466 lines
14 KiB
Go
466 lines
14 KiB
Go
package dns
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import (
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"context"
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"crypto/tls"
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"encoding/binary"
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"errors"
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"fmt"
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"net"
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"runtime"
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"strconv"
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"sync"
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"time"
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tlsC "github.com/Dreamacro/clash/component/tls"
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"github.com/metacubex/quic-go"
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"github.com/Dreamacro/clash/log"
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D "github.com/miekg/dns"
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)
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const NextProtoDQ = "doq"
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const (
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// QUICCodeNoError is used when the connection or stream needs to be closed,
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// but there is no error to signal.
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QUICCodeNoError = quic.ApplicationErrorCode(0)
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// QUICCodeInternalError signals that the DoQ implementation encountered
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// an internal error and is incapable of pursuing the transaction or the
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// connection.
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QUICCodeInternalError = quic.ApplicationErrorCode(1)
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// QUICKeepAlivePeriod is the value that we pass to *quic.Config and that
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// controls the period with with keep-alive frames are being sent to the
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// connection. We set it to 20s as it would be in the quic-go@v0.27.1 with
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// KeepAlive field set to true This value is specified in
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// https://pkg.go.dev/github.com/metacubex/quic-go/internal/protocol#MaxKeepAliveInterval.
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//
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// TODO(ameshkov): Consider making it configurable.
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QUICKeepAlivePeriod = time.Second * 20
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DefaultTimeout = time.Second * 5
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)
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// dnsOverQUIC is a struct that implements the Upstream interface for the
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// DNS-over-QUIC protocol (spec: https://www.rfc-editor.org/rfc/rfc9250.html).
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type dnsOverQUIC struct {
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// quicConfig is the QUIC configuration that is used for establishing
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// connections to the upstream. This configuration includes the TokenStore
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// that needs to be stored for the lifetime of dnsOverQUIC since we can
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// re-create the connection.
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quicConfig *quic.Config
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quicConfigGuard sync.Mutex
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// conn is the current active QUIC connection. It can be closed and
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// re-opened when needed.
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conn quic.Connection
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connMu sync.RWMutex
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// bytesPool is a *sync.Pool we use to store byte buffers in. These byte
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// buffers are used to read responses from the upstream.
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bytesPool *sync.Pool
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bytesPoolGuard sync.Mutex
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addr string
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proxyAdapter string
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r *Resolver
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}
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// type check
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var _ dnsClient = (*dnsOverQUIC)(nil)
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// newDoQ returns the DNS-over-QUIC Upstream.
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func newDoQ(resolver *Resolver, addr string, adapter string) (dnsClient, error) {
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doq := &dnsOverQUIC{
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addr: addr,
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proxyAdapter: adapter,
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r: resolver,
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quicConfig: &quic.Config{
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KeepAlivePeriod: QUICKeepAlivePeriod,
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TokenStore: newQUICTokenStore(),
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},
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}
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runtime.SetFinalizer(doq, (*dnsOverQUIC).Close)
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return doq, nil
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}
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// Address implements the Upstream interface for *dnsOverQUIC.
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func (doq *dnsOverQUIC) Address() string { return doq.addr }
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func (doq *dnsOverQUIC) ExchangeContext(ctx context.Context, m *D.Msg) (msg *D.Msg, err error) {
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// When sending queries over a QUIC connection, the DNS Message ID MUST be
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// set to zero.
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id := m.Id
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m.Id = 0
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defer func() {
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// Restore the original ID to not break compatibility with proxies.
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m.Id = id
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if msg != nil {
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msg.Id = id
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}
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}()
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// Check if there was already an active conn before sending the request.
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// We'll only attempt to re-connect if there was one.
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hasConnection := doq.hasConnection()
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// Make the first attempt to send the DNS query.
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msg, err = doq.exchangeQUIC(ctx, m)
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// Make up to 2 attempts to re-open the QUIC connection and send the request
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// again. There are several cases where this workaround is necessary to
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// make DoQ usable. We need to make 2 attempts in the case when the
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// connection was closed (due to inactivity for example) AND the server
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// refuses to open a 0-RTT connection.
