| /* |
| * Copyright (C) 2016 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #include "dns_responder.h" |
| |
| #include <arpa/inet.h> |
| #include <fcntl.h> |
| #include <netdb.h> |
| #include <stdarg.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <sys/epoll.h> |
| #include <sys/socket.h> |
| #include <sys/types.h> |
| #include <unistd.h> |
| |
| #include <iostream> |
| #include <vector> |
| |
| #include <log/log.h> |
| |
| namespace test { |
| |
| std::string errno2str() { |
| char error_msg[512] = { 0 }; |
| if (strerror_r(errno, error_msg, sizeof(error_msg))) |
| return std::string(); |
| return std::string(error_msg); |
| } |
| |
| #define APLOGI(fmt, ...) ALOGI(fmt ": [%d] %s", __VA_ARGS__, errno, errno2str().c_str()) |
| |
| std::string str2hex(const char* buffer, size_t len) { |
| std::string str(len*2, '\0'); |
| for (size_t i = 0 ; i < len ; ++i) { |
| static const char* hex = "0123456789ABCDEF"; |
| uint8_t c = buffer[i]; |
| str[i*2] = hex[c >> 4]; |
| str[i*2 + 1] = hex[c & 0x0F]; |
| } |
| return str; |
| } |
| |
| std::string addr2str(const sockaddr* sa, socklen_t sa_len) { |
| char host_str[NI_MAXHOST] = { 0 }; |
| int rv = getnameinfo(sa, sa_len, host_str, sizeof(host_str), nullptr, 0, |
| NI_NUMERICHOST); |
| if (rv == 0) return std::string(host_str); |
| return std::string(); |
| } |
| |
| /* DNS struct helpers */ |
| |
| const char* dnstype2str(unsigned dnstype) { |
| static std::unordered_map<unsigned, const char*> kTypeStrs = { |
| { ns_type::ns_t_a, "A" }, |
| { ns_type::ns_t_ns, "NS" }, |
| { ns_type::ns_t_md, "MD" }, |
| { ns_type::ns_t_mf, "MF" }, |
| { ns_type::ns_t_cname, "CNAME" }, |
| { ns_type::ns_t_soa, "SOA" }, |
| { ns_type::ns_t_mb, "MB" }, |
| { ns_type::ns_t_mb, "MG" }, |
| { ns_type::ns_t_mr, "MR" }, |
| { ns_type::ns_t_null, "NULL" }, |
| { ns_type::ns_t_wks, "WKS" }, |
| { ns_type::ns_t_ptr, "PTR" }, |
| { ns_type::ns_t_hinfo, "HINFO" }, |
| { ns_type::ns_t_minfo, "MINFO" }, |
| { ns_type::ns_t_mx, "MX" }, |
| { ns_type::ns_t_txt, "TXT" }, |
| { ns_type::ns_t_rp, "RP" }, |
| { ns_type::ns_t_afsdb, "AFSDB" }, |
| { ns_type::ns_t_x25, "X25" }, |
| { ns_type::ns_t_isdn, "ISDN" }, |
| { ns_type::ns_t_rt, "RT" }, |
| { ns_type::ns_t_nsap, "NSAP" }, |
| { ns_type::ns_t_nsap_ptr, "NSAP-PTR" }, |
| { ns_type::ns_t_sig, "SIG" }, |
| { ns_type::ns_t_key, "KEY" }, |
| { ns_type::ns_t_px, "PX" }, |
| { ns_type::ns_t_gpos, "GPOS" }, |
| { ns_type::ns_t_aaaa, "AAAA" }, |
| { ns_type::ns_t_loc, "LOC" }, |
| { ns_type::ns_t_nxt, "NXT" }, |
| { ns_type::ns_t_eid, "EID" }, |
| { ns_type::ns_t_nimloc, "NIMLOC" }, |
| { ns_type::ns_t_srv, "SRV" }, |
| { ns_type::ns_t_naptr, "NAPTR" }, |
| { ns_type::ns_t_kx, "KX" }, |
| { ns_type::ns_t_cert, "CERT" }, |
| { ns_type::ns_t_a6, "A6" }, |
| { ns_type::ns_t_dname, "DNAME" }, |
| { ns_type::ns_t_sink, "SINK" }, |
| { ns_type::ns_t_opt, "OPT" }, |
| { ns_type::ns_t_apl, "APL" }, |
| { ns_type::ns_t_tkey, "TKEY" }, |
| { ns_type::ns_t_tsig, "TSIG" }, |
| { ns_type::ns_t_ixfr, "IXFR" }, |
| { ns_type::ns_t_axfr, "AXFR" }, |
| { ns_type::ns_t_mailb, "MAILB" }, |
| { ns_type::ns_t_maila, "MAILA" }, |
| { ns_type::ns_t_any, "ANY" }, |
| { ns_type::ns_t_zxfr, "ZXFR" }, |
