1 | /* vi: set sw=4 ts=4: */
|
---|
2 |
|
---|
3 | /* RFC1035 domain compression routines (C) 2007 Gabriel Somlo <somlo at cmu.edu>
|
---|
4 | *
|
---|
5 | * Loosely based on the isc-dhcpd implementation by dhankins@isc.org
|
---|
6 | *
|
---|
7 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
|
---|
8 | */
|
---|
9 | #ifdef DNS_COMPR_TESTING
|
---|
10 | # define _GNU_SOURCE
|
---|
11 | # define FAST_FUNC /* nothing */
|
---|
12 | # define xmalloc malloc
|
---|
13 | # include <stdlib.h>
|
---|
14 | # include <stdint.h>
|
---|
15 | # include <string.h>
|
---|
16 | # include <stdio.h>
|
---|
17 | #else
|
---|
18 | # include "common.h"
|
---|
19 | #endif
|
---|
20 |
|
---|
21 | #define NS_MAXDNAME 1025 /* max domain name length */
|
---|
22 | #define NS_MAXCDNAME 255 /* max compressed domain name length */
|
---|
23 | #define NS_MAXLABEL 63 /* max label length */
|
---|
24 | #define NS_MAXDNSRCH 6 /* max domains in search path */
|
---|
25 | #define NS_CMPRSFLGS 0xc0 /* name compression pointer flag */
|
---|
26 |
|
---|
27 |
|
---|
28 | /* Expand a RFC1035-compressed list of domain names "cstr", of length "clen";
|
---|
29 | * returns a newly allocated string containing the space-separated domains,
|
---|
30 | * prefixed with the contents of string pre, or NULL if an error occurs.
|
---|
31 | */
|
---|
32 | char* FAST_FUNC dname_dec(const uint8_t *cstr, int clen, const char *pre)
|
---|
33 | {
|
---|
34 | char *ret = ret; /* for compiler */
|
---|
35 | char *dst = NULL;
|
---|
36 |
|
---|
37 | /* We make two passes over the cstr string. First, we compute
|
---|
38 | * how long the resulting string would be. Then we allocate a
|
---|
39 | * new buffer of the required length, and fill it in with the
|
---|
40 | * expanded content. The advantage of this approach is not
|
---|
41 | * having to deal with requiring callers to supply their own
|
---|
42 | * buffer, then having to check if it's sufficiently large, etc.
|
---|
43 | */
|
---|
44 | while (1) {
|
---|
45 | /* note: "return NULL" below are leak-safe since
|
---|
46 | * dst isn't allocated yet */
|
---|
47 | const uint8_t *c;
|
---|
48 | unsigned crtpos, retpos, depth, len;
|
---|
49 |
|
---|
50 | crtpos = retpos = depth = len = 0;
|
---|
51 | while (crtpos < clen) {
|
---|
52 | c = cstr + crtpos;
|
---|
53 |
|
---|
54 | if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) {
|
---|
55 | /* pointer */
|
---|
56 | if (crtpos + 2 > clen) /* no offset to jump to? abort */
|
---|
57 | return NULL;
|
---|
58 | if (retpos == 0) /* toplevel? save return spot */
|
---|
59 | retpos = crtpos + 2;
|
---|
60 | depth++;
|
---|
61 | crtpos = ((c[0] & 0x3f) << 8) | c[1]; /* jump */
|
---|
62 | } else if (*c) {
|
---|
63 | /* label */
|
---|
64 | if (crtpos + *c + 1 > clen) /* label too long? abort */
|
---|
65 | return NULL;
|
---|
66 | if (dst)
|
---|
67 | /* \3com ---> "com." */
|
---|
68 | ((char*)mempcpy(dst + len, c + 1, *c))[0] = '.';
|
---|
69 | len += *c + 1;
|
---|
70 | crtpos += *c + 1;
|
---|
71 | } else {
|
---|
72 | /* NUL: end of current domain name */
|
---|
73 | if (retpos == 0) {
|
---|
74 | /* toplevel? keep going */
|
---|
75 | crtpos++;
|
---|
76 | } else {
|
---|
77 | /* return to toplevel saved spot */
|
---|
78 | crtpos = retpos;
|
---|
79 | retpos = depth = 0;
|
---|
80 | }
|
---|
81 | if (dst && len != 0)
|
---|
82 | /* \4host\3com\0\4host and we are at \0:
|
---|
83 | * \3com was converted to "com.", change dot to space.
