ip6tables: filter table support

`ip6tables -t filter` is now usable. NAT support will come in a future CL.

#3549

PiperOrigin-RevId: 332381801

12 files changed, 515 insertions, 93 deletions

diff --git a/Makefile b/Makefile
index e4b5b5b8e..d0d1840f6 100644
--- a/Makefile
+++ b/Makefile
@@ -200,6 +200,8 @@ kvm-tests: load-basic-images
 .PHONY: kvm-tests
 
 iptables-tests: load-iptables
+	@sudo modprobe iptable_filter
+	@sudo modprobe ip6table_filter
 	@$(call submake,test-runtime RUNTIME="runc" TARGETS="//test/iptables:iptables_test")
 	@$(call submake,install-test-runtime RUNTIME="iptables" ARGS="--net-raw")
 	@$(call submake,test-runtime RUNTIME="iptables" TARGETS="//test/iptables:iptables_test")
diff --git a/pkg/sentry/socket/netfilter/netfilter.go b/pkg/sentry/socket/netfilter/netfilter.go
index 3e1735079..871ea80ee 100644
--- a/pkg/sentry/socket/netfilter/netfilter.go
+++ b/pkg/sentry/socket/netfilter/netfilter.go
@@ -146,6 +146,10 @@ func SetEntries(stk *stack.Stack, optVal []byte, ipv6 bool) *syserr.Error {
 	case stack.FilterTable:
 		table = stack.EmptyFilterTable()
 	case stack.NATTable:
+		if ipv6 {
+			nflog("IPv6 redirection not yet supported (gvisor.dev/issue/3549)")
+			return syserr.ErrInvalidArgument
+		}
 		table = stack.EmptyNATTable()
 	default:
 		nflog("we don't yet support writing to the %q table (gvisor.dev/issue/170)", replace.Name.String())
diff --git a/pkg/sentry/socket/netfilter/tcp_matcher.go b/pkg/sentry/socket/netfilter/tcp_matcher.go
index 0bfd6c1f4..844acfede 100644
--- a/pkg/sentry/socket/netfilter/tcp_matcher.go
+++ b/pkg/sentry/socket/netfilter/tcp_matcher.go
@@ -97,17 +97,33 @@ func (*TCPMatcher) Name() string {
 
 // Match implements Matcher.Match.
 func (tm *TCPMatcher) Match(hook stack.Hook, pkt *stack.PacketBuffer, interfaceName string) (bool, bool) {
-	netHeader := header.IPv4(pkt.NetworkHeader().View())
+	// TODO(gvisor.dev/issue/170): Proto checks should ultimately be moved
+	// into the stack.Check codepath as matchers are added.
+	switch pkt.NetworkProtocolNumber {
+	case header.IPv4ProtocolNumber:
+		netHeader := header.IPv4(pkt.NetworkHeader().View())
+		if netHeader.TransportProtocol() != header.TCPProtocolNumber {
+			return false, false
+		}
 
-	if netHeader.TransportProtocol() != header.TCPProtocolNumber {
-		return false, false
-	}
+		// We don't match fragments.
+		if frag := netHeader.FragmentOffset(); frag != 0 {
+			if frag == 1 {
+				return false, true
+			}
+			return false, false
+		}
 
-	// We dont't match fragments.
-	if frag := netHeader.FragmentOffset(); frag != 0 {
-		if frag == 1 {
-			return false, true
+	case header.IPv6ProtocolNumber:
+		// As in Linux, we do not perform an IPv6 fragment check. See
+		// xt_action_param.fragoff in
+		// include/linux/netfilter/x_tables.h.
+		if header.IPv6(pkt.NetworkHeader().View()).TransportProtocol() != header.TCPProtocolNumber {
+			return false, false
 		}
+
+	default:
+		// We don't know the network protocol.
 		return false, false
 	}
 
diff --git a/pkg/sentry/socket/netfilter/udp_matcher.go b/pkg/sentry/socket/netfilter/udp_matcher.go
index 7ed05461d..63201201c 100644
--- a/pkg/sentry/socket/netfilter/udp_matcher.go
+++ b/pkg/sentry/socket/netfilter/udp_matcher.go
@@ -94,19 +94,33 @@ func (*UDPMatcher) Name() string {
 
 // Match implements Matcher.Match.
 func (um *UDPMatcher) Match(hook stack.Hook, pkt *stack.PacketBuffer, interfaceName string) (bool, bool) {
-	netHeader := header.IPv4(pkt.NetworkHeader().View())
-
 	// TODO(gvisor.dev/issue/170): Proto checks should ultimately be moved
 	// into the stack.Check codepath as matchers are added.
-	if netHeader.TransportProtocol() != header.UDPProtocolNumber {
-		return false, false
-	}
+	switch pkt.NetworkProtocolNumber {
+	case header.IPv4ProtocolNumber:
+		netHeader := header.IPv4(pkt.NetworkHeader().View())
+		if netHeader.TransportProtocol() != header.UDPProtocolNumber {
+			return false, false
+		}
 