| }; |
| auto it = kTypeStrs.find(dnstype); |
| static const char* kUnknownStr{ "UNKNOWN" }; |
| if (it == kTypeStrs.end()) return kUnknownStr; |
| return it->second; |
| } |
| |
| const char* dnsclass2str(unsigned dnsclass) { |
| static std::unordered_map<unsigned, const char*> kClassStrs = { |
| { ns_class::ns_c_in , "Internet" }, |
| { 2, "CSNet" }, |
| { ns_class::ns_c_chaos, "ChaosNet" }, |
| { ns_class::ns_c_hs, "Hesiod" }, |
| { ns_class::ns_c_none, "none" }, |
| { ns_class::ns_c_any, "any" } |
| }; |
| auto it = kClassStrs.find(dnsclass); |
| static const char* kUnknownStr{ "UNKNOWN" }; |
| if (it == kClassStrs.end()) return kUnknownStr; |
| return it->second; |
| return "unknown"; |
| } |
| |
| struct DNSName { |
| std::string name; |
| const char* read(const char* buffer, const char* buffer_end); |
| char* write(char* buffer, const char* buffer_end) const; |
| const char* toString() const; |
| private: |
| const char* parseField(const char* buffer, const char* buffer_end, |
| bool* last); |
| }; |
| |
| const char* DNSName::toString() const { |
| return name.c_str(); |
| } |
| |
| const char* DNSName::read(const char* buffer, const char* buffer_end) { |
| const char* cur = buffer; |
| bool last = false; |
| do { |
| cur = parseField(cur, buffer_end, &last); |
| if (cur == nullptr) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| } while (!last); |
| return cur; |
| } |
| |
| char* DNSName::write(char* buffer, const char* buffer_end) const { |
| char* buffer_cur = buffer; |
| for (size_t pos = 0 ; pos < name.size() ; ) { |
| size_t dot_pos = name.find('.', pos); |
| if (dot_pos == std::string::npos) { |
| // Sanity check, should never happen unless parseField is broken. |
| ALOGI("logic error: all names are expected to end with a '.'"); |
| return nullptr; |
| } |
| size_t len = dot_pos - pos; |
| if (len >= 256) { |
| ALOGI("name component '%s' is %zu long, but max is 255", |
| name.substr(pos, dot_pos - pos).c_str(), len); |
| return nullptr; |
| } |
| if (buffer_cur + sizeof(uint8_t) + len > buffer_end) { |
| ALOGI("buffer overflow at line %d", __LINE__); |
| return nullptr; |
| } |
| *buffer_cur++ = len; |
| buffer_cur = std::copy(std::next(name.begin(), pos), |
| std::next(name.begin(), dot_pos), |
| buffer_cur); |
| pos = dot_pos + 1; |
| } |
| // Write final zero. |
| *buffer_cur++ = 0; |
| return buffer_cur; |
| } |
| |
| const char* DNSName::parseField(const char* buffer, const char* buffer_end, |
| bool* last) { |
| if (buffer + sizeof(uint8_t) > buffer_end) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| unsigned field_type = *buffer >> 6; |
| unsigned ofs = *buffer & 0x3F; |
| const char* cur = buffer + sizeof(uint8_t); |
| if (field_type == 0) { |
| // length + name component |
| if (ofs == 0) { |
| *last = true; |
| return cur; |
| } |
| if (cur + ofs > buffer_end) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| name.append(cur, ofs); |
| name.push_back('.'); |
| return cur + ofs; |
| } else if (field_type == 3) { |
| ALOGI("name compression not implemented"); |
| return nullptr; |
| } |
| ALOGI("invalid name field type"); |
| return nullptr; |
| } |
| |
| struct DNSQuestion { |
| DNSName qname; |