|
---|
84 | */
|
---|
85 | dst[len - 1] = ' ';
|
---|
86 | }
|
---|
87 |
|
---|
88 | if (depth > NS_MAXDNSRCH /* too many jumps? abort, it's a loop */
|
---|
89 | || len > NS_MAXDNAME * NS_MAXDNSRCH /* result too long? abort */
|
---|
90 | ) {
|
---|
91 | return NULL;
|
---|
92 | }
|
---|
93 | }
|
---|
94 |
|
---|
95 | if (!len) /* expanded string has 0 length? abort */
|
---|
96 | return NULL;
|
---|
97 |
|
---|
98 | if (!dst) { /* first pass? */
|
---|
99 | /* allocate dst buffer and copy pre */
|
---|
100 | unsigned plen = strlen(pre);
|
---|
101 | ret = xmalloc(plen + len);
|
---|
102 | dst = stpcpy(ret, pre);
|
---|
103 | } else {
|
---|
104 | dst[len - 1] = '\0';
|
---|
105 | break;
|
---|
106 | }
|
---|
107 | }
|
---|
108 |
|
---|
109 | return ret;
|
---|
110 | }
|
---|
111 |
|
---|
112 | /* Convert a domain name (src) from human-readable "foo.blah.com" format into
|
---|
113 | * RFC1035 encoding "\003foo\004blah\003com\000". Return allocated string, or
|
---|
114 | * NULL if an error occurs.
|
---|
115 | */
|
---|
116 | static uint8_t *convert_dname(const char *src)
|
---|
117 | {
|
---|
118 | uint8_t c, *res, *lenptr, *dst;
|
---|
119 | int len;
|
---|
120 |
|
---|
121 | res = xmalloc(strlen(src) + 2);
|
---|
122 | dst = lenptr = res;
|
---|
123 | dst++;
|
---|
124 |
|
---|
125 | for (;;) {
|
---|
126 | c = (uint8_t)*src++;
|
---|
127 | if (c == '.' || c == '\0') { /* end of label */
|
---|
128 | len = dst - lenptr - 1;
|
---|
129 | /* label too long, too short, or two '.'s in a row? abort */
|
---|
130 | if (len > NS_MAXLABEL || len == 0 || (c == '.' && *src == '.')) {
|
---|
131 | free(res);
|
---|
132 | return NULL;
|
---|
133 | }
|
---|
134 | *lenptr = len;
|
---|
135 | if (c == '\0' || *src == '\0') /* "" or ".": end of src */
|
---|
136 | break;
|
---|
137 | lenptr = dst++;
|
---|
138 | continue;
|
---|
139 | }
|
---|
140 | if (c >= 'A' && c <= 'Z') /* uppercase? convert to lower */
|
---|
141 | c += ('a' - 'A');
|
---|
142 | *dst++ = c;
|
---|
143 | }
|
---|
144 |
|
---|
145 | if (dst - res >= NS_MAXCDNAME) { /* dname too long? abort */
|
---|
146 | free(res);
|
---|
147 | return NULL;
|
---|
148 | }
|
---|
149 |
|
---|
150 | *dst = 0;
|
---|
151 | return res;
|
---|
152 | }
|
---|
153 |
|
---|
154 | /* Returns the offset within cstr at which dname can be found, or -1 */
|
---|
155 | static int find_offset(const uint8_t *cstr, int clen, const uint8_t *dname)
|
---|
156 | {
|
---|
157 | const uint8_t *c, *d;
|
---|
158 | int off;
|
---|
159 |
|
---|
160 | /* find all labels in cstr */
|
---|
161 | off = 0;
|
---|
162 | while (off < clen) {
|
---|
163 | c = cstr + off;
|
---|
164 |
|
---|
165 | if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) { /* pointer, skip */
|
---|
166 | off += 2;
|
---|
167 | continue;
|
---|
168 | }
|
---|
169 | if (*c) { /* label, try matching dname */
|
---|
170 | d = dname;
|
---|
171 | while (1) {
|
---|
172 | unsigned len1 = *c + 1;
|
---|
173 | if (memcmp(c, d, len1) != 0)
|
---|
174 | break;
|
---|
175 | if (len1 == 1) /* at terminating NUL - match, return offset */
|
---|
176 | return off;
|
---|
177 | d += len1;
|
---|
178 | c += len1;
|
---|
179 | if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) /* pointer, jump */
|
---|
180 | c = cstr + (((c[0] & 0x3f) << 8) | c[1]);
|
---|
181 | }
|
---|
182 | off += cstr[off] + 1;
|
---|
183 | continue;
|
---|
184 | }
|
---|
185 | /* NUL, skip */
|
---|
186 | off++;
|
---|
187 | }
|
---|
188 |
|
---|
189 | return -1;
|
---|
190 | }
|
---|
191 |
|
---|
192 | /* Computes string to be appended to cstr so that src would be added to
|
---|
193 | * the compression (best case, it's a 2-byte pointer to some offset within
|
---|
194 | * cstr; worst case, it's all of src, converted to <4>host<3>com<0> format).
