source: MondoRescue/branches/3.3/mindi-busybox/networking/udhcp/domain_codec.c@ 3621

Last change on this file since 3621 was 3621, checked in by Bruno Cornec, 7 years ago

New 3?3 banch for incorporation of latest busybox 1.25. Changing minor version to handle potential incompatibilities.
  • Property svn:eol-style set to native
File size: 6.9 KB
Line 
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 */
32char* 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 */
116static 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 */
155static 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 */
198uint8_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 */
228int 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
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