| unsigned qtype; |
| unsigned qclass; |
| const char* read(const char* buffer, const char* buffer_end); |
| char* write(char* buffer, const char* buffer_end) const; |
| std::string toString() const; |
| }; |
| |
| const char* DNSQuestion::read(const char* buffer, const char* buffer_end) { |
| const char* cur = qname.read(buffer, buffer_end); |
| if (cur == nullptr) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| if (cur + 2*sizeof(uint16_t) > buffer_end) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| qtype = ntohs(*reinterpret_cast<const uint16_t*>(cur)); |
| qclass = ntohs(*reinterpret_cast<const uint16_t*>(cur + sizeof(uint16_t))); |
| return cur + 2*sizeof(uint16_t); |
| } |
| |
| char* DNSQuestion::write(char* buffer, const char* buffer_end) const { |
| char* buffer_cur = qname.write(buffer, buffer_end); |
| if (buffer_cur == nullptr) return nullptr; |
| if (buffer_cur + 2*sizeof(uint16_t) > buffer_end) { |
| ALOGI("buffer overflow on line %d", __LINE__); |
| return nullptr; |
| } |
| *reinterpret_cast<uint16_t*>(buffer_cur) = htons(qtype); |
| *reinterpret_cast<uint16_t*>(buffer_cur + sizeof(uint16_t)) = |
| htons(qclass); |
| return buffer_cur + 2*sizeof(uint16_t); |
| } |
| |
| std::string DNSQuestion::toString() const { |
| char buffer[4096]; |
| int len = snprintf(buffer, sizeof(buffer), "Q<%s,%s,%s>", qname.toString(), |
| dnstype2str(qtype), dnsclass2str(qclass)); |
| return std::string(buffer, len); |
| } |
| |
| struct DNSRecord { |
| DNSName name; |
| unsigned rtype; |
| unsigned rclass; |
| unsigned ttl; |
| std::vector<char> rdata; |
| const char* read(const char* buffer, const char* buffer_end); |
| char* write(char* buffer, const char* buffer_end) const; |
| std::string toString() const; |
| private: |
| struct IntFields { |
| uint16_t rtype; |
| uint16_t rclass; |
| uint32_t ttl; |
| uint16_t rdlen; |
| } __attribute__((__packed__)); |
| |
| const char* readIntFields(const char* buffer, const char* buffer_end, |
| unsigned* rdlen); |
| char* writeIntFields(unsigned rdlen, char* buffer, |
| const char* buffer_end) const; |
| }; |
| |
| const char* DNSRecord::read(const char* buffer, const char* buffer_end) { |
| const char* cur = name.read(buffer, buffer_end); |
| if (cur == nullptr) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| unsigned rdlen = 0; |
| cur = readIntFields(cur, buffer_end, &rdlen); |
| if (cur == nullptr) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| if (cur + rdlen > buffer_end) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| rdata.assign(cur, cur + rdlen); |
| return cur + rdlen; |
| } |
| |
| char* DNSRecord::write(char* buffer, const char* buffer_end) const { |
| char* buffer_cur = name.write(buffer, buffer_end); |
| if (buffer_cur == nullptr) return nullptr; |
| buffer_cur = writeIntFields(rdata.size(), buffer_cur, buffer_end); |
| if (buffer_cur == nullptr) return nullptr; |
| if (buffer_cur + rdata.size() > buffer_end) { |
| ALOGI("buffer overflow on line %d", __LINE__); |
| return nullptr; |
| } |
| return std::copy(rdata.begin(), rdata.end(), buffer_cur); |
| } |
| |
| std::string DNSRecord::toString() const { |
| char buffer[4096]; |
