slirp/dnssearch.c

   1 /*
   2  * Domain search option for DHCP (RFC 3397)
   3  *
   4  * Copyright (c) 2012 Klaus Stengel
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 #include "qemu/osdep.h"
  26 #include <glib.h>
  27 #include "slirp.h"
  28
  29 static const uint8_t RFC3397_OPT_DOMAIN_SEARCH = 119;
  30 static const uint8_t MAX_OPT_LEN = 255;
  31 static const uint8_t OPT_HEADER_LEN = 2;
  32 static const uint8_t REFERENCE_LEN = 2;
  33
  34 struct compact_domain;
  35
  36 typedef struct compact_domain {
  37     struct compact_domain *self;
  38     struct compact_domain *refdom;
  39     uint8_t *labels;
  40     size_t len;
  41     size_t common_octets;
  42 } CompactDomain;
  43
  44 static size_t
  45 domain_suffix_diffoff(const CompactDomain *a, const CompactDomain *b)
  46 {
  47     size_t la = a->len, lb = b->len;
  48     uint8_t *da = a->labels + la, *db = b->labels + lb;
  49     size_t i, lm = (la < lb) ? la : lb;
  50
  51     for (i = 0; i < lm; i++) {
  52         da--; db--;
  53         if (*da != *db) {
  54             break;
  55         }
  56     }
  57     return i;
  58 }
  59
  60 static int domain_suffix_ord(const void *cva, const void *cvb)
  61 {
  62     const CompactDomain *a = cva, *b = cvb;
  63     size_t la = a->len, lb = b->len;
  64     size_t doff = domain_suffix_diffoff(a, b);
  65     uint8_t ca = a->labels[la - doff];
  66     uint8_t cb = b->labels[lb - doff];
  67
  68     if (ca < cb) {
  69         return -1;
  70     }
  71     if (ca > cb) {
  72         return 1;
  73     }
  74     if (la < lb) {
  75         return -1;
  76     }
  77     if (la > lb) {
  78         return 1;
  79     }
  80     return 0;
  81 }
  82
  83 static size_t domain_common_label(CompactDomain *a, CompactDomain *b)
  84 {
  85     size_t res, doff = domain_suffix_diffoff(a, b);
  86     uint8_t *first_eq_pos = a->labels + (a->len - doff);
  87     uint8_t *label = a->labels;
  88
  89     while (*label && label < first_eq_pos) {
  90         label += *label + 1;
  91     }
  92     res = a->len - (label - a->labels);
  93     /* only report if it can help to reduce the packet size */
  94     return (res > REFERENCE_LEN) ? res : 0;
  95 }
  96
  97 static void domain_fixup_order(CompactDomain *cd, size_t n)
  98 {
  99     size_t i;
 100
 101     for (i = 0; i < n; i++) {
 102         CompactDomain *cur = cd + i, *next = cd[i].self;
 103
 104         while (!cur->common_octets) {
 105             CompactDomain *tmp = next->self; /* backup target value */
 106
 107             next->self = cur;
 108             cur->common_octets++;
 109
 110             cur = next;
 111             next = tmp;
 112         }
 113     }
 114 }
 115
 116 static void domain_mklabels(CompactDomain *cd, const char *input)
 117 {
 118     uint8_t *len_marker = cd->labels;
 119     uint8_t *output = len_marker; /* pre-incremented */
 120     const char *in = input;
 121     char cur_chr;
 122     size_t len = 0;
 123
 124     if (cd->len == 0) {
 125         goto fail;
 126     }
 127     cd->len++;
 128
 129     do {
 130         cur_chr = *in++;
 131         if (cur_chr == '.' || cur_chr == '\0') {
 132             len = output - len_marker;
 133             if ((len == 0 && cur_chr == '.') || len >= 64) {
 134                 goto fail;
 135             }
 136             *len_marker = len;
 137
 138             output++;
 139             len_marker = output;
 140         } else {
 141             output++;
 142             *output = cur_chr;
 143         }
 144     } while (cur_chr != '\0');
 145
 146     /* ensure proper zero-termination */
 147     if (len != 0) {
 148         *len_marker = 0;
 149         cd->len++;
 150     }
 151     return;
 152
 153 fail:
 154     g_warning("failed to parse domain name '%s'\n", input);
 155     cd->len = 0;
 156 }
 157
 158 static void
 159 domain_mkxrefs(CompactDomain *doms, CompactDomain *last, size_t depth)
 160 {
 161     CompactDomain *i = doms, *target = doms;
 162
 163     do {
 164         if (i->labels < target->labels) {
 165             target = i;
 166         }
 167     } while (i++ != last);
 168
 169     for (i = doms; i != last; i++) {
 170         CompactDomain *group_last;
 171         size_t next_depth;
 172
 173         if (i->common_octets == depth) {
 174             continue;
 175         }
 176
 177         next_depth = -1;
