dht: Except local network addresses from security checks

dht/dht.go

@@ -139,8 +139,6 @@ func (n *node) IsSecure() bool {
 	if n.id.IsUnset() {
 		return false
 	}
-	// TODO (@onetruecathal): Exempt local peers from security
-	// check as per security extension recommendations
 	return NodeIdSecure(n.id.ByteString(), n.addr.IP())
 }
 

dht/security.go

@@ -43,6 +43,9 @@ func SecureNodeId(id []byte, ip net.IP) {
 // Returns whether the node ID is considered secure. The id is the 20 raw
 // bytes. http://www.libtorrent.org/dht_sec.html
 func NodeIdSecure(id string, ip net.IP) bool {
+	if isLocalNetwork(ip) {
+		return true
+	}
 	if len(id) != 20 {
 		panic(fmt.Sprintf("%q", id))
 	}
@@ -61,3 +64,43 @@ func NodeIdSecure(id string, ip net.IP) bool {
 	}
 	return true
 }
+
+var (
+	classA, classB, classC *net.IPNet
+)
+
+func mustParseCIDRIPNet(s string) *net.IPNet {
+	_, ret, err := net.ParseCIDR(s)
+	if err != nil {
+		panic(err)
+	}
+	return ret
+}
+
+func init() {
+	classA = mustParseCIDRIPNet("10.0.0.0/8")
+	classB = mustParseCIDRIPNet("172.16.0.0/12")
+	classC = mustParseCIDRIPNet("192.168.0.0/16")
+}
+
+// Per http://www.libtorrent.org/dht_sec.html#enforcement, the IP is
+// considered a local network address and should be exempted from node ID
+// verification.
+func isLocalNetwork(ip net.IP) bool {
+	if classA.Contains(ip) {
+		return true
+	}
+	if classB.Contains(ip) {
+		return true
+	}
+	if classC.Contains(ip) {
+		return true
+	}
+	if ip.IsLinkLocalUnicast() {
+		return true
+	}
+	if ip.IsLoopback() {
+		return true
+	}
+	return false
+}

dht/security_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"github.com/anacrolix/missinggo"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -31,19 +32,22 @@ func TestDHTSec(t *testing.T) {
 		{"84.124.73.14", "1b0321dd1bb1fe518101ceef99462b947a01fe01", true},
 		// spec[4] with the 3rd last bit changed. Not valid.
 		{"43.213.53.83", "e56f6cbf5b7c4be0237986d5243b87aa6d51303e", false},
+		// Because class A network.
+		{"10.213.53.83", "e56f6cbf5b7c4be0237986d5243b87aa6d51305a", true},
+		// Because not class A, and id[0]&3 does not match.
+		{"12.213.53.83", "e56f6cbf5b7c4be0237986d5243b87aa6d51305a", false},
+		// Because class C.
+		{"192.168.53.83", "e56f6cbf5b7c4be0237986d5243b87aa6d51305a", true},
 	} {
 		ip := net.ParseIP(case_.ipStr)
 		id, err := hex.DecodeString(case_.nodeIDHex)
 		require.NoError(t, err)
 		secure := NodeIdSecure(string(id), ip)
-		if secure != case_.valid {
-			t.Fatalf("case failed: %v", case_)
-		}
+		assert.Equal(t, case_.valid, secure, "%v", case_)
 		if !secure {
+			// It's not secure, so secure it in place and then check it again.
 			SecureNodeId(id, ip)
-			if !NodeIdSecure(string(id), ip) {
-				t.Fatal("failed to secure node id")
-			}
+			assert.True(t, NodeIdSecure(string(id), ip), "%v", case_)
 		}
 	}
 }