fix(dnssec): fix DNSSEC by adding TCP fallback to DoUDP

common/dnssec/validator.go

@@ -5,6 +5,12 @@ import (
 	"github.com/miekg/dns"
 )
 
+type Exchanger interface {
+	Query(msg *dns.Msg) (sent, resp *dns.Msg, err error)
+	Close()
+}
+type ExchangeFactory func(server string) (Exchanger, error)
+
 type ValidationStats struct {
 	Queries       int
 	BytesSent     int
@@ -28,8 +34,8 @@ func NewValidator(send SendFunc) *Validator {
 	return &Validator{walker: newTrustWalker(send)}
 }
 
-func NewAuthoritativeValidator() *Validator {
-	return &Validator{walker: newIterativeWalker()}
+func NewAuthoritativeValidator(f ExchangeFactory) *Validator {
+	return &Validator{walker: newIterativeWalker(f)}
 }
 
 func (v *Validator) ValidateResponse(msg *dns.Msg, qname string, qtype uint16) error {

common/dnssec/walker_iterative.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"net"
 	"strings"
-	"time"
 
 	"github.com/afonsofrancof/sdns-proxy/common/logger"
 	"github.com/miekg/dns"
@@ -12,15 +11,15 @@ import (
 
 // iterativeWalker validates top-down.
 type iterativeWalker struct {
-	client  *dns.Client
-	st      ValidationStats
-	ipCache map[string]string
+	newClient ExchangeFactory
+	st        ValidationStats
+	ipCache   map[string]string
 }
 
-func newIterativeWalker() *iterativeWalker {
+func newIterativeWalker(f ExchangeFactory) *iterativeWalker {
 	return &iterativeWalker{
-		client:  &dns.Client{Timeout: 5 * time.Second},
-		ipCache: make(map[string]string),
+		newClient: f,
+		ipCache:   make(map[string]string),
 	}
 }
 
@@ -38,7 +37,13 @@ func (w *iterativeWalker) exchange(server, name string, qtype uint16) (*dns.Msg,
 	}
 	w.st.Queries++
 
-	resp, _, err := w.client.Exchange(m, server)
+	cl, err := w.newClient(server)
+	if err != nil {
+		return nil, err
+	}
+	defer cl.Close()
+
+	_, resp, err := cl.Query(m)
 	if err == nil && resp != nil {
 		if b, perr := resp.Pack(); perr == nil {
 			w.st.BytesReceived += len(b)

common/protocols/doudp/doudp.go

@@ -115,9 +115,43 @@ func (c *Client) Query(msg *dns.Msg) (*dns.Msg, *dns.Msg, error) {
 		return msg, nil, fmt.Errorf("doudp: failed to unpack DNS response: %w", err)
 	}
 
+	// RFC 1123 / 7766: a truncated UDP answer must be retried over TCP.
+	if response.Truncated {
+		logger.Debug("DoUDP response from %s truncated (TC set), retrying over TCP", c.hostAndPort)
+		tcpResp, terr := c.queryTCP(msg)
+		if terr != nil {
+			return msg, nil, fmt.Errorf("doudp: TCP fallback failed: %w", terr)
+		}
+		response = tcpResp
+	}
+
 	if len(response.Answer) > 0 {
 		logger.Debug("DoUDP response from %s: %d answers", c.hostAndPort, len(response.Answer))
 	}
 
 	return msg, response, nil
 }
+
+func (c *Client) queryTCP(msg *dns.Msg) (*dns.Msg, error) {
+	conn, err := net.DialTimeout("tcp", c.hostAndPort, c.config.WriteTimeout)
+	if err != nil {
+		return nil, fmt.Errorf("dial tcp: %w", err)
+	}
+	defer conn.Close()
+
+	co := &dns.Conn{Conn: conn}
+	if err := co.SetWriteDeadline(time.Now().Add(c.config.WriteTimeout)); err != nil {
+		return nil, fmt.Errorf("set write deadline: %w", err)
+	}
+	if err := co.WriteMsg(msg); err != nil {
+		return nil, fmt.Errorf("write: %w", err)
+	}
+	if err := co.SetReadDeadline(time.Now().Add(c.config.ReadTimeout)); err != nil {
+		return nil, fmt.Errorf("set read deadline: %w", err)
+	}
+	resp, err := co.ReadMsg()
+	if err != nil {
+		return nil, fmt.Errorf("read: %w", err)
+	}
+	return resp, nil
+}