1 | /* Convert a DNS packet to a human-readable representation. |
2 | Copyright (C) 2016-2017 Free Software Foundation, Inc. |
3 | This file is part of the GNU C Library. |
4 | |
5 | The GNU C Library is free software; you can redistribute it and/or |
6 | modify it under the terms of the GNU Lesser General Public |
7 | License as published by the Free Software Foundation; either |
8 | version 2.1 of the License, or (at your option) any later version. |
9 | |
10 | The GNU C Library is distributed in the hope that it will be useful, |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
13 | Lesser General Public License for more details. |
14 | |
15 | You should have received a copy of the GNU Lesser General Public |
16 | License along with the GNU C Library; if not, see |
17 | <http://www.gnu.org/licenses/>. */ |
18 | |
19 | #include <support/format_nss.h> |
20 | |
21 | #include <arpa/inet.h> |
22 | #include <resolv.h> |
23 | #include <support/check.h> |
24 | #include <support/support.h> |
25 | #include <support/xmemstream.h> |
26 | |
27 | struct in_buffer |
28 | { |
29 | const unsigned char *data; |
30 | size_t size; |
31 | }; |
32 | |
33 | static inline bool |
34 | (struct in_buffer *in, unsigned char *value) |
35 | { |
36 | if (in->size == 0) |
37 | return false; |
38 | *value = in->data[0]; |
39 | ++in->data; |
40 | --in->size; |
41 | return true; |
42 | } |
43 | |
44 | static inline bool |
45 | (struct in_buffer *in, unsigned short *value) |
46 | { |
47 | if (in->size < 2) |
48 | return false; |
49 | *value = (in->data[0] << 8) | in->data[1]; |
50 | in->data += 2; |
51 | in->size -= 2; |
52 | return true; |
53 | } |
54 | |
55 | static inline bool |
56 | (struct in_buffer *in, unsigned *value) |
57 | { |
58 | if (in->size < 4) |
59 | return false; |
60 | unsigned a = in->data[0]; |
61 | unsigned b = in->data[1]; |
62 | unsigned c = in->data[2]; |
63 | unsigned d = in->data[3]; |
64 | *value = (a << 24) | (b << 16) | (c << 8) | d; |
65 | in->data += 4; |
66 | in->size -= 4; |
67 | return true; |
68 | } |
69 | |
70 | static inline bool |
71 | (struct in_buffer *in, size_t length, struct in_buffer *value) |
72 | { |
73 | if (in->size < length) |
74 | return false; |
75 | *value = (struct in_buffer) {in->data, length}; |
76 | in->data += length; |
77 | in->size -= length; |
78 | return true; |
79 | } |
80 | |
81 | struct dname |
82 | { |
83 | char name[MAXDNAME + 1]; |
84 | }; |
85 | |
86 | static bool |
87 | (struct in_buffer full, struct in_buffer *in, struct dname *value) |
88 | { |
89 | const unsigned char *full_end = full.data + full.size; |
90 | /* Sanity checks; these indicate buffer misuse. */ |
91 | TEST_VERIFY_EXIT |
92 | (!(in->data < full.data || in->data > full_end |
93 | || in->size > (size_t) (full_end - in->data))); |
94 | int ret = dn_expand (full.data, full_end, in->data, |
95 | value->name, sizeof (value->name)); |
96 | if (ret < 0) |
97 | return false; |
98 | in->data += ret; |
99 | in->size -= ret; |
100 | return true; |
101 | } |
102 | |
103 | char * |
104 | support_format_dns_packet (const unsigned char *buffer, size_t length) |
105 | { |
106 | struct in_buffer full = { buffer, length }; |
107 | struct in_buffer in = full; |
108 | struct xmemstream mem; |
109 | xopen_memstream (&mem); |
110 | |
