plugin/dns64 : add support for DNS requests over IPv4 network (#4809)

5 files changed, 106 insertions, 9 deletions

diff --git a/plugin/dns64/README.md b/plugin/dns64/README.md
index 65a338b63..c3f4d9680 100644
--- a/plugin/dns64/README.md
+++ b/plugin/dns64/README.md
@@ -27,11 +27,13 @@ Or use this slightly longer form with more options:
 dns64 [PREFIX] {
     [translate_all]
     prefix PREFIX
+    [allow_ipv4]
 }
 ~~~
 
 * `prefix` specifies any local IPv6 prefix to use, instead of the well known prefix (64:ff9b::/96)
 * `translate_all` translates all queries, including responses that have AAAA results.
+* `allow_ipv4` Allow translating queries if they come in over IPv4, default is IPv6 only translation.
 
 ## Examples
 
@@ -70,6 +72,19 @@ Enable translation even if an existing AAAA record is present.
 }
 ~~~
 
+Apply translation even to the requests which arrived over IPv4 network. Warning, the `allow_ipv4` feature will apply 
+translations to requests coming from dual-stack clients. This means that a request for a client that sends an `AAAA`
+that would normal result in an `NXDOMAIN` would get a translated result. 
+This may cause unwanted IPv6 dns64 traffic when a dualstack client would normally use the result of an `A` record request.
+
+~~~ corefile
+. {
+    dns64 {
+        allow_ipv4
+    }
+}
+~~~
+
 ## Metrics
 
 If monitoring is enabled (via the _prometheus_ plugin) then the following metrics are exported:
diff --git a/plugin/dns64/dns64.go b/plugin/dns64/dns64.go
index b06b0bdb9..110bfeadd 100644
--- a/plugin/dns64/dns64.go
+++ b/plugin/dns64/dns64.go
@@ -28,13 +28,14 @@ type DNS64 struct {
 	Next         plugin.Handler
 	Prefix       *net.IPNet
 	TranslateAll bool // Not comply with 5.1.1
+	AllowIPv4    bool
 	Upstream     UpstreamInt
 }
 
 // ServeDNS implements the plugin.Handler interface.
 func (d *DNS64) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
 	// Don't proxy if we don't need to.
-	if !requestShouldIntercept(&request.Request{W: w, Req: r}) {
+	if !d.requestShouldIntercept(&request.Request{W: w, Req: r}) {
 		return d.Next.ServeDNS(ctx, w, r)
 	}
 
@@ -69,13 +70,13 @@ func (d *DNS64) Name() string { return "dns64" }
 
 // requestShouldIntercept returns true if the request represents one that is eligible
 // for DNS64 rewriting:
-// 1. The request came in over IPv6 (not in RFC)
+// 1. The request came in over IPv6 or the 'allow_ipv4' option is set
 // 2. The request is of type AAAA
 // 3. The request is of class INET
-func requestShouldIntercept(req *request.Request) bool {
-	// Only intercept with this when the request came in over IPv6. This is not mentioned in the RFC.
-	// File an issue if you think we should translate even requests made using IPv4, or have a configuration flag
-	if req.Family() == 1 { // If it came in over v4, don't do anything.
+func (d *DNS64) requestShouldIntercept(req *request.Request) bool {
+	// Make sure that request came in over IPv4 unless AllowIPv4 option is enabled.
+	// Translating requests without taking into consideration client (source) IP might be problematic in dual-stack networks.
+	if !d.AllowIPv4 && req.Family() == 1 {
 		return false
 	}
 
diff --git a/plugin/dns64/dns64_test.go b/plugin/dns64/dns64_test.go
index d7f9fdade..de7ab65a8 100644
--- a/plugin/dns64/dns64_test.go
+++ b/plugin/dns64/dns64_test.go
@@ -21,6 +21,58 @@ func To6(prefix, address string) (net.IP, error) {
 	return to6(pref, addr)
 }
 
+func TestRequestShouldIntercept(t *testing.T) {
+	tests := []struct {
+		name      string
+		allowIpv4 bool
+		remoteIP  string
+		msg       *dns.Msg
+		want      bool
+	}{
+		{
+			name:      "should intercept request from IPv6 network - AAAA - IN",
+			allowIpv4: true,
+			remoteIP:  "::1",
+			msg: new(dns.Msg).SetQuestion("example.com", dns.TypeAAAA),
+			want:      true,
+		},
+		{
+			name:      "should intercept request from IPv4 network - AAAA - IN",
+			allowIpv4: true,
+			remoteIP:  "127.0.0.1",
+			msg: new(dns.Msg).SetQuestion("example.com", dns.TypeAAAA),
+			want:      true,
+		},
+		{
+			name:      "should not intercept request from IPv4 network - AAAA - IN",
+			allowIpv4: false,
+			remoteIP:  "127.0.0.1",
+			msg: new(dns.Msg).SetQuestion("example.com", dns.TypeAAAA),
+			want:      false,
+		},
+		{
+			name:      "should not intercept request from IPv6 network - A - IN",
+			allowIpv4: false,
+			remoteIP:  "::1",
+			msg: new(dns.Msg).SetQuestion("example.com", dns.TypeA),
+			want:      false,
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			h := DNS64{AllowIPv4: tc.allowIpv4}
+			rec := dnstest.NewRecorder(&test.ResponseWriter{RemoteIP: tc.remoteIP})
+			r := request.Request{W: rec, Req: tc.msg}
+
+			actual := h.requestShouldIntercept(&r)
+
+			if actual != tc.want {
+				t.Fatalf("Expected %v, but got %v", tc.want, actual)
+			}
+		})
+	}
+}
+
 func TestTo6(t *testing.T) {
 
