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/*
* This file is part of PowerDNS or dnsdist.
* Copyright -- PowerDNS.COM B.V. and its contributors
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of version 2 of the GNU General Public License as
* published by the Free Software Foundation.
*
* In addition, for the avoidance of any doubt, permission is granted to
* link this program with OpenSSL and to (re)distribute the binaries
* produced as the result of such linking.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "dnsdist-dnsparser.hh"
#include "dnsparser.hh"
namespace dnsdist
{
DNSPacketOverlay::DNSPacketOverlay(const std::string_view& packet)
{
if (packet.size() < sizeof(dnsheader)) {
throw std::runtime_error("Packet is too small for a DNS packet");
}
memcpy(&d_header, packet.data(), sizeof(dnsheader));
uint64_t numRecords = ntohs(d_header.ancount) + ntohs(d_header.nscount) + ntohs(d_header.arcount);
d_records.reserve(numRecords);
try {
PacketReader reader(std::string_view(reinterpret_cast<const char*>(packet.data()), packet.size()));
for (uint16_t n = 0; n < ntohs(d_header.qdcount); ++n) {
reader.xfrName(d_qname);
reader.xfrType(d_qtype);
reader.xfrType(d_qclass);
}
for (uint64_t n = 0; n < numRecords; ++n) {
Record rec;
reader.xfrName(rec.d_name);
rec.d_place = n < ntohs(d_header.ancount) ? DNSResourceRecord::ANSWER : (n < (ntohs(d_header.ancount) + ntohs(d_header.nscount)) ? DNSResourceRecord::AUTHORITY : DNSResourceRecord::ADDITIONAL);
reader.xfrType(rec.d_type);
reader.xfrType(rec.d_class);
reader.xfr32BitInt(rec.d_ttl);
reader.xfr16BitInt(rec.d_contentLength);
rec.d_contentOffset = reader.getPosition();
reader.skip(rec.d_contentLength);
d_records.push_back(std::move(rec));
}
}
catch (const std::exception& e) {
throw std::runtime_error("Unable to parse DNS packet: " + std::string(e.what()));
}
catch (...) {
throw std::runtime_error("Unable to parse DNS packet");
}
}
bool changeNameInDNSPacket(PacketBuffer& initialPacket, const DNSName& from, const DNSName& to)
{
if (initialPacket.size() < sizeof(dnsheader)) {
return false;
}
PacketReader pr(std::string_view(reinterpret_cast<const char*>(initialPacket.data()), initialPacket.size()));
dnsheader dh;
memcpy(&dh, initialPacket.data(), sizeof(dh));
size_t idx = 0;
DNSName rrname;
uint16_t qdcount = ntohs(dh.qdcount);
uint16_t ancount = ntohs(dh.ancount);
uint16_t nscount = ntohs(dh.nscount);
uint16_t arcount = ntohs(dh.arcount);
uint16_t rrtype;
uint16_t rrclass;
string blob;
size_t recordsCount = ancount + nscount + arcount;
struct dnsrecordheader ah;
rrname = pr.getName();
if (rrname == from) {
rrname = to;
}
rrtype = pr.get16BitInt();
rrclass = pr.get16BitInt();
PacketBuffer newContent;
newContent.reserve(initialPacket.size());
GenericDNSPacketWriter<PacketBuffer> pw(newContent, rrname, rrtype, rrclass, dh.opcode);
/* we want to copy the flags and ID but not the counts since we recreate the records below */
pw.getHeader()->id = dh.id;
pw.getHeader()->qr = dh.qr;
pw.getHeader()->aa = dh.aa;
pw.getHeader()->tc = dh.tc;
pw.getHeader()->rd = dh.rd;
pw.getHeader()->ra = dh.ra;
