114 lines
4.2 KiB
C#
114 lines
4.2 KiB
C#
using System.Collections.Concurrent;
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using System.Net;
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using System.Security.Cryptography;
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namespace Fleet.Identity;
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/// <summary>
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/// 监听方的敲门关卡：新连接的前 32 字节必须是名册里某个成员的敲门包，否则不写任何字节、直接断开。
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/// 每个来源地址限速（陌生人用随机数据也要消耗 HMAC 计算），nonce 在时间窗内去重（防重放）。
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/// 名册由调用方提供（对端公钥列表）；配对密钥按公钥缓存，名册变了自然只算新的。
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/// </summary>
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public sealed class KnockGate
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{
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private static readonly TimeSpan s_readTimeout = TimeSpan.FromSeconds(3);
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private readonly NodeIdentity _own;
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private readonly Func<IReadOnlyList<byte[]>> _peers;
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private readonly TimeProvider _time;
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private readonly int _attemptsPerPeriod;
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private readonly long _periodMs;
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private readonly ConcurrentDictionary<string, byte[]> _keys = new();
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private readonly object _gate = new();
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private readonly Dictionary<string, long> _seenNonces = [];
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private readonly Dictionary<string, (long WindowStartMs, int Count)> _sources = [];
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private long _lastSweepMs;
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public KnockGate(NodeIdentity own, Func<IReadOnlyList<byte[]>> peers, TimeProvider time, int attemptsPerPeriod = 300, TimeSpan? period = null)
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{
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_own = own;
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_peers = peers;
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_time = time;
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_attemptsPerPeriod = attemptsPerPeriod;
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_periodMs = (long)(period ?? TimeSpan.FromSeconds(10)).TotalMilliseconds;
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}
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/// <summary>读 32 字节并核对。通过返回 true，流从敲门包之后继续（TLS 或明文首帧）；不通过返回 false，调用方直接关闭连接，不要写任何东西。</summary>
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public async ValueTask<bool> AdmitAsync(Stream stream, IPAddress? source, CancellationToken ct)
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{
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long now = _time.GetUtcNow().ToUnixTimeMilliseconds();
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if (!TryCountSource(source, now))
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{
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return false;
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}
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byte[] packet = new byte[Knock.PacketBytes];
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using var timeout = CancellationTokenSource.CreateLinkedTokenSource(ct);
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timeout.CancelAfter(s_readTimeout);
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try
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{
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await stream.ReadExactlyAsync(packet, timeout.Token);
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}
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catch (Exception ex) when (ex is EndOfStreamException or OperationCanceledException or IOException or ObjectDisposedException)
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{
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return false;
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}
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return Accept(packet, now);
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}
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/// <summary>核对一个敲门包（不读流）：名册里有成员的密钥对得上，并且 nonce 没用过。</summary>
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public bool Accept(ReadOnlySpan<byte> packet, long nowMs)
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{
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bool matched = false;
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foreach (byte[] peer in _peers())
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{
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byte[] key = _keys.GetOrAdd(Convert.ToBase64String(peer), _ => Knock.DeriveKey(_own, peer));
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matched |= Knock.Check(key, packet, nowMs);
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}
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if (!matched)
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{
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return false;
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}
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string nonce = Convert.ToHexString(packet[..Knock.NonceBytes]);
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lock (_gate)
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{
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Sweep(nowMs);
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return _seenNonces.TryAdd(nonce, nowMs + (Knock.WindowSeconds * 3 * 1000L));
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}
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}
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private bool TryCountSource(IPAddress? source, long nowMs)
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{
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string key = source is null ? "" : source.IsIPv4MappedToIPv6 ? source.MapToIPv4().ToString() : source.ToString();
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lock (_gate)
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{
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Sweep(nowMs);
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(long start, int count) = _sources.TryGetValue(key, out var entry) && nowMs - entry.WindowStartMs < _periodMs ? entry : (nowMs, 0);
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_sources[key] = (start, count + 1);
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return count < _attemptsPerPeriod;
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}
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}
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private void Sweep(long nowMs)
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{
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if (nowMs - _lastSweepMs < 5000 && _seenNonces.Count < 4096 && _sources.Count < 4096)
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{
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return;
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}
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_lastSweepMs = nowMs;
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foreach (string nonce in _seenNonces.Where(p => p.Value <= nowMs).Select(p => p.Key).ToList())
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{
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_seenNonces.Remove(nonce);
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}
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foreach (string source in _sources.Where(p => nowMs - p.Value.WindowStartMs >= _periodMs).Select(p => p.Key).ToList())
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{
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_sources.Remove(source);
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}
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}
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}
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