backend.go

// MIT License
//
// Copyright (c) 2023 TTBT Enterprises LLC
// Copyright (c) 2023 Robin Thellend <rthellend@rthellend.com>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package proxy

import (
	"context"
	"crypto/tls"
	"crypto/x509"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"log"
	"net"
	"slices"
	"time"

	"github.com/pires/go-proxyproto"

	"github.com/c2FmZQ/tlsproxy/proxy/internal/netw"
)

func (be *Backend) incInFlight(delta int) int {
	be.mu.Lock()
	defer be.mu.Unlock()
	be.inFlight += delta
	if be.inFlight == 0 && be.shutdown && be.httpServer != nil {
		close(be.httpConnChan)
		be.httpServer = nil
	}
	return be.inFlight
}

func (be *Backend) close(ctx context.Context) {
	be.mu.Lock()
	defer be.mu.Unlock()
	if be.httpServer == nil {
		return
	}
	if ctx == nil {
		be.httpServer.Close()
		close(be.httpConnChan)
		be.httpServer = nil
		return
	}
	go be.httpServer.Shutdown(ctx)
	be.shutdown = true
	if be.inFlight == 0 {
		close(be.httpConnChan)
		be.httpServer = nil
	}
}

func (be *Backend) dial(ctx context.Context, protos ...string) (net.Conn, error) {
	var (
		addresses          = be.Addresses
		mode               = be.Mode
		timeout            = be.ForwardTimeout
		insecureSkipVerify = be.InsecureSkipVerify
		serverName         = be.ForwardServerName
		rootCAs            = be.forwardRootCAs
		proxyProtoVersion  = be.proxyProtocolVersion
		next               = &be.next
	)
	if id, ok := ctx.Value(ctxOverrideIDKey).(int); ok && id >= 0 && id < len(be.PathOverrides) {
		po := be.PathOverrides[id]
		addresses = po.Addresses
		mode = po.Mode
		timeout = po.ForwardTimeout
		insecureSkipVerify = po.InsecureSkipVerify
		serverName = po.ForwardServerName
		rootCAs = po.forwardRootCAs
		proxyProtoVersion = po.proxyProtocolVersion
		next = &po.next
	}

	if len(addresses) == 0 {
		return nil, errors.New("no backend addresses")
	}
	tc := &tls.Config{
		InsecureSkipVerify:   insecureSkipVerify,
		ServerName:           serverName,
		NextProtos:           protos,
		RootCAs:              rootCAs,
		GetClientCertificate: be.getClientCert(ctx),
		VerifyConnection: func(cs tls.ConnectionState) error {
			if len(cs.PeerCertificates) == 0 {
				return tlsCertificateRequired
			}
			cert := cs.PeerCertificates[0]
			if m, ok := be.pkiMap[hex.EncodeToString(cert.AuthorityKeyId)]; ok {
				if m.IsRevoked(cert.SerialNumber) {
					return tlsCertificateRevoked
				}
			} else if len(cert.OCSPServer) > 0 {
				if err := be.ocspCache.VerifyChains(cs.VerifiedChains, cs.OCSPResponse); err != nil {
					be.recordEvent(fmt.Sprintf("backend X509 %s [%s] (OCSP:%v)", idnaToUnicode(cs.ServerName), cert.Subject, err))
					return tlsCertificateRevoked
				}
			}
			return nil
		},
	}
	var max int
	for {
		be.mu.Lock()
		sz := len(addresses)
		if max == 0 {
			max = sz
		}
		addr := addresses[*next]
		*next = (*next + 1) % sz
		be.mu.Unlock()

		var c net.Conn
		var err error
		if mode == ModeQUIC {
			ctx, cancel := context.WithTimeout(ctx, timeout)
			c, err = be.dialQUICStream(ctx, addr, tc)
			cancel()
		} else {
			dialer := &net.Dialer{
				Timeout:   timeout,
				KeepAlive: 30 * time.Second,
			}
			c, err = dialer.DialContext(ctx, "tcp", addr)
			if err == nil && proxyProtoVersion > 0 {
				if err = sendProxyHeader(proxyProtoVersion, c, ctx.Value(connCtxKey).(net.Conn)); err != nil {
					c.Close()
				}
			}
		}
		if err != nil {
			max--
			if max > 0 {
				log.Printf("ERR dial %q: %v", addr, err)
				continue
			}
			return nil, err
		}
		if mode == ModeTLS || mode == ModeHTTPS {
			c = tls.Client(c, tc)
		}
		return c, nil
	}
}

