1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
|
/*
DNS should have used LZ77 instead of its own sophomoric compression algorithm.
*/
#include <errno.h>
#include "dns.h"
/** Copy a block of data out of a packet.
\returns the offset of the next byte of data, or \c 0 if the packet was too short.
*/
unsigned int dns_packet_copy(const char *buf,unsigned int len,unsigned int pos,unsigned char *out,unsigned int outlen)
{
while (outlen) {
if (pos >= len) { errno = EPROTO; return 0; }
*out = buf[pos++];
++out; --outlen;
}
return pos;
}
/** Skip over a domain name within a packet. */
unsigned int dns_packet_skipname(const char *buf,unsigned int len,unsigned int pos)
{
unsigned char ch;
for (;;) {
if (pos >= len) break;
ch = buf[pos++];
if (ch >= 192) return pos + 1;
if (ch >= 64) break;
if (!ch) return pos;
pos += ch;
}
errno = EPROTO;
return 0;
}
/** Extract a domain name out of a packet, handling name compression. */
unsigned int dns_packet_getname(const char *buf,unsigned int len,unsigned int pos,char **d)
{
unsigned int loop = 0;
unsigned int state = 0;
unsigned int firstcompress = 0;
unsigned int where;
unsigned char ch;
char name[255];
unsigned int namelen = 0;
for (;;) {
if (pos >= len) goto PROTO; ch = buf[pos++];
if (++loop >= 1000) goto PROTO;
if (state) {
if (namelen + 1 > sizeof name) goto PROTO; name[namelen++] = ch;
--state;
}
else {
while (ch >= 192) {
where = ch; where -= 192; where <<= 8;
if (pos >= len) goto PROTO; ch = buf[pos++];
if (!firstcompress) firstcompress = pos;
pos = where + ch;
if (pos >= len) goto PROTO; ch = buf[pos++];
if (++loop >= 1000) goto PROTO;
}
if (ch >= 64) goto PROTO;
if (namelen + 1 > sizeof name) goto PROTO; name[namelen++] = ch;
if (!ch) break;
state = ch;
}
}
if (!dns_domain_copy(d,name)) return 0;
if (firstcompress) return firstcompress;
return pos;
PROTO:
errno = EPROTO;
return 0;
}
/** Extract a series of records from a packet.
\param out The result buffer into which to put the output.
\param buf The packet buffer to parse.
\param len The length of \c buf .
\param rrtype The resource record type, one of \c DNS_T_*.
\param rrclass The resource record class, one of \c DNS_C_*.
\param sizefn The function to call to determine the required
buffer size for each record.
\param copy The function to call to copy each record into the result.
*/
int dns_packet_extract(struct dns_result* out, const char* buf, unsigned int len, uint16 rrtype, uint16 rrclass,
int (*sizefn)(const char* buf, unsigned int len, unsigned int pos, uint16 datalen),
int (*copy)(struct dns_result* out, unsigned int index, unsigned int offset,
const char* buf, unsigned int len, unsigned int pos, uint16 datalen))
{
unsigned int pos;
unsigned int start;
unsigned char header[12];
uint16 numanswers;
uint16 datalen;
unsigned int i;
unsigned int size;
int r;
pos = dns_packet_copy(buf,len,0,header,12); if (!pos) return -1;
numanswers = uint16_get_msb(header + 6);
pos = dns_packet_skipname(buf,len,pos); if (!pos) return -1;
start = pos += 4;
/* Count the number of records */
for (i = size = 0; numanswers > 0; pos += datalen, --numanswers) {
pos = dns_packet_skipname(buf,len,pos); if (!pos) return -1;
pos = dns_packet_copy(buf,len,pos,header,10); if (!pos) return -1;
datalen = uint16_get_msb(header + 8);
if (uint16_get_msb(header) == rrtype && uint16_get_msb(header + 2) == rrclass) {
if (sizefn) {
if ((r = sizefn(buf, len, pos, datalen)) < 0) {
errno = EPROTO;
return -1;
}
size += r;
}
++i;
}
}
if (dns_result_alloc(out, rrtype, i, size) < 0)
return -1;
/* Copy the records into out */
pos = start;
numanswers = i;
for (i = size = 0; i < numanswers; pos += datalen) {
pos = dns_packet_skipname(buf,len,pos); if (!pos) return -1;
pos = dns_packet_copy(buf,len,pos,header,10); if (!pos) return -1;
datalen = uint16_get_msb(header + 8);
if (uint16_get_msb(header) == rrtype && uint16_get_msb(header + 2) == rrclass) {
if ((r = copy(out, i, size, buf, len, pos, datalen)) < 0)
return -1;
size += r;
++i;
}
}
return 0;
}
|
