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 "slirp.h"
  27
  28 static const uint8_t RFC3397_OPT_DOMAIN_SEARCH = 119;
  29 static const uint8_t MAX_OPT_LEN = 255;
  30 static const uint8_t OPT_HEADER_LEN = 2;
  31 static const uint8_t REFERENCE_LEN = 2;
  32
  33 struct compact_domain;
  34
  35 typedef struct compact_domain {
  36     struct compact_domain *self;
  37     struct compact_domain *refdom;
  38     uint8_t *labels;
  39     size_t len;
  40     size_t common_octets;
  41 } CompactDomain;
  42
  43 static size_t
  44 domain_suffix_diffoff(const CompactDomain *a, const CompactDomain *b)
  45 {
  46     size_t la = a->len, lb = b->len;
  47     uint8_t *da = a->labels + la, *db = b->labels + lb;
  48     size_t i, lm = (la < lb) ? la : lb;
  49
  50     for (i = 0; i < lm; i++) {
  51         da--; db--;
  52         if (*da != *db) {
  53             break;
  54         }
  55     }
  56     return i;
  57 }
  58
  59 static int domain_suffix_ord(const void *cva, const void *cvb)
  60 {
  61     const CompactDomain *a = cva, *b = cvb;
  62     size_t la = a->len, lb = b->len;
  63     size_t doff = domain_suffix_diffoff(a, b);
  64     uint8_t ca = a->labels[la - doff];
  65     uint8_t cb = b->labels[lb - doff];
  66
  67     if (ca < cb) {
  68         return -1;
  69     }
  70     if (ca > cb) {
  71         return 1;
  72     }
  73     if (la < lb) {
  74         return -1;
  75     }
  76     if (la > lb) {
  77         return 1;
  78     }
  79     return 0;
  80 }
  81
  82 static size_t domain_common_label(CompactDomain *a, CompactDomain *b)
  83 {
  84     size_t res, doff = domain_suffix_diffoff(a, b);
  85     uint8_t *first_eq_pos = a->labels + (a->len - doff);
  86     uint8_t *label = a->labels;
  87
  88     while (*label && label < first_eq_pos) {
  89         label += *label + 1;
  90     }
  91     res = a->len - (label - a->labels);
  92     /* only report if it can help to reduce the packet size */
  93     return (res > REFERENCE_LEN) ? res : 0;
  94 }
  95
  96 static void domain_fixup_order(CompactDomain *cd, size_t n)
  97 {
  98     size_t i;
  99
 100     for (i = 0; i < n; i++) {
 101         CompactDomain *cur = cd + i, *next = cd[i].self;
 102
 103         while (!cur->common_octets) {
 104             CompactDomain *tmp = next->self; /* backup target value */
 105
 106             next->self = cur;
 107             cur->common_octets++;
 108
 109             cur = next;
 110             next = tmp;
 111         }
 112     }
 113 }
 114
 115 static void domain_mklabels(CompactDomain *cd, const char *input)
 116 {
 117     uint8_t *len_marker = cd->labels;
 118     uint8_t *output = len_marker; /* pre-incremented */
 119     const char *in = input;
 120     char cur_chr;
 121     size_t len = 0;
 122
 123     if (cd->len == 0) {
 124         goto fail;
 125     }
 126     cd->len++;
 127
 128     do {
 129         cur_chr = *in++;
 130         if (cur_chr == '.' || cur_chr == '\0') {
 131             len = output - len_marker;
 132             if ((len == 0 && cur_chr == '.') || len >= 64) {
 133                 goto fail;
 134             }
 135             *len_marker = len;
 136
 137             output++;
 138             len_marker = output;
 139         } else {
 140             output++;
 141             *output = cur_chr;
 142         }
 143     } while (cur_chr != '\0');
 144
 145     /* ensure proper zero-termination */
 146     if (len != 0) {
 147         *len_marker = 0;
 148         cd->len++;
 149     }
 150     return;
 151
 152 fail:
 153     g_warning("failed to parse domain name '%s'\n", input);
 154     cd->len = 0;
 155 }
 156
 157 static void
 158 domain_mkxrefs(CompactDomain *doms, CompactDomain *last, size_t depth)
 159 {
 160     CompactDomain *i = doms, *target = doms;
 161
 162     do {
 163         if (i->labels < target->labels) {
 164             target = i;
 165         }
 166     } while (i++ != last);
 167
 168     for (i = doms; i != last; i++) {
 169         CompactDomain *group_last;
 170         size_t next_depth;
 171
 172         if (i->common_octets == depth) {
 173             continue;
 174         }
 175
 176         next_depth = -1;
 177         for (group_last = i; group_last != last; group_last++) {