 	v6, err := To6("64:ff9b::/96", "64.64.64.64")
diff --git a/plugin/dns64/setup.go b/plugin/dns64/setup.go
index 0c53fab4b..134a12a65 100644
--- a/plugin/dns64/setup.go
+++ b/plugin/dns64/setup.go
@@ -66,6 +66,8 @@ func dns64Parse(c *caddy.Controller) (*DNS64, error) {
 				dns64.Prefix = pref
 			case "translate_all":
 				dns64.TranslateAll = true
+			case "allow_ipv4":
+				dns64.AllowIPv4 = true
 			default:
 				return nil, c.Errf("unknown property '%s'", c.Val())
 			}
diff --git a/plugin/dns64/setup_test.go b/plugin/dns64/setup_test.go
index 3b4a4fe0e..e7d13f418 100644
--- a/plugin/dns64/setup_test.go
+++ b/plugin/dns64/setup_test.go
@@ -10,17 +10,20 @@ func TestSetupDns64(t *testing.T) {
 	tests := []struct {
 		inputUpstreams string
 		shouldErr      bool
-		prefix         string
+		wantPrefix     string
+		wantAllowIpv4  bool
 	}{
 		{
 			`dns64`,
 			false,
 			"64:ff9b::/96",
+			false,
 		},
 		{
 			`dns64 64:dead::/96`,
 			false,
 			"64:dead::/96",
+			false,
 		},
 		{
 			`dns64 {
@@ -28,11 +31,13 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			false,
 			"64:ff9b::/96",
+			false,
 		},
 		{
 			`dns64`,
 			false,
 			"64:ff9b::/96",
+			false,
 		},
 		{
 			`dns64 {
@@ -40,6 +45,7 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			false,
 			"64:ff9b::/96",
+			false,
 		},
 		{
 			`dns64 {
@@ -47,6 +53,7 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			false,
 			"64:ff9b::/32",
+			false,
 		},
 		{
 			`dns64 {
@@ -54,6 +61,7 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			true,
 			"64:ff9b::/52",
+			false,
 		},
 		{
 			`dns64 {
@@ -61,6 +69,7 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			true,
 			"64:ff9b::/104",
+			false,
 		},
 		{
 			`dns64 {
@@ -68,6 +77,7 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			true,
 			"8.8.9.9/24",
+			false,
 		},
 		{
 			`dns64 {
@@ -75,6 +85,7 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			false,
 			"64:ff9b::/96",
+			false,
 		},
 		{
 			`dns64 {
@@ -82,6 +93,7 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			false,
 			"2002:ac12:b083::/96",
+			false,
 		},
 		{
 			`dns64 {
@@ -89,6 +101,7 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			false,
 			"2002:c0a8:a88a::/48",
+			false,
 		},
 		{
 			`dns64 foobar {
@@ -96,11 +109,13 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			true,
 			"64:ff9b::/96",
+			false,
 		},
 		{
 			`dns64 foobar`,
 			true,
 			"64:ff9b::/96",
+			false,
 		},
 		{
 			`dns64 {
@@ -108,6 +123,15 @@ func TestSetupDns64(t *testing.T) {
 			}`,
 			true,
 			"64:ff9b::/96",
+			false,
+		},
+		{
+			`dns64 {
+				allow_ipv4
+			}`,
+			false,
+			"64:ff9b::/96",
+			true,
 		},
 	}
 
@@ -118,8 +142,11 @@ func TestSetupDns64(t *testing.T) {
 			t.Errorf("Test %d expected %v error, got %v for %s", i+1, test.shouldErr, err, test.inputUpstreams)
 		}
 		if err == nil {
-			if dns64.Prefix.String() != test.prefix {
-				t.Errorf("Test %d expected prefix %s, got %v", i+1, test.prefix, dns64.Prefix.String())
+			if dns64.Prefix.String() != test.wantPrefix {
+				t.Errorf("Test %d expected prefix %s, got %v", i+1, test.wantPrefix, dns64.Prefix.String())
+			}
+			if dns64.AllowIPv4 != test.wantAllowIpv4 {
+				t.Errorf("Test %d expected prefix %v, got %v", i+1, test.wantAllowIpv4, dns64.AllowIPv4)
 			}
 		}
 	}