release/src/router/busybox/networking/udhcp/domain_codec.c

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