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doq.go
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doq.go
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package upstream
import (
"context"
"crypto/tls"
"fmt"
"net"
"net/url"
"os"
"runtime"
"sync"
"time"
"github.com/AdguardTeam/dnsproxy/proxyutil"
"github.com/AdguardTeam/golibs/errors"
"github.com/AdguardTeam/golibs/log"
"github.com/miekg/dns"
"github.com/quic-go/quic-go"
"github.com/quic-go/quic-go/http3"
)
const (
// QUICCodeNoError is used when the connection or stream needs to be closed,
// but there is no error to signal.
QUICCodeNoError = quic.ApplicationErrorCode(0)
// QUICCodeInternalError signals that the DoQ implementation encountered
// an internal error and is incapable of pursuing the transaction or the
// connection.
QUICCodeInternalError = quic.ApplicationErrorCode(1)
// QUICKeepAlivePeriod is the value that we pass to *quic.Config and that
// controls the period with with keep-alive frames are being sent to the
// connection. We set it to 20s as it would be in the quic-go@v0.27.1 with
// KeepAlive field set to true This value is specified in
// https://pkg.go.dev/github.com/quic-go/quic-go/internal/protocol#MaxKeepAliveInterval.
//
// TODO(ameshkov): Consider making it configurable.
QUICKeepAlivePeriod = time.Second * 20
// NextProtoDQ is the ALPN token for DoQ. During the connection establishment,
// DNS/QUIC support is indicated by selecting the ALPN token "doq" in the
// crypto handshake.
//
// See https://datatracker.ietf.org/doc/rfc9250.
NextProtoDQ = "doq"
)
// compatProtoDQ is a list of ALPN tokens used by a QUIC connection.
// NextProtoDQ is the latest draft version supported by dnsproxy, but it also
// includes previous drafts.
var compatProtoDQ = []string{NextProtoDQ, "doq-i00", "dq", "doq-i02"}
// dnsOverQUIC implements the [Upstream] interface for the DNS-over-QUIC
// protocol (spec: https://www.rfc-editor.org/rfc/rfc9250.html).
type dnsOverQUIC struct {
// getDialer either returns an initialized dial handler or creates a new
// one.
getDialer DialerInitializer
// addr is the DNS-over-QUIC server URL.
addr *url.URL
// tlsConf is the configuration of TLS.
tlsConf *tls.Config
// quicConfig is the QUIC configuration that is used for establishing
// connections to the upstream. This configuration includes the TokenStore
// that needs to be stored for the lifetime of dnsOverQUIC since we can
// re-create the connection.
quicConfig *quic.Config
// conn is the current active QUIC connection. It can be closed and
// re-opened when needed.
conn quic.Connection
// bytesPool is a *sync.Pool we use to store byte buffers in. These byte
// buffers are used to read responses from the upstream.
bytesPool *sync.Pool
// quicConfigMu protects quicConfig.
quicConfigMu *sync.Mutex
// connMu protects conn.
connMu *sync.Mutex
// bytesPoolGuard protects bytesPool.
bytesPoolMu *sync.Mutex
// timeout is the timeout for the upstream connection.
timeout time.Duration
}
// newDoQ returns the DNS-over-QUIC Upstream.
func newDoQ(addr *url.URL, opts *Options) (u Upstream, err error) {
addPort(addr, defaultPortDoQ)
u = &dnsOverQUIC{
getDialer: newDialerInitializer(addr, opts),
addr: addr,
quicConfig: &quic.Config{
KeepAlivePeriod: QUICKeepAlivePeriod,
TokenStore: newQUICTokenStore(),
Tracer: opts.QUICTracer,
},
tlsConf: &tls.Config{
ServerName: addr.Hostname(),
RootCAs: opts.RootCAs,
CipherSuites: opts.CipherSuites,
// Use the default capacity for the LRU cache. It may be useful to
// store several caches since the user may be routed to different
// servers in case there's load balancing on the server-side.
ClientSessionCache: tls.NewLRUClientSessionCache(0),
MinVersion: tls.VersionTLS12,
// #nosec G402 -- TLS certificate verification could be disabled by
// configuration.
