世界
124 lines
3.5 KiB
Go
124 lines
3.5 KiB
Go
//go:build linux || darwin || (windows && (amd64 || 386))
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//nolint:unused
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package bridge
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import (
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"net/netip"
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"sync"
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"github.com/sagernet/sing-tun/gtcpip"
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"github.com/sagernet/sing-tun/gtcpip/checksum"
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"github.com/sagernet/sing-tun/gtcpip/header"
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E "github.com/sagernet/sing/common/exceptions"
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)
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const (
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bridgeTunMTU = 0xffff
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maxPacketLength = 0xffff
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bridgeMaxInstances = 254
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bridgeWriteBatchSize = 32
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)
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var (
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bridgeInet4Base = netip.MustParseAddr("192.0.2.1")
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bridgeInet6Base = netip.MustParseAddr("2001:db8::1")
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bridgeIndexAccess sync.Mutex
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bridgeIndexInUse [bridgeMaxInstances]bool
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)
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func allocateBridgeIndex() (uint32, error) {
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bridgeIndexAccess.Lock()
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defer bridgeIndexAccess.Unlock()
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for index := range bridgeMaxInstances {
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if !bridgeIndexInUse[index] {
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bridgeIndexInUse[index] = true
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return uint32(index), nil
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}
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}
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return 0, E.New("too many bridge outbounds: limit is ", bridgeMaxInstances)
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}
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func releaseBridgeIndex(index uint32) {
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bridgeIndexAccess.Lock()
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defer bridgeIndexAccess.Unlock()
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bridgeIndexInUse[index] = false
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}
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func addressAt(base netip.Addr, offset uint32) netip.Addr {
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addr := base
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for range offset {
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addr = addr.Next()
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}
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return addr
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}
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func fixReturnChecksum(packet []byte) {
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switch header.IPVersion(packet) {
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case header.IPv4Version:
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if len(packet) < header.IPv4MinimumSize {
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return
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}
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ipHdr := header.IPv4(packet)
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if !ipHdr.IsValid(len(packet)) {
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return
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}
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if ipHdr.Flags()&header.IPv4FlagMoreFragments != 0 || ipHdr.FragmentOffset() != 0 {
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return
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}
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ipHdr.SetChecksum(0)
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ipHdr.SetChecksum(^ipHdr.CalculateChecksum())
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recomputeTransportChecksum(ipHdr.TransportProtocol(), ipHdr.Payload(), ipHdr.SourceAddressSlice(), ipHdr.DestinationAddressSlice())
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case header.IPv6Version:
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if len(packet) < header.IPv6MinimumSize {
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return
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}
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ipHdr := header.IPv6(packet)
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recomputeTransportChecksum(ipHdr.TransportProtocol(), ipHdr.Payload(), ipHdr.SourceAddressSlice(), ipHdr.DestinationAddressSlice())
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}
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}
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func recomputeTransportChecksum(protocol tcpip.TransportProtocolNumber, transport []byte, source []byte, destination []byte) {
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switch protocol {
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case header.TCPProtocolNumber:
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if len(transport) < header.TCPMinimumSize {
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return
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}
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tcpHdr := header.TCP(transport)
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tcpHdr.SetChecksum(0)
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payloadChecksum := checksum.Checksum(tcpHdr.Payload(), 0)
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pseudoChecksum := header.PseudoHeaderChecksum(header.TCPProtocolNumber, source, destination, uint16(len(transport)))
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tcpHdr.SetChecksum(^tcpHdr.CalculateChecksum(checksum.Combine(pseudoChecksum, payloadChecksum)))
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case header.UDPProtocolNumber:
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if len(transport) < header.UDPMinimumSize {
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return
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}
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udpHdr := header.UDP(transport)
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udpHdr.SetChecksum(0)
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payloadChecksum := checksum.Checksum(udpHdr.Payload(), 0)
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pseudoChecksum := header.PseudoHeaderChecksum(header.UDPProtocolNumber, source, destination, udpHdr.Length())
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udpChecksum := ^udpHdr.CalculateChecksum(checksum.Combine(pseudoChecksum, payloadChecksum))
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if udpChecksum == 0 {
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udpChecksum = 0xffff
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}
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udpHdr.SetChecksum(udpChecksum)
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case header.ICMPv4ProtocolNumber:
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if len(transport) < header.ICMPv4MinimumSize {
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return
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}
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icmpHdr := header.ICMPv4(transport)
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icmpHdr.SetChecksum(header.ICMPv4Checksum(icmpHdr, 0))
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case header.ICMPv6ProtocolNumber:
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if len(transport) < header.ICMPv6MinimumSize {
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return
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}
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icmpHdr := header.ICMPv6(transport)
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icmpHdr.SetChecksum(header.ICMPv6Checksum(header.ICMPv6ChecksumParams{
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Header: icmpHdr,
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Src: source,
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Dst: destination,
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}))
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}
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}
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