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/* Copyright (C) 2004-2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2004.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <netdb.h>
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#include <resolv.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <arpa/nameser.h>
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#include <nsswitch.h>
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#include <resolv/resolv_context.h>
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#include <resolv/resolv-internal.h>
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#if PACKETSZ > 65536
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# define MAXPACKET PACKETSZ
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#else
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# define MAXPACKET 65536
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#endif
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/* We need this time later. */
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typedef union querybuf
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{
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HEADER hdr;
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unsigned char buf[MAXPACKET];
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} querybuf;
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static const short int qtypes[] = { ns_t_a, ns_t_aaaa };
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#define nqtypes (sizeof (qtypes) / sizeof (qtypes[0]))
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enum nss_status
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_nss_dns_getcanonname_r (const char *name, char *buffer, size_t buflen,
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char **result,int *errnop, int *h_errnop)
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{
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/* Just an alibi buffer, res_nquery will allocate a real buffer for
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us. */
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unsigned char buf[20];
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union
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{
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querybuf *buf;
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unsigned char *ptr;
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} ansp = { .ptr = buf };
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enum nss_status status = NSS_STATUS_UNAVAIL;
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struct resolv_context *ctx = __resolv_context_get ();
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if (ctx == NULL)
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{
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*errnop = errno;
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*h_errnop = NETDB_INTERNAL;
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return NSS_STATUS_UNAVAIL;
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}
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for (int i = 0; i < nqtypes; ++i)
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{
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int r = __res_context_query (ctx, name, ns_c_in, qtypes[i],
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buf, sizeof (buf), &ansp.ptr, NULL, NULL,
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NULL, NULL);
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if (r > 0)
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{
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/* We need to decode the response. Just one question record.
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And if we got no answers we bail out, too. */
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if (ansp.buf->hdr.qdcount != htons (1))
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continue;
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/* Number of answers. */
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unsigned int ancount = ntohs (ansp.buf->hdr.ancount);
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/* Beginning and end of the buffer with query, answer, and the
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rest. */
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unsigned char *ptr = &ansp.buf->buf[sizeof (HEADER)];
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unsigned char *endptr = ansp.ptr + r;
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/* Skip over the query. This is the name, type, and class. */
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int s = __dn_skipname (ptr, endptr);
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if (s < 0)
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{
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unavail:
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status = NSS_STATUS_UNAVAIL;
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break;
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}
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/* Skip over the name and the two 16-bit values containing type
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and class. */
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ptr += s + 2 * sizeof (uint16_t);
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while (ancount-- > 0)
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{
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/* Now the reply. First again the name from the query,
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then type, class, TTL, and the length of the RDATA.
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We remember the name start. */
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unsigned char *namestart = ptr;
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s = __dn_skipname (ptr, endptr);
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if (s < 0)
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goto unavail;
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ptr += s;
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/* Check that there are enough bytes for the RR
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metadata. */
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if (endptr - ptr < 10)
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goto unavail;
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/* Check whether type and class match. */
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uint_fast16_t type;
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NS_GET16 (type, ptr);
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if (type == qtypes[i])
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{
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/* We found the record. */
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s = __dn_expand (ansp.buf->buf, endptr, namestart,
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buffer, buflen);
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if (s < 0)
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{
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if (errno != EMSGSIZE)
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goto unavail;
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/* The buffer is too small. */
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*errnop = ERANGE;
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status = NSS_STATUS_TRYAGAIN;
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h_errno = NETDB_INTERNAL;
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}
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else
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{
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/* Success. */
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*result = buffer;
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status = NSS_STATUS_SUCCESS;
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}
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goto out;
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}
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if (type != ns_t_cname)
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goto unavail;
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if (__ns_get16 (ptr) != ns_c_in)
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goto unavail;
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/* Also skip over class and TTL. */
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ptr += sizeof (uint16_t) + sizeof (uint32_t);
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/* Skip over RDATA length and RDATA itself. */
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uint16_t rdatalen = __ns_get16 (ptr);
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ptr += sizeof (uint16_t);
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/* Not enough room for RDATA. */
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if (endptr - ptr < rdatalen)
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goto unavail;
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ptr += rdatalen;
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}
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}
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/* Restore original buffer before retry. */
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if (ansp.ptr != buf)
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{
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free (ansp.ptr);
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ansp.ptr = buf;
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}
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}
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out:
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*h_errnop = h_errno;
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if (ansp.ptr != buf)
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free (ansp.ptr);
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__resolv_context_put (ctx);
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return status;
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}
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