rule: add Rule.Type to allow adding/listing unreachable (RTN_UNREACHABLE) rules

Updates #710

Co-authored-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Signed-off-by: Percy Wegmann <percy@tailscale.com>

rule.go

@@ -28,6 +28,7 @@ type Rule struct {
 	IPProto           int
 	UIDRange          *RuleUIDRange
 	Protocol          uint8
+	Type              uint8
 }
 
 func (r Rule) String() string {
@@ -41,8 +42,8 @@ func (r Rule) String() string {
 		to = r.Dst.String()
 	}
 
-	return fmt.Sprintf("ip rule %d: from %s to %s table %d",
-		r.Priority, from, to, r.Table)
+	return fmt.Sprintf("ip rule %d: from %s to %s table %d %s",
+		r.Priority, from, to, r.Table, r.typeString())
 }
 
 // NewRule return empty rules.

rule_linux.go

@@ -43,8 +43,8 @@ func ruleHandle(rule *Rule, req *nl.NetlinkRequest) error {
 	msg.Protocol = unix.RTPROT_BOOT
 	msg.Scope = unix.RT_SCOPE_UNIVERSE
 	msg.Table = unix.RT_TABLE_UNSPEC
-	msg.Type = unix.RTN_UNSPEC
-	if req.NlMsghdr.Flags&unix.NLM_F_CREATE > 0 {
+	msg.Type = rule.Type // usually 0, same as unix.RTN_UNSPEC
+	if msg.Type == 0 && req.NlMsghdr.Flags&unix.NLM_F_CREATE > 0 {
 		msg.Type = unix.RTN_UNICAST
 	}
 	if rule.Invert {
@@ -332,3 +332,34 @@ func ptrEqual(a, b *uint32) bool {
 	}
 	return *a == *b
 }
+
+func (r Rule) typeString() string {
+	switch r.Type {
+	case unix.RTN_UNSPEC: // zero
+		return ""
+	case unix.RTN_UNICAST:
+		return ""
+	case unix.RTN_LOCAL:
+		return "local"
+	case unix.RTN_BROADCAST:
+		return "broadcast"
+	case unix.RTN_ANYCAST:
+		return "anycast"
+	case unix.RTN_MULTICAST:
+		return "multicast"
+	case unix.RTN_BLACKHOLE:
+		return "blackhole"
+	case unix.RTN_UNREACHABLE:
+		return "unreachable"
+	case unix.RTN_PROHIBIT:
+		return "prohibit"
+	case unix.RTN_THROW:
+		return "throw"
+	case unix.RTN_NAT:
+		return "nat"
+	case unix.RTN_XRESOLVE:
+		return "xresolve"
+	default:
+		return fmt.Sprintf("type(0x%x)", r.Type)
+	}
+}

rule_nonlinux.go

@@ -0,0 +1,8 @@
+//go:build !linux
+// +build !linux
+
+package netlink
+
+func (r Rule) typeString() string {
+	return ""
+}

rule_test.go

@@ -633,6 +633,13 @@ func TestRuleString(t *testing.T) {
 			},
 			s: "ip rule 100: from 10.0.0.0/24 to 20.0.0.0/24 table 99 ",
 		},
+		"rule with type": {
+			r: Rule{
+				Priority: 101,
+				Type:     unix.RTN_UNREACHABLE,
+			},
+			s: "ip rule 101: from all to all table 0 unreachable",
+		},
 	}
 
 	for name, testCase := range testCases {
@@ -671,6 +678,7 @@ func ruleEquals(a, b Rule) bool {
 		a.IifName == b.IifName &&
 		a.Invert == b.Invert &&
 		a.Tos == b.Tos &&
+		a.Type == b.Type &&
 		a.IPProto == b.IPProto &&
 		a.Protocol == b.Protocol &&
 		a.Mark == b.Mark &&