resolv/nss_dns/dns-canon.c

   1 /* Copyright (C) 2004-2015 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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <netdb.h>
  21 #include <resolv.h>
  22 #include <stdlib.h>
  23 #include <stdint.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 static const short int qtypes[] = { ns_t_a, ns_t_aaaa };
  44 #define nqtypes (sizeof (qtypes) / sizeof (qtypes[0]))
  45
  46
  47 enum nss_status
  48 _nss_dns_getcanonname_r (const char *name, char *buffer, size_t buflen,
  49                          char **result,int *errnop, int *h_errnop)
  50 {
  51   /* Just an alibi buffer, res_nquery will allocate a real buffer for
  52      us.  */
  53   unsigned char buf[20];
  54   union
  55   {
  56     querybuf *buf;
  57     unsigned char *ptr;
  58   } ansp = { .ptr = buf };
  59   enum nss_status status = NSS_STATUS_UNAVAIL;
  60
  61   for (int i = 0; i < nqtypes; ++i)
  62     {
  63       int r = __libc_res_nquery (&_res, name, ns_c_in, qtypes[i],
  64                                  buf, sizeof (buf), &ansp.ptr, NULL, NULL,
  65                                  NULL, NULL);
  66       if (r > 0)
  67         {
  68           /* We need to decode the response.  Just one question record.
  69              And if we got no answers we bail out, too.  */
  70           if (ansp.buf->hdr.qdcount != htons (1))
  71             continue;
  72
  73           /* Number of answers.   */
  74           unsigned int ancount = ntohs (ansp.buf->hdr.ancount);
  75
  76           /* Beginning and end of the buffer with query, answer, and the
  77              rest.  */
  78           unsigned char *ptr = &ansp.buf->buf[sizeof (HEADER)];
  79           unsigned char *endptr = ansp.ptr + r;
  80
  81           /* Skip over the query.  This is the name, type, and class.  */
  82           int s = __dn_skipname (ptr, endptr);
  83           if (s < 0)
  84             {
  85             unavail:
  86               status = NSS_STATUS_UNAVAIL;
  87               break;
  88             }
  89
  90           /* Skip over the name and the two 16-bit values containing type
  91              and class.  */
  92           ptr += s + 2 * sizeof (uint16_t);
  93
  94           while (ancount-- > 0)
  95             {
  96               /* Now the reply.  First again the name from the query,
  97                  then type, class, TTL, and the length of the RDATA.
  98                  We remember the name start.  */
  99               unsigned char *namestart = ptr;
 100               s = __dn_skipname (ptr, endptr);
 101               if (s < 0)
 102                 goto unavail;
 103
 104               ptr += s;
 105
 106               /* Check whether type and class match.  */
 107               uint_fast16_t type;
 108               NS_GET16 (type, ptr);
 109               if (type == qtypes[i])
 110                 {
 111                   /* We found the record.  */
 112                   s = __dn_expand (ansp.buf->buf, endptr, namestart,
 113                                    buffer, buflen);
 114                   if (s < 0)
 115                     {
 116                       if (errno != EMSGSIZE)
 117                         goto unavail;
 118
 119                       /* The buffer is too small.  */
 120                       *errnop = ERANGE;
 121                       status = NSS_STATUS_TRYAGAIN;
 122                       h_errno = NETDB_INTERNAL;
 123                     }
 124                   else
 125                     {
 126                       /* Success.  */
 127                       *result = buffer;
 128                       status = NSS_STATUS_SUCCESS;
 129                     }
 130
 131                   goto out;
 132                 }
 133
 134               if (type != ns_t_cname)
 135                 goto unavail;
 136
 137               if (__ns_get16 (ptr) != ns_c_in)
 138                 goto unavail;
 139
 140               /* Also skip over the TTL.  */
 141               ptr += sizeof (uint16_t) + sizeof (uint32_t);
 142
 143               /* Skip over the data length and data.  */
 144               ptr += sizeof (uint16_t) + __ns_get16 (ptr);
 145             }
 146         }
 147     }
 148
 149  out:
 150   *h_errnop = h_errno;
 151
 152   if (ansp.ptr != buf)
 153     free (ansp.ptr);
 154
 155   return status;
 156 }