111 | unsigned short txnid; |
112 | unsigned short flags; |
113 | unsigned short qdcount; |
114 | unsigned short ancount; |
115 | unsigned short nscount; |
116 | unsigned short adcount; |
117 | if (!(extract_16 (&in, &txnid) |
118 | && extract_16 (&in, &flags) |
119 | && extract_16 (&in, &qdcount) |
120 | && extract_16 (&in, &ancount) |
121 | && extract_16 (&in, &nscount) |
122 | && extract_16 (&in, &adcount))) |
123 | { |
124 | fprintf (mem.out, "error: could not parse DNS header\n" ); |
125 | goto out; |
126 | } |
127 | if (qdcount != 1) |
128 | { |
129 | fprintf (mem.out, "error: question count is %d, not 1\n" , qdcount); |
130 | goto out; |
131 | } |
132 | struct dname qname; |
133 | if (!extract_name (full, &in, &qname)) |
134 | { |
135 | fprintf (mem.out, "error: malformed QNAME\n" ); |
136 | goto out; |
137 | } |
138 | unsigned short qtype; |
139 | unsigned short qclass; |
140 | if (!(extract_16 (&in, &qtype) |
141 | && extract_16 (&in, &qclass))) |
142 | { |
143 | fprintf (mem.out, "error: malformed question\n" ); |
144 | goto out; |
145 | } |
146 | if (qtype != T_A && qtype != T_AAAA && qtype != T_PTR) |
147 | { |
148 | fprintf (mem.out, "error: unsupported QTYPE %d\n" , qtype); |
149 | goto out; |
150 | } |
151 | |
152 | fprintf (mem.out, "name: %s\n" , qname.name); |
153 | |
154 | for (int i = 0; i < ancount; ++i) |
155 | { |
156 | struct dname rname; |
157 | if (!extract_name (full, &in, &rname)) |
158 | { |
159 | fprintf (mem.out, "error: malformed record name\n" ); |
160 | goto out; |
161 | } |
162 | unsigned short rtype; |
163 | unsigned short rclass; |
164 | unsigned ttl; |
165 | unsigned short rdlen; |
166 | struct in_buffer rdata; |
167 | if (!(extract_16 (&in, &rtype) |
168 | && extract_16 (&in, &rclass) |
169 | && extract_32 (&in, &ttl) |
170 | && extract_16 (&in, &rdlen) |
171 | && extract_bytes (&in, rdlen, &rdata))) |
172 | { |
173 | fprintf (mem.out, "error: malformed record header\n" ); |
174 | goto out; |
175 | } |
176 | /* Skip non-matching record types. */ |
177 | if ((rtype != qtype && rtype != T_CNAME) || rclass != qclass) |
178 | continue; |
179 | switch (rtype) |
180 | { |
181 | case T_A: |
182 | if (rdlen == 4) |
183 | fprintf (mem.out, "address: %d.%d.%d.%d\n" , |
184 | rdata.data[0], |
185 | rdata.data[1], |
186 | rdata.data[2], |
187 | rdata.data[3]); |
188 | else |
189 | fprintf (mem.out, "error: A record of size %d: %s\n" , |
190 | rdlen, rname.name); |
191 | break; |
192 | case T_AAAA: |
193 | { |
194 | if (rdlen == 16) |
195 | { |
196 | char buf[100]; |
197 | if (inet_ntop (AF_INET6, rdata.data, buf, sizeof (buf)) == NULL) |
198 | fprintf (mem.out, "error: AAAA record decoding failed: %m\n" ); |
199 | else |
200 | fprintf (mem.out, "address: %s\n" , buf); |
201 | } |
202 | else |
203 | fprintf (mem.out, "error: AAAA record of size %d: %s\n" , |
204 | rdlen, rname.name); |
205 | } |
206 | break; |
207 | case T_CNAME: |
208 | case T_PTR: |
209 | { |
210 | struct dname name; |
211 | if (extract_name (full, &rdata, &name)) |
212 | fprintf (mem.out, "name: %s\n" , name.name); |
213 | else |
214 | fprintf (mem.out, "error: malformed CNAME/PTR record\n" ); |
215 | } |
216 | } |
217 | } |
218 | |
219 | out: |
220 | xfclose_memstream (&mem); |
221 | return mem.buffer; |
222 | } |
223 | |