xemu/slirp/dnssearch.c

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/*
* Domain search option for DHCP (RFC 3397)
*
* Copyright (c) 2012 Klaus Stengel
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "qemu/osdep.h"
#include "slirp.h"
static const uint8_t RFC3397_OPT_DOMAIN_SEARCH = 119;
static const uint8_t MAX_OPT_LEN = 255;
static const uint8_t OPT_HEADER_LEN = 2;
static const uint8_t REFERENCE_LEN = 2;
struct compact_domain;
typedef struct compact_domain {
struct compact_domain *self;
struct compact_domain *refdom;
uint8_t *labels;
size_t len;
size_t common_octets;
} CompactDomain;
static size_t
domain_suffix_diffoff(const CompactDomain *a, const CompactDomain *b)
{
size_t la = a->len, lb = b->len;
uint8_t *da = a->labels + la, *db = b->labels + lb;
size_t i, lm = (la < lb) ? la : lb;
for (i = 0; i < lm; i++) {
da--; db--;
if (*da != *db) {
break;
}
}
return i;
}
static int domain_suffix_ord(const void *cva, const void *cvb)
{
const CompactDomain *a = cva, *b = cvb;
size_t la = a->len, lb = b->len;
size_t doff = domain_suffix_diffoff(a, b);
uint8_t ca = a->labels[la - doff];
uint8_t cb = b->labels[lb - doff];
if (ca < cb) {
return -1;
}
if (ca > cb) {
return 1;
}
if (la < lb) {
return -1;
}
if (la > lb) {
return 1;
}
return 0;
}
static size_t domain_common_label(CompactDomain *a, CompactDomain *b)
{
size_t res, doff = domain_suffix_diffoff(a, b);
uint8_t *first_eq_pos = a->labels + (a->len - doff);
uint8_t *label = a->labels;
while (*label && label < first_eq_pos) {
label += *label + 1;
}
res = a->len - (label - a->labels);
/* only report if it can help to reduce the packet size */
return (res > REFERENCE_LEN) ? res : 0;
}
static void domain_fixup_order(CompactDomain *cd, size_t n)
{
size_t i;
for (i = 0; i < n; i++) {
CompactDomain *cur = cd + i, *next = cd[i].self;
while (!cur->common_octets) {
CompactDomain *tmp = next->self; /* backup target value */
next->self = cur;
cur->common_octets++;
cur = next;
next = tmp;
}
}
}
static void domain_mklabels(CompactDomain *cd, const char *input)
{
uint8_t *len_marker = cd->labels;
uint8_t *output = len_marker; /* pre-incremented */
const char *in = input;
char cur_chr;
size_t len = 0;
if (cd->len == 0) {
goto fail;
}
cd->len++;
do {
cur_chr = *in++;
if (cur_chr == '.' || cur_chr == '\0') {
len = output - len_marker;
if ((len == 0 && cur_chr == '.') || len >= 64) {
goto fail;
}
*len_marker = len;
output++;
len_marker = output;
} else {
output++;
*output = cur_chr;
}
} while (cur_chr != '\0');
/* ensure proper zero-termination */
if (len != 0) {
*len_marker = 0;
cd->len++;
}
return;
fail:
g_warning("failed to parse domain name '%s'\n", input);
cd->len = 0;
}
static void
domain_mkxrefs(CompactDomain *doms, CompactDomain *last, size_t depth)
{
CompactDomain *i = doms, *target = doms;
do {
if (i->labels < target->labels) {
target = i;
}
} while (i++ != last);
for (i = doms; i != last; i++) {
CompactDomain *group_last;
size_t next_depth;
if (i->common_octets == depth) {
continue;
}
next_depth = -1;
for (group_last = i; group_last != last; group_last++) {
size_t co = group_last->common_octets;
if (co <= depth) {
break;
}
if (co < next_depth) {
next_depth = co;
}
}
domain_mkxrefs(i, group_last, next_depth);
i = group_last;
if (i == last) {
break;
}
}
if (depth == 0) {
return;
}
i = doms;
do {
if (i != target && i->refdom == NULL) {
i->refdom = target;
i->common_octets = depth;
}
} while (i++ != last);
}
static size_t domain_compactify(CompactDomain *domains, size_t n)
{
uint8_t *start = domains->self->labels, *outptr = start;
size_t i;
for (i = 0; i < n; i++) {
CompactDomain *cd = domains[i].self;
CompactDomain *rd = cd->refdom;
if (rd != NULL) {
size_t moff = (rd->labels - start)
+ (rd->len - cd->common_octets);
if (moff < 0x3FFFu) {
cd->len -= cd->common_octets - 2;
cd->labels[cd->len - 1] = moff & 0xFFu;
cd->labels[cd->len - 2] = 0xC0u | (moff >> 8);
}
}
if (cd->labels != outptr) {
memmove(outptr, cd->labels, cd->len);
cd->labels = outptr;
}
outptr += cd->len;
}
return outptr - start;
}
int translate_dnssearch(Slirp *s, const char **names)
{
size_t blocks, bsrc_start, bsrc_end, bdst_start;
size_t i, num_domains, memreq = 0;
uint8_t *result = NULL, *outptr;
CompactDomain *domains = NULL;
const char **nameptr = names;
while (*nameptr != NULL) {
nameptr++;
}
num_domains = nameptr - names;
if (num_domains == 0) {
return -2;
}
domains = g_malloc(num_domains * sizeof(*domains));
for (i = 0; i < num_domains; i++) {
size_t nlen = strlen(names[i]);
memreq += nlen + 2; /* 1 zero octet + 1 label length octet */
domains[i].self = domains + i;
domains[i].len = nlen;
domains[i].common_octets = 0;
domains[i].refdom = NULL;
}
/* reserve extra 2 header bytes for each 255 bytes of output */
memreq += DIV_ROUND_UP(memreq, MAX_OPT_LEN) * OPT_HEADER_LEN;
result = g_malloc(memreq * sizeof(*result));
outptr = result;
for (i = 0; i < num_domains; i++) {
domains[i].labels = outptr;
domain_mklabels(domains + i, names[i]);
outptr += domains[i].len;
}
if (outptr == result) {
g_free(domains);
g_free(result);
return -1;
}
qsort(domains, num_domains, sizeof(*domains), domain_suffix_ord);
domain_fixup_order(domains, num_domains);
for (i = 1; i < num_domains; i++) {
size_t cl = domain_common_label(domains + i - 1, domains + i);
domains[i - 1].common_octets = cl;
}
domain_mkxrefs(domains, domains + num_domains - 1, 0);
memreq = domain_compactify(domains, num_domains);
blocks = DIV_ROUND_UP(memreq, MAX_OPT_LEN);
bsrc_end = memreq;
bsrc_start = (blocks - 1) * MAX_OPT_LEN;
bdst_start = bsrc_start + blocks * OPT_HEADER_LEN;
memreq += blocks * OPT_HEADER_LEN;
while (blocks--) {
size_t len = bsrc_end - bsrc_start;
memmove(result + bdst_start, result + bsrc_start, len);
result[bdst_start - 2] = RFC3397_OPT_DOMAIN_SEARCH;
result[bdst_start - 1] = len;
bsrc_end = bsrc_start;
bsrc_start -= MAX_OPT_LEN;
bdst_start -= MAX_OPT_LEN + OPT_HEADER_LEN;
}
g_free(domains);
s->vdnssearch = result;
s->vdnssearch_len = memreq;
return 0;
}