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
ares_parse_a_reply(const unsigned char * abuf,int alen,struct hostent ** host,struct ares_addrttl * addrttls,int * naddrttls)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