 178         for (group_last = i; group_last != last; group_last++) {
 179             size_t co = group_last->common_octets;
 180             if (co <= depth) {
 181                 break;
 182             }
 183             if (co < next_depth) {
 184                 next_depth = co;
 185             }
 186         }
 187         domain_mkxrefs(i, group_last, next_depth);
 188
 189         i = group_last;
 190         if (i == last) {
 191             break;
 192         }
 193     }
 194
 195     if (depth == 0) {
 196         return;
 197     }
 198
 199     i = doms;
 200     do {
 201         if (i != target && i->refdom == NULL) {
 202             i->refdom = target;
 203             i->common_octets = depth;
 204         }
 205     } while (i++ != last);
 206 }
 207
 208 static size_t domain_compactify(CompactDomain *domains, size_t n)
 209 {
 210     uint8_t *start = domains->self->labels, *outptr = start;
 211     size_t i;
 212
 213     for (i = 0; i < n; i++) {
 214         CompactDomain *cd = domains[i].self;
 215         CompactDomain *rd = cd->refdom;
 216
 217         if (rd != NULL) {
 218             size_t moff = (rd->labels - start)
 219                     + (rd->len - cd->common_octets);
 220             if (moff < 0x3FFFu) {
 221                 cd->len -= cd->common_octets - 2;
 222                 cd->labels[cd->len - 1] = moff & 0xFFu;
 223                 cd->labels[cd->len - 2] = 0xC0u | (moff >> 8);
 224             }
 225         }
 226
 227         if (cd->labels != outptr) {
 228             memmove(outptr, cd->labels, cd->len);
 229             cd->labels = outptr;
 230         }
 231         outptr += cd->len;
 232     }
 233     return outptr - start;
 234 }
 235
 236 int translate_dnssearch(Slirp *s, const char **names)
 237 {
 238     size_t blocks, bsrc_start, bsrc_end, bdst_start;
 239     size_t i, num_domains, memreq = 0;
 240     uint8_t *result = NULL, *outptr;
 241     CompactDomain *domains = NULL;
 242     const char **nameptr = names;
 243
 244     while (*nameptr != NULL) {
 245         nameptr++;
 246     }
 247
 248     num_domains = nameptr - names;
 249     if (num_domains == 0) {
 250         return -2;
 251     }
 252
 253     domains = g_malloc(num_domains * sizeof(*domains));
 254
 255     for (i = 0; i < num_domains; i++) {
 256         size_t nlen = strlen(names[i]);
 257         memreq += nlen + 2; /* 1 zero octet + 1 label length octet */
 258         domains[i].self = domains + i;
 259         domains[i].len = nlen;
 260         domains[i].common_octets = 0;
 261         domains[i].refdom = NULL;
 262     }
 263
 264     /* reserve extra 2 header bytes for each 255 bytes of output */
 265     memreq += ((memreq + MAX_OPT_LEN - 1) / MAX_OPT_LEN) * OPT_HEADER_LEN;
 266     result = g_malloc(memreq * sizeof(*result));
 267
 268     outptr = result;
 269     for (i = 0; i < num_domains; i++) {
 270         domains[i].labels = outptr;
 271         domain_mklabels(domains + i, names[i]);
 272         outptr += domains[i].len;
 273     }
 274
 275     if (outptr == result) {
 276         g_free(domains);
 277         g_free(result);
 278         return -1;
 279     }
 280
 281     qsort(domains, num_domains, sizeof(*domains), domain_suffix_ord);
 282     domain_fixup_order(domains, num_domains);
 283
 284     for (i = 1; i < num_domains; i++) {
 285         size_t cl = domain_common_label(domains + i - 1, domains + i);
 286         domains[i - 1].common_octets = cl;
 287     }
 288
 289     domain_mkxrefs(domains, domains + num_domains - 1, 0);
 290     memreq = domain_compactify(domains, num_domains);
 291
 292     blocks = (memreq + MAX_OPT_LEN - 1) / MAX_OPT_LEN;
 293     bsrc_end = memreq;
 294     bsrc_start = (blocks - 1) * MAX_OPT_LEN;
 295     bdst_start = bsrc_start + blocks * OPT_HEADER_LEN;
 296     memreq += blocks * OPT_HEADER_LEN;
 297
 298     while (blocks--) {
 299         size_t len = bsrc_end - bsrc_start;
 300         memmove(result + bdst_start, result + bsrc_start, len);
 301         result[bdst_start - 2] = RFC3397_OPT_DOMAIN_SEARCH;
 302         result[bdst_start - 1] = len;
 303         bsrc_end = bsrc_start;
 304         bsrc_start -= MAX_OPT_LEN;
 305         bdst_start -= MAX_OPT_LEN + OPT_HEADER_LEN;
 306     }
 307
 308     g_free(domains);
 309     s->vdnssearch = result;
 310     s->vdnssearch_len = memreq;
 311     return 0;
 312 }