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c-ares
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c-ares/ares_parse_a_reply.c

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/* Copyright 1998 by the Massachusetts Institute of Technology.
*
* Permission to use, copy, modify, and distribute this
* software and its documentation for any purpose and without
* fee is hereby granted, provided that the above copyright
* notice appear in all copies and that both that copyright
* notice and this permission notice appear in supporting
* documentation, and that the name of M.I.T. not be used in
* advertising or publicity pertaining to distribution of the
* software without specific, written prior permission.
* M.I.T. makes no representations about the suitability of
* this software for any purpose. It is provided "as is"
* without express or implied warranty.
*/
#include "ares_setup.h"
#ifdef HAVE_NETINET_IN_H
# include <netinet/in.h>
#endif
#ifdef HAVE_NETDB_H
# include <netdb.h>
#endif
#ifdef HAVE_ARPA_INET_H
# include <arpa/inet.h>
#endif
#ifdef HAVE_ARPA_NAMESER_H
# include <arpa/nameser.h>
#else
# include "nameser.h"
#endif
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
# include <arpa/nameser_compat.h>
#endif
#ifdef HAVE_STRINGS_H
# include <strings.h>
#endif
#ifdef HAVE_LIMITS_H
# include <limits.h>
#endif
#include "ares.h"
#include "ares_dns.h"
#include "ares_private.h"
int ares_parse_a_reply(const unsigned char *abuf, int alen,
struct hostent **host,
struct ares_addrttl *addrttls, int *naddrttls)
{
unsigned int qdcount, ancount;
int status, i, rr_type, rr_class, rr_len, rr_ttl, naddrs;
int cname_ttl = INT_MAX; /* the TTL imposed by the CNAME chain */
int naliases;
long len;
const unsigned char *aptr;
char *hostname, *rr_name, *rr_data, **aliases;
struct in_addr *addrs;
struct hostent *hostent;
const int max_addr_ttls = (addrttls && naddrttls) ? *naddrttls : 0;
/* Set *host to NULL for all failure cases. */
if (host)
*host = NULL;
/* Same with *naddrttls. */
if (naddrttls)
*naddrttls = 0;
/* Give up if abuf doesn't have room for a header. */
if (alen < HFIXEDSZ)
return ARES_EBADRESP;
/* Fetch the question and answer count from the header. */
qdcount = DNS_HEADER_QDCOUNT(abuf);
ancount = DNS_HEADER_ANCOUNT(abuf);
if (qdcount != 1)
return ARES_EBADRESP;
/* Expand the name from the question, and skip past the question. */
aptr = abuf + HFIXEDSZ;
status = ares__expand_name_for_response(aptr, abuf, alen, &hostname, &len);
if (status != ARES_SUCCESS)
return status;
if (aptr + len + QFIXEDSZ > abuf + alen)
{
ares_free(hostname);
return ARES_EBADRESP;
}
aptr += len + QFIXEDSZ;
if (host)
{
/* Allocate addresses and aliases; ancount gives an upper bound for
both. */
addrs = ares_malloc(ancount * sizeof(struct in_addr));
if (!addrs)
{
ares_free(hostname);
return ARES_ENOMEM;
}
aliases = ares_malloc((ancount + 1) * sizeof(char *));
if (!aliases)
{
ares_free(hostname);
ares_free(addrs);
return ARES_ENOMEM;
}
}
else
{
addrs = NULL;
aliases = NULL;
}
naddrs = 0;
naliases = 0;
/* Examine each answer resource record (RR) in turn. */
for (i = 0; i < (int)ancount; i++)
{
/* Decode the RR up to the data field. */
