1 2 /* Copyright 1998 by the Massachusetts Institute of Technology. 3 * 4 * Permission to use, copy, modify, and distribute this 5 * software and its documentation for any purpose and without 6 * fee is hereby granted, provided that the above copyright 7 * notice appear in all copies and that both that copyright 8 * notice and this permission notice appear in supporting 9 * documentation, and that the name of M.I.T. not be used in 10 * advertising or publicity pertaining to distribution of the 11 * software without specific, written prior permission. 12 * M.I.T. makes no representations about the suitability of 13 * this software for any purpose. It is provided "as is" 14 * without express or implied warranty. 15 */ 16 17 #include "ares_setup.h" 18 19 #ifdef HAVE_SYS_SOCKET_H 20 # include <sys/socket.h> 21 #endif 22 #ifdef HAVE_NETINET_IN_H 23 # include <netinet/in.h> 24 #endif 25 #ifdef HAVE_NETDB_H 26 # include <netdb.h> 27 #endif 28 #ifdef HAVE_ARPA_INET_H 29 # include <arpa/inet.h> 30 #endif 31 #ifdef HAVE_ARPA_NAMESER_H 32 # include <arpa/nameser.h> 33 #else 34 # include "nameser.h" 35 #endif 36 #ifdef HAVE_ARPA_NAMESER_COMPAT_H 37 # include <arpa/nameser_compat.h> 38 #endif 39 40 #ifdef HAVE_STRINGS_H 41 # include <strings.h> 42 #endif 43 44 #include <stdlib.h> 45 #include <string.h> 46 #ifdef HAVE_LIMITS_H 47 # include <limits.h> 48 #endif 49 50 #include "ares.h" 51 #include "ares_dns.h" 52 #include "ares_private.h" 53 54 int ares_parse_a_reply(const unsigned char *abuf, int alen, 55 struct hostent **host, 56 struct ares_addrttl *addrttls, int *naddrttls) 57 { 58 unsigned int qdcount, ancount; 59 int status, i, rr_type, rr_class, rr_len, rr_ttl, naddrs; 60 int cname_ttl = INT_MAX; /* the TTL imposed by the CNAME chain */ 61 int naliases; 62 long len; 63 const unsigned char *aptr; 64 char *hostname, *rr_name, *rr_data, **aliases; 65 struct in_addr *addrs; 66 struct hostent *hostent; 67 const int max_addr_ttls = (addrttls && naddrttls) ? *naddrttls : 0; 68 69 /* Set *host to NULL for all failure cases. */ 70 if (host) 71 *host = NULL; 72 /* Same with *naddrttls. */ 73 if (naddrttls) 74 *naddrttls = 0; 75 76 /* Give up if abuf doesn't have room for a header. */ 77 if (alen < HFIXEDSZ) 78 return ARES_EBADRESP; 79 80 /* Fetch the question and answer count from the header. */ 81 qdcount = DNS_HEADER_QDCOUNT(abuf); 82 ancount = DNS_HEADER_ANCOUNT(abuf); 83 if (qdcount != 1) 84 return ARES_EBADRESP; 85 86 /* Expand the name from the question, and skip past the question. */ 87 aptr = abuf + HFIXEDSZ; 88 status = ares__expand_name_for_response(aptr, abuf, alen, &hostname, &len); 89 if (status != ARES_SUCCESS) 90 return status; 91 if (aptr + len + QFIXEDSZ > abuf + alen) 92 { 93 free(hostname); 94 return ARES_EBADRESP; 95 } 96 aptr += len + QFIXEDSZ; 97 98 if (host) 99 { 100 /* Allocate addresses and aliases; ancount gives an upper bound for 101 both. */ 102 addrs = malloc(ancount * sizeof(struct in_addr)); 103 if (!addrs) 104 { 105 free(hostname); 106 return ARES_ENOMEM; 107 } 108 aliases = malloc((ancount + 1) * sizeof(char *)); 109 if (!aliases) 110 { 111 free(hostname); 112 free(addrs); 113 return ARES_ENOMEM; 114 } 115 } 116 else 117 { 118 addrs = NULL; 119 aliases = NULL; 120 } 121 122 naddrs = 0; 123 naliases = 0; 124 125 /* Examine each answer resource record (RR) in turn. */ 126 for (i = 0; i < (int)ancount; i++) 127 { 128 /* Decode the RR up to the data field. */ 129 status = ares__expand_name_for_response(aptr, abuf, alen, &rr_name, &len); 130 if (status != ARES_SUCCESS) 131 break; 132 aptr += len; 133 if (aptr + RRFIXEDSZ > abuf + alen) 134 { 135 free(rr_name); 136 status = ARES_EBADRESP; 137 break; 138 } 139 rr_type = DNS_RR_TYPE(aptr); 140 rr_class = DNS_RR_CLASS(aptr); 141 rr_len = DNS_RR_LEN(aptr); 142 rr_ttl = DNS_RR_TTL(aptr); 143 aptr += RRFIXEDSZ; 144 145 if (rr_class == C_IN && rr_type == T_A 146 && rr_len == sizeof(struct in_addr) 147 && strcasecmp(rr_name, hostname) == 0) 148 { 149 if (addrs) 150 { 151 if (aptr + sizeof(struct in_addr) > abuf + alen) 152 { 153 free(rr_name); 154 status = ARES_EBADRESP; 155 break; 156 } 157 memcpy(&addrs[naddrs], aptr, sizeof(struct in_addr)); 158 } 159 if (naddrs < max_addr_ttls) 160 { 161 struct ares_addrttl * const at = &addrttls[naddrs]; 162 if (aptr + sizeof(struct in_addr) > abuf + alen) 163 { 164 free(rr_name); 165 status = ARES_EBADRESP; 166 break; 167 } 168 memcpy(&at->ipaddr, aptr, sizeof(struct in_addr)); 169 at->ttl = rr_ttl; 170 } 171 naddrs++; 172 status = ARES_SUCCESS; 173 } 174 175 if (rr_class == C_IN && rr_type == T_CNAME) 176 { 177 /* Record the RR name as an alias. */ 178 if (aliases) 179 aliases[naliases] = rr_name; 180 else 181 free(rr_name); 182 naliases++; 183 184 /* Decode the RR data and replace the hostname with it. */ 185 status = ares__expand_name_for_response(aptr, abuf, alen, &rr_data, 186 &len); 187 if (status != ARES_SUCCESS) 188 break; 189 free(hostname); 190 hostname = rr_data; 191 192 /* Take the min of the TTLs we see in the CNAME chain. */ 193 if (cname_ttl > rr_ttl) 194 cname_ttl = rr_ttl; 195 } 196 else 197 free(rr_name); 198 199 aptr += rr_len; 200 if (aptr > abuf + alen) 201 { 202 status = ARES_EBADRESP; 203 break; 204 } 205 } 206 207 if (status == ARES_SUCCESS && naddrs == 0 && naliases == 0) 208 /* the check for naliases to be zero is to make sure CNAME responses 209 don't get caught here */ 210 status = ARES_ENODATA; 211 if (status == ARES_SUCCESS) 212 { 213 /* We got our answer. */ 214 if (naddrttls) 215 { 216 const int n = naddrs < max_addr_ttls ? naddrs : max_addr_ttls; 217 for (i = 0; i < n; i++) 218 { 219 /* Ensure that each A TTL is no larger than the CNAME TTL. */ 220 if (addrttls[i].ttl > cname_ttl) 221 addrttls[i].ttl = cname_ttl; 222 } 223 *naddrttls = n; 224 } 225 if (aliases) 226 aliases[naliases] = NULL; 227 if (host) 228 { 229 /* Allocate memory to build the host entry. */ 230 hostent = malloc(sizeof(struct hostent)); 231 if (hostent) 232 { 233 hostent->h_addr_list = malloc((naddrs + 1) * sizeof(char *)); 234 if (hostent->h_addr_list) 235 { 236 /* Fill in the hostent and return successfully. */ 237 hostent->h_name = hostname; 238 hostent->h_aliases = aliases; 239 hostent->h_addrtype = AF_INET; 240 hostent->h_length = sizeof(struct in_addr); 241 for (i = 0; i < naddrs; i++) 242 hostent->h_addr_list[i] = (char *) &addrs[i]; 243 hostent->h_addr_list[naddrs] = NULL; 244 if (!naddrs && addrs) 245 free(addrs); 246 *host = hostent; 247 return ARES_SUCCESS; 248 } 249 free(hostent); 250 } 251 status = ARES_ENOMEM; 252 } 253 } 254 if (aliases) 255 { 256 for (i = 0; i < naliases; i++) 257 free(aliases[i]); 258 free(aliases); 259 } 260 free(addrs); 261 free(hostname); 262 return status; 263 } 264
