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1 
2 /* Copyright 1998 by the Massachusetts Institute of Technology.
3  * Copyright (C) 2009 by Jakub Hrozek <jhrozek@redhat.com>
4  *
5  * Permission to use, copy, modify, and distribute this
6  * software and its documentation for any purpose and without
7  * fee is hereby granted, provided that the above copyright
8  * notice appear in all copies and that both that copyright
9  * notice and this permission notice appear in supporting
10  * documentation, and that the name of M.I.T. not be used in
11  * advertising or publicity pertaining to distribution of the
12  * software without specific, written prior permission.
13  * M.I.T. makes no representations about the suitability of
14  * this software for any purpose.  It is provided "as is"
15  * without express or implied warranty.
16  */
17 
18 #include "ares_setup.h"
19 
20 #ifdef HAVE_SYS_SOCKET_H
21 #  include <sys/socket.h>
22 #endif
23 #ifdef HAVE_NETINET_IN_H
24 #  include <netinet/in.h>
25 #endif
26 #ifdef HAVE_NETDB_H
27 #  include <netdb.h>
28 #endif
29 #ifdef HAVE_ARPA_INET_H
30 #  include <arpa/inet.h>
31 #endif
32 #ifdef HAVE_ARPA_NAMESER_H
33 #  include <arpa/nameser.h>
34 #else
35 #  include "nameser.h"
36 #endif
37 #ifdef HAVE_ARPA_NAMESER_COMPAT_H
38 #  include <arpa/nameser_compat.h>
39 #endif
40 
41 #ifdef HAVE_STRINGS_H
42 #  include <strings.h>
43 #endif
44 
45 #include <stdlib.h>
46 #include <string.h>
47 
48 #include "ares.h"
49 #include "ares_dns.h"
50 #include "ares_data.h"
51 #include "ares_private.h"
52 
53 int
ares_parse_txt_reply(const unsigned char * abuf,int alen,struct ares_txt_reply ** txt_out)54 ares_parse_txt_reply (const unsigned char *abuf, int alen,
55                       struct ares_txt_reply **txt_out)
56 {
57   size_t substr_len, str_len;
58   unsigned int qdcount, ancount, i;
59   const unsigned char *aptr;
60   const unsigned char *strptr;
61   int status, rr_type, rr_class, rr_len;
62   long len;
63   char *hostname = NULL, *rr_name = NULL;
64   struct ares_txt_reply *txt_head = NULL;
65   struct ares_txt_reply *txt_last = NULL;
66   struct ares_txt_reply *txt_curr;
67 
68   /* Set *txt_out to NULL for all failure cases. */
69   *txt_out = NULL;
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   if (ancount == 0)
81     return ARES_ENODATA;
82 
83   /* Expand the name from the question, and skip past the question. */
84   aptr = abuf + HFIXEDSZ;
85   status = ares_expand_name (aptr, abuf, alen, &hostname, &len);
86   if (status != ARES_SUCCESS)
87     return status;
88 
89   if (aptr + len + QFIXEDSZ > abuf + alen)
90     {
91       free (hostname);
92       return ARES_EBADRESP;
93     }
94   aptr += len + QFIXEDSZ;
95 
96   /* Examine each answer resource record (RR) in turn. */
97   for (i = 0; i < ancount; i++)
98     {
99       /* Decode the RR up to the data field. */
100       status = ares_expand_name (aptr, abuf, alen, &rr_name, &len);
101       if (status != ARES_SUCCESS)
102         {
103           break;
104         }
105       aptr += len;
106       if (aptr + RRFIXEDSZ > abuf + alen)
107         {
108           status = ARES_EBADRESP;
109           break;
110         }
111       rr_type = DNS_RR_TYPE (aptr);
112       rr_class = DNS_RR_CLASS (aptr);
113       rr_len = DNS_RR_LEN (aptr);
114       aptr += RRFIXEDSZ;
115 
116       /* Check if we are really looking at a TXT record */
117       if (rr_class == C_IN && rr_type == T_TXT)
118         {
119           /* Allocate storage for this TXT answer appending it to the list */
120           txt_curr = ares_malloc_data(ARES_DATATYPE_TXT_REPLY);
121           if (!txt_curr)
122             {
123               status = ARES_ENOMEM;
124               break;
125             }
126           if (txt_last)
127             {
128               txt_last->next = txt_curr;
129             }
130           else
131             {
132               txt_head = txt_curr;
133             }
134           txt_last = txt_curr;
135 
136           /*
137            * There may be multiple substrings in a single TXT record. Each
138            * substring may be up to 255 characters in length, with a
139            * "length byte" indicating the size of the substring payload.
140            * RDATA contains both the length-bytes and payloads of all
141            * substrings contained therein.
142            */
143 
144           /* Compute total length to allow a single memory allocation */
145           strptr = aptr;
146           while (strptr < (aptr + rr_len))
147             {
148               substr_len = (unsigned char)*strptr;
149               txt_curr->length += substr_len;
150               strptr += substr_len + 1;
151             }
152 
153           /* Including null byte */
154           txt_curr->txt = malloc (txt_curr->length + 1);
155           if (txt_curr->txt == NULL)
156             {
157               status = ARES_ENOMEM;
158               break;
159             }
160 
161           /* Step through the list of substrings, concatenating them */
162           str_len = 0;
163           strptr = aptr;
164           while (strptr < (aptr + rr_len))
165             {
166               substr_len = (unsigned char)*strptr;
167               strptr++;
168               memcpy ((char *) txt_curr->txt + str_len, strptr, substr_len);
169               str_len += substr_len;
170               strptr += substr_len;
171             }
172           /* Make sure we NULL-terminate */
173           *((char *) txt_curr->txt + txt_curr->length) = '\0';
174         }
175 
176       /* Don't lose memory in the next iteration */
177       free (rr_name);
178       rr_name = NULL;
179 
180       /* Move on to the next record */
181       aptr += rr_len;
182     }
183 
184   if (hostname)
185     free (hostname);
186   if (rr_name)
187     free (rr_name);
188 
189   /* clean up on error */
190   if (status != ARES_SUCCESS)
191     {
192       if (txt_head)
193         ares_free_data (txt_head);
194       return status;
195     }
196 
197   /* everything looks fine, return the data */
198   *txt_out = txt_head;
199 
200   return ARES_SUCCESS;
201 }
202