| /* |
| * 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. |
| * |
| */ |
| |
| #ifndef DNS_RESPONDER_H |
| #define DNS_RESPONDER_H |
| |
| #include <arpa/nameser.h> |
| |
| #include <atomic> |
| #include <condition_variable> |
| #include <mutex> |
| #include <string> |
| #include <thread> |
| #include <unordered_map> |
| #include <vector> |
| |
| #include <android-base/thread_annotations.h> |
| #include "android-base/unique_fd.h" |
| |
| namespace test { |
| |
| struct DNSName { |
| std::string name; |
| const char* read(const char* buffer, const char* buffer_end); |
| char* write(char* buffer, const char* buffer_end) const; |
| |
| private: |
| const char* parseField(const char* buffer, const char* buffer_end, bool* last); |
| }; |
| |
| 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; |
| }; |
| |
| 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; |
| }; |
| |
| struct DNSHeader { |
| unsigned id; |
| bool ra; |
| uint8_t rcode; |
| bool qr; |
| uint8_t opcode; |
| bool aa; |
| bool tr; |
| bool rd; |
| bool ad; |
| 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); |
| }; |
| |
| inline const std::string kDefaultListenAddr = "127.0.0.3"; |
| inline const std::string kDefaultListenService = "53"; |
| |
| /* |
| * Simple DNS responder, which replies to queries with the registered response |
| * for that type. Class is assumed to be IN. If no response is registered, the |
| * default error response code is returned. |
| */ |
| class DNSResponder { |
| public: |
| DNSResponder(std::string listen_address = kDefaultListenAddr, |
| std::string listen_service = kDefaultListenService, |
| ns_rcode error_rcode = ns_rcode::ns_r_servfail); |
| ~DNSResponder(); |
| |
| enum class Edns : uint8_t { |
| ON, |
| FORMERR_ON_EDNS, // DNS server not supporting EDNS will reply FORMERR. |
| FORMERR_UNCOND, // DNS server reply FORMERR unconditionally |
| DROP // DNS server not supporting EDNS will not do any response. |
| }; |
| |
| void addMapping(const std::string& name, ns_type type, const std::string& addr); |
| void removeMapping(const std::string& name, ns_type type); |
| void setResponseProbability(double response_probability); |
| void setEdns(Edns edns); |
| bool running() const; |
| bool startServer(); |
| bool stopServer(); |
| const std::string& listen_address() const { |
| return listen_address_; |
| } |
| const std::string& listen_service() const { |
| return listen_service_; |
| } |
| std::vector<std::pair<std::string, ns_type>> queries() const; |
| std::string dumpQueries() const; |
| void clearQueries(); |
| std::condition_variable& getCv() { return cv; } |
| std::mutex& getCvMutex() { return cv_mutex_; } |
| void setDeferredResp(bool deferred_resp); |
| static bool fillAnswerRdata(const std::string& rdatastr, DNSRecord& record); |
| |
| private: |
| // Key used for accessing mappings. |
| struct QueryKey { |
| std::string name; |
| unsigned type; |
| |
| QueryKey(std::string n, unsigned t) : name(move(n)), type(t) {} |
| bool operator == (const QueryKey& o) const { |
| return name == o.name && type == o.type; |
| } |
| bool operator < (const QueryKey& o) const { |
| if (name < o.name) return true; |
| if (name > o.name) return false; |
| return type < o.type; |
| } |
| }; |
| |
| struct QueryKeyHash { |
| size_t operator() (const QueryKey& key) const { |
| return std::hash<std::string>()(key.name) + |
| static_cast<size_t>(key.type); |
| } |
| }; |
| |
| void requestHandler(); |
| |
| // Parses and generates a response message for incoming DNS requests. |
| // Returns false to ignore the request, which might be due to either parsing error |
| // or unresponsiveness. |
| bool handleDNSRequest(const char* buffer, ssize_t buffer_len, |
| char* response, size_t* response_len) const; |
| |
| bool addAnswerRecords(const DNSQuestion& question, std::vector<DNSRecord>* answers) const; |
| |
| bool generateErrorResponse(DNSHeader* header, ns_rcode rcode, |
| char* response, size_t* response_len) const; |
| bool makeErrorResponse(DNSHeader* header, ns_rcode rcode, char* response, |
| size_t* response_len) const; |
| |
| // Add a new file descriptor to be polled by the handler thread. |
| bool addFd(int fd, uint32_t events); |
| |
| // Read the query sent from the client and send the answer back to the client. It |
| // makes sure the I/O communicated with the client is correct. |
| void handleQuery(); |
| |
| // Trigger the handler thread to terminate. |
| bool sendToEventFd(); |
| |
| // Used in the handler thread for the termination signal. |
| void handleEventFd(); |
| |
| // Address and service to listen on, currently limited to UDP. |
| const std::string listen_address_; |
| const std::string listen_service_; |
| // Error code to return for requests for an unknown name. |
| const ns_rcode error_rcode_; |
| // Probability that a valid response is being sent instead of being sent |
| // instead of returning error_rcode_. |
| std::atomic<double> response_probability_ = 1.0; |
| // Maximum number of fds for epoll. |
| const int EPOLL_MAX_EVENTS = 2; |
| |
| // Control how the DNS server behaves when it receives the requests containing OPT RR. |
| // If it's set Edns::ON, the server can recognize and reply the response; if it's set |
| // Edns::FORMERR_ON_EDNS, the server behaves like an old DNS server that doesn't support EDNS0, |
| // and replying FORMERR; if it's Edns::DROP, the server doesn't support EDNS0 either, and |
| // ignoring the requests. |
| std::atomic<Edns> edns_ = Edns::ON; |
| |
| // Mappings from (name, type) to registered response and the |
| // mutex protecting them. |
| std::unordered_map<QueryKey, std::string, QueryKeyHash> mappings_ |
| GUARDED_BY(mappings_mutex_); |
| mutable std::mutex mappings_mutex_; |
| // Query names received so far and the corresponding mutex. |
| mutable std::vector<std::pair<std::string, ns_type>> queries_ |
| GUARDED_BY(queries_mutex_); |
| mutable std::mutex queries_mutex_; |
| // Socket on which the server is listening. |
| android::base::unique_fd socket_; |
| // File descriptor for epoll. |
| android::base::unique_fd epoll_fd_; |
| // Eventfd used to signal for the handler thread termination. |
| android::base::unique_fd event_fd_; |
| // Thread for handling incoming threads. |
| std::thread handler_thread_ GUARDED_BY(update_mutex_); |
| std::mutex update_mutex_; |
| std::condition_variable cv; |
| std::mutex cv_mutex_; |
| |
| std::condition_variable cv_for_deferred_resp_; |
| std::mutex cv_mutex_for_deferred_resp_; |
| bool deferred_resp_ GUARDED_BY(cv_mutex_for_deferred_resp_) = false; |
| }; |
| |
| } // namespace test |
| |
| #endif // DNS_RESPONDER_H |