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for i := 0; hasConnection && doq.shouldRetry(err) && i < 2; i++ {
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log.Debugln("re-creating the QUIC connection and retrying due to %v", err)
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// Close the active connection to make sure we'll try to re-connect.
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doq.closeConnWithError(err)
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// Retry sending the request.
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msg, err = doq.exchangeQUIC(ctx, m)
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}
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if err != nil {
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// If we're unable to exchange messages, make sure the connection is
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// closed and signal about an internal error.
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doq.closeConnWithError(err)
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}
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return msg, err
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}
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// Exchange implements the Upstream interface for *dnsOverQUIC.
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func (doq *dnsOverQUIC) Exchange(m *D.Msg) (msg *D.Msg, err error) {
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return doq.ExchangeContext(context.Background(), m)
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}
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// Close implements the Upstream interface for *dnsOverQUIC.
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func (doq *dnsOverQUIC) Close() (err error) {
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doq.connMu.Lock()
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defer doq.connMu.Unlock()
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runtime.SetFinalizer(doq, nil)
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if doq.conn != nil {
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err = doq.conn.CloseWithError(QUICCodeNoError, "")
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}
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return err
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}
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// exchangeQUIC attempts to open a QUIC connection, send the DNS message
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// through it and return the response it got from the server.
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func (doq *dnsOverQUIC) exchangeQUIC(ctx context.Context, msg *D.Msg) (resp *D.Msg, err error) {
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var conn quic.Connection
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conn, err = doq.getConnection(ctx, true)
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if err != nil {
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return nil, err
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}
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var buf []byte
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buf, err = msg.Pack()
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if err != nil {
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return nil, fmt.Errorf("failed to pack DNS message for DoQ: %w", err)
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}
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var stream quic.Stream
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stream, err = doq.openStream(ctx, conn)
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if err != nil {
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return nil, err
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}
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_, err = stream.Write(AddPrefix(buf))
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if err != nil {
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return nil, fmt.Errorf("failed to write to a QUIC stream: %w", err)
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}
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// The client MUST send the DNS query over the selected stream, and MUST
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// indicate through the STREAM FIN mechanism that no further data will
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// be sent on that stream. Note, that stream.Close() closes the
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// write-direction of the stream, but does not prevent reading from it.
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_ = stream.Close()
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return doq.readMsg(stream)
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}
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// AddPrefix adds a 2-byte prefix with the DNS message length.
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func AddPrefix(b []byte) (m []byte) {
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m = make([]byte, 2+len(b))
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binary.BigEndian.PutUint16(m, uint16(len(b)))
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copy(m[2:], b)
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return m
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}
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// shouldRetry checks what error we received and decides whether it is required
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// to re-open the connection and retry sending the request.
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func (doq *dnsOverQUIC) shouldRetry(err error) (ok bool) {
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return isQUICRetryError(err)
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}
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// getBytesPool returns (creates if needed) a pool we store byte buffers in.
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func (doq *dnsOverQUIC) getBytesPool() (pool *sync.Pool) {
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doq.bytesPoolGuard.Lock()
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defer doq.bytesPoolGuard.Unlock()
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if doq.bytesPool == nil {
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doq.bytesPool = &sync.Pool{
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New: func() interface{} {
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b := make([]byte, MaxMsgSize)
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return &b
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},
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}
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}
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return doq.bytesPool
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}
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// getConnection opens or returns an existing quic.Connection. useCached
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// argument controls whether we should try to use the existing cached
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// connection. If it is false, we will forcibly create a new connection and
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// close the existing one if needed.
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func (doq *dnsOverQUIC) getConnection(ctx context.Context, useCached bool) (quic.Connection, error) {
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var conn quic.Connection
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doq.connMu.RLock()
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conn = doq.conn
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if conn != nil && useCached {
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doq.connMu.RUnlock()
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return conn, nil
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}
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if conn != nil {
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// we're recreating the connection, let's create a new one.