-	// We dont't match fragments.
-	if frag := netHeader.FragmentOffset(); frag != 0 {
-		if frag == 1 {
-			return false, true
+		// We don't match fragments.
+		if frag := netHeader.FragmentOffset(); frag != 0 {
+			if frag == 1 {
+				return false, true
+			}
+			return false, false
 		}
+
+	case header.IPv6ProtocolNumber:
+		// As in Linux, we do not perform an IPv6 fragment check. See
+		// xt_action_param.fragoff in
+		// include/linux/netfilter/x_tables.h.
+		if header.IPv6(pkt.NetworkHeader().View()).TransportProtocol() != header.UDPProtocolNumber {
+			return false, false
+		}
+
+	default:
+		// We don't know the network protocol.
 		return false, false
 	}
 
diff --git a/pkg/tcpip/network/ipv4/ipv4.go b/pkg/tcpip/network/ipv4/ipv4.go
index f4394749d..a75c4cdda 100644
--- a/pkg/tcpip/network/ipv4/ipv4.go
+++ b/pkg/tcpip/network/ipv4/ipv4.go
@@ -238,11 +238,13 @@ func (e *endpoint) WritePacket(r *stack.Route, gso *stack.GSO, params stack.Netw
 		return nil
 	}
 
-	// If the packet is manipulated as per NAT Ouput rules, handle packet
-	// based on destination address and do not send the packet to link layer.
-	// TODO(gvisor.dev/issue/170): We should do this for every packet, rather than
-	// only NATted packets, but removing this check short circuits broadcasts
-	// before they are sent out to other hosts.
+	// If the packet is manipulated as per NAT Output rules, handle packet
+	// based on destination address and do not send the packet to link
+	// layer.
+	//
+	// TODO(gvisor.dev/issue/170): We should do this for every
+	// packet, rather than only NATted packets, but removing this check
+	// short circuits broadcasts before they are sent out to other hosts.
 	if pkt.NatDone {
 		netHeader := header.IPv4(pkt.NetworkHeader().View())
 		ep, err := e.stack.FindNetworkEndpoint(header.IPv4ProtocolNumber, netHeader.DestinationAddress())
@@ -298,7 +300,7 @@ func (e *endpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts stack.Packe
 		return n, err
 	}
 
-	// Slow Path as we are dropping some packets in the batch degrade to
+	// Slow path as we are dropping some packets in the batch degrade to
 	// emitting one packet at a time.
 	n := 0
 	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index e821a8bff..fc8dfea42 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -107,6 +107,31 @@ func (e *endpoint) addIPHeader(r *stack.Route, pkt *stack.PacketBuffer, params s
 func (e *endpoint) WritePacket(r *stack.Route, gso *stack.GSO, params stack.NetworkHeaderParams, pkt *stack.PacketBuffer) *tcpip.Error {
 	e.addIPHeader(r, pkt, params)
 
+	// iptables filtering. All packets that reach here are locally
+	// generated.
+	nicName := e.stack.FindNICNameFromID(e.NICID())
+	ipt := e.stack.IPTables()
+	if ok := ipt.Check(stack.Output, pkt, gso, r, "", nicName); !ok {
+		// iptables is telling us to drop the packet.
+		return nil
+	}
+
+	// If the packet is manipulated as per NAT Output rules, handle packet
+	// based on destination address and do not send the packet to link
+	// layer.
+	//
+	// TODO(gvisor.dev/issue/170): We should do this for every
+	// packet, rather than only NATted packets, but removing this check
+	// short circuits broadcasts before they are sent out to other hosts.
+	if pkt.NatDone {
+		netHeader := header.IPv6(pkt.NetworkHeader().View())
+		if ep, err := e.stack.FindNetworkEndpoint(header.IPv6ProtocolNumber, netHeader.DestinationAddress()); err == nil {
+			route := r.ReverseRoute(netHeader.SourceAddress(), netHeader.DestinationAddress())
+			ep.HandlePacket(&route, pkt)
+			return nil
+		}
+	}
+
 	if r.Loop&stack.PacketLoop != 0 {
 		loopedR := r.MakeLoopedRoute()
 
@@ -138,9 +163,46 @@ func (e *endpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts stack.Packe
 		e.addIPHeader(r, pb, params)
 	}
 
-	n, err := e.linkEP.WritePackets(r, gso, pkts, ProtocolNumber)
+	// iptables filtering. All packets that reach here are locally
+	// generated.
+	nicName := e.stack.FindNICNameFromID(e.NICID())
+	ipt := e.stack.IPTables()
+	dropped, natPkts := ipt.CheckPackets(stack.Output, pkts, gso, r, nicName)
+	if len(dropped) == 0 && len(natPkts) == 0 {
+		// Fast path: If no packets are to be dropped then we can just invoke the
+		// faster WritePackets API directly.
+		n, err := e.linkEP.WritePackets(r, gso, pkts, ProtocolNumber)
+		r.Stats().IP.PacketsSent.IncrementBy(uint64(n))
+		return n, err
+	}
+
+	// Slow path as we are dropping some packets in the batch degrade to
+	// emitting one packet at a time.
+	n := 0
+	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
+		if _, ok := dropped[pkt]; ok {
+			continue
+		}
+		if _, ok := natPkts[pkt]; ok {
+			netHeader := header.IPv6(pkt.NetworkHeader().View())
+			if ep, err := e.stack.FindNetworkEndpoint(header.IPv6ProtocolNumber, netHeader.DestinationAddress()); err == nil {
+				src := netHeader.SourceAddress()
+				dst := netHeader.DestinationAddress()
+				route := r.ReverseRoute(src, dst)
+				ep.HandlePacket(&route, pkt)
+				n++
+				continue
+			}
+		}
+		if err := e.linkEP.WritePacket(r, gso, ProtocolNumber, pkt); err != nil {
+			r.Stats().IP.PacketsSent.IncrementBy(uint64(n))
+			return n, err
+		}
+		n++
+	}
+
 	r.Stats().IP.PacketsSent.IncrementBy(uint64(n))
-	return n, err
+	return n, nil
 }
 