| int len = snprintf(buffer, sizeof(buffer), "R<%s,%s,%s>", name.toString(), |
| dnstype2str(rtype), dnsclass2str(rclass)); |
| return std::string(buffer, len); |
| } |
| |
| const char* DNSRecord::readIntFields(const char* buffer, const char* buffer_end, |
| unsigned* rdlen) { |
| if (buffer + sizeof(IntFields) > buffer_end ) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| const auto& intfields = *reinterpret_cast<const IntFields*>(buffer); |
| rtype = ntohs(intfields.rtype); |
| rclass = ntohs(intfields.rclass); |
| ttl = ntohl(intfields.ttl); |
| *rdlen = ntohs(intfields.rdlen); |
| return buffer + sizeof(IntFields); |
| } |
| |
| char* DNSRecord::writeIntFields(unsigned rdlen, char* buffer, |
| const char* buffer_end) const { |
| if (buffer + sizeof(IntFields) > buffer_end ) { |
| ALOGI("buffer overflow on line %d", __LINE__); |
| return nullptr; |
| } |
| auto& intfields = *reinterpret_cast<IntFields*>(buffer); |
| intfields.rtype = htons(rtype); |
| intfields.rclass = htons(rclass); |
| intfields.ttl = htonl(ttl); |
| intfields.rdlen = htons(rdlen); |
| return buffer + sizeof(IntFields); |
| } |
| |
| struct DNSHeader { |
| unsigned id; |
| bool ra; |
| uint8_t rcode; |
| bool qr; |
| uint8_t opcode; |
| bool aa; |
| bool tr; |
| bool rd; |
| std::vector<DNSQuestion> questions; |
| std::vector<DNSRecord> answers; |
| std::vector<DNSRecord> authorities; |
| std::vector<DNSRecord> additionals; |
| const char* read(const char* buffer, const char* buffer_end); |
| char* write(char* buffer, const char* buffer_end) const; |
| std::string toString() const; |
| |
| private: |
| struct Header { |
| uint16_t id; |
| uint8_t flags0; |
| uint8_t flags1; |
| uint16_t qdcount; |
| uint16_t ancount; |
| uint16_t nscount; |
| uint16_t arcount; |
| } __attribute__((__packed__)); |
| |
| const char* readHeader(const char* buffer, const char* buffer_end, |
| unsigned* qdcount, unsigned* ancount, |
| unsigned* nscount, unsigned* arcount); |
| }; |
| |
| const char* DNSHeader::read(const char* buffer, const char* buffer_end) { |
| unsigned qdcount; |
| unsigned ancount; |
| unsigned nscount; |
| unsigned arcount; |
| const char* cur = readHeader(buffer, buffer_end, &qdcount, &ancount, |
| &nscount, &arcount); |
| if (cur == nullptr) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| if (qdcount) { |
| questions.resize(qdcount); |
| for (unsigned i = 0 ; i < qdcount ; ++i) { |
| cur = questions[i].read(cur, buffer_end); |
| if (cur == nullptr) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| } |
| } |
| if (ancount) { |
| answers.resize(ancount); |
| for (unsigned i = 0 ; i < ancount ; ++i) { |
| cur = answers[i].read(cur, buffer_end); |
| if (cur == nullptr) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| } |
| } |
| if (nscount) { |
| authorities.resize(nscount); |
| for (unsigned i = 0 ; i < nscount ; ++i) { |
| cur = authorities[i].read(cur, buffer_end); |
| if (cur == nullptr) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| } |
| } |
| if (arcount) { |
| additionals.resize(arcount); |
| for (unsigned i = 0 ; i < arcount ; ++i) { |
| cur = additionals[i].read(cur, buffer_end); |
| if (cur == nullptr) { |
| ALOGI("parsing failed at line %d", __LINE__); |
