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_NETINET_IN_H
20 # include <netinet/in.h>
21 #endif
22 #ifdef HAVE_NETDB_H
23 # include <netdb.h>
24 #endif
25 #ifdef HAVE_ARPA_INET_H
26 # include <arpa/inet.h>
27 #endif
28 #ifdef HAVE_ARPA_NAMESER_H
29 # include <arpa/nameser.h>
30 #else
31 # include "nameser.h"
32 #endif
33 #ifdef HAVE_ARPA_NAMESER_COMPAT_H
34 # include <arpa/nameser_compat.h>
35 #endif
36
37 #ifdef HAVE_STRINGS_H
38 # include <strings.h>
39 #endif
40
41 #ifdef HAVE_LIMITS_H
42 # include <limits.h>
43 #endif
44
45 #include "ares.h"
46 #include "ares_dns.h"
47 #include "ares_private.h"
48
ares_parse_a_reply(const unsigned char * abuf,int alen,struct hostent ** host,struct ares_addrttl * addrttls,int * naddrttls)49 int ares_parse_a_reply(const unsigned char *abuf, int alen,
50 struct hostent **host,
51 struct ares_addrttl *addrttls, int *naddrttls)
52 {
53 unsigned int qdcount, ancount;
54 int status, i, rr_type, rr_class, rr_len, rr_ttl, naddrs;
55 int cname_ttl = INT_MAX; /* the TTL imposed by the CNAME chain */
56 int naliases;
57 long len;
58 const unsigned char *aptr;
59 char *hostname, *rr_name, *rr_data, **aliases;
60 struct in_addr *addrs;
61 struct hostent *hostent;
62 const int max_addr_ttls = (addrttls && naddrttls) ? *naddrttls : 0;
63
64 /* Set *host to NULL for all failure cases. */
65 if (host)
66 *host = NULL;
67 /* Same with *naddrttls. */
68 if (naddrttls)
69 *naddrttls = 0;
70
71 /* Give up if abuf doesn't have room for a header. */
72 if (alen < HFIXEDSZ)
73 return ARES_EBADRESP;
74
75 /* Fetch the question and answer count from the header. */
76 qdcount = DNS_HEADER_QDCOUNT(abuf);
77 ancount = DNS_HEADER_ANCOUNT(abuf);
78 if (qdcount != 1)
79 return ARES_EBADRESP;
80
81 /* Expand the name from the question, and skip past the question. */
82 aptr = abuf + HFIXEDSZ;
83 status = ares__expand_name_for_response(aptr, abuf, alen, &hostname, &len);
84 if (status != ARES_SUCCESS)
85 return status;
86 if (aptr + len + QFIXEDSZ > abuf + alen)
87 {
88 ares_free(hostname);
89 return ARES_EBADRESP;
90 }
91 aptr += len + QFIXEDSZ;
92
93 if (host)
94 {
95 /* Allocate addresses and aliases; ancount gives an upper bound for
96 both. */
97 addrs = ares_malloc(ancount * sizeof(struct in_addr));
98 if (!addrs)
99 {
100 ares_free(hostname);
101 return ARES_ENOMEM;
102 }
103 aliases = ares_malloc((ancount + 1) * sizeof(char *));
104 if (!aliases)
105 {
106 ares_free(hostname);
107 ares_free(addrs);
108 return ARES_ENOMEM;
109 }
110 }
111 else
112 {
113 addrs = NULL;
114 aliases = NULL;
115 }
116
117 naddrs = 0;
118 naliases = 0;
119
120 /* Examine each answer resource record (RR) in turn. */
121 for (i = 0; i < (int)ancount; i++)
122 {
123 /* Decode the RR up to the data field. */
124 status = ares__expand_name_for_response(aptr, abuf, alen, &rr_name, &len);
125 if (status != ARES_SUCCESS)
126 break;
127 aptr += len;
128 if (aptr + RRFIXEDSZ > abuf + alen)
129 {
130 ares_free(rr_name);
131 status = ARES_EBADRESP;
132 break;
133 }
134 rr_type = DNS_RR_TYPE(aptr);
135 rr_class = DNS_RR_CLASS(aptr);
136 rr_len = DNS_RR_LEN(aptr);
137 rr_ttl = DNS_RR_TTL(aptr);
138 aptr += RRFIXEDSZ;
139 if (aptr + rr_len > abuf + alen)
140 {