 // WriteHeaderIncludedPacker implements stack.NetworkEndpoint. It is not yet
@@ -169,6 +231,14 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 	it := header.MakeIPv6PayloadIterator(header.IPv6ExtensionHeaderIdentifier(h.NextHeader()), vv)
 	hasFragmentHeader := false
 
+	// iptables filtering. All packets that reach here are intended for
+	// this machine and will not be forwarded.
+	ipt := e.stack.IPTables()
+	if ok := ipt.Check(stack.Input, pkt, nil, nil, "", ""); !ok {
+		// iptables is telling us to drop the packet.
+		return
+	}
+
 	for firstHeader := true; ; firstHeader = false {
 		extHdr, done, err := it.Next()
 		if err != nil {
diff --git a/pkg/tcpip/network/ipv6/ipv6_test.go b/pkg/tcpip/network/ipv6/ipv6_test.go
index 5f9822c49..354d3b60d 100644
--- a/pkg/tcpip/network/ipv6/ipv6_test.go
+++ b/pkg/tcpip/network/ipv6/ipv6_test.go
@@ -1709,3 +1709,211 @@ func TestInvalidIPv6Fragments(t *testing.T) {
 		})
 	}
 }
+
+func TestWritePacketsStats(t *testing.T) {
+	const nPackets = 3
+	tests := []struct {
+		name       string
+		setup      func(*testing.T, *stack.Stack)
+		linkEP     stack.LinkEndpoint
+		expectSent int
+	}{
+		{
+			name: "Accept all",
+			// No setup needed, tables accept everything by default.
+			setup:      func(*testing.T, *stack.Stack) {},
+			linkEP:     &limitedEP{nPackets},
+			expectSent: nPackets,
+		}, {
+			name: "Accept all with error",
+			// No setup needed, tables accept everything by default.
+			setup:      func(*testing.T, *stack.Stack) {},
+			linkEP:     &limitedEP{nPackets - 1},
+			expectSent: nPackets - 1,
+		}, {
+			name: "Drop all",
+			setup: func(t *testing.T, stk *stack.Stack) {
+				// Install Output DROP rule.
+				t.Helper()
+				ipt := stk.IPTables()
+				filter, ok := ipt.GetTable(stack.FilterTable, true /* ipv6 */)
+				if !ok {
+					t.Fatalf("failed to find filter table")
+				}
+				ruleIdx := filter.BuiltinChains[stack.Output]
+				filter.Rules[ruleIdx].Target = stack.DropTarget{}
+				if err := ipt.ReplaceTable(stack.FilterTable, filter, true /* ipv6 */); err != nil {
+					t.Fatalf("failed to replace table: %v", err)
+				}
+			},
+			linkEP:     &limitedEP{nPackets},
+			expectSent: 0,
+		}, {
+			name: "Drop some",
+			setup: func(t *testing.T, stk *stack.Stack) {
+				// Install Output DROP rule that matches only 1
+				// of the 3 packets.
+				t.Helper()
+				ipt := stk.IPTables()
+				filter, ok := ipt.GetTable(stack.FilterTable, true /* ipv6 */)
+				if !ok {
+					t.Fatalf("failed to find filter table")
+				}
+				// We'll match and DROP the last packet.
+				ruleIdx := filter.BuiltinChains[stack.Output]
+				filter.Rules[ruleIdx].Target = stack.DropTarget{}
+				filter.Rules[ruleIdx].Matchers = []stack.Matcher{&limitedMatcher{nPackets - 1}}
+				// Make sure the next rule is ACCEPT.
+				filter.Rules[ruleIdx+1].Target = stack.AcceptTarget{}
+				if err := ipt.ReplaceTable(stack.FilterTable, filter, true /* ipv6 */); err != nil {
+					t.Fatalf("failed to replace table: %v", err)
+				}
+			},
+			linkEP:     &limitedEP{nPackets},
+			expectSent: nPackets - 1,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			rt := buildRoute(t, nil, test.linkEP)
+
+			var pbl stack.PacketBufferList
+			for i := 0; i < nPackets; i++ {
+				pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
+					ReserveHeaderBytes: header.UDPMinimumSize + int(rt.MaxHeaderLength()),
+					Data:               buffer.NewView(1).ToVectorisedView(),
+				})
+				pkt.TransportHeader().Push(header.UDPMinimumSize)
+				pbl.PushBack(pkt)
+			}
+
+			test.setup(t, rt.Stack())
+
+			nWritten, err := rt.WritePackets(nil, pbl, stack.NetworkHeaderParams{})
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			got := int(rt.Stats().IP.PacketsSent.Value())
+			if got != test.expectSent {
+				t.Errorf("sent %d packets, but expected to send %d", got, test.expectSent)
+			}
+			if got != nWritten {
+				t.Errorf("sent %d packets, WritePackets returned %d", got, nWritten)
+			}
+		})
+	}
+}
+
+func buildRoute(t *testing.T, packetCollectorErrors []*tcpip.Error, linkEP stack.LinkEndpoint) stack.Route {
+	s := stack.New(stack.Options{
+		NetworkProtocols: []stack.NetworkProtocol{NewProtocol()},
+	})
+	s.CreateNIC(1, linkEP)
+	const (
+		src = "\xfc\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01"
+		dst = "\xfc\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02"
+	)
+	s.AddAddress(1, ProtocolNumber, src)
+	{
+		subnet, err := tcpip.NewSubnet(dst, tcpip.AddressMask("\xfc\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"))
+		if err != nil {
+			t.Fatal(err)
+		}
+		s.SetRouteTable([]tcpip.Route{{
+			Destination: subnet,
+			NIC:         1,
+		}})
+	}
+	rt, err := s.FindRoute(0, src, dst, ProtocolNumber, false /* multicastLoop */)