| return nullptr; |
| } |
| } |
| } |
| return cur; |
| } |
| |
| char* DNSHeader::write(char* buffer, const char* buffer_end) const { |
| if (buffer + sizeof(Header) > buffer_end) { |
| ALOGI("buffer overflow on line %d", __LINE__); |
| return nullptr; |
| } |
| Header& header = *reinterpret_cast<Header*>(buffer); |
| // bytes 0-1 |
| header.id = htons(id); |
| // byte 2: 7:qr, 3-6:opcode, 2:aa, 1:tr, 0:rd |
| header.flags0 = (qr << 7) | (opcode << 3) | (aa << 2) | (tr << 1) | rd; |
| // byte 3: 7:ra, 6:zero, 5:ad, 4:cd, 0-3:rcode |
| header.flags1 = rcode; |
| // rest of header |
| header.qdcount = htons(questions.size()); |
| header.ancount = htons(answers.size()); |
| header.nscount = htons(authorities.size()); |
| header.arcount = htons(additionals.size()); |
| char* buffer_cur = buffer + sizeof(Header); |
| for (const DNSQuestion& question : questions) { |
| buffer_cur = question.write(buffer_cur, buffer_end); |
| if (buffer_cur == nullptr) return nullptr; |
| } |
| for (const DNSRecord& answer : answers) { |
| buffer_cur = answer.write(buffer_cur, buffer_end); |
| if (buffer_cur == nullptr) return nullptr; |
| } |
| for (const DNSRecord& authority : authorities) { |
| buffer_cur = authority.write(buffer_cur, buffer_end); |
| if (buffer_cur == nullptr) return nullptr; |
| } |
| for (const DNSRecord& additional : additionals) { |
| buffer_cur = additional.write(buffer_cur, buffer_end); |
| if (buffer_cur == nullptr) return nullptr; |
| } |
| return buffer_cur; |
| } |
| |
| std::string DNSHeader::toString() const { |
| // TODO |
| return std::string(); |
| } |
| |
| const char* DNSHeader::readHeader(const char* buffer, const char* buffer_end, |
| unsigned* qdcount, unsigned* ancount, |
| unsigned* nscount, unsigned* arcount) { |
| if (buffer + sizeof(Header) > buffer_end) |
| return 0; |
| const auto& header = *reinterpret_cast<const Header*>(buffer); |
| // bytes 0-1 |
| id = ntohs(header.id); |
| // byte 2: 7:qr, 3-6:opcode, 2:aa, 1:tr, 0:rd |
| qr = header.flags0 >> 7; |
| opcode = (header.flags0 >> 3) & 0x0F; |
| aa = (header.flags0 >> 2) & 1; |
| tr = (header.flags0 >> 1) & 1; |
| rd = header.flags0 & 1; |
| // byte 3: 7:ra, 6:zero, 5:ad, 4:cd, 0-3:rcode |
| ra = header.flags1 >> 7; |
| rcode = header.flags1 & 0xF; |
| // rest of header |
| *qdcount = ntohs(header.qdcount); |
| *ancount = ntohs(header.ancount); |
| *nscount = ntohs(header.nscount); |
| *arcount = ntohs(header.arcount); |
| return buffer + sizeof(Header); |
| } |
| |
| /* DNS responder */ |
| |
| DNSResponder::DNSResponder(const char* listen_address, |
| const char* listen_service, int poll_timeout_ms, |
| uint16_t error_rcode, double response_probability) : |
| listen_address_(listen_address), listen_service_(listen_service), |
| poll_timeout_ms_(poll_timeout_ms), error_rcode_(error_rcode), |
| response_probability_(response_probability), |
| socket_(-1), epoll_fd_(-1), terminate_(false) { } |
| |
| DNSResponder::~DNSResponder() { |
| stopServer(); |
| } |
| |
| void DNSResponder::addMapping(const char* name, ns_type type, |
| const char* addr) { |
| std::lock_guard<std::mutex> lock(mappings_mutex_); |
| auto it = mappings_.find(QueryKey(name, type)); |