141 ares_free(rr_name);
142 status = ARES_EBADRESP;
143 break;
144 }
145
146 if (rr_class == C_IN && rr_type == T_A
147 && rr_len == sizeof(struct in_addr)
148 && strcasecmp(rr_name, hostname) == 0)
149 {
150 if (addrs)
151 {
152 if (aptr + sizeof(struct in_addr) > abuf + alen)
153 { /* LCOV_EXCL_START: already checked above */
154 ares_free(rr_name);
155 status = ARES_EBADRESP;
156 break;
157 } /* LCOV_EXCL_STOP */
158 memcpy(&addrs[naddrs], aptr, sizeof(struct in_addr));
159 }
160 if (naddrs < max_addr_ttls)
161 {
162 struct ares_addrttl * const at = &addrttls[naddrs];
163 if (aptr + sizeof(struct in_addr) > abuf + alen)
164 { /* LCOV_EXCL_START: already checked above */
165 ares_free(rr_name);
166 status = ARES_EBADRESP;
167 break;
168 } /* LCOV_EXCL_STOP */
169 memcpy(&at->ipaddr, aptr, sizeof(struct in_addr));
170 at->ttl = rr_ttl;
171 }
172 naddrs++;
173 status = ARES_SUCCESS;
174 }
175
176 if (rr_class == C_IN && rr_type == T_CNAME)
177 {
178 /* Record the RR name as an alias. */
179 if (aliases)
180 aliases[naliases] = rr_name;
181 else
182 ares_free(rr_name);
183 naliases++;
184
185 /* Decode the RR data and replace the hostname with it. */
186 status = ares__expand_name_for_response(aptr, abuf, alen, &rr_data,
187 &len);
188 if (status != ARES_SUCCESS)
189 break;
190 ares_free(hostname);
191 hostname = rr_data;
192
193 /* Take the min of the TTLs we see in the CNAME chain. */
194 if (cname_ttl > rr_ttl)
195 cname_ttl = rr_ttl;
196 }
197 else
198 ares_free(rr_name);
199
200 aptr += rr_len;
201 if (aptr > abuf + alen)
202 { /* LCOV_EXCL_START: already checked above */
203 status = ARES_EBADRESP;
204 break;
205 } /* LCOV_EXCL_STOP */
206 }
207
208 if (status == ARES_SUCCESS && naddrs == 0 && naliases == 0)
209 /* the check for naliases to be zero is to make sure CNAME responses
210 don't get caught here */
211 status = ARES_ENODATA;
212 if (status == ARES_SUCCESS)
213 {
214 /* We got our answer. */
215 if (naddrttls)
216 {
217 const int n = naddrs < max_addr_ttls ? naddrs : max_addr_ttls;
218 for (i = 0; i < n; i++)
219 {
220 /* Ensure that each A TTL is no larger than the CNAME TTL. */
221 if (addrttls[i].ttl > cname_ttl)
222 addrttls[i].ttl = cname_ttl;
223 }
224 *naddrttls = n;
225 }
226 if (aliases)
227 aliases[naliases] = NULL;
228 if (host)
229 {
230 /* Allocate memory to build the host entry. */
231 hostent = ares_malloc(sizeof(struct hostent));
232 if (hostent)
233 {
234 hostent->h_addr_list = ares_malloc((naddrs + 1) * sizeof(char *));
235 if (hostent->h_addr_list)
236 {
237 /* Fill in the hostent and return successfully. */
238 hostent->h_name = hostname;
239 hostent->h_aliases = aliases;
240 hostent->h_addrtype = AF_INET;
241 hostent->h_length = sizeof(struct in_addr);
242 for (i = 0; i < naddrs; i++)
243 hostent->h_addr_list[i] = (char *) &addrs[i];
244 hostent->h_addr_list[naddrs] = NULL;
245 if (!naddrs && addrs)
246 ares_free(addrs);
247 *host = hostent;
248 return ARES_SUCCESS;
249 }
250 ares_free(hostent);
251 }
252 status = ARES_ENOMEM;
253 }
254 }
255 if (aliases)
256 {
257 for (i = 0; i < naliases; i++)
258 ares_free(aliases[i]);
259 ares_free(aliases);
260 }
261 ares_free(addrs);
262 ares_free(hostname);
263 return status;
264 }
265