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
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
|
/* vi: set sw=4 ts=4: */
/* RFC1035 domain compression routines (C) 2007 Gabriel Somlo <somlo at cmu.edu>
*
* Loosely based on the isc-dhcpd implementation by dhankins@isc.org
*
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/
#ifdef DNS_COMPR_TESTING
# define FAST_FUNC /* nothing */
# define xmalloc malloc
# include <stdlib.h>
# include <stdint.h>
# include <string.h>
# include <stdio.h>
#else
# include "common.h"
#endif
#define NS_MAXDNAME 1025 /* max domain name length */
#define NS_MAXCDNAME 255 /* max compressed domain name length */
#define NS_MAXLABEL 63 /* max label length */
#define NS_MAXDNSRCH 6 /* max domains in search path */
#define NS_CMPRSFLGS 0xc0 /* name compression pointer flag */
/* Expand a RFC1035-compressed list of domain names "cstr", of length "clen";
* returns a newly allocated string containing the space-separated domains,
* prefixed with the contents of string pre, or NULL if an error occurs.
*/
char* FAST_FUNC dname_dec(const uint8_t *cstr, int clen, const char *pre)
{
char *ret = ret; /* for compiler */
char *dst = NULL;
/* We make two passes over the cstr string. First, we compute
* how long the resulting string would be. Then we allocate a
* new buffer of the required length, and fill it in with the
* expanded content. The advantage of this approach is not
* having to deal with requiring callers to supply their own
* buffer, then having to check if it's sufficiently large, etc.
*/
while (1) {
/* note: "return NULL" below are leak-safe since
* dst isn't yet allocated */
const uint8_t *c;
unsigned crtpos, retpos, depth, len;
crtpos = retpos = depth = len = 0;
while (crtpos < clen) {
c = cstr + crtpos;
if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) {
/* pointer */
if (crtpos + 2 > clen) /* no offset to jump to? abort */
return NULL;
if (retpos == 0) /* toplevel? save return spot */
retpos = crtpos + 2;
depth++;
crtpos = ((c[0] & 0x3f) << 8) | c[1]; /* jump */
} else if (*c) {
/* label */
if (crtpos + *c + 1 > clen) /* label too long? abort */
return NULL;
if (dst)
memcpy(dst + len, c + 1, *c);
len += *c + 1;
crtpos += *c + 1;
if (dst)
dst[len - 1] = '.';
} else {
/* NUL: end of current domain name */
if (retpos == 0) {
/* toplevel? keep going */
crtpos++;
} else {
/* return to toplevel saved spot */
crtpos = retpos;
retpos = depth = 0;
}
if (dst)
dst[len - 1] = ' ';
}
if (depth > NS_MAXDNSRCH /* too many jumps? abort, it's a loop */
|| len > NS_MAXDNAME * NS_MAXDNSRCH /* result too long? abort */
) {
return NULL;
}
}
if (!len) /* expanded string has 0 length? abort */
return NULL;
if (!dst) { /* first pass? */
/* allocate dst buffer and copy pre */
unsigned plen = strlen(pre);
ret = dst = xmalloc(plen + len);
memcpy(dst, pre, plen);
dst += plen;
} else {
dst[len - 1] = '\0';
break;
}
}
return ret;
}
/* Convert a domain name (src) from human-readable "foo.blah.com" format into
* RFC1035 encoding "\003foo\004blah\003com\000". Return allocated string, or
* NULL if an error occurs.
*/
static uint8_t *convert_dname(const char *src)
{
uint8_t c, *res, *lenptr, *dst;
int len;
res = xmalloc(strlen(src) + 2);
dst = lenptr = res;
dst++;
for (;;) {
c = (uint8_t)*src++;
if (c == '.' || c == '\0') { /* end of label */
len = dst - lenptr - 1;
/* label too long, too short, or two '.'s in a row? abort */
if (len > NS_MAXLABEL || len == 0 || (c == '.' && *src == '.')) {
free(res);
return NULL;
}
*lenptr = len;
if (c == '\0' || *src == '\0') /* "" or ".": end of src */
break;
lenptr = dst++;
continue;
}
if (c >= 'A' && c <= 'Z') /* uppercase? convert to lower */
c += ('a' - 'A');
*dst++ = c;
}
if (dst - res >= NS_MAXCDNAME) { /* dname too long? abort */
free(res);
return NULL;
}
*dst = 0;
return res;
}
/* Returns the offset within cstr at which dname can be found, or -1 */
static int find_offset(const uint8_t *cstr, int clen, const uint8_t *dname)
{
const uint8_t *c, *d;
int off;
/* find all labels in cstr */
off = 0;
while (off < clen) {
c = cstr + off;
if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) { /* pointer, skip */
off += 2;
continue;
}
if (*c) { /* label, try matching dname */
d = dname;
while (1) {
unsigned len1 = *c + 1;
if (memcmp(c, d, len1) != 0)
break;
if (len1 == 1) /* at terminating NUL - match, return offset */
return off;
d += len1;
c += len1;
if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) /* pointer, jump */
c = cstr + (((c[0] & 0x3f) << 8) | c[1]);
}
off += cstr[off] + 1;
continue;
}
/* NUL, skip */
off++;
}
return -1;
}
/* Computes string to be appended to cstr so that src would be added to
* the compression (best case, it's a 2-byte pointer to some offset within
* cstr; worst case, it's all of src, converted to <4>host<3>com<0> format).
* The computed string is returned directly; its length is returned via retlen;
* NULL and 0, respectively, are returned if an error occurs.
*/
uint8_t* FAST_FUNC dname_enc(const uint8_t *cstr, int clen, const char *src, int *retlen)
{
uint8_t *d, *dname;
int off;
dname = convert_dname(src);
if (dname == NULL) {
*retlen = 0;
return NULL;
}
d = dname;
while (*d) {
if (cstr) {
off = find_offset(cstr, clen, d);
if (off >= 0) { /* found a match, add pointer and return */
*d++ = NS_CMPRSFLGS | (off >> 8);
*d = off;
break;
}
}
d += *d + 1;
}
*retlen = d - dname + 1;
return dname;
}
#ifdef DNS_COMPR_TESTING
/* gcc -Wall -DDNS_COMPR_TESTING domain_codec.c -o domain_codec && ./domain_codec */
int main(int argc, char **argv)
{
int len;
uint8_t *encoded;
#define DNAME_DEC(encoded,pre) dname_dec((uint8_t*)(encoded), sizeof(encoded), (pre))
printf("'%s'\n", DNAME_DEC("\4host\3com\0", "test1:"));
printf("test2:'%s'\n", DNAME_DEC("\4host\3com\0\4host\3com\0", ""));
printf("test3:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\0", ""));
printf("test4:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5", ""));
printf("test5:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5\1z\xC0\xA", ""));
#define DNAME_ENC(cache,source,lenp) dname_enc((uint8_t*)(cache), sizeof(cache), (source), (lenp))
encoded = dname_enc(NULL, 0, "test.net", &len);
printf("test6:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
encoded = DNAME_ENC("\3net\0", "test.net", &len);
printf("test7:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
encoded = DNAME_ENC("\4test\3net\0", "test.net", &len);
printf("test8:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
return 0;
}
#endif
|