| if (it != mappings_.end()) { |
| ALOGI("Overwriting mapping for (%s, %s), previous address %s, new " |
| "address %s", name, dnstype2str(type), it->second.c_str(), |
| addr); |
| it->second = addr; |
| return; |
| } |
| mappings_.emplace(std::piecewise_construct, |
| std::forward_as_tuple(name, type), |
| std::forward_as_tuple(addr)); |
| } |
| |
| void DNSResponder::removeMapping(const char* name, ns_type type) { |
| std::lock_guard<std::mutex> lock(mappings_mutex_); |
| auto it = mappings_.find(QueryKey(name, type)); |
| if (it != mappings_.end()) { |
| ALOGI("Cannot remove mapping mapping from (%s, %s), not present", name, |
| dnstype2str(type)); |
| return; |
| } |
| mappings_.erase(it); |
| } |
| |
| void DNSResponder::setResponseProbability(double response_probability) { |
| response_probability_ = response_probability; |
| } |
| |
| bool DNSResponder::running() const { |
| return socket_ != -1; |
| } |
| |
| bool DNSResponder::startServer() { |
| if (running()) { |
| ALOGI("server already running"); |
| return false; |
| } |
| addrinfo ai_hints{ |
| .ai_family = AF_UNSPEC, |
| .ai_socktype = SOCK_DGRAM, |
| .ai_flags = AI_PASSIVE |
| }; |
| addrinfo* ai_res; |
| int rv = getaddrinfo(listen_address_.c_str(), listen_service_.c_str(), |
| &ai_hints, &ai_res); |
| if (rv) { |
| ALOGI("getaddrinfo(%s, %s) failed: %s", listen_address_.c_str(), |
| listen_service_.c_str(), gai_strerror(rv)); |
| return false; |
| } |
| int s = -1; |
| for (const addrinfo* ai = ai_res ; ai ; ai = ai->ai_next) { |
| s = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol); |
| if (s < 0) continue; |
| const int one = 1; |
| setsockopt(s, SOL_SOCKET, SO_REUSEPORT, &one, sizeof(one)); |
| if (bind(s, ai->ai_addr, ai->ai_addrlen)) { |
| APLOGI("bind failed for socket %d", s); |
| close(s); |
| s = -1; |
| continue; |
| } |
| std::string host_str = addr2str(ai->ai_addr, ai->ai_addrlen); |
| ALOGI("bound to UDP %s:%s", host_str.c_str(), listen_service_.c_str()); |
| break; |
| } |
| freeaddrinfo(ai_res); |
| if (s < 0) { |
| ALOGI("bind() failed"); |
| return false; |
| } |
| |
| int flags = fcntl(s, F_GETFL, 0); |
| if (flags < 0) flags = 0; |
| if (fcntl(s, F_SETFL, flags | O_NONBLOCK) < 0) { |
| APLOGI("fcntl(F_SETFL) failed for socket %d", s); |
| close(s); |
| return false; |
| } |
| |
| int ep_fd = epoll_create(1); |
| if (ep_fd < 0) { |
| char error_msg[512] = { 0 }; |
| if (strerror_r(errno, error_msg, sizeof(error_msg))) |
| strncpy(error_msg, "UNKNOWN", sizeof(error_msg)); |
| APLOGI("epoll_create() failed: %s", error_msg); |
| close(s); |
| return false; |
| } |
| epoll_event ev; |
| ev.events = EPOLLIN; |
| ev.data.fd = s; |
| if (epoll_ctl(ep_fd, EPOLL_CTL_ADD, s, &ev) < 0) { |
| APLOGI("epoll_ctl() failed for socket %d", s); |
| close(ep_fd); |
| close(s); |
| return false; |
| } |
| |
| epoll_fd_ = ep_fd; |
| socket_ = s; |
| { |
| std::lock_guard<std::mutex> lock(update_mutex_); |
| handler_thread_ = std::thread(&DNSResponder::requestHandler, this); |
| } |
| ALOGI("server started successfully"); |
| return true; |
| } |
| |
| bool DNSResponder::stopServer() { |
| std::lock_guard<std::mutex> lock(update_mutex_); |
| if (!running()) { |