status = ares__expand_name_for_response(aptr, abuf, alen, &rr_name, &len);
if (status != ARES_SUCCESS)
break;
aptr += len;
if (aptr + RRFIXEDSZ > abuf + alen)
{
ares_free(rr_name);
status = ARES_EBADRESP;
break;
}
rr_type = DNS_RR_TYPE(aptr);
rr_class = DNS_RR_CLASS(aptr);
rr_len = DNS_RR_LEN(aptr);
rr_ttl = DNS_RR_TTL(aptr);
aptr += RRFIXEDSZ;
if (aptr + rr_len > abuf + alen)
{
ares_free(rr_name);
status = ARES_EBADRESP;
break;
}
if (rr_class == C_IN && rr_type == T_A
&& rr_len == sizeof(struct in_addr)
&& strcasecmp(rr_name, hostname) == 0)
{
if (addrs)
{
if (aptr + sizeof(struct in_addr) > abuf + alen)
{ /* LCOV_EXCL_START: already checked above */
ares_free(rr_name);
status = ARES_EBADRESP;
break;
} /* LCOV_EXCL_STOP */
memcpy(&addrs[naddrs], aptr, sizeof(struct in_addr));
}
if (naddrs < max_addr_ttls)
{
struct ares_addrttl * const at = &addrttls[naddrs];
if (aptr + sizeof(struct in_addr) > abuf + alen)
{ /* LCOV_EXCL_START: already checked above */
ares_free(rr_name);
status = ARES_EBADRESP;
break;
} /* LCOV_EXCL_STOP */
memcpy(&at->ipaddr, aptr, sizeof(struct in_addr));
at->ttl = rr_ttl;
}
naddrs++;
status = ARES_SUCCESS;
}
if (rr_class == C_IN && rr_type == T_CNAME)
{
/* Record the RR name as an alias. */
if (aliases)
aliases[naliases] = rr_name;
else
ares_free(rr_name);
naliases++;
/* Decode the RR data and replace the hostname with it. */
status = ares__expand_name_for_response(aptr, abuf, alen, &rr_data,
&len);
if (status != ARES_SUCCESS)
break;
ares_free(hostname);
hostname = rr_data;
/* Take the min of the TTLs we see in the CNAME chain. */
if (cname_ttl > rr_ttl)
cname_ttl = rr_ttl;
}
else
ares_free(rr_name);
aptr += rr_len;
if (aptr > abuf + alen)
{ /* LCOV_EXCL_START: already checked above */
status = ARES_EBADRESP;
break;
} /* LCOV_EXCL_STOP */
}
if (status == ARES_SUCCESS && naddrs == 0 && naliases == 0)
/* the check for naliases to be zero is to make sure CNAME responses
don't get caught here */
status = ARES_ENODATA;
if (status == ARES_SUCCESS)
{
/* We got our answer. */
if (naddrttls)
{
const int n = naddrs < max_addr_ttls ? naddrs : max_addr_ttls;
for (i = 0; i < n; i++)
{
/* Ensure that each A TTL is no larger than the CNAME TTL. */
if (addrttls[i].ttl > cname_ttl)
addrttls[i].ttl = cname_ttl;
}
*naddrttls = n;
}
if (aliases)
aliases[naliases] = NULL;
if (host)
{
/* Allocate memory to build the host entry. */
hostent = ares_malloc(sizeof(struct hostent));
if (hostent)
{
hostent->h_addr_list = ares_malloc((naddrs + 1) * sizeof(char *));
if (hostent->h_addr_list)
{
/* Fill in the hostent and return successfully. */
hostent->h_name = hostname;
hostent->h_aliases = aliases;
hostent->h_addrtype = AF_INET;
hostent->h_length = sizeof(struct in_addr);
for (i = 0; i < naddrs; i++)
hostent->h_addr_list[i] = (char *) &addrs[i];
hostent->h_addr_list[naddrs] = NULL;
if (!naddrs && addrs)
ares_free(addrs);
*host = hostent;
return ARES_SUCCESS;
}
ares_free(hostent);
}
status = ARES_ENOMEM;
}
}
if (aliases)
{
for (i = 0; i < naliases; i++)
ares_free(aliases[i]);
ares_free(aliases);
}
ares_free(addrs);
ares_free(hostname);
return status;
}
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