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
23 #include "ares_nameser.h"
24
25 #include "ares.h"
26 #include "ares_dns.h"
27 #include "ares_private.h"
28
29
30 /* Header format, from RFC 1035:
31 * 1 1 1 1 1 1
32 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
33 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
34 * | ID |
35 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
36 * |QR| Opcode |AA|TC|RD|RA| Z | RCODE |
37 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
38 * | QDCOUNT |
39 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
40 * | ANCOUNT |
41 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
42 * | NSCOUNT |
43 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
44 * | ARCOUNT |
45 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
46 *
47 * AA, TC, RA, and RCODE are only set in responses. Brief description
48 * of the remaining fields:
49 * ID Identifier to match responses with queries
50 * QR Query (0) or response (1)
51 * Opcode For our purposes, always O_QUERY
52 * RD Recursion desired
53 * Z Reserved (zero)
54 * QDCOUNT Number of queries
55 * ANCOUNT Number of answers
56 * NSCOUNT Number of name server records
57 * ARCOUNT Number of additional records
58 *
59 * Question format, from RFC 1035:
60 * 1 1 1 1 1 1
61 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
62 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
63 * | |
64 * / QNAME /
65 * / /
66 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
67 * | QTYPE |
68 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
69 * | QCLASS |
70 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
71 *
72 * The query name is encoded as a series of labels, each represented
73 * as a one-byte length (maximum 63) followed by the text of the
74 * label. The list is terminated by a label of length zero (which can
75 * be thought of as the root domain).
76 */
77
ares_create_query(const char * name,int dnsclass,int type,unsigned short id,int rd,unsigned char ** bufp,int * buflenp,int max_udp_size)78 int ares_create_query(const char *name, int dnsclass, int type,
79 unsigned short id, int rd, unsigned char **bufp,
80 int *buflenp, int max_udp_size)
81 {
82 size_t len;
83 unsigned char *q;
84 const char *p;
85 size_t buflen;
86 unsigned char *buf;
87
88 /* Set our results early, in case we bail out early with an error. */
89 *buflenp = 0;
90 *bufp = NULL;
91
92 /* Per RFC 7686, reject queries for ".onion" domain names with NXDOMAIN. */
93 if (ares__is_onion_domain(name))
94 return ARES_ENOTFOUND;
95
96 /* Allocate a memory area for the maximum size this packet might need. +2
97 * is for the length byte and zero termination if no dots or ecscaping is
98 * used.
99 */
100 len = strlen(name) + 2 + HFIXEDSZ + QFIXEDSZ +
101 (max_udp_size ? EDNSFIXEDSZ : 0);
102 buf = ares_malloc(len);
103 if (!buf)
104 return ARES_ENOMEM;
105
106 /* Set up the header. */
107 q = buf;
108 memset(q, 0, HFIXEDSZ);
109 DNS_HEADER_SET_QID(q, id);
110 DNS_HEADER_SET_OPCODE(q, O_QUERY);
111 if (rd) {
112 DNS_HEADER_SET_RD(q, 1);
113 }
114 else {
115 DNS_HEADER_SET_RD(q, 0);
116 }
117 DNS_HEADER_SET_QDCOUNT(q, 1);
118
119 if (max_udp_size) {
120 DNS_HEADER_SET_ARCOUNT(q, 1);
121 }
122
123 /* A name of "." is a screw case for the loop below, so adjust it. */
124 if (strcmp(name, ".") == 0)
125 name++;
126
127 /* Start writing out the name after the header. */
128 q += HFIXEDSZ;
129 while (*name)
130 {
131 if (*name == '.') {
132 ares_free (buf);
133 return ARES_EBADNAME;
134 }
135
136 /* Count the number of bytes in this label. */
137 len = 0;
138 for (p = name; *p && *p != '.'; p++)
139 {
140 if (*p == '\\' && *(p + 1) != 0)
141 p++;
142 len++;
143 }
144 if (len > MAXLABEL) {
145 ares_free (buf);
146 return ARES_EBADNAME;
147 }
148
149 /* Encode the length and copy the data. */
150 *q++ = (unsigned char)len;
151 for (p = name; *p && *p != '.'; p++)
152 {
153 if (*p == '\\' && *(p + 1) != 0)
154 p++;
155 *q++ = *p;
156 }
157
158 /* Go to the next label and repeat, unless we hit the end. */
159 if (!*p)
160 break;
161 name = p + 1;
162 }
163
164 /* Add the zero-length label at the end. */
165 *q++ = 0;
166
167 /* Finish off the question with the type and class. */
168 DNS_QUESTION_SET_TYPE(q, type);
169 DNS_QUESTION_SET_CLASS(q, dnsclass);
170
171 q += QFIXEDSZ;
172 if (max_udp_size)
173 {
174 memset(q, 0, EDNSFIXEDSZ);
175 q++;
176 DNS_RR_SET_TYPE(q, T_OPT);
177 DNS_RR_SET_CLASS(q, max_udp_size);
178 q += (EDNSFIXEDSZ-1);
179 }
180 buflen = (q - buf);
181
182 /* Reject names that are longer than the maximum of 255 bytes that's
183 * specified in RFC 1035 ("To simplify implementations, the total length of
184 * a domain name (i.e., label octets and label length octets) is restricted
185 * to 255 octets or less."). */
186 if (buflen > (size_t)(MAXCDNAME + HFIXEDSZ + QFIXEDSZ +
187 (max_udp_size ? EDNSFIXEDSZ : 0))) {
188 ares_free (buf);
189 return ARES_EBADNAME;
190 }
191
192 /* we know this fits in an int at this point */
193 *buflenp = (int) buflen;
194 *bufp = buf;
195
196 return ARES_SUCCESS;
197 }
198