 178             size_t co = group_last->common_octets;
 179             if (co <= depth) {
 180                 break;
 181             }
 182             if (co < next_depth) {
 183                 next_depth = co;
 184             }
 185         }
 186         domain_mkxrefs(i, group_last, next_depth);
 187
 188         i = group_last;
 189         if (i == last) {
 190             break;
 191         }
 192     }
 193
 194     if (depth == 0) {
 195         return;
 196     }
 197
 198     i = doms;
 199     do {
 200         if (i != target && i->refdom == NULL) {
 201             i->refdom = target;
 202             i->common_octets = depth;
 203         }
 204     } while (i++ != last);
 205 }
 206
 207 static size_t domain_compactify(CompactDomain *domains, size_t n)
 208 {
 209     uint8_t *start = domains->self->labels, *outptr = start;
 210     size_t i;
 211
 212     for (i = 0; i < n; i++) {
 213         CompactDomain *cd = domains[i].self;
 214         CompactDomain *rd = cd->refdom;
 215
 216         if (rd != NULL) {
 217             size_t moff = (rd->labels - start)
 218                     + (rd->len - cd->common_octets);
 219             if (moff < 0x3FFFu) {
 220                 cd->len -= cd->common_octets - 2;
 221                 cd->labels[cd->len - 1] = moff & 0xFFu;
 222                 cd->labels[cd->len - 2] = 0xC0u | (moff >> 8);
 223             }
 224         }
 225
 226         if (cd->labels != outptr) {
 227             memmove(outptr, cd->labels, cd->len);
 228             cd->labels = outptr;
 229         }
 230         outptr += cd->len;
 231     }
 232     return outptr - start;
 233 }
 234
 235 int translate_dnssearch(Slirp *s, const char **names)
 236 {
 237     size_t blocks, bsrc_start, bsrc_end, bdst_start;
 238     size_t i, num_domains, memreq = 0;
 239     uint8_t *result = NULL, *outptr;
 240     CompactDomain *domains = NULL;
 241     const char **nameptr = names;
 242
 243     while (*nameptr != NULL) {
 244         nameptr++;
 245     }
 246
 247     num_domains = nameptr - names;
 248     if (num_domains == 0) {
 249         return -2;
 250     }
 251
 252     domains = g_malloc(num_domains * sizeof(*domains));
 253
 254     for (i = 0; i < num_domains; i++) {
 255         size_t nlen = strlen(names[i]);
 256         memreq += nlen + 2; /* 1 zero octet + 1 label length octet */
 257         domains[i].self = domains + i;
 258         domains[i].len = nlen;
 259         domains[i].common_octets = 0;
 260         domains[i].refdom = NULL;
 261     }
 262
 263     /* reserve extra 2 header bytes for each 255 bytes of output */
 264     memreq += DIV_ROUND_UP(memreq, MAX_OPT_LEN) * OPT_HEADER_LEN;
 265     result = g_malloc(memreq * sizeof(*result));
 266
 267     outptr = result;
 268     for (i = 0; i < num_domains; i++) {
 269         domains[i].labels = outptr;
 270         domain_mklabels(domains + i, names[i]);
 271         outptr += domains[i].len;
 272     }
 273
 274     if (outptr == result) {
 275         g_free(domains);
 276         g_free(result);
 277         return -1;
 278     }
 279
 280     qsort(domains, num_domains, sizeof(*domains), domain_suffix_ord);
 281     domain_fixup_order(domains, num_domains);
 282
 283     for (i = 1; i < num_domains; i++) {
 284         size_t cl = domain_common_label(domains + i - 1, domains + i);
 285         domains[i - 1].common_octets = cl;
 286     }
 287
 288     domain_mkxrefs(domains, domains + num_domains - 1, 0);
 289     memreq = domain_compactify(domains, num_domains);
 290
 291     blocks = DIV_ROUND_UP(memreq, MAX_OPT_LEN);
 292     bsrc_end = memreq;
 293     bsrc_start = (blocks - 1) * MAX_OPT_LEN;
 294     bdst_start = bsrc_start + blocks * OPT_HEADER_LEN;
 295     memreq += blocks * OPT_HEADER_LEN;
 296
 297     while (blocks--) {
 298         size_t len = bsrc_end - bsrc_start;
 299         memmove(result + bdst_start, result + bsrc_start, len);
 300         result[bdst_start - 2] = RFC3397_OPT_DOMAIN_SEARCH;
 301         result[bdst_start - 1] = len;
 302         bsrc_end = bsrc_start;
 303         bsrc_start -= MAX_OPT_LEN;
 304         bdst_start -= MAX_OPT_LEN + OPT_HEADER_LEN;
 305     }
 306
 307     g_free(domains);
 308     s->vdnssearch = result;
 309     s->vdnssearch_len = memreq;
 310     return 0;
 311 }