1 // Copyright 2020 The Chromium Authors 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef NET_DNS_DNS_UDP_TRACKER_H_ 6 #define NET_DNS_DNS_UDP_TRACKER_H_ 7 8 #include <stdint.h> 9 10 #include "base/containers/circular_deque.h" 11 #include "base/memory/raw_ptr.h" 12 #include "base/time/default_tick_clock.h" 13 #include "base/time/time.h" 14 #include "net/base/net_export.h" 15 16 namespace base { 17 class TickClock; 18 } // namespace base 19 20 namespace net { 21 22 // Data tracker for DNS UDP and its usage of local ports. Intended to be owned 23 // by a DnsSession and thus keep track of the data session-wide. Responsible for 24 // related metrics and used to inform behavior based on the stored data. 25 // 26 // TODO(ericorth@chromium.org): Add methods to access the stored data or 27 // conclusions about it. 28 class NET_EXPORT_PRIVATE DnsUdpTracker { 29 public: 30 static constexpr base::TimeDelta kMaxAge = base::Minutes(10); 31 static constexpr size_t kMaxRecordedQueries = 256; 32 33 // How recently an ID needs to be recorded in a recent query to be considered 34 // "recognized". 35 static constexpr base::TimeDelta kMaxRecognizedIdAge = base::Seconds(15); 36 37 // Numbers of ID mismatches required to set the |low_entropy_| flag. Also 38 // serves as the max number of mismatches to be recorded, as no more entries 39 // are recorded after setting the flag. 40 static constexpr size_t kUnrecognizedIdMismatchThreshold = 8; 41 static constexpr size_t kRecognizedIdMismatchThreshold = 128; 42 43 // Number of reuses of the same port required to set the |low_entropy_| flag. 44 // Note: The original value of this parameter was 2, but it caused a problem 45 // on Windows (crbug.com/1413620). The low entropy checker in DnsUdpTracker 46 // was too sensitive and caused many TCP fallbacks. This happened because the 47 // dynamic port range for UDP on Windows is too small (only 16384 ports). This 48 // meant that there was a high probability (about 1%) of reusing the same port 49 // number three or more times out of 256 records. To avoid these unnecessary 50 // TCP fallbacks, the value was changed to 3. The probability of reusing the 51 // same port number to 4 or more times out of 256 records is 3.92566e-05. And 52 // if the available port count is 2048, the probability: 0.0182851. So it is 53 // likely to activate when getting into the low entropy. 54 // (See crrev.com/c/4374511 for the calculation). 55 static constexpr int kPortReuseThreshold = 3; 56 57 DnsUdpTracker(); 58 ~DnsUdpTracker(); 59 60 DnsUdpTracker(DnsUdpTracker&&); 61 DnsUdpTracker& operator=(DnsUdpTracker&&); 62 63 void RecordQuery(uint16_t port, uint16_t query_id); 64 void RecordResponseId(uint16_t query_id, uint16_t response_id); 65 void RecordConnectionError(int connection_error); 66 67 // If true, the entropy from random UDP port and DNS ID has been detected to 68 // potentially be low, e.g. due to exhaustion of the port pool or mismatches 69 // on IDs. low_entropy()70 bool low_entropy() const { return low_entropy_; } 71 set_tick_clock_for_testing(base::TickClock * tick_clock)72 void set_tick_clock_for_testing(base::TickClock* tick_clock) { 73 tick_clock_ = tick_clock; 74 } 75 76 private: 77 struct QueryData; 78 79 void PurgeOldRecords(); 80 void SaveQuery(QueryData query); 81 void SaveIdMismatch(uint16_t it); 82 83 bool low_entropy_ = false; 84 base::circular_deque<QueryData> recent_queries_; 85 86 // Times of recent ID mismatches, separated by whether or not the ID was 87 // recognized from recent queries. 88 base::circular_deque<base::TimeTicks> recent_unrecognized_id_hits_; 89 base::circular_deque<base::TimeTicks> recent_recognized_id_hits_; 90 91 raw_ptr<const base::TickClock> tick_clock_ = 92 base::DefaultTickClock::GetInstance(); 93 }; 94 95 } // namespace net 96 97 #endif // NET_DNS_DNS_UDP_TRACKER_H_ 98