| ALOGI("server not running"); |
| return false; |
| } |
| if (terminate_) { |
| ALOGI("LOGIC ERROR"); |
| return false; |
| } |
| ALOGI("stopping server"); |
| terminate_ = true; |
| handler_thread_.join(); |
| close(epoll_fd_); |
| close(socket_); |
| terminate_ = false; |
| socket_ = -1; |
| ALOGI("server stopped successfully"); |
| return true; |
| } |
| |
| std::vector<std::pair<std::string, ns_type >> DNSResponder::queries() const { |
| std::lock_guard<std::mutex> lock(queries_mutex_); |
| return queries_; |
| } |
| |
| void DNSResponder::clearQueries() { |
| std::lock_guard<std::mutex> lock(queries_mutex_); |
| queries_.clear(); |
| } |
| |
| void DNSResponder::requestHandler() { |
| epoll_event evs[1]; |
| while (!terminate_) { |
| int n = epoll_wait(epoll_fd_, evs, 1, poll_timeout_ms_); |
| if (n == 0) continue; |
| if (n < 0) { |
| ALOGI("epoll_wait() failed"); |
| // TODO(imaipi): terminate on error. |
| return; |
| } |
| char buffer[4096]; |
| sockaddr_storage sa; |
| socklen_t sa_len = sizeof(sa); |
| ssize_t len; |
| do { |
| len = recvfrom(socket_, buffer, sizeof(buffer), 0, |
| (sockaddr*) &sa, &sa_len); |
| } while (len < 0 && (errno == EAGAIN || errno == EINTR)); |
| if (len <= 0) { |
| ALOGI("recvfrom() failed"); |
| continue; |
| } |
| ALOGI("read %zd bytes", len); |
| char response[4096]; |
| size_t response_len = sizeof(response); |
| if (handleDNSRequest(buffer, len, response, &response_len) && |
| response_len > 0) { |
| len = sendto(socket_, response, response_len, 0, |
| reinterpret_cast<const sockaddr*>(&sa), sa_len); |
| std::string host_str = |
| addr2str(reinterpret_cast<const sockaddr*>(&sa), sa_len); |
| if (len > 0) { |
| ALOGI("sent %zu bytes to %s", len, host_str.c_str()); |
| } else { |
| APLOGI("sendto() failed for %s", host_str.c_str()); |
| } |
| // Test that the response is actually a correct DNS message. |
| const char* response_end = response + len; |
| DNSHeader header; |
| const char* cur = header.read(response, response_end); |
| if (cur == nullptr) ALOGI("response is flawed"); |
| |
| } else { |
| ALOGI("not responding"); |
| } |
| } |
| } |
| |
| bool DNSResponder::handleDNSRequest(const char* buffer, ssize_t len, |
| char* response, size_t* response_len) |
| const { |
| ALOGI("request: '%s'", str2hex(buffer, len).c_str()); |
| const char* buffer_end = buffer + len; |
| DNSHeader header; |
| const char* cur = header.read(buffer, buffer_end); |
| // TODO(imaipi): for now, unparsable messages are silently dropped, fix. |
| if (cur == nullptr) { |
| ALOGI("failed to parse query"); |
| return false; |
| } |
| if (header.qr) { |
| ALOGI("response received instead of a query"); |
| return false; |
| } |
| if (header.opcode != ns_opcode::ns_o_query) { |
| ALOGI("unsupported request opcode received"); |
| return makeErrorResponse(&header, ns_rcode::ns_r_notimpl, response, |
| response_len); |
| } |
| if (header.questions.empty()) { |
| ALOGI("no questions present"); |
| return makeErrorResponse(&header, ns_rcode::ns_r_formerr, response, |
| response_len); |
| } |
| if (!header.answers.empty()) { |
| ALOGI("already %zu answers present in query", header.answers.size()); |