+	if err != nil {
+		t.Fatalf("s.FindRoute got %v, want %v", err, nil)
+	}
+	return rt
+}
+
+// limitedEP is a link endpoint that writes up to a certain number of packets
+// before returning errors.
+type limitedEP struct {
+	limit int
+}
+
+// MTU implements LinkEndpoint.MTU.
+func (*limitedEP) MTU() uint32 { return 0 }
+
+// Capabilities implements LinkEndpoint.Capabilities.
+func (*limitedEP) Capabilities() stack.LinkEndpointCapabilities { return 0 }
+
+// MaxHeaderLength implements LinkEndpoint.MaxHeaderLength.
+func (*limitedEP) MaxHeaderLength() uint16 { return 0 }
+
+// LinkAddress implements LinkEndpoint.LinkAddress.
+func (*limitedEP) LinkAddress() tcpip.LinkAddress { return "" }
+
+// WritePacket implements LinkEndpoint.WritePacket.
+func (ep *limitedEP) WritePacket(*stack.Route, *stack.GSO, tcpip.NetworkProtocolNumber, *stack.PacketBuffer) *tcpip.Error {
+	if ep.limit == 0 {
+		return tcpip.ErrInvalidEndpointState
+	}
+	ep.limit--
+	return nil
+}
+
+// WritePackets implements LinkEndpoint.WritePackets.
+func (ep *limitedEP) WritePackets(_ *stack.Route, _ *stack.GSO, pkts stack.PacketBufferList, _ tcpip.NetworkProtocolNumber) (int, *tcpip.Error) {
+	if ep.limit == 0 {
+		return 0, tcpip.ErrInvalidEndpointState
+	}
+	nWritten := ep.limit
+	if nWritten > pkts.Len() {
+		nWritten = pkts.Len()
+	}
+	ep.limit -= nWritten
+	return nWritten, nil
+}
+
+// WriteRawPacket implements LinkEndpoint.WriteRawPacket.
+func (ep *limitedEP) WriteRawPacket(_ buffer.VectorisedView) *tcpip.Error {
+	if ep.limit == 0 {
+		return tcpip.ErrInvalidEndpointState
+	}
+	ep.limit--
+	return nil
+}
+
+// Attach implements LinkEndpoint.Attach.
+func (*limitedEP) Attach(_ stack.NetworkDispatcher) {}
+
+// IsAttached implements LinkEndpoint.IsAttached.
+func (*limitedEP) IsAttached() bool { return false }
+
+// Wait implements LinkEndpoint.Wait.
+func (*limitedEP) Wait() {}
+
+// ARPHardwareType implements LinkEndpoint.ARPHardwareType.
+func (*limitedEP) ARPHardwareType() header.ARPHardwareType { return header.ARPHardwareEther }
+
+// AddHeader implements LinkEndpoint.AddHeader.
+func (*limitedEP) AddHeader(_, _ tcpip.LinkAddress, _ tcpip.NetworkProtocolNumber, _ *stack.PacketBuffer) {
+}
+
+// limitedMatcher is an iptables matcher that matches after a certain number of
+// packets are checked against it.
+type limitedMatcher struct {
+	limit int
+}
+
+// Name implements Matcher.Name.
+func (*limitedMatcher) Name() string {
+	return "limitedMatcher"
+}
+
+// Match implements Matcher.Match.
+func (lm *limitedMatcher) Match(stack.Hook, *stack.PacketBuffer, string) (bool, bool) {
+	if lm.limit == 0 {
+		return true, false
+	}
+	lm.limit--
+	return false, false
+}
diff --git a/pkg/tcpip/stack/iptables.go b/pkg/tcpip/stack/iptables.go
index 0e33cbe92..b6ef04d32 100644
--- a/pkg/tcpip/stack/iptables.go
+++ b/pkg/tcpip/stack/iptables.go
@@ -57,7 +57,72 @@ const reaperDelay = 5 * time.Second
 // all packets.
 func DefaultTables() *IPTables {
 	return &IPTables{
-		tables: [numTables]Table{
+		v4Tables: [numTables]Table{
+			natID: Table{
+				Rules: []Rule{
+					Rule{Target: AcceptTarget{}},
+					Rule{Target: AcceptTarget{}},
+					Rule{Target: AcceptTarget{}},
+					Rule{Target: AcceptTarget{}},
+					Rule{Target: ErrorTarget{}},
+				},
+				BuiltinChains: [NumHooks]int{
+					Prerouting:  0,
+					Input:       1,
+					Forward:     HookUnset,
+					Output:      2,
+					Postrouting: 3,
+				},
+				Underflows: [NumHooks]int{
+					Prerouting:  0,
+					Input:       1,
+					Forward:     HookUnset,
+					Output:      2,
+					Postrouting: 3,
+				},
+			},
+			mangleID: Table{
+				Rules: []Rule{
+					Rule{Target: AcceptTarget{}},
+					Rule{Target: AcceptTarget{}},
+					Rule{Target: ErrorTarget{}},
+				},
+				BuiltinChains: [NumHooks]int{
+					Prerouting: 0,
+					Output:     1,
+				},
+				Underflows: [NumHooks]int{
+					Prerouting:  0,
+					Input:       HookUnset,
+					Forward:     HookUnset,
+					Output:      1,
+					Postrouting: HookUnset,
+				},
+			},
+			filterID: Table{
+				Rules: []Rule{
+					Rule{Target: AcceptTarget{}},
+					Rule{Target: AcceptTarget{}},
+					Rule{Target: AcceptTarget{}},
+					Rule{Target: ErrorTarget{}},
+				},
+				BuiltinChains: [NumHooks]int{
+					Prerouting:  HookUnset,
+					Input:       0,
+					Forward:     1,
+					Output:      2,
+					Postrouting: HookUnset,
+				},
+				Underflows: [NumHooks]int{
+					Prerouting:  HookUnset,
+					Input:       0,
+					Forward:     1,
+					Output:      2,
+					Postrouting: HookUnset,
+				},
+			},
+		},
+		v6Tables: [numTables]Table{
 			natID: Table{
 				Rules: []Rule{
 					Rule{Target: AcceptTarget{}},
@@ -166,25 +231,20 @@ func EmptyNATTable() Table {
 
