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 # define xzalloc(s) calloc(s, 1)
14 # define xstrdup strdup
15 # define xrealloc realloc
16 # include <stdlib.h>
17 # include <stdint.h>
18 # include <string.h>
19 # include <stdio.h>
20 # include <ctype.h>
21 #else
22 # include "common.h"
23 #endif
24
25 #define NS_MAXDNAME 1025 /* max domain name length */
26 #define NS_MAXCDNAME 255 /* max compressed domain name length */
27 #define NS_MAXLABEL 63 /* max label length */
28 #define NS_MAXDNSRCH 6 /* max domains in search path */
29 #define NS_CMPRSFLGS 0xc0 /* name compression pointer flag */
30
31
32 /* Expand a RFC1035-compressed list of domain names "cstr", of length "clen";
33 * return a newly allocated string containing the space-separated domains,
34 * prefixed with the contents of string pre, or NULL if an error occurs.
35 */
dname_dec(const uint8_t * cstr,int clen,const char * pre)36 char* FAST_FUNC dname_dec(const uint8_t *cstr, int clen, const char *pre)
37 {
38 char *ret, *end;
39 unsigned len, crtpos, retpos, depth;
40
41 crtpos = retpos = depth = 0;
42 len = strlen(pre);
43 end = ret = xstrdup(pre);
44
45 /* Scan the string once, allocating new memory as needed */
46 while (crtpos < clen) {
47 const uint8_t *c;
48 c = cstr + crtpos;
49
50 if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) {
51 /* pointer */
52 if (crtpos + 2 > clen) /* no offset to jump to? abort */
53 goto error;
54 if (retpos == 0) /* toplevel? save return spot */
55 retpos = crtpos + 2;
56 depth++;
57 crtpos = ((c[0] << 8) | c[1]) & 0x3fff; /* jump */
58 } else if (*c) {
59 unsigned label_len;
60 /* label */
61 if (crtpos + *c + 1 > clen) /* label too long? abort */
62 goto error;
63 ret = xrealloc(ret, len + *c + 1);
64 /* \3com ---> "com." */
65 end = (char *)mempcpy(ret + len, c + 1, *c);
66 *end = '.';
67
68 label_len = *c + 1;
69 len += label_len;
70 crtpos += label_len;
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
82 if (len != 0) {
83 /* \4host\3com\0\4host and we are at \0:
84 * \3com was converted to "com.", change dot to space.
85 */
86 ret[len - 1] = ' ';
87 }
88 }
89
90 if (depth > NS_MAXDNSRCH /* too many jumps? abort, it's a loop */
91 || len > NS_MAXDNAME * NS_MAXDNSRCH /* result too long? abort */
92 ) {
93 goto error;
94 }
95 }
96
97 if (ret == end) { /* expanded string is empty? abort */
98 error:
99 free(ret);
100 return NULL;
101 }
102
103 *end = '\0';
104 return ret;
105 }
106
107 /* Convert a domain name (src) from human-readable "foo.BLAH.com" format into
108 * RFC1035 encoding "\003foo\004blah\003com\000". Return allocated string, or
109 * NULL if an error occurs.