func sendProxyHeader(v byte, out, in net.Conn) error {
	header := proxyproto.HeaderProxyFromAddrs(v, in.RemoteAddr(), in.LocalAddr())
	header.Command = proxyproto.PROXY
	var tlvs []proxyproto.TLV
	if sn := connServerName(in); sn != "" {
		tlvs = append(tlvs, proxyproto.TLV{
			Type:  proxyproto.PP2_TYPE_AUTHORITY,
			Value: []byte(sn),
		})
	}
	if proto := connProto(in); proto != "" {
		tlvs = append(tlvs, proxyproto.TLV{
			Type:  proxyproto.PP2_TYPE_ALPN,
			Value: []byte(proto),
		})
	}
	if err := header.SetTLVs(tlvs); err != nil {
		return err
	}
	if _, err := header.WriteTo(out); err != nil {
		return err
	}
	return nil
}

func (be *Backend) authorize(cert *x509.Certificate) error {
	if be.ClientAuth == nil || be.ClientAuth.ACL == nil {
		return nil
	}
	if subject := cert.Subject.String(); subject != "" && (slices.Contains(*be.ClientAuth.ACL, subject) || slices.Contains(*be.ClientAuth.ACL, "SUBJECT:"+subject)) {
		return nil
	}
	for _, v := range cert.DNSNames {
		if slices.Contains(*be.ClientAuth.ACL, "DNS:"+v) {
			return nil
		}
	}
	for _, v := range cert.EmailAddresses {
		if slices.Contains(*be.ClientAuth.ACL, "EMAIL:"+v) {
			return nil
		}
	}
	for _, v := range cert.URIs {
		if slices.Contains(*be.ClientAuth.ACL, "URI:"+v.String()) {
			return nil
		}
	}
	return tlsAccessDenied
}

func (be *Backend) checkIP(addr net.Addr) error {
	var ip net.IP
	switch a := addr.(type) {
	case *net.TCPAddr:
		ip = a.IP
	case *net.UDPAddr:
		ip = a.IP
	default:
		return fmt.Errorf("can't get IP address from %T", addr)
	}
	if be.denyIPs != nil {
		for _, n := range *be.denyIPs {
			if n.Contains(ip) {
				return errAccessDenied
			}
		}
	}
	if be.allowIPs != nil {
		for _, n := range *be.allowIPs {
			if n.Contains(ip) {
				return nil
			}
		}
		return errAccessDenied
	}
	return nil
}

func (be *Backend) bridgeConns(client, server net.Conn) error {
	serverClose := true
	if be.ServerCloseEndsConnection != nil {
		serverClose = *be.ServerCloseEndsConnection
	}
	clientClose := false
	if be.ClientCloseEndsConnection != nil {
		clientClose = *be.ClientCloseEndsConnection
	}
	timeout := time.Minute
	if be.HalfCloseTimeout != nil {
		timeout = *be.HalfCloseTimeout
	}
	ch := make(chan error)
	go func() {
		ch <- forward(client, server, serverClose, timeout)
	}()
	var retErr error
	if err := forward(server, client, clientClose, timeout); err != nil && !errors.Is(err, net.ErrClosed) {
		retErr = fmt.Errorf("[ext➔ int]: %w", unwrapErr(err))
	}
	if err := <-ch; err != nil && !errors.Is(err, net.ErrClosed) {
		retErr = fmt.Errorf("[int➔ ext]: %w", unwrapErr(err))
	}
	return retErr
}

func forward(out net.Conn, in net.Conn, closeWhenDone bool, halfClosedTimeout time.Duration) error {
	if _, err := io.Copy(out, in); err != nil || closeWhenDone {
		out.Close()
		in.Close()
		return err
	}
	if err := closeWrite(out); err != nil {
		out.Close()
		in.Close()
		return nil
	}
	if err := closeRead(in); err != nil {
		out.Close()
		in.Close()
		return nil
	}
	// At this point, the connection is either half closed, or fully closed.
	// If it is half closed, the remote end will get an EOF on the next
	// read. It can still send data back in the other direction. There are
	// some broken clients or network devices that never close their end of
	// the connection. So, we need to set a deadline to avoid keeping
	// connections open forever.
	out.SetReadDeadline(time.Now().Add(halfClosedTimeout))
	return nil
}

func closeWrite(c net.Conn) error {
	type closeWriter interface {
		CloseWrite() error
	}
	if cc, ok := c.(closeWriter); ok {
		return cc.CloseWrite()
	}
	if cc, ok := c.(*netw.Conn); ok {
		return closeWrite(cc.Conn)
	}
	return fmt.Errorf("unexpected type: %T", c)
}

func closeRead(c net.Conn) error {
	type closeReader interface {
		CloseRead() error
	}
	if cc, ok := c.(closeReader); ok {
		return cc.CloseRead()
	}
	if cc, ok := c.(*netw.Conn); ok {
		return closeRead(cc.Conn)
	}
	return nil
}