1 /*
2  * Copyright (C) 2018 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef DNS_DNS64CONFIGURATION_H_
18 #define DNS_DNS64CONFIGURATION_H_
19 
20 #include <netinet/in.h>
21 #include <condition_variable>
22 #include <cstdlib>
23 #include <mutex>
24 #include <unordered_map>
25 
26 #include <android-base/thread_annotations.h>
27 #include <netdutils/DumpWriter.h>
28 #include <netdutils/InternetAddresses.h>
29 
30 struct android_net_context;
31 
32 namespace android {
33 namespace net {
34 
35 /**
36  * This class handles RFC 7050 -style DNS64 prefix discovery.
37  *
38  * The ResolverController starts DNS64 prefix discovery when it observes a
39  * a network with only IPv6 nameservers. (It stops discovery whenever an IPv4
40  * nameserver is added or the network is deleted.)
41  *
42  * Each time prefix discovery is started, a new discoveryId is generated so
43  * that running resolution threads can notice they are no longer the most
44  * recent resolution attempt. This results in the backoff schedule of resolution
45  * being reset.
46  *
47  * Thread-safety: All public methods in this class MUST be thread-safe.
48  * (In other words: this class handles all its locking privately.)
49  */
50 class Dns64Configuration {
51   public:
52     // Simple data struct for passing back packet NAT64 prefix event information to the
53     // Dns64PrefixCallback callback.
54     struct Nat64PrefixInfo {
55         unsigned netId;
56         bool added;
57         std::string prefixString;
58         uint8_t prefixLength;
59     };
60 
61     // Callback that is triggered for every NAT64 prefix event.
62     using Nat64PrefixCallback = std::function<void(const Nat64PrefixInfo&)>;
63 
64     using GetNetworkContextCallback = std::function<void(uint32_t, uint32_t, android_net_context*)>;
65 
66     // Parameters from RFC 7050 section 8.
67     static const char kIPv4OnlyHost[];  // "ipv4only.arpa."
68     static const char kIPv4Literal1[];  // 192.0.0.170
69     static const char kIPv4Literal2[];  // 192.0.0.171
70 
71     Dns64Configuration() = delete;
Dns64Configuration(GetNetworkContextCallback getNetworkCallback,Nat64PrefixCallback prefixCallback)72     Dns64Configuration(GetNetworkContextCallback getNetworkCallback,
73                        Nat64PrefixCallback prefixCallback)
74         : mGetNetworkContextCallback(std::move(getNetworkCallback)),
75           mPrefixCallback(std::move(prefixCallback)) {}
76     Dns64Configuration(const Dns64Configuration&) = delete;
77     Dns64Configuration(Dns64Configuration&&) = delete;
78     Dns64Configuration& operator=(const Dns64Configuration&) = delete;
79     Dns64Configuration& operator=(Dns64Configuration&&) = delete;
80 
81     void startPrefixDiscovery(unsigned netId);
82     void stopPrefixDiscovery(unsigned netId);
83     netdutils::IPPrefix getPrefix64(unsigned netId) const;
84 
85     int setPrefix64(unsigned netId, const netdutils::IPPrefix& pfx) EXCLUDES(mMutex);
86     int clearPrefix64(unsigned netId) EXCLUDES(mMutex);
87 
88     void dump(netdutils::DumpWriter& dw, unsigned netId);
89 
90   private:
91     struct Dns64Config {
Dns64ConfigDns64Config92         Dns64Config(unsigned pseudoRandomId, unsigned network)
93             : discoveryId(pseudoRandomId), netId(network) {}
94 
95         // ID of the discovery operation, or kNoDiscoveryId if no discovery was performed (i.e., the
96         // prefix was discovered and passed in via setPrefix64).
97         const unsigned int discoveryId;
98         const unsigned int netId;
99         netdutils::IPPrefix prefix64{};
100 
isFromPrefixDiscoveryDns64Config101         bool isFromPrefixDiscovery() const { return discoveryId != kNoDiscoveryId; }
102     };
103 
104     static constexpr int kNoDiscoveryId = 0;
105 
106     enum { PREFIX_REMOVED, PREFIX_ADDED };
107 
108     static bool doRfc7050PrefixDiscovery(const android_net_context& netcontext, Dns64Config* cfg);
109 
110     // Picks the next discovery ID. Never returns kNoDiscoveryId.
getNextId()111     unsigned getNextId() REQUIRES(mMutex) { return ++mNextId ? mNextId : ++mNextId; }
112 
113     netdutils::IPPrefix getPrefix64Locked(unsigned netId) const REQUIRES(mMutex);
114     bool isDiscoveryInProgress(const Dns64Config& cfg) const REQUIRES(mMutex);
115     bool reportNat64PrefixStatus(unsigned netId, bool added, const netdutils::IPPrefix& pfx)
116             REQUIRES(mMutex);
117 
118     bool shouldContinueDiscovery(const Dns64Config& cfg);
119     void recordDns64Config(const Dns64Config& cfg);
120     void removeDns64Config(unsigned netId) REQUIRES(mMutex);
121 
122     mutable std::mutex mMutex;
123     std::condition_variable mCv;
124     unsigned int mNextId GUARDED_BY(mMutex);
125     std::unordered_map<unsigned, Dns64Config> mDns64Configs GUARDED_BY(mMutex);
126     const GetNetworkContextCallback mGetNetworkContextCallback;
127     const Nat64PrefixCallback mPrefixCallback;
128 };
129 
130 }  // namespace net
131 }  // namespace android
132 
133 #endif  // DNS_DNS64CONFIGURATION_H_
134