Fix FouList attribute body truncated error with kernel 5.2+

fou module added a bunch of new attributes in commit
torvalds/linux@1713cb3

which caused the old parsing logic failed, fix and add support for these attrributes.

fou.go

@@ -1,21 +1,16 @@
 package netlink
 
 import (
-	"errors"
-)
-
-var (
-	// ErrAttrHeaderTruncated is returned when a netlink attribute's header is
-	// truncated.
-	ErrAttrHeaderTruncated = errors.New("attribute header truncated")
-	// ErrAttrBodyTruncated is returned when a netlink attribute's body is
-	// truncated.
-	ErrAttrBodyTruncated = errors.New("attribute body truncated")
+	"net"
 )
 
 type Fou struct {
 	Family    int
 	Port      int
 	Protocol  int
 	EncapType int
+	Local     net.IP
+	Peer      net.IP
+	PeerPort  int
+	IfIndex   int
 }

fou_linux.go

@@ -1,10 +1,13 @@
+//go:build linux
 // +build linux
 
 package netlink
 
 import (
 	"encoding/binary"
 	"errors"
+	"log"
+	"net"
 
 	"github.com/vishvananda/netlink/nl"
 	"golang.org/x/sys/unix"
@@ -29,6 +32,12 @@ const (
 	FOU_ATTR_IPPROTO
 	FOU_ATTR_TYPE
 	FOU_ATTR_REMCSUM_NOPARTIAL
+	FOU_ATTR_LOCAL_V4
+	FOU_ATTR_LOCAL_V6
+	FOU_ATTR_PEER_V4
+	FOU_ATTR_PEER_V6
+	FOU_ATTR_PEER_PORT
+	FOU_ATTR_IFINDEX
 	FOU_ATTR_MAX = FOU_ATTR_REMCSUM_NOPARTIAL
 )
 
@@ -169,41 +178,28 @@ func (h *Handle) FouList(fam int) ([]Fou, error) {
 }
 
 func deserializeFouMsg(msg []byte) (Fou, error) {
-	// we'll skip to byte 4 to first attribute
-	msg = msg[3:]
-	var shift int
 	fou := Fou{}
 
-	for {
-		// attribute header is at least 16 bits
-		if len(msg) < 4 {
-			return fou, ErrAttrHeaderTruncated
-		}
-
-		lgt := int(binary.BigEndian.Uint16(msg[0:2]))
-		if len(msg) < lgt+4 {
-			return fou, ErrAttrBodyTruncated
-		}
-		attr := binary.BigEndian.Uint16(msg[2:4])
-
-		shift = lgt + 3
-		switch attr {
+	for attr := range nl.ParseAttributes(msg[4:]) {
+		switch attr.Type {
 		case FOU_ATTR_AF:
-			fou.Family = int(msg[5])
+			fou.Family = int(attr.Value[0])
 		case FOU_ATTR_PORT:
-			fou.Port = int(binary.BigEndian.Uint16(msg[5:7]))
-			// port is 2 bytes
-			shift = lgt + 2
+			fou.Port = int(networkOrder.Uint16(attr.Value))
 		case FOU_ATTR_IPPROTO:
-			fou.Protocol = int(msg[5])
+			fou.Protocol = int(attr.Value[0])
 		case FOU_ATTR_TYPE:
-			fou.EncapType = int(msg[5])
-		}
-
-		msg = msg[shift:]
-
-		if len(msg) < 4 {
-			break
+			fou.EncapType = int(attr.Value[0])
+		case FOU_ATTR_LOCAL_V4, FOU_ATTR_LOCAL_V6:
+			fou.Local = net.IP(attr.Value)
+		case FOU_ATTR_PEER_V4, FOU_ATTR_PEER_V6:
+			fou.Peer = net.IP(attr.Value)
+		case FOU_ATTR_PEER_PORT:
+			fou.PeerPort = int(networkOrder.Uint16(attr.Value))
+		case FOU_ATTR_IFINDEX:
+			fou.IfIndex = int(native.Uint16(attr.Value))
+		default:
+			log.Printf("unknown fou attribute from kernel: %+v %v", attr, attr.Type&nl.NLA_TYPE_MASK)
 		}
 	}
 

fou_test.go

@@ -1,8 +1,10 @@
+//go:build linux
 // +build linux
 
 package netlink
 
 import (
+	"net"
 	"testing"
 )
 
@@ -33,20 +35,50 @@ func TestFouDeserializeMsg(t *testing.T) {
 		}
 	}
 
-	// deserialize truncated attribute header
-	msg = []byte{3, 1, 0, 0, 5, 0}
-	if _, err := deserializeFouMsg(msg); err == nil {
-		t.Error("expected attribute header truncated error")
-	} else if err != ErrAttrHeaderTruncated {
-		t.Errorf("unexpected error: %s", err.Error())
+	// deserialize a valid message(kernel >= 5.2)
+	msg = []byte{3, 1, 0, 0, 5, 0, 2, 0, 2, 0, 0, 0, 6, 0, 1, 0, 43, 103, 0, 0, 6, 0, 10, 0, 86, 206, 0, 0, 5, 0, 3, 0, 0, 0, 0, 0, 5, 0, 4, 0, 2, 0, 0, 0, 8, 0, 11, 0, 0, 0, 0, 0, 8, 0, 6, 0, 1, 2, 3, 4, 8, 0, 8, 0, 5, 6, 7, 8}
+	if fou, err := deserializeFouMsg(msg); err != nil {
+		t.Error(err.Error())
+	} else {
+		if fou.Family != FAMILY_V4 {
+			t.Errorf("expected family %d, got %d", FAMILY_V4, fou.Family)
+		}
+
+		if fou.Port != 11111 {
+			t.Errorf("expected port 5555, got %d", fou.Port)
+		}
+
+		if fou.Protocol != 0 { // gue
+			t.Errorf("expected protocol 0, got %d", fou.Protocol)
+		}
+
+		if fou.IfIndex != 0 {
+			t.Errorf("expected ifindex 0, got %d", fou.Protocol)
+		}
+
+		if fou.EncapType != FOU_ENCAP_GUE {
+			t.Errorf("expected encap type %d, got %d", FOU_ENCAP_GUE, fou.EncapType)
+		}
+
+		if expected := net.IPv4(1, 2, 3, 4); !fou.Local.Equal(expected) {
+			t.Errorf("expected local %v, got %v", expected, fou.Local)
+		}
+
+		if expected := net.IPv4(5, 6, 7, 8); !fou.Peer.Equal(expected) {
+			t.Errorf("expected peer %v, got %v", expected, fou.Peer)
+		}
+
+		if fou.PeerPort != 22222 {
+			t.Errorf("expected peer port 0, got %d", fou.PeerPort)
+		}
 	}
 
-	// deserialize truncated attribute header
-	msg = []byte{3, 1, 0, 0, 5, 0, 2, 0, 2, 0, 0}
-	if _, err := deserializeFouMsg(msg); err == nil {
-		t.Error("expected attribute body truncated error")
-	} else if err != ErrAttrBodyTruncated {
+	// unknown attribute should be skipped
+	msg = []byte{3, 1, 0, 0, 5, 0, 112, 0, 2, 0, 0, 0, 5, 0, 2, 0, 2, 0, 0}
+	if fou, err := deserializeFouMsg(msg); err != nil {
 		t.Errorf("unexpected error: %s", err.Error())
+	} else if fou.Family != 2 {
+		t.Errorf("expected family 2, got %d", fou.Family)
 	}
 }
 

fou_unspecified.go

@@ -1,3 +1,4 @@
+//go:build !linux
 // +build !linux
 
 package netlink