net/dns/dns_response.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/dns/dns_response.h"
   6
   7 #include "base/string_util.h"
   8 #include "base/sys_byteorder.h"
   9 #include "net/base/address_list.h"
  10 #include "net/base/big_endian.h"
  11 #include "net/base/dns_util.h"
  12 #include "net/base/io_buffer.h"
  13 #include "net/base/net_errors.h"
  14 #include "net/dns/dns_protocol.h"
  15 #include "net/dns/dns_query.h"
  16
  17 namespace net {
  18
  19 DnsResourceRecord::DnsResourceRecord() {
  20 }
  21
  22 DnsResourceRecord::~DnsResourceRecord() {
  23 }
  24
  25 DnsRecordParser::DnsRecordParser() : packet_(NULL), length_(0), cur_(0) {
  26 }
  27
  28 DnsRecordParser::DnsRecordParser(const void* packet,
  29                                  size_t length,
  30                                  size_t offset)
  31     : packet_(reinterpret_cast<const char*>(packet)),
  32       length_(length),
  33       cur_(packet_ + offset) {
  34   DCHECK_LE(offset, length);
  35 }
  36
  37 unsigned DnsRecordParser::ReadName(const void* const vpos,
  38                                    std::string* out) const {
  39   const char* const pos = reinterpret_cast<const char*>(vpos);
  40   DCHECK(packet_);
  41   DCHECK_LE(packet_, pos);
  42   DCHECK_LE(pos, packet_ + length_);
  43
  44   const char* p = pos;
  45   const char* end = packet_ + length_;
  46   // Count number of seen bytes to detect loops.
  47   unsigned seen = 0;
  48   // Remember how many bytes were consumed before first jump.
  49   unsigned consumed = 0;
  50
  51   if (pos >= end)
  52     return 0;
  53
  54   if (out) {
  55     out->clear();
  56     out->reserve(dns_protocol::kMaxNameLength);
  57   }
  58
  59   for (;;) {
  60     // The first two bits of the length give the type of the length. It's
  61     // either a direct length or a pointer to the remainder of the name.
  62     switch (*p & dns_protocol::kLabelMask) {
  63       case dns_protocol::kLabelPointer: {
  64         if (p + sizeof(uint16) > end)
  65           return 0;
  66         if (consumed == 0) {
  67           consumed = p - pos + sizeof(uint16);
  68           if (!out)
  69             return consumed;  // If name is not stored, that's all we need.
  70         }
  71         seen += sizeof(uint16);
  72         // If seen the whole packet, then we must be in a loop.
  73         if (seen > length_)
  74           return 0;
  75         uint16 offset;
  76         ReadBigEndian<uint16>(p, &offset);
  77         offset &= dns_protocol::kOffsetMask;
  78         p = packet_ + offset;
  79         if (p >= end)
  80           return 0;
  81         break;
  82       }
  83       case dns_protocol::kLabelDirect: {
  84         uint8 label_len = *p;
  85         ++p;
  86         // Note: root domain (".") is NOT included.
  87         if (label_len == 0) {
  88           if (consumed == 0) {
  89             consumed = p - pos;
  90           }  // else we set |consumed| before first jump
  91           return consumed;
  92         }
  93         if (p + label_len >= end)
  94           return 0;  // Truncated or missing label.
  95         if (out) {
  96           if (!out->empty())
  97             out->append(".");
  98           out->append(p, label_len);
  99         }
 100         p += label_len;
 101         seen += 1 + label_len;
 102         break;
 103       }
 104       default:
 105         // unhandled label type
 106         return 0;
 107     }
 108   }
 109 }
 110
 111 bool DnsRecordParser::ReadRecord(DnsResourceRecord* out) {
 112   DCHECK(packet_);
 113   size_t consumed = ReadName(cur_, &out->name);
 114   if (!consumed)
 115     return false;
 116   BigEndianReader reader(cur_ + consumed,
 117                          packet_ + length_ - (cur_ + consumed));
 118   uint16 rdlen;
 119   if (reader.ReadU16(&out->type) &&
 120       reader.ReadU16(&out->klass) &&
 121       reader.ReadU32(&out->ttl) &&
 122       reader.ReadU16(&rdlen) &&
 123       reader.ReadPiece(&out->rdata, rdlen)) {
 124     cur_ = reader.ptr();
 125     return true;
 126   }
 127   return false;
 128 }
 129
 130 DnsResponse::DnsResponse()
 131     : io_buffer_(new IOBufferWithSize(dns_protocol::kMaxUDPSize + 1)) {
 132 }
 133
 134 DnsResponse::DnsResponse(size_t length)
 135     : io_buffer_(new IOBufferWithSize(length)) {
 136 }
 137
 138 DnsResponse::DnsResponse(const void* data,
 139                          size_t length,
 140                          size_t answer_offset)
 141     : io_buffer_(new IOBufferWithSize(length)),
 142       parser_(io_buffer_->data(), length, answer_offset) {
 143   DCHECK(data);
 144   memcpy(io_buffer_->data(), data, length);
 145 }
 146
 147 DnsResponse::~DnsResponse() {
 148 }
 149
 150 bool DnsResponse::InitParse(int nbytes, const DnsQuery& query) {
 151   // Response includes query, it should be at least that size.
 152   if (nbytes < query.io_buffer()->size() || nbytes >= io_buffer_->size())
 153     return false;
 154
 155   // Match the query id.
 156   if (base::NetToHost16(header()->id) != query.id())
 157     return false;
 158
 159   // Match question count.
 160   if (base::NetToHost16(header()->qdcount) != 1)
 161     return false;
 162
 163   // Match the question section.