 // GetTable returns a table by name.
 func (it *IPTables) GetTable(name string, ipv6 bool) (Table, bool) {
-	// TODO(gvisor.dev/issue/3549): Enable IPv6.
-	if ipv6 {
-		return Table{}, false
-	}
 	id, ok := nameToID[name]
 	if !ok {
 		return Table{}, false
 	}
 	it.mu.RLock()
 	defer it.mu.RUnlock()
-	return it.tables[id], true
+	if ipv6 {
+		return it.v6Tables[id], true
+	}
+	return it.v4Tables[id], true
 }
 
 // ReplaceTable replaces or inserts table by name.
 func (it *IPTables) ReplaceTable(name string, table Table, ipv6 bool) *tcpip.Error {
-	// TODO(gvisor.dev/issue/3549): Enable IPv6.
-	if ipv6 {
-		return tcpip.ErrInvalidOptionValue
-	}
 	id, ok := nameToID[name]
 	if !ok {
 		return tcpip.ErrInvalidOptionValue
@@ -198,7 +258,11 @@ func (it *IPTables) ReplaceTable(name string, table Table, ipv6 bool) *tcpip.Err
 		it.startReaper(reaperDelay)
 	}
 	it.modified = true
-	it.tables[id] = table
+	if ipv6 {
+		it.v6Tables[id] = table
+	} else {
+		it.v4Tables[id] = table
+	}
 	return nil
 }
 
