/* $Id: ares_parse_a_reply.c,v 1.20 2009-11-23 01:24:17 yangtse Exp $ */ /* 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_SYS_SOCKET_H # include <sys/socket.h> #endif #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 #include <stdlib.h> #include <string.h> #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) { free(hostname); return ARES_EBADRESP; } aptr += len + QFIXEDSZ; if (host) { /* Allocate addresses and aliases; ancount gives an upper bound for both. */ addrs = malloc(ancount * sizeof(struct in_addr)); if (!addrs) { free(hostname); return ARES_ENOMEM; } aliases = malloc((ancount + 1) * sizeof(char *)); if (!aliases) { free(hostname); 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) { 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 (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) { status = ARES_EBADRESP; break; } 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) { status = ARES_EBADRESP; break; } 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 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; 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 free(rr_name); aptr += rr_len; if (aptr > abuf + alen) { status = ARES_EBADRESP; break; } } if (status == ARES_SUCCESS && naddrs == 0) 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 = malloc(sizeof(struct hostent)); if (hostent) { hostent->h_addr_list = 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; *host = hostent; return ARES_SUCCESS; } free(hostent); } status = ARES_ENOMEM; } } if (aliases) { for (i = 0; i < naliases; i++) free(aliases[i]); free(aliases); } free(addrs); free(hostname); return status; }