InsecureSkipVerify: opts.InsecureSkipVerify,
VerifyPeerCertificate: opts.VerifyServerCertificate,
VerifyConnection: opts.VerifyConnection,
NextProtos: compatProtoDQ,
},
quicConfigMu: &sync.Mutex{},
connMu: &sync.Mutex{},
bytesPoolMu: &sync.Mutex{},
timeout: opts.Timeout,
}
runtime.SetFinalizer(u, (*dnsOverQUIC).Close)
return u, nil
}
// type check
var _ Upstream = (*dnsOverQUIC)(nil)
// Address implements the [Upstream] interface for *dnsOverQUIC.
func (p *dnsOverQUIC) Address() string { return p.addr.String() }
// Exchange implements the [Upstream] interface for *dnsOverQUIC.
func (p *dnsOverQUIC) Exchange(m *dns.Msg) (resp *dns.Msg, err error) {
// When sending queries over a QUIC connection, the DNS Message ID MUST be
// set to zero.
id := m.Id
m.Id = 0
defer func() {
// Restore the original ID to not break compatibility with proxies.
m.Id = id
if resp != nil {
resp.Id = id
}
}()
// Check if there was already an active conn before sending the request.
// We'll only attempt to re-connect if there was one.
hasConnection := p.hasConnection()
// Make the first attempt to send the DNS query.
resp, err = p.exchangeQUIC(m)
// Make up to 2 attempts to re-open the QUIC connection and send the request
// again. There are several cases where this workaround is necessary to
// make DoQ usable. We need to make 2 attempts in the case when the
// connection was closed (due to inactivity for example) AND the server
// refuses to open a 0-RTT connection.
for i := 0; hasConnection && isQUICRetryError(err) && i < 2; i++ {
log.Debug("dnsproxy: re-creating the QUIC connection and retrying due to %v", err)
// Close the active connection to make sure we'll try to re-connect.
p.closeConnWithError(err)
// Retry sending the request.
resp, err = p.exchangeQUIC(m)
}
if err != nil {
// If we're unable to exchange messages, make sure the connection is
// closed and signal about an internal error.
p.closeConnWithError(err)
}
return resp, err
}
// Close implements the [Upstream] interface for *dnsOverQUIC.
func (p *dnsOverQUIC) Close() (err error) {
p.connMu.Lock()
defer p.connMu.Unlock()
runtime.SetFinalizer(p, nil)
if p.conn != nil {
err = p.conn.CloseWithError(QUICCodeNoError, "")
}
return err
}
// exchangeQUIC attempts to open a QUIC connection, send the DNS message
// through it and return the response it got from the server.
func (p *dnsOverQUIC) exchangeQUIC(req *dns.Msg) (resp *dns.Msg, err error) {
addr := p.Address()
logBegin(addr, networkUDP, req)
defer func() { logFinish(addr, networkUDP, err) }()
conn, err := p.getConnection(true)
if err != nil {
return nil, err
}
buf, err := req.Pack()
if err != nil {
return nil, fmt.Errorf("failed to pack DNS message for DoQ: %w", err)
}
stream, err := p.openStream(conn)
if err != nil {
return nil, fmt.Errorf("opening stream: %w", err)
}
if p.timeout > 0 {
err = stream.SetDeadline(time.Now().Add(p.timeout))
if err != nil {
return nil, fmt.Errorf("setting deadline: %w", err)
}
}
_, err = stream.Write(proxyutil.AddPrefix(buf))
if err != nil {
return nil, fmt.Errorf("failed to write to a QUIC stream: %w", err)
}
// The client MUST send the DNS query over the selected stream, and MUST
// indicate through the STREAM FIN mechanism that no further data will be
// sent on that stream. Note, that stream.Close() closes the write-direction
// of the stream, but does not prevent reading from it.
err = stream.Close()
if err != nil {
log.Debug("dnsproxy: closing quic stream: %s", err)
}
return p.readMsg(stream)
}
// getBytesPool returns (creates if needed) a pool we store byte buffers in.
func (p *dnsOverQUIC) getBytesPool() (pool *sync.Pool) {
p.bytesPoolMu.Lock()
defer p.bytesPoolMu.Unlock()
if p.bytesPool == nil {
p.bytesPool = &sync.Pool{
New: func() interface{} {
b := make([]byte, dns.MaxMsgSize)
return &b
},
}
}
return p.bytesPool
}
// getConnection opens or returns an existing quic.Connection. useCached
// argument controls whether we should try to use the existing cached
// connection. If it is false, we will forcibly create a new connection and
// close the existing one if needed.