@@ -221,8 +285,17 @@ const (
 // should continue traversing the network stack and false when it should be
 // dropped.
 //
+// TODO(gvisor.dev/issue/170): PacketBuffer should hold the GSO and route, from
+// which address and nicName can be gathered. Currently, address is only
+// needed for prerouting and nicName is only needed for output.
+//
+// TODO(gvisor.dev/issue/170): Dropped packets should be counted.
+//
 // Precondition: pkt.NetworkHeader is set.
-func (it *IPTables) Check(hook Hook, pkt *PacketBuffer, gso *GSO, r *Route, address tcpip.Address, nicName string) bool {
+func (it *IPTables) Check(hook Hook, pkt *PacketBuffer, gso *GSO, r *Route, preroutingAddr tcpip.Address, nicName string) bool {
+	if pkt.NetworkProtocolNumber != header.IPv4ProtocolNumber && pkt.NetworkProtocolNumber != header.IPv6ProtocolNumber {
+		return true
+	}
 	// Many users never configure iptables. Spare them the cost of rule
 	// traversal if rules have never been set.
 	it.mu.RLock()
@@ -243,9 +316,14 @@ func (it *IPTables) Check(hook Hook, pkt *PacketBuffer, gso *GSO, r *Route, addr
 		if tableID == natID && pkt.NatDone {
 			continue
 		}
-		table := it.tables[tableID]
+		var table Table
+		if pkt.NetworkProtocolNumber == header.IPv6ProtocolNumber {
+			table = it.v6Tables[tableID]
+		} else {
+			table = it.v4Tables[tableID]
+		}
 		ruleIdx := table.BuiltinChains[hook]
-		switch verdict := it.checkChain(hook, pkt, table, ruleIdx, gso, r, address, nicName); verdict {
+		switch verdict := it.checkChain(hook, pkt, table, ruleIdx, gso, r, preroutingAddr, nicName); verdict {
 		// If the table returns Accept, move on to the next table.
 		case chainAccept:
 			continue
@@ -256,7 +334,7 @@ func (it *IPTables) Check(hook Hook, pkt *PacketBuffer, gso *GSO, r *Route, addr
 			// Any Return from a built-in chain means we have to
 			// call the underflow.
 			underflow := table.Rules[table.Underflows[hook]]
-			switch v, _ := underflow.Target.Action(pkt, &it.connections, hook, gso, r, address); v {
+			switch v, _ := underflow.Target.Action(pkt, &it.connections, hook, gso, r, preroutingAddr); v {
 			case RuleAccept:
 				continue
 			case RuleDrop:
@@ -351,11 +429,11 @@ func (it *IPTables) CheckPackets(hook Hook, pkts PacketBufferList, gso *GSO, r *
 // Preconditions:
 // * pkt is a IPv4 packet of at least length header.IPv4MinimumSize.
 // * pkt.NetworkHeader is not nil.
-func (it *IPTables) checkChain(hook Hook, pkt *PacketBuffer, table Table, ruleIdx int, gso *GSO, r *Route, address tcpip.Address, nicName string) chainVerdict {
+func (it *IPTables) checkChain(hook Hook, pkt *PacketBuffer, table Table, ruleIdx int, gso *GSO, r *Route, preroutingAddr tcpip.Address, nicName string) chainVerdict {
 	// Start from ruleIdx and walk the list of rules until a rule gives us
 	// a verdict.
 	for ruleIdx < len(table.Rules) {
-		switch verdict, jumpTo := it.checkRule(hook, pkt, table, ruleIdx, gso, r, address, nicName); verdict {
+		switch verdict, jumpTo := it.checkRule(hook, pkt, table, ruleIdx, gso, r, preroutingAddr, nicName); verdict {
 		case RuleAccept:
 			return chainAccept
 
@@ -372,7 +450,7 @@ func (it *IPTables) checkChain(hook Hook, pkt *PacketBuffer, table Table, ruleId
 				ruleIdx++
 				continue
 			}
-			switch verdict := it.checkChain(hook, pkt, table, jumpTo, gso, r, address, nicName); verdict {
+			switch verdict := it.checkChain(hook, pkt, table, jumpTo, gso, r, preroutingAddr, nicName); verdict {
 			case chainAccept:
 				return chainAccept
 			case chainDrop:
@@ -398,11 +476,11 @@ func (it *IPTables) checkChain(hook Hook, pkt *PacketBuffer, table Table, ruleId
 // Preconditions:
 // * pkt is a IPv4 packet of at least length header.IPv4MinimumSize.
 // * pkt.NetworkHeader is not nil.
-func (it *IPTables) checkRule(hook Hook, pkt *PacketBuffer, table Table, ruleIdx int, gso *GSO, r *Route, address tcpip.Address, nicName string) (RuleVerdict, int) {
+func (it *IPTables) checkRule(hook Hook, pkt *PacketBuffer, table Table, ruleIdx int, gso *GSO, r *Route, preroutingAddr tcpip.Address, nicName string) (RuleVerdict, int) {
 	rule := table.Rules[ruleIdx]
 
 	// Check whether the packet matches the IP header filter.
-	if !rule.Filter.match(header.IPv4(pkt.NetworkHeader().View()), hook, nicName) {
+	if !rule.Filter.match(pkt, hook, nicName) {
 		// Continue on to the next rule.
 		return RuleJump, ruleIdx + 1
 	}
@@ -421,7 +499,7 @@ func (it *IPTables) checkRule(hook Hook, pkt *PacketBuffer, table Table, ruleIdx
 	}
 
 	// All the matchers matched, so run the target.
-	return rule.Target.Action(pkt, &it.connections, hook, gso, r, address)
+	return rule.Target.Action(pkt, &it.connections, hook, gso, r, preroutingAddr)
 }
 
 // OriginalDst returns the original destination of redirected connections. It
diff --git a/pkg/tcpip/stack/iptables_types.go b/pkg/tcpip/stack/iptables_types.go
index fbbd2f50f..093ee6881 100644
--- a/pkg/tcpip/stack/iptables_types.go
+++ b/pkg/tcpip/stack/iptables_types.go
@@ -15,6 +15,7 @@
 package stack
 
 import (
+	"fmt"
 	"strings"
 	"sync"
 
@@ -81,26 +82,25 @@ const (
 //
 // +stateify savable
 type IPTables struct {
-	// mu protects tables, priorities, and modified.
+	// mu protects v4Tables, v6Tables, and modified.
 	mu sync.RWMutex
-
-	// tables maps tableIDs to tables. Holds builtin tables only, not user
-	// tables. mu must be locked for accessing.
-	tables [numTables]Table
-
-	// priorities maps each hook to a list of table names. The order of the
-	// list is the order in which each table should be visited for that
-	// hook. mu needs to be locked for accessing.
-	priorities [NumHooks][]tableID
-
+	// v4Tables and v6tables map tableIDs to tables. They hold builtin
+	// tables only, not user tables. mu must be locked for accessing.
+	v4Tables [numTables]Table
+	v6Tables [numTables]Table
 	// modified is whether tables have been modified at least once. It is
 	// used to elide the iptables performance overhead for workloads that
 	// don't utilize iptables.
 	modified bool
 