pw.getHeader()->ad = dh.ad;
pw.getHeader()->cd = dh.cd;
pw.getHeader()->rcode = dh.rcode;
/* consume remaining qd if any, but do not copy it */
for (idx = 1; idx < qdcount; idx++) {
rrname = pr.getName();
(void)pr.get16BitInt();
(void)pr.get16BitInt();
}
static const std::unordered_set<QType> nameOnlyTypes{QType::NS, QType::PTR, QType::CNAME, QType::DNAME};
static const std::unordered_set<QType> noNameTypes{QType::A, QType::AAAA, QType::DHCID, QType::TXT, QType::OPT, QType::HINFO, QType::DNSKEY, QType::CDNSKEY, QType::DS, QType::CDS, QType::DLV, QType::SSHFP, QType::KEY, QType::CERT, QType::TLSA, QType::SMIMEA, QType::OPENPGPKEY, QType::NSEC, QType::NSEC3, QType::CSYNC, QType::NSEC3PARAM, QType::LOC, QType::NID, QType::L32, QType::L64, QType::EUI48, QType::EUI64, QType::URI, QType::CAA};
/* copy AN, NS and AR */
for (idx = 0; idx < recordsCount; idx++) {
rrname = pr.getName();
if (rrname == from) {
rrname = to;
}
pr.getDnsrecordheader(ah);
auto place = idx < ancount ? DNSResourceRecord::ANSWER : (idx < (ancount + nscount) ? DNSResourceRecord::AUTHORITY : DNSResourceRecord::ADDITIONAL);
pw.startRecord(rrname, ah.d_type, ah.d_ttl, ah.d_class, place, true);
if (nameOnlyTypes.count(ah.d_type)) {
rrname = pr.getName();
pw.xfrName(rrname);
}
else if (noNameTypes.count(ah.d_type)) {
pr.xfrBlob(blob);
pw.xfrBlob(blob);
}
else if (ah.d_type == QType::RRSIG) {
/* good luck */
pr.xfrBlob(blob);
pw.xfrBlob(blob);
}
else if (ah.d_type == QType::MX) {
auto prio = pr.get16BitInt();
rrname = pr.getName();
pw.xfr16BitInt(prio);
pw.xfrName(rrname);
}
else if (ah.d_type == QType::SOA) {
auto mname = pr.getName();
pw.xfrName(mname);
auto rname = pr.getName();
pw.xfrName(rname);
/* serial */
pw.xfr32BitInt(pr.get32BitInt());
/* refresh */
pw.xfr32BitInt(pr.get32BitInt());
/* retry */
pw.xfr32BitInt(pr.get32BitInt());
/* expire */
pw.xfr32BitInt(pr.get32BitInt());
/* minimal */
pw.xfr32BitInt(pr.get32BitInt());
}
else if (ah.d_type == QType::SRV) {
/* preference */
pw.xfr16BitInt(pr.get16BitInt());
/* weight */
pw.xfr16BitInt(pr.get16BitInt());
/* port */
pw.xfr16BitInt(pr.get16BitInt());
auto target = pr.getName();
pw.xfrName(target);
}
else {
/* sorry, unsafe type */
return false;
}
}
pw.commit();
initialPacket = std::move(newContent);
return true;
}
namespace PacketMangling
{
bool editDNSHeaderFromPacket(PacketBuffer& packet, const std::function<bool(dnsheader& header)>& editFunction)
{
if (packet.size() < sizeof(dnsheader)) {
throw std::runtime_error("Trying to edit the DNS header of a too small packet");
}
return editDNSHeaderFromRawPacket(packet.data(), editFunction);
}
bool editDNSHeaderFromRawPacket(void* packet, const std::function<bool(dnsheader& header)>& editFunction)
{
if (dnsheader_aligned::isMemoryAligned(packet)) {
// NOLINTNEXTLINE(cppcoreguidelines-pro-type-reinterpret-cast)
auto* header = reinterpret_cast<dnsheader*>(packet);
return editFunction(*header);
}
dnsheader header{};
memcpy(&header, packet, sizeof(header));
if (!editFunction(header)) {
return false;
}
memcpy(packet, &header, sizeof(header));
return true;
}
}
}
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