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_ = conn.CloseWithError(QUICCodeNoError, "")
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}
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doq.connMu.RUnlock()
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doq.connMu.Lock()
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defer doq.connMu.Unlock()
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var err error
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conn, err = doq.openConnection(ctx)
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if err != nil {
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return nil, err
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}
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doq.conn = conn
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return conn, nil
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}
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// hasConnection returns true if there's an active QUIC connection.
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func (doq *dnsOverQUIC) hasConnection() (ok bool) {
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doq.connMu.Lock()
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defer doq.connMu.Unlock()
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return doq.conn != nil
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}
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// getQUICConfig returns the QUIC config in a thread-safe manner. Note, that
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// this method returns a pointer, it is forbidden to change its properties.
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func (doq *dnsOverQUIC) getQUICConfig() (c *quic.Config) {
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doq.quicConfigGuard.Lock()
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defer doq.quicConfigGuard.Unlock()
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return doq.quicConfig
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}
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// resetQUICConfig re-creates the tokens store as we may need to use a new one
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// if we failed to connect.
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func (doq *dnsOverQUIC) resetQUICConfig() {
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doq.quicConfigGuard.Lock()
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defer doq.quicConfigGuard.Unlock()
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doq.quicConfig = doq.quicConfig.Clone()
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doq.quicConfig.TokenStore = newQUICTokenStore()
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}
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// openStream opens a new QUIC stream for the specified connection.
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func (doq *dnsOverQUIC) openStream(ctx context.Context, conn quic.Connection) (quic.Stream, error) {
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ctx, cancel := context.WithCancel(ctx)
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defer cancel()
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stream, err := conn.OpenStreamSync(ctx)
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if err == nil {
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return stream, nil
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}
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// We can get here if the old QUIC connection is not valid anymore. We
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// should try to re-create the connection again in this case.
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newConn, err := doq.getConnection(ctx, false)
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if err != nil {
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return nil, err
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}
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// Open a new stream.
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return newConn.OpenStreamSync(ctx)
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}
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// openConnection opens a new QUIC connection.
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func (doq *dnsOverQUIC) openConnection(ctx context.Context) (conn quic.Connection, err error) {
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tlsConfig := tlsC.GetGlobalFingerprintTLCConfig(
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&tls.Config{
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InsecureSkipVerify: false,
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NextProtos: []string{
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NextProtoDQ,
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},
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SessionTicketsDisabled: false,
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})
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// we're using bootstrapped address instead of what's passed to the function
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// it does not create an actual connection, but it helps us determine
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// what IP is actually reachable (when there're v4/v6 addresses).
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rawConn, err := getDialHandler(doq.r, doq.proxyAdapter)(ctx, "udp", doq.addr)
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if err != nil {
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return nil, fmt.Errorf("failed to open a QUIC connection: %w", err)
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}
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addr := rawConn.RemoteAddr().String()
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// It's never actually used
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_ = rawConn.Close()
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ip, port, err := net.SplitHostPort(addr)
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if err != nil {
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return nil, err
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}
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p, err := strconv.Atoi(port)
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udpAddr := net.UDPAddr{IP: net.ParseIP(ip), Port: p}
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udp, err := listenPacket(ctx, doq.proxyAdapter, "udp", addr, doq.r)
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if err != nil {
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return nil, err
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}
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host, _, err := net.SplitHostPort(doq.addr)
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if err != nil {
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return nil, err
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}
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conn, err = quic.DialContext(ctx, udp, &udpAddr, host, tlsConfig, doq.getQUICConfig())
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if err != nil {
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return nil, fmt.Errorf("opening quic connection to %s: %w", doq.addr, err)
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}
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return conn, nil
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}
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// closeConnWithError closes the active connection with error to make sure that
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// new queries were processed in another connection. We can do that in the case
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// of a fatal error.
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func (doq *dnsOverQUIC) closeConnWithError(err error) {
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doq.connMu.Lock()
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defer doq.connMu.Unlock()
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if doq.conn == nil {
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// Do nothing, there's no active conn anyways.
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return
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}
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code := QUICCodeNoError
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if err != nil {
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code = QUICCodeInternalError
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}
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if errors.Is(err, quic.Err0RTTRejected) {
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// Reset the TokenStore only if 0-RTT was rejected.