110 */
convert_dname(const char * src,int * retlen)111 static uint8_t *convert_dname(const char *src, int *retlen)
112 {
113 uint8_t *res, *lenptr, *dst;
114
115 res = xzalloc(strlen(src) + 2);
116 dst = lenptr = res;
117 dst++;
118
119 for (;;) {
120 uint8_t c;
121 int len;
122
123 c = (uint8_t)*src++;
124 if (c == '.' || c == '\0') { /* end of label */
125 len = dst - lenptr - 1;
126 /* label too long, too short, or two '.'s in a row (len will be 0) */
127 if (len > NS_MAXLABEL || len == 0)
128 goto error;
129
130 *lenptr = len;
131 if (c == '\0' || *src == '\0') /* "" or ".": end of src */
132 break;
133 lenptr = dst++;
134 continue;
135 }
136 *dst++ = tolower(c);
137 }
138
139 *retlen = dst + 1 - res;
140 if (*retlen > NS_MAXCDNAME) { /* dname too long? abort */
141 error:
142 free(res);
143 *retlen = 0;
144 return NULL;
145 }
146
147 return res;
148 }
149
150 #if 0 //UNUSED
151 /* Returns the offset within cstr at which dname can be found, or -1 */
152 static int find_offset(const uint8_t *cstr, int clen, const uint8_t *dname)
153 {
154 const uint8_t *c, *d;
155 int off;
156
157 /* find all labels in cstr */
158 off = 0;
159 while (off < clen) {
160 c = cstr + off;
161
162 if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) { /* pointer, skip */
163 off += 2;
164 continue;
165 }
166 if (*c) { /* label, try matching dname */
167 d = dname;
168 while (1) {
169 unsigned len1 = *c + 1;
170 if (memcmp(c, d, len1) != 0)
171 break;
172 if (len1 == 1) /* at terminating NUL - match, return offset */
173 return off;
174 d += len1;
175 c += len1;
176 if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) /* pointer, jump */
177 c = cstr + (((c[0] & 0x3f) << 8) | c[1]);
178 }
179 off += cstr[off] + 1;
180 continue;
181 }
182 /* NUL, skip */
183 off++;
184 }
185
186 return -1;
187 }
188 #endif
189
dname_enc(const char * src,int * retlen)190 uint8_t* FAST_FUNC dname_enc(/*const uint8_t *cstr, int clen,*/ const char *src, int *retlen)
191 {
192 #if 0 //UNUSED, was intended for long, repetitive DHCP_DOMAIN_SEARCH options?
193 uint8_t *d, *dname;
194 /* Computes string to be appended to cstr so that src would be added to
195 * the compression (best case, it's a 2-byte pointer to some offset within
196 * cstr; worst case, it's all of src, converted to <4>host<3>com<0> format).
197 * The computed string is returned directly; its length is returned via retlen;
198 * NULL and 0, respectively, are returned if an error occurs.
199 */
200 dname = convert_dname(src, retlen);
201 if (dname == NULL) {
202 return NULL;
203 }
204
205 d = dname;
206 while (*d) {
207 if (cstr) {
208 int off = find_offset(cstr, clen, d);
209 if (off >= 0) { /* found a match, add pointer and return */
210 *d++ = NS_CMPRSFLGS | (off >> 8);
211 *d = off;
212 break;
213 }
214 }
215 d += *d + 1;
216 }
217
218 *retlen = d - dname + 1;
219 return dname;
220 #endif
221 return convert_dname(src, retlen);
222 }
223
224 #ifdef DNS_COMPR_TESTING
225 /* gcc -Wall -DDNS_COMPR_TESTING domain_codec.c -o domain_codec && ./domain_codec */
main(int argc,char ** argv)226 int main(int argc, char **argv)
227 {
228 int len;
229 uint8_t *encoded;
230
231 uint8_t str[6] = { 0x00, 0x00, 0x02, 0x65, 0x65, 0x00 };
232 printf("NUL:'%s'\n", dname_dec(str, 6, ""));
233
234 #define DNAME_DEC(encoded,pre) dname_dec((uint8_t*)(encoded), sizeof(encoded), (pre))
235 printf("'%s'\n", DNAME_DEC("\4host\3com\0", "test1:"));
236 printf("test2:'%s'\n", DNAME_DEC("\4host\3com\0\4host\3com\0", ""));
237 printf("test3:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\0", ""));
238 printf("test4:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5", ""));
239 printf("test5:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5\1z\xC0\xA", ""));
240
241 #if 0
242 #define DNAME_ENC(cache,source,lenp) dname_enc((uint8_t*)(cache), sizeof(cache), (source), (lenp))
243 encoded = dname_enc(NULL, 0, "test.net", &len);
244 printf("test6:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
245 encoded = DNAME_ENC("\3net\0", "test.net", &len);
246 printf("test7:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
247 encoded = DNAME_ENC("\4test\3net\0", "test.net", &len);
248 printf("test8:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
249 #endif
250
251 encoded = dname_enc("test.net", &len);
252 printf("test6:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
253 encoded = dname_enc("test.host.com", &len);
254 printf("test7:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
255
256 return 0;
257 }
258 #endif
259