func (p *dnsOverQUIC) getConnection(useCached bool) (c quic.Connection, err error) {
var conn quic.Connection
p.connMu.Lock()
defer p.connMu.Unlock()
conn = p.conn
if conn != nil {
if useCached {
return conn, nil
}
// We're recreating the connection, let's create a new one.
err = conn.CloseWithError(QUICCodeNoError, "")
if err != nil {
log.Debug("dnsproxy: closing stale connection: %s", err)
}
}
conn, err = p.openConnection()
if err != nil {
return nil, err
}
p.conn = conn
return conn, nil
}
// hasConnection returns true if there's an active QUIC connection.
func (p *dnsOverQUIC) hasConnection() (ok bool) {
p.connMu.Lock()
defer p.connMu.Unlock()
return p.conn != nil
}
// getQUICConfig returns the QUIC config in a thread-safe manner. Note, that
// this method returns a pointer, it is forbidden to change its properties.
func (p *dnsOverQUIC) getQUICConfig() (c *quic.Config) {
p.quicConfigMu.Lock()
defer p.quicConfigMu.Unlock()
return p.quicConfig
}
// resetQUICConfig re-creates the tokens store as we may need to use a new one
// if we failed to connect.
func (p *dnsOverQUIC) resetQUICConfig() {
p.quicConfigMu.Lock()
defer p.quicConfigMu.Unlock()
p.quicConfig = p.quicConfig.Clone()
p.quicConfig.TokenStore = newQUICTokenStore()
}
// openStream opens a new QUIC stream for the specified connection.
func (p *dnsOverQUIC) openStream(conn quic.Connection) (quic.Stream, error) {
ctx, cancel := p.withDeadline(context.Background())
defer cancel()
stream, err := conn.OpenStreamSync(ctx)
if err != nil {
log.Debug("dnsproxy: opening quic stream: %s", err)
} else {
return stream, nil
}
// We can get here if the old QUIC connection is not valid anymore. We
// should try to re-create the connection again in this case.
newConn, err := p.getConnection(false)
if err != nil {
return nil, err
}
// Open a new stream.
return newConn.OpenStreamSync(ctx)
}
// openConnection dials a new QUIC connection.
func (p *dnsOverQUIC) openConnection() (conn quic.Connection, err error) {
dialContext, err := p.getDialer()
if err != nil {
return nil, fmt.Errorf("bootstrapping %s: %w", p.addr, err)
}
// we're using bootstrapped address instead of what's passed to the function
// it does not create an actual connection, but it helps us determine
// what IP is actually reachable (when there're v4/v6 addresses).
rawConn, err := dialContext(context.Background(), "udp", "")
if err != nil {
return nil, fmt.Errorf("dialing raw connection to %s: %w", p.addr, err)
}
// It's never actually used.
err = rawConn.Close()
if err != nil {
log.Debug("dnsproxy: closing raw connection for %s: %s", p.addr, err)
}
udpConn, ok := rawConn.(*net.UDPConn)
if !ok {
return nil, fmt.Errorf("unexpected type %T of connection; should be %T", rawConn, udpConn)
}
addr := udpConn.RemoteAddr().String()
ctx, cancel := p.withDeadline(context.Background())
defer cancel()
conn, err = quic.DialAddrEarly(ctx, addr, p.tlsConf.Clone(), p.getQUICConfig())
if err != nil {
return nil, fmt.Errorf("dialing quic connection to %s: %w", p.addr, err)
}
return conn, nil
}
// closeConnWithError closes the active connection with error to make sure that
// new queries were processed in another connection. We can do that in the case
// of a fatal error.
func (p *dnsOverQUIC) closeConnWithError(err error) {
p.connMu.Lock()
defer p.connMu.Unlock()
if p.conn == nil {
// Do nothing, there's no active conn anyways.
return
}
code := QUICCodeNoError
if err != nil {
code = QUICCodeInternalError
}
if errors.Is(err, quic.Err0RTTRejected) {
// Reset the TokenStore only if 0-RTT was rejected.
