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// Copyright 2017 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package tcpproxy
import (
"bufio"
"bytes"
"context"
"crypto/tls"
"io"
"net"
"strings"
)
// AddSNIRoute appends a route to the ipPort listener that routes to
// dest if the incoming TLS SNI server name is sni. If it doesn't
// match, rule processing continues for any additional routes on
// ipPort.
//
// By default, the proxy will route all ACME tls-sni-01 challenges
// received on ipPort to all SNI dests. You can disable ACME routing
// with AddStopACMESearch.
//
// The ipPort is any valid net.Listen TCP address.
func (p *Proxy) AddSNIRoute(ipPort, sni string, dest Target) {
p.AddSNIMatchRoute(ipPort, equals(sni), dest)
}
// AddSNIMatchRoute appends a route to the ipPort listener that routes
// to dest if the incoming TLS SNI server name is accepted by
// matcher. If it doesn't match, rule processing continues for any
// additional routes on ipPort.
//
// By default, the proxy will route all ACME tls-sni-01 challenges
// received on ipPort to all SNI dests. You can disable ACME routing
// with AddStopACMESearch.
//
// The ipPort is any valid net.Listen TCP address.
func (p *Proxy) AddSNIMatchRoute(ipPort string, matcher Matcher, dest Target) {
cfg := p.configFor(ipPort)
if !cfg.stopACME {
if len(cfg.acmeTargets) == 0 {
p.addRoute(ipPort, &acmeMatch{cfg})
}
cfg.acmeTargets = append(cfg.acmeTargets, dest)
}
p.addRoute(ipPort, sniMatch{matcher, dest})
}
// AddStopACMESearch prevents ACME probing of subsequent SNI routes.
// Any ACME challenges on ipPort for SNI routes previously added
// before this call will still be proxied to all possible SNI
// backends.
func (p *Proxy) AddStopACMESearch(ipPort string) {
p.configFor(ipPort).stopACME = true
}
type sniMatch struct {
matcher Matcher
target Target
}
func (m sniMatch) match(br *bufio.Reader) (Target, string) {
sni := clientHelloServerName(br)
if m.matcher(context.TODO(), sni) {
return m.target, sni
}
return nil, ""
}
// acmeMatch matches "*.acme.invalid" ACME tls-sni-01 challenges and
// searches for a Target in cfg.acmeTargets that has the challenge
// response.
type acmeMatch struct {
cfg *config
}
func (m *acmeMatch) match(br *bufio.Reader) (Target, string) {
sni := clientHelloServerName(br)
if !strings.HasSuffix(sni, ".acme.invalid") {
return nil, ""
}
// TODO: cache. ACME issuers will hit multiple times in a short
// burst for each issuance event. A short TTL cache + singleflight
// should have an excellent hit rate.
// TODO: maybe an acme-specific timeout as well?
// TODO: plumb context upwards?
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
ch := make(chan Target, len(m.cfg.acmeTargets))
for _, target := range m.cfg.acmeTargets {
go tryACME(ctx, ch, target, sni)
}
for range m.cfg.acmeTargets {
if target := <-ch; target != nil {
return target, sni
}
}
// No target was happy with the provided challenge.
return nil, ""
}
func tryACME(ctx context.Context, ch chan<- Target, dest Target, sni string) {
var ret Target
defer func() { ch <- ret }()
conn, targetConn := net.Pipe()
defer conn.Close()
go dest.HandleConn(targetConn)
deadline, ok := ctx.Deadline()
if ok {
conn.SetDeadline(deadline)
}
client := tls.Client(conn, &tls.Config{
ServerName: sni,
InsecureSkipVerify: true,
})
if err := client.Handshake(); err != nil {
// TODO: log?
return
}
certs := client.ConnectionState().PeerCertificates
if len(certs) == 0 {
// TODO: log?
return
}
// acme says the first cert offered by the server must match the
// challenge hostname.
if err := certs[0].VerifyHostname(sni); err != nil {
// TODO: log?
return
}
// Target presented what looks like a valid challenge
// response, send it back to the matcher.
ret = dest
}
// clientHelloServerName returns the SNI server name inside the TLS ClientHello,
// without consuming any bytes from br.
// On any error, the empty string is returned.
func clientHelloServerName(br *bufio.Reader) (sni string) {
const recordHeaderLen = 5
hdr, err := br.Peek(recordHeaderLen)
if err != nil {
return ""
}
const recordTypeHandshake = 0x16
if hdr[0] != recordTypeHandshake {
return "" // Not TLS.
}
recLen := int(hdr[3])<<8 | int(hdr[4]) // ignoring version in hdr[1:3]
helloBytes, err := br.Peek(recordHeaderLen + recLen)
if err != nil {
return ""
}
tls.Server(sniSniffConn{r: bytes.NewReader(helloBytes)}, &tls.Config{
GetConfigForClient: func(hello *tls.ClientHelloInfo) (*tls.Config, error) {
sni = hello.ServerName
return nil, nil
},
}).Handshake()
return
}
// sniSniffConn is a net.Conn that reads from r, fails on Writes,
// and crashes otherwise.
type sniSniffConn struct {
r io.Reader
net.Conn // nil; crash on any unexpected use
}
func (c sniSniffConn) Read(p []byte) (int, error) { return c.r.Read(p) }
func (sniSniffConn) Write(p []byte) (int, error) { return 0, io.EOF }