+	// priorities maps each hook to a list of table names. The order of the
+	// list is the order in which each table should be visited for that
+	// hook. It is immutable.
+	priorities [NumHooks][]tableID
+
 	connections ConnTrack
 
-	// reaperDone can be signalled to stop the reaper goroutine.
+	// reaperDone can be signaled to stop the reaper goroutine.
 	reaperDone chan struct{}
 }
 
@@ -148,7 +148,7 @@ type Rule struct {
 	Target Target
 }
 
-// IPHeaderFilter holds basic IP filtering data common to every rule.
+// IPHeaderFilter performs basic IP header matching common to every rule.
 //
 // +stateify savable
 type IPHeaderFilter struct {
@@ -196,16 +196,43 @@ type IPHeaderFilter struct {
 	OutputInterfaceInvert bool
 }
 
-// match returns whether hdr matches the filter.
-func (fl IPHeaderFilter) match(hdr header.IPv4, hook Hook, nicName string) bool {
-	// TODO(gvisor.dev/issue/170): Support other fields of the filter.
+// match returns whether pkt matches the filter.
+//
+// Preconditions: pkt.NetworkHeader is set and is at least of the minimal IPv4
+// or IPv6 header length.
+func (fl IPHeaderFilter) match(pkt *PacketBuffer, hook Hook, nicName string) bool {
+	// Extract header fields.
+	var (
+		// TODO(gvisor.dev/issue/170): Support other filter fields.
+		transProto tcpip.TransportProtocolNumber
+		dstAddr    tcpip.Address
+		srcAddr    tcpip.Address
+	)
+	switch proto := pkt.NetworkProtocolNumber; proto {
+	case header.IPv4ProtocolNumber:
+		hdr := header.IPv4(pkt.NetworkHeader().View())
+		transProto = hdr.TransportProtocol()
+		dstAddr = hdr.DestinationAddress()
+		srcAddr = hdr.SourceAddress()
+
+	case header.IPv6ProtocolNumber:
+		hdr := header.IPv6(pkt.NetworkHeader().View())
+		transProto = hdr.TransportProtocol()
+		dstAddr = hdr.DestinationAddress()
+		srcAddr = hdr.SourceAddress()
+
+	default:
+		panic(fmt.Sprintf("unknown network protocol with EtherType: %d", proto))
+	}
+
 	// Check the transport protocol.
-	if fl.Protocol != 0 && fl.Protocol != hdr.TransportProtocol() {
+	if fl.CheckProtocol && fl.Protocol != transProto {
 		return false
 	}
 
-	// Check the source and destination IPs.
-	if !filterAddress(hdr.DestinationAddress(), fl.DstMask, fl.Dst, fl.DstInvert) || !filterAddress(hdr.SourceAddress(), fl.SrcMask, fl.Src, fl.SrcInvert) {
+	// Check the addresses.
+	if !filterAddress(dstAddr, fl.DstMask, fl.Dst, fl.DstInvert) ||
+		!filterAddress(srcAddr, fl.SrcMask, fl.Src, fl.SrcInvert) {
 		return false
 	}
 
diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index 1f1a1426b..821d3feb9 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -1282,9 +1282,8 @@ func (n *NIC) DeliverNetworkPacket(remote, local tcpip.LinkAddress, protocol tcp
 		return
 	}
 
-	// TODO(gvisor.dev/issue/170): Not supporting iptables for IPv6 yet.
 	// Loopback traffic skips the prerouting chain.
-	if protocol == header.IPv4ProtocolNumber && !n.isLoopback() {
+	if !n.isLoopback() {
 		// iptables filtering.
 		ipt := n.stack.IPTables()
 		address := n.primaryAddress(protocol)
diff --git a/pkg/tcpip/stack/packet_buffer.go b/pkg/tcpip/stack/packet_buffer.go
index 17b8beebb..1932aaeb7 100644
--- a/pkg/tcpip/stack/packet_buffer.go
+++ b/pkg/tcpip/stack/packet_buffer.go
@@ -80,7 +80,7 @@ type PacketBuffer struct {
 	// data are held in the same underlying buffer storage.
 	header buffer.Prependable
 
-	// NetworkProtocol is only valid when NetworkHeader is set.
+	// NetworkProtocolNumber is only valid when NetworkHeader is set.
 	// TODO(gvisor.dev/issue/3574): Remove the separately passed protocol
 	// numbers in registration APIs that take a PacketBuffer.
 	NetworkProtocolNumber tcpip.NetworkProtocolNumber
diff --git a/test/iptables/iptables_test.go b/test/iptables/iptables_test.go
index e2beb30d5..398f70ecd 100644
--- a/test/iptables/iptables_test.go
+++ b/test/iptables/iptables_test.go
@@ -48,6 +48,13 @@ func singleTest(t *testing.T, test TestCase) {
 	}
 }
 