| return makeErrorResponse(&header, ns_rcode::ns_r_formerr, response, |
| response_len); |
| } |
| { |
| std::lock_guard<std::mutex> lock(queries_mutex_); |
| for (const DNSQuestion& question : header.questions) { |
| queries_.push_back(make_pair(question.qname.name, |
| ns_type(question.qtype))); |
| } |
| } |
| |
| // Ignore requests with the preset probability. |
| auto constexpr bound = std::numeric_limits<unsigned>::max(); |
| if (arc4random_uniform(bound) > bound*response_probability_) { |
| ALOGI("returning SRVFAIL in accordance with probability distribution"); |
| return makeErrorResponse(&header, ns_rcode::ns_r_servfail, response, |
| response_len); |
| } |
| |
| for (const DNSQuestion& question : header.questions) { |
| if (question.qclass != ns_class::ns_c_in && |
| question.qclass != ns_class::ns_c_any) { |
| ALOGI("unsupported question class %u", question.qclass); |
| return makeErrorResponse(&header, ns_rcode::ns_r_notimpl, response, |
| response_len); |
| } |
| if (!addAnswerRecords(question, &header.answers)) { |
| return makeErrorResponse(&header, ns_rcode::ns_r_servfail, response, |
| response_len); |
| } |
| } |
| header.qr = true; |
| char* response_cur = header.write(response, response + *response_len); |
| if (response_cur == nullptr) { |
| return false; |
| } |
| *response_len = response_cur - response; |
| return true; |
| } |
| |
| bool DNSResponder::addAnswerRecords(const DNSQuestion& question, |
| std::vector<DNSRecord>* answers) const { |
| auto it = mappings_.find(QueryKey(question.qname.name, question.qtype)); |
| if (it == mappings_.end()) { |
| // TODO(imaipi): handle correctly |
| ALOGI("no mapping found for %s %s, lazily refusing to add an answer", |
| question.qname.name.c_str(), dnstype2str(question.qtype)); |
| return true; |
| } |
| ALOGI("mapping found for %s %s: %s", question.qname.name.c_str(), |
| dnstype2str(question.qtype), it->second.c_str()); |
| DNSRecord record; |
| record.name = question.qname; |
| record.rtype = question.qtype; |
| record.rclass = ns_class::ns_c_in; |
| record.ttl = 1; |
| if (question.qtype == ns_type::ns_t_a) { |
| record.rdata.resize(4); |
| if (inet_pton(AF_INET, it->second.c_str(), record.rdata.data()) != 1) { |
| ALOGI("inet_pton(AF_INET, %s) failed", it->second.c_str()); |
| return false; |
| } |
| } else if (question.qtype == ns_type::ns_t_aaaa) { |
| record.rdata.resize(16); |
| if (inet_pton(AF_INET6, it->second.c_str(), record.rdata.data()) != 1) { |
| ALOGI("inet_pton(AF_INET6, %s) failed", it->second.c_str()); |
| return false; |
| } |
| } else { |
| ALOGI("unhandled qtype %s", dnstype2str(question.qtype)); |
| return false; |
| } |
| answers->push_back(std::move(record)); |
| return true; |
| } |
| |
| bool DNSResponder::makeErrorResponse(DNSHeader* header, ns_rcode rcode, |
| char* response, size_t* response_len) |
| const { |
| header->answers.clear(); |
| header->authorities.clear(); |
| header->additionals.clear(); |
| header->rcode = rcode; |
| header->qr = true; |
| char* response_cur = header->write(response, response + *response_len); |
| if (response_cur == nullptr) return false; |
| *response_len = response_cur - response; |
| return true; |
| } |
| |
| } // namespace test |
| |
