errno != EMSGSIZE)
 113                         goto unavail;
 114
 115                       /* The buffer is too small.  */
 116                       *errnop = ERANGE;
 117                       status = NSS_STATUS_TRYAGAIN;
 118                       h_errno = NETDB_INTERNAL;
 119                     }
 120                   else
 121                     {
 122                       /* Success.  */
 123                       *result = buffer;
 124                       status = NSS_STATUS_SUCCESS;
 125                     }
 126
 127                   goto out;
 128                 }
 129
 130               if (type != ns_t_cname)
 131                 goto unavail;
 132
 133               ptr += sizeof (uint16_t);
 134               if (*(uint16_t *) ptr != htons (ns_c_in))
 135                 goto unavail;
 136
 137               /* Also skip over the TTL.  */
 138               ptr += sizeof (uint16_t) + sizeof (uint32_t);
 139
 140               /* Skip over the data length and data.  */
 141               ptr += sizeof (uint16_t) + ntohs (*(uint16_t *) ptr);
 142             }
 143         }
 144     }
 145
 146  out:
 147   *h_errnop = h_errno;
 148
 149   if (ansp.ptr != buf)
 150     free (ansp.ptr);
 151
 152   return status;
 153 }