LXR busybox/networking/udhcp/domain

   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 */
  36char* 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 */
 111static 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 */
 152static 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
 190uint8_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 */
 226int 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