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doq.resetQUICConfig()
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}
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err = doq.conn.CloseWithError(code, "")
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if err != nil {
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log.Errorln("failed to close the conn: %v", err)
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}
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doq.conn = nil
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}
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// readMsg reads the incoming DNS message from the QUIC stream.
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func (doq *dnsOverQUIC) readMsg(stream quic.Stream) (m *D.Msg, err error) {
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pool := doq.getBytesPool()
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bufPtr := pool.Get().(*[]byte)
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defer pool.Put(bufPtr)
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respBuf := *bufPtr
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n, err := stream.Read(respBuf)
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if err != nil && n == 0 {
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return nil, fmt.Errorf("reading response from %s: %w", doq.Address(), err)
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}
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// All DNS messages (queries and responses) sent over DoQ connections MUST
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// be encoded as a 2-octet length field followed by the message content as
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// specified in [RFC1035].
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// IMPORTANT: Note, that we ignore this prefix here as this implementation
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// does not support receiving multiple messages over a single connection.
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m = new(D.Msg)
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err = m.Unpack(respBuf[2:])
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if err != nil {
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return nil, fmt.Errorf("unpacking response from %s: %w", doq.Address(), err)
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}
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return m, nil
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}
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// newQUICTokenStore creates a new quic.TokenStore that is necessary to have
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// in order to benefit from 0-RTT.
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func newQUICTokenStore() (s quic.TokenStore) {
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// You can read more on address validation here:
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// https://datatracker.ietf.org/doc/html/rfc9000#section-8.1
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// Setting maxOrigins to 1 and tokensPerOrigin to 10 assuming that this is
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// more than enough for the way we use it (one connection per upstream).
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return quic.NewLRUTokenStore(1, 10)
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}
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// isQUICRetryError checks the error and determines whether it may signal that
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// we should re-create the QUIC connection. This requirement is caused by
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// quic-go issues, see the comments inside this function.
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// TODO(ameshkov): re-test when updating quic-go.
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func isQUICRetryError(err error) (ok bool) {
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var qAppErr *quic.ApplicationError
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if errors.As(err, &qAppErr) && qAppErr.ErrorCode == 0 {
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// This error is often returned when the server has been restarted,
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// and we try to use the same connection on the client-side. It seems,
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// that the old connections aren't closed immediately on the server-side
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// and that's why one can run into this.
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// In addition to that, quic-go HTTP3 client implementation does not
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// clean up dead connections (this one is specific to DoH3 upstream):
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// https://github.com/metacubex/quic-go/issues/765
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return true
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}
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var qIdleErr *quic.IdleTimeoutError
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if errors.As(err, &qIdleErr) {
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// This error means that the connection was closed due to being idle.
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// In this case we should forcibly re-create the QUIC connection.
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// Reproducing is rather simple, stop the server and wait for 30 seconds
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// then try to send another request via the same upstream.
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return true
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}
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var resetErr *quic.StatelessResetError
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if errors.As(err, &resetErr) {
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// A stateless reset is sent when a server receives a QUIC packet that
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// it doesn't know how to decrypt. For instance, it may happen when
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// the server was recently rebooted. We should reconnect and try again
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// in this case.
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return true
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}
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var qTransportError *quic.TransportError
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if errors.As(err, &qTransportError) && qTransportError.ErrorCode == quic.NoError {
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// A transport error with the NO_ERROR error code could be sent by the
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// server when it considers that it's time to close the connection.
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// For example, Google DNS eventually closes an active connection with
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// the NO_ERROR code and "Connection max age expired" message:
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// https://github.com/AdguardTeam/dnsproxy/issues/283
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return true
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}
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if errors.Is(err, quic.Err0RTTRejected) {
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// This error happens when we try to establish a 0-RTT connection with
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// a token the server is no more aware of. This can be reproduced by
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// restarting the QUIC server (it will clear its tokens cache). The
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// next connection attempt will return this error until the client's
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// tokens cache is purged.
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return true
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}
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return false
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}
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