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MHSanaei
5e6ffebdf2
The embedded interface's TCP forwarder admits 65535 connections in flight for all peers together, and a forwarded request holds its slot until the handshake ends or gVisor gives up on it. One client sending bare SYNs from fresh source ports therefore took every slot and left the other clients' connections unanswered. The UDP relay likewise opened a SOCKS5 association and a host UDP socket for every fresh tunnel source port with no per-peer bound. The forwarder now names the peer on the SYN, refuses a source no peer owns and caps one peer at 4096 connections; the UDP relay caps one peer at 1024 sessions and drops the datagrams that would need more.
100 lines
3.1 KiB
Go
100 lines
3.1 KiB
Go
package amneziawgnet
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import (
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"net/netip"
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"sync"
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"gvisor.dev/gvisor/pkg/tcpip/adapters/gonet"
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"gvisor.dev/gvisor/pkg/tcpip/stack"
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"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
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"gvisor.dev/gvisor/pkg/waiter"
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)
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// One datagram or bare SYN from a fresh source port buys a flow its sockets, goroutine and
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// buffers, so each peer gets a share of an interface instead of the whole of it.
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const (
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maxTCPFlowsPerPeer = 4096
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maxUDPSessionsPerPeer = 1024
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)
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// peerSlots counts the flows each peer holds; every successful acquire needs one release.
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type peerSlots struct {
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mu sync.Mutex
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limit int
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held map[string]int
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}
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func newPeerSlots(limit int) *peerSlots {
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return &peerSlots{limit: limit, held: map[string]int{}}
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}
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func (s *peerSlots) acquire(peer string) bool {
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s.mu.Lock()
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defer s.mu.Unlock()
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if s.held[peer] >= s.limit {
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return false
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}
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s.held[peer]++
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return true
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}
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func (s *peerSlots) release(peer string) {
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s.mu.Lock()
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defer s.mu.Unlock()
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if s.held[peer]--; s.held[peer] <= 0 {
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delete(s.held, peer)
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}
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}
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// AttachTCPForwarder attaches a TCP forwarder to gstack in promiscuous +
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// spoofing mode, so it accepts connections addressed to any destination --
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// not just the stack's own configured local address -- and hands the
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// handler the accepted connection, the tunnel client's source and its real,
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// dynamically-arbitrary destination (recovered from the connection's own
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// TransportEndpointID, not from any preconfigured routing table). This is
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// the mechanism the whole embedded-AmneziaWG design depends on: what the
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// handler does with that destination (dial it directly, relay it into
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// Xray's SOCKS5 inbound, ...) is entirely up to the caller.
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//
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// Handlers must identify the peer by src, never conn.RemoteAddr(): that asks
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// the live endpoint and is nil once a RST is processed, possibly before the call.
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//
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// owner names the peer a tunnel source belongs to; it is asked on the SYN, before anything
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// is allocated, and refuses a source nobody owns or one whose owner holds its full share.
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//
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// Adapted from xtls/xray-core's proxy/wireguard/tun.go createForwarder (MIT).
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func AttachTCPForwarder(gstack *stack.Stack, owner func(src netip.Addr) (string, bool), handler func(conn *gonet.TCPConn, src, dest netip.AddrPort)) {
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enablePromiscuousRouting(gstack)
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slots := newPeerSlots(maxTCPFlowsPerPeer)
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fwd := tcp.NewForwarder(gstack, 0, 65535, func(r *tcp.ForwarderRequest) {
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peer, ok := owner(addrFromTcpip(r.ID().RemoteAddress).Unmap())
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if !ok {
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r.Complete(true)
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return
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}
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// CreateEndpoint holds the request until the handshake ends, so a bare SYN costs a slot.
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if !slots.acquire(peer) {
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r.Complete(false)
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return
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}
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go func(r *tcp.ForwarderRequest) {
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defer slots.release(peer)
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var wq waiter.Queue
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id := r.ID()
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ep, err := r.CreateEndpoint(&wq)
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if err != nil {
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r.Complete(true)
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return
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}
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src := netip.AddrPortFrom(addrFromTcpip(id.RemoteAddress), id.RemotePort)
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dest := netip.AddrPortFrom(addrFromTcpip(id.LocalAddress), id.LocalPort)
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handler(gonet.NewTCPConn(&wq, ep), src, dest)
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ep.Close()
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r.Complete(false)
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}(r)
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})
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gstack.SetTransportProtocolHandler(tcp.ProtocolNumber, fwd.HandlePacket)
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}
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