+// TODO(gvisor.dev/issue/3549): IPv6 NAT support.
+func ipv4Test(t *testing.T, test TestCase) {
+	t.Run("IPv4", func(t *testing.T) {
+		iptablesTest(t, test, false)
+	})
+}
+
 func iptablesTest(t *testing.T, test TestCase, ipv6 bool) {
 	if _, ok := Tests[test.Name()]; !ok {
 		t.Fatalf("no test found with name %q. Has it been registered?", test.Name())
@@ -72,11 +79,6 @@ func iptablesTest(t *testing.T, test TestCase, ipv6 bool) {
 		d.CleanUp(context.Background())
 	}()
 
-	// TODO(gvisor.dev/issue/170): Skipping IPv6 gVisor tests.
-	if ipv6 && dockerutil.Runtime() != "runc" {
-		t.Skip("gVisor ip6tables not yet implemented")
-	}
-
 	// Create and start the container.
 	opts := dockerutil.RunOpts{
 		Image:  "iptables",
@@ -314,75 +316,75 @@ func TestInputInvertDestination(t *testing.T) {
 	singleTest(t, FilterInputInvertDestination{})
 }
 
-func TestOutputDestination(t *testing.T) {
+func TestFilterOutputDestination(t *testing.T) {
 	singleTest(t, FilterOutputDestination{})
 }
 
-func TestOutputInvertDestination(t *testing.T) {
+func TestFilterOutputInvertDestination(t *testing.T) {
 	singleTest(t, FilterOutputInvertDestination{})
 }
 
 func TestNATPreRedirectUDPPort(t *testing.T) {
-	singleTest(t, NATPreRedirectUDPPort{})
+	ipv4Test(t, NATPreRedirectUDPPort{})
 }
 
 func TestNATPreRedirectTCPPort(t *testing.T) {
-	singleTest(t, NATPreRedirectTCPPort{})
+	ipv4Test(t, NATPreRedirectTCPPort{})
 }
 
 func TestNATPreRedirectTCPOutgoing(t *testing.T) {
-	singleTest(t, NATPreRedirectTCPOutgoing{})
+	ipv4Test(t, NATPreRedirectTCPOutgoing{})
 }
 
 func TestNATOutRedirectTCPIncoming(t *testing.T) {
-	singleTest(t, NATOutRedirectTCPIncoming{})
+	ipv4Test(t, NATOutRedirectTCPIncoming{})
 }
 func TestNATOutRedirectUDPPort(t *testing.T) {
-	singleTest(t, NATOutRedirectUDPPort{})
+	ipv4Test(t, NATOutRedirectUDPPort{})
 }
 
 func TestNATOutRedirectTCPPort(t *testing.T) {
-	singleTest(t, NATOutRedirectTCPPort{})
+	ipv4Test(t, NATOutRedirectTCPPort{})
 }
 
 func TestNATDropUDP(t *testing.T) {
-	singleTest(t, NATDropUDP{})
+	ipv4Test(t, NATDropUDP{})
 }
 
 func TestNATAcceptAll(t *testing.T) {
-	singleTest(t, NATAcceptAll{})
+	ipv4Test(t, NATAcceptAll{})
 }
 
 func TestNATOutRedirectIP(t *testing.T) {
-	singleTest(t, NATOutRedirectIP{})
+	ipv4Test(t, NATOutRedirectIP{})
 }
 
 func TestNATOutDontRedirectIP(t *testing.T) {
-	singleTest(t, NATOutDontRedirectIP{})
+	ipv4Test(t, NATOutDontRedirectIP{})
 }
 
 func TestNATOutRedirectInvert(t *testing.T) {
-	singleTest(t, NATOutRedirectInvert{})
+	ipv4Test(t, NATOutRedirectInvert{})
 }
 
 func TestNATPreRedirectIP(t *testing.T) {
-	singleTest(t, NATPreRedirectIP{})
+	ipv4Test(t, NATPreRedirectIP{})
 }
 
 func TestNATPreDontRedirectIP(t *testing.T) {
-	singleTest(t, NATPreDontRedirectIP{})
+	ipv4Test(t, NATPreDontRedirectIP{})
 }
 
 func TestNATPreRedirectInvert(t *testing.T) {
-	singleTest(t, NATPreRedirectInvert{})
+	ipv4Test(t, NATPreRedirectInvert{})
 }
 
 func TestNATRedirectRequiresProtocol(t *testing.T) {
-	singleTest(t, NATRedirectRequiresProtocol{})
+	ipv4Test(t, NATRedirectRequiresProtocol{})
 }
 
 func TestNATLoopbackSkipsPrerouting(t *testing.T) {
-	singleTest(t, NATLoopbackSkipsPrerouting{})
+	ipv4Test(t, NATLoopbackSkipsPrerouting{})
 }
 
 func TestInputSource(t *testing.T) {
@@ -419,9 +421,9 @@ func TestFilterAddrs(t *testing.T) {
 }
 
 func TestNATPreOriginalDst(t *testing.T) {
-	singleTest(t, NATPreOriginalDst{})
+	ipv4Test(t, NATPreOriginalDst{})
 }
 
 func TestNATOutOriginalDst(t *testing.T) {
-	singleTest(t, NATOutOriginalDst{})
+	ipv4Test(t, NATOutOriginalDst{})
 }