|
---|
195 | * The computed string is returned directly; its length is returned via retlen;
|
---|
196 | * NULL and 0, respectively, are returned if an error occurs.
|
---|
197 | */
|
---|
198 | uint8_t* FAST_FUNC dname_enc(const uint8_t *cstr, int clen, const char *src, int *retlen)
|
---|
199 | {
|
---|
200 | uint8_t *d, *dname;
|
---|
201 | int off;
|
---|
202 |
|
---|
203 | dname = convert_dname(src);
|
---|
204 | if (dname == NULL) {
|
---|
205 | *retlen = 0;
|
---|
206 | return NULL;
|
---|
207 | }
|
---|
208 |
|
---|
209 | d = dname;
|
---|
210 | while (*d) {
|
---|
211 | if (cstr) {
|
---|
212 | off = find_offset(cstr, clen, d);
|
---|
213 | if (off >= 0) { /* found a match, add pointer and return */
|
---|
214 | *d++ = NS_CMPRSFLGS | (off >> 8);
|
---|
215 | *d = off;
|
---|
216 | break;
|
---|
217 | }
|
---|
218 | }
|
---|
219 | d += *d + 1;
|
---|
220 | }
|
---|
221 |
|
---|
222 | *retlen = d - dname + 1;
|
---|
223 | return dname;
|
---|
224 | }
|
---|
225 |
|
---|
226 | #ifdef DNS_COMPR_TESTING
|
---|
227 | /* gcc -Wall -DDNS_COMPR_TESTING domain_codec.c -o domain_codec && ./domain_codec */
|
---|
228 | int main(int argc, char **argv)
|
---|
229 | {
|
---|
230 | int len;
|
---|
231 | uint8_t *encoded;
|
---|
232 |
|
---|
233 | uint8_t str[6] = { 0x00, 0x00, 0x02, 0x65, 0x65, 0x00 };
|
---|
234 | printf("NUL:'%s'\n", dname_dec(str, 6, ""));
|
---|
235 |
|
---|
236 | #define DNAME_DEC(encoded,pre) dname_dec((uint8_t*)(encoded), sizeof(encoded), (pre))
|
---|
237 | printf("'%s'\n", DNAME_DEC("\4host\3com\0", "test1:"));
|
---|
238 | printf("test2:'%s'\n", DNAME_DEC("\4host\3com\0\4host\3com\0", ""));
|
---|
239 | printf("test3:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\0", ""));
|
---|
240 | printf("test4:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5", ""));
|
---|
241 | printf("test5:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5\1z\xC0\xA", ""));
|
---|
242 |
|
---|
243 | #define DNAME_ENC(cache,source,lenp) dname_enc((uint8_t*)(cache), sizeof(cache), (source), (lenp))
|
---|
244 | encoded = dname_enc(NULL, 0, "test.net", &len);
|
---|
245 | printf("test6:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
|
---|
246 | encoded = DNAME_ENC("\3net\0", "test.net", &len);
|
---|
247 | printf("test7:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
|
---|
248 | encoded = DNAME_ENC("\4test\3net\0", "test.net", &len);
|
---|
249 | printf("test8:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
|
---|
250 | return 0;
|
---|
251 | }
|
---|
252 | #endif
|
---|