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 _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