p.resetQUICConfig()
}
err = p.conn.CloseWithError(code, "")
if err != nil {
log.Error("dnsproxy: failed to close the conn: %v", err)
}
p.conn = nil
}
// readMsg reads the incoming DNS message from the QUIC stream.
func (p *dnsOverQUIC) readMsg(stream quic.Stream) (m *dns.Msg, err error) {
pool := p.getBytesPool()
bufPtr := pool.Get().(*[]byte)
defer pool.Put(bufPtr)
respBuf := *bufPtr
n, err := stream.Read(respBuf)
if err != nil && n == 0 {
return nil, fmt.Errorf("reading response from %s: %w", p.addr, err)
}
stream.CancelRead(0)
// All DNS messages (queries and responses) sent over DoQ connections MUST
// be encoded as a 2-octet length field followed by the message content as
// specified in [RFC1035].
// IMPORTANT: Note, that we ignore this prefix here as this implementation
// does not support receiving multiple messages over a single connection.
m = new(dns.Msg)
err = m.Unpack(respBuf[2:])
if err != nil {
return nil, fmt.Errorf("unpacking response from %s: %w", p.addr, err)
}
return m, nil
}
// newQUICTokenStore creates a new quic.TokenStore that is necessary to have
// in order to benefit from 0-RTT.
func newQUICTokenStore() (s quic.TokenStore) {
// You can read more on address validation here:
// https://datatracker.ietf.org/doc/html/rfc9000#section-8.1
// Setting maxOrigins to 1 and tokensPerOrigin to 10 assuming that this is
// more than enough for the way we use it (one connection per upstream).
return quic.NewLRUTokenStore(1, 10)
}
// isQUICRetryError checks the error and determines whether it may signal that
// we should re-create the QUIC connection. This requirement is caused by
// quic-go issues, see the comments inside this function.
// TODO(ameshkov): re-test when updating quic-go.
func isQUICRetryError(err error) (ok bool) {
var qAppErr *quic.ApplicationError
if errors.As(err, &qAppErr) {
// Error code 0 is often returned when the server has been restarted,
// and we try to use the same connection on the client-side.
// http3.ErrCodeNoError may be used by an HTTP/3 server when closing
// an idle connection. These connections are not immediately closed
// by the HTTP client so this case should be handled.
if qAppErr.ErrorCode == 0 ||
qAppErr.ErrorCode == quic.ApplicationErrorCode(http3.ErrCodeNoError) {
return true
}
}
var qIdleErr *quic.IdleTimeoutError
if errors.As(err, &qIdleErr) {
// This error means that the connection was closed due to being idle.
// In this case we should forcibly re-create the QUIC connection.
// Reproducing is rather simple, stop the server and wait for 30 seconds
// then try to send another request via the same upstream.
return true
}
var resetErr *quic.StatelessResetError
if errors.As(err, &resetErr) {
// A stateless reset is sent when a server receives a QUIC packet that
// it doesn't know how to decrypt. For instance, it may happen when
// the server was recently rebooted. We should reconnect and try again
// in this case.
return true
}
var qTransportError *quic.TransportError
if errors.As(err, &qTransportError) && qTransportError.ErrorCode == quic.NoError {
// A transport error with the NO_ERROR error code could be sent by the
// server when it considers that it's time to close the connection.
// For example, Google DNS eventually closes an active connection with
// the NO_ERROR code and "Connection max age expired" message:
// https://github.com/AdguardTeam/dnsproxy/issues/283
return true
}
if errors.Is(err, quic.Err0RTTRejected) {
// This error happens when we try to establish a 0-RTT connection with
// a token the server is no more aware of. This can be reproduced by
// restarting the QUIC server (it will clear its tokens cache). The
// next connection attempt will return this error until the client's
// tokens cache is purged.
return true
}
if errors.Is(err, os.ErrDeadlineExceeded) {
// A timeout that could happen when the server has been restarted.
return true
}
return false
}
func (p *dnsOverQUIC) withDeadline(
parent context.Context,
) (ctx context.Context, cancel context.CancelFunc) {
ctx, cancel = parent, func() {}
if p.timeout > 0 {
ctx, cancel = context.WithDeadline(ctx, time.Now().Add(p.timeout))
}
return ctx, cancel
}