 164   const size_t hdr_size = sizeof(dns_protocol::Header);
 165   const base::StringPiece question = query.question();
 166   if (question != base::StringPiece(io_buffer_->data() + hdr_size,
 167                                     question.size())) {
 168     return false;
 169   }
 170
 171   // Construct the parser.
 172   parser_ = DnsRecordParser(io_buffer_->data(),
 173                             nbytes,
 174                             hdr_size + question.size());
 175   return true;
 176 }
 177
 178 bool DnsResponse::IsValid() const {
 179   return parser_.IsValid();
 180 }
 181
 182 uint16 DnsResponse::flags() const {
 183   DCHECK(parser_.IsValid());
 184   return base::NetToHost16(header()->flags) & ~(dns_protocol::kRcodeMask);
 185 }
 186
 187 uint8 DnsResponse::rcode() const {
 188   DCHECK(parser_.IsValid());
 189   return base::NetToHost16(header()->flags) & dns_protocol::kRcodeMask;
 190 }
 191
 192 unsigned DnsResponse::answer_count() const {
 193   DCHECK(parser_.IsValid());
 194   return base::NetToHost16(header()->ancount);
 195 }
 196
 197 base::StringPiece DnsResponse::qname() const {
 198   DCHECK(parser_.IsValid());
 199   // The response is HEADER QNAME QTYPE QCLASS ANSWER.
 200   // |parser_| is positioned at the beginning of ANSWER, so the end of QNAME is
 201   // two uint16s before it.
 202   const size_t hdr_size = sizeof(dns_protocol::Header);
 203   const size_t qname_size = parser_.GetOffset() - 2 * sizeof(uint16) - hdr_size;
 204   return base::StringPiece(io_buffer_->data() + hdr_size, qname_size);
 205 }
 206
 207 uint16 DnsResponse::qtype() const {
 208   DCHECK(parser_.IsValid());
 209   // QTYPE starts where QNAME ends.
 210   const size_t type_offset = parser_.GetOffset() - 2 * sizeof(uint16);
 211   uint16 type;
 212   ReadBigEndian<uint16>(io_buffer_->data() + type_offset, &type);
 213   return type;
 214 }
 215
 216 std::string DnsResponse::GetDottedName() const {
 217   return DNSDomainToString(qname());
 218 }
 219
 220 DnsRecordParser DnsResponse::Parser() const {
 221   DCHECK(parser_.IsValid());
 222   // Return a copy of the parser.
 223   return parser_;
 224 }
 225
 226 const dns_protocol::Header* DnsResponse::header() const {
 227   return reinterpret_cast<const dns_protocol::Header*>(io_buffer_->data());
 228 }
 229
 230 DnsResponse::Result DnsResponse::ParseToAddressList(
 231     AddressList* addr_list,
 232     base::TimeDelta* ttl) const {
 233   DCHECK(IsValid());
 234   // DnsTransaction already verified that |response| matches the issued query.
 235   // We still need to determine if there is a valid chain of CNAMEs from the
 236   // query name to the RR owner name.
 237   // We err on the side of caution with the assumption that if we are too picky,
 238   // we can always fall back to the system getaddrinfo.
 239
 240   // Expected owner of record. No trailing dot.
 241   std::string expected_name = GetDottedName();
 242
 243   uint16 expected_type = qtype();
 244   DCHECK(expected_type == dns_protocol::kTypeA ||
 245          expected_type == dns_protocol::kTypeAAAA);
 246
 247   size_t expected_size = (expected_type == dns_protocol::kTypeAAAA)
 248       ? kIPv6AddressSize : kIPv4AddressSize;
 249
 250   uint32 ttl_sec = kuint32max;
 251   IPAddressList ip_addresses;
 252   DnsRecordParser parser = Parser();
 253   DnsResourceRecord record;
 254   unsigned ancount = answer_count();
 255   for (unsigned i = 0; i < ancount; ++i) {
 256     if (!parser.ReadRecord(&record))
 257       return DNS_MALFORMED_RESPONSE;
 258
 259     if (record.type == dns_protocol::kTypeCNAME) {
 260       // Following the CNAME chain, only if no addresses seen.
 261       if (!ip_addresses.empty())
 262         return DNS_CNAME_AFTER_ADDRESS;
 263
 264       if (base::strcasecmp(record.name.c_str(), expected_name.c_str()) != 0)
 265         return DNS_NAME_MISMATCH;
 266
 267       if (record.rdata.size() !=
 268           parser.ReadName(record.rdata.begin(), &expected_name))
 269         return DNS_MALFORMED_CNAME;
 270
 271       ttl_sec = std::min(ttl_sec, record.ttl);
 272     } else if (record.type == expected_type) {
 273       if (record.rdata.size() != expected_size)
 274         return DNS_SIZE_MISMATCH;
 275
 276       if (base::strcasecmp(record.name.c_str(), expected_name.c_str()) != 0)
 277         return DNS_NAME_MISMATCH;
 278
 279       ttl_sec = std::min(ttl_sec, record.ttl);
 280       ip_addresses.push_back(IPAddressNumber(record.rdata.begin(),
 281                                              record.rdata.end()));
 282     }
 283   }
 284
 285   // TODO(szym): Extract TTL for NODATA results. http://crbug.com/115051
 286
 287   // getcanonname in eglibc returns the first owner name of an A or AAAA RR.
 288   // If the response passed all the checks so far, then |expected_name| is it.
 289   *addr_list = AddressList::CreateFromIPAddressList(ip_addresses,
 290                                                     expected_name);
 291   *ttl = base::TimeDelta::FromSeconds(ttl_sec);
 292   return DNS_PARSE_OK;
 293 }
 294
 295 }  // namespace net