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/* udns_parse.c
raw DNS packet parsing routines
Copyright (C) 2005 Michael Tokarev <mjt@corpit.ru>
This file is part of UDNS library, an async DNS stub resolver.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library, in file named COPYING.LGPL; if not,
write to the Free Software Foundation, Inc., 59 Temple Place,
Suite 330, Boston, MA 02111-1307 USA
*/
#include <string.h>
#include <assert.h>
#include "udns.h"
dnscc_t *dns_skipdn(dnscc_t *cur, dnscc_t *end) {
unsigned c;
for(;;) {
if (cur >= end)
return NULL;
c = *cur++;
if (!c)
return cur;
if (c & 192) /* jump */
return cur + 1 >= end ? NULL : cur + 1;
cur += c;
}
}
int
dns_getdn(dnscc_t *pkt, dnscc_t **cur, dnscc_t *end,
register dnsc_t *dn, unsigned dnsiz) {
unsigned c;
dnscc_t *pp = *cur; /* current packet pointer */
dnsc_t *dp = dn; /* current dn pointer */
dnsc_t *const de /* end of the DN dest */
= dn + (dnsiz < DNS_MAXDN ? dnsiz : DNS_MAXDN);
dnscc_t *jump = NULL; /* ptr after first jump if any */
unsigned loop = 100; /* jump loop counter */
for(;;) { /* loop by labels */
if (pp >= end) /* reached end of packet? */
return -1;
c = *pp++; /* length of the label */
if (!c) { /* empty label: terminate */
if (dn >= de) /* can't fit terminator */
goto noroom;
*dp++ = 0;
/* return next pos: either after the first jump or current */
*cur = jump ? jump : pp;
return dp - dn;
}
if (c & 192) { /* jump */
if (pp >= end) /* eop instead of jump pos */
return -1;
if (!jump) jump = pp + 1; /* remember first jump */
else if (!--loop) return -1; /* too many jumps */
c = ((c & ~192) << 8) | *pp; /* new pos */
if (c < DNS_HSIZE) /* don't allow jump into the header */
return -1;
pp = pkt + c;
continue;
}
if (c > DNS_MAXLABEL) /* too long label? */
return -1;
if (pp + c > end) /* label does not fit in packet? */
return -1;
if (dp + c + 1 > de) /* if enouth room for the label */
goto noroom;
*dp++ = c; /* label length */
memcpy(dp, pp, c); /* and the label itself */
dp += c;
pp += c; /* advance to the next label */
}
noroom:
return dnsiz < DNS_MAXDN ? 0 : -1;
}
void dns_rewind(struct dns_parse *p, dnscc_t *qdn) {
p->dnsp_qdn = qdn;
p->dnsp_cur = p->dnsp_ans;
p->dnsp_rrl = dns_numan(p->dnsp_pkt);
p->dnsp_ttl = 0xffffffffu;
p->dnsp_nrr = 0;
}
void
dns_initparse(struct dns_parse *p, dnscc_t *qdn,
dnscc_t *pkt, dnscc_t *cur, dnscc_t *end) {
p->dnsp_pkt = pkt;
p->dnsp_end = end;
p->dnsp_rrl = dns_numan(pkt);
p->dnsp_qdn = qdn;
assert(cur + 4 <= end);
if ((p->dnsp_qtyp = dns_get16(cur+0)) == DNS_T_ANY) p->dnsp_qtyp = 0;
if ((p->dnsp_qcls = dns_get16(cur+2)) == DNS_C_ANY) p->dnsp_qcls = 0;
p->dnsp_cur = p->dnsp_ans = cur + 4;
p->dnsp_ttl = 0xffffffffu;
p->dnsp_nrr = 0;
}
int dns_nextrr(struct dns_parse *p, struct dns_rr *rr) {
dnscc_t *cur = p->dnsp_cur;
while(p->dnsp_rrl > 0) {
--p->dnsp_rrl;
if (dns_getdn(p->dnsp_pkt, &cur, p->dnsp_end,
rr->dnsrr_dn, sizeof(rr->dnsrr_dn)) <= 0)
return -1;
if (cur + 10 > p->dnsp_end)
return -1;
rr->dnsrr_typ = dns_get16(cur);
rr->dnsrr_cls = dns_get16(cur+2);
rr->dnsrr_ttl = dns_get32(cur+4);
rr->dnsrr_dsz = dns_get16(cur+8);
rr->dnsrr_dptr = cur = cur + 10;
rr->dnsrr_dend = cur = cur + rr->dnsrr_dsz;
if (cur > p->dnsp_end)
return -1;
if (p->dnsp_qdn && !dns_dnequal(p->dnsp_qdn, rr->dnsrr_dn))
continue;
if ((!p->dnsp_qcls || p->dnsp_qcls == rr->dnsrr_cls) &&
(!p->dnsp_qtyp || p->dnsp_qtyp == rr->dnsrr_typ)) {
p->dnsp_cur = cur;
++p->dnsp_nrr;
if (p->dnsp_ttl > rr->dnsrr_ttl) p->dnsp_ttl = rr->dnsrr_ttl;
return 1;
}
if (p->dnsp_qdn && rr->dnsrr_typ == DNS_T_CNAME && !p->dnsp_nrr) {
if (dns_getdn(p->dnsp_pkt, &rr->dnsrr_dptr, p->dnsp_end,
p->dnsp_dnbuf, sizeof(p->dnsp_dnbuf)) <= 0 ||
rr->dnsrr_dptr != rr->dnsrr_dend)
return -1;
p->dnsp_qdn = p->dnsp_dnbuf;
if (p->dnsp_ttl > rr->dnsrr_ttl) p->dnsp_ttl = rr->dnsrr_ttl;
}
}
p->dnsp_cur = cur;
return 0;
}
int dns_stdrr_size(const struct dns_parse *p) {
return
dns_dntop_size(p->dnsp_qdn) +
(p->dnsp_qdn == dns_payload(p->dnsp_pkt) ? 0 :
dns_dntop_size(dns_payload(p->dnsp_pkt)));
}
void *dns_stdrr_finish(struct dns_rr_null *ret, char *cp,
const struct dns_parse *p) {
cp += dns_dntop(p->dnsp_qdn, (ret->dnsn_cname = cp), DNS_MAXNAME);
if (p->dnsp_qdn == dns_payload(p->dnsp_pkt))
ret->dnsn_qname = ret->dnsn_cname;
else
dns_dntop(dns_payload(p->dnsp_pkt), (ret->dnsn_qname = cp), DNS_MAXNAME);
ret->dnsn_ttl = p->dnsp_ttl;
return ret;
}
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