Join all routers group when forwarding is enabled

See comments inline code for rationale.

Test: ip_test.TestJoinLeaveAllRoutersGroup
PiperOrigin-RevId: 367449434

4 files changed, 59 insertions, 16 deletions

diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index c6d9d8f0d..2a2ad6482 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -410,22 +410,65 @@ func (e *endpoint) dupTentativeAddrDetected(addr tcpip.Address, holderLinkAddr t
 //
 // Must only be called when the forwarding status changes.
 func (e *endpoint) transitionForwarding(forwarding bool) {
+	allRoutersGroups := [...]tcpip.Address{
+		header.IPv6AllRoutersInterfaceLocalMulticastAddress,
+		header.IPv6AllRoutersLinkLocalMulticastAddress,
+		header.IPv6AllRoutersSiteLocalMulticastAddress,
+	}
+
 	e.mu.Lock()
 	defer e.mu.Unlock()
 
-	if !e.Enabled() {
-		return
-	}
-
 	if forwarding {
 		// When transitioning into an IPv6 router, host-only state (NDP discovered
 		// routers, discovered on-link prefixes, and auto-generated addresses) is
 		// cleaned up/invalidated and NDP router solicitations are stopped.
 		e.mu.ndp.stopSolicitingRouters()
 		e.mu.ndp.cleanupState(true /* hostOnly */)
-	} else {
-		// When transitioning into an IPv6 host, NDP router solicitations are
-		// started.
+
+		// As per RFC 4291 section 2.8:
+		//
+		//   A router is required to recognize all addresses that a host is
+		//   required to recognize, plus the following addresses as identifying
+		//   itself:
+		//
+		//      o The All-Routers multicast addresses defined in Section 2.7.1.
+		//
+		// As per RFC 4291 section 2.7.1,
+		//
+		//      All Routers Addresses:   FF01:0:0:0:0:0:0:2
+		//                               FF02:0:0:0:0:0:0:2
+		//                               FF05:0:0:0:0:0:0:2
+		//
+		//   The above multicast addresses identify the group of all IPv6 routers,
+		//   within scope 1 (interface-local), 2 (link-local), or 5 (site-local).
+		for _, g := range allRoutersGroups {
+			if err := e.joinGroupLocked(g); err != nil {
+				// joinGroupLocked only returns an error if the group address is not a
+				// valid IPv6 multicast address.
+				panic(fmt.Sprintf("e.joinGroupLocked(%s): %s", g, err))
+			}
+		}
+
+		return
+	}
+
+	for _, g := range allRoutersGroups {
+		switch err := e.leaveGroupLocked(g).(type) {
+		case nil:
+		case *tcpip.ErrBadLocalAddress:
+			// The endpoint may have already left the multicast group.
+		default:
+			panic(fmt.Sprintf("e.leaveGroupLocked(%s): %s", g, err))
+		}
+	}
+
+	// When transitioning into an IPv6 host, NDP router solicitations are
+	// started if the endpoint is enabled.
+	//
+	// If the endpoint is not currently enabled, routers will be solicited when
+	// the endpoint becomes enabled (if it is still a host).
+	if e.Enabled() {
 		e.mu.ndp.startSolicitingRouters()
 	}
 }
@@ -573,7 +616,7 @@ func (e *endpoint) disableLocked() {
 	e.mu.ndp.cleanupState(false /* hostOnly */)
 
 	// The endpoint may have already left the multicast group.
-	switch err := e.leaveGroupLocked(header.IPv6AllNodesMulticastAddress); err.(type) {
+	switch err := e.leaveGroupLocked(header.IPv6AllNodesMulticastAddress).(type) {
 	case nil, *tcpip.ErrBadLocalAddress:
 	default:
 		panic(fmt.Sprintf("unexpected error when leaving group = %s: %s", header.IPv6AllNodesMulticastAddress, err))
@@ -1979,9 +2022,9 @@ func (p *protocol) Forwarding() bool {
 // Returns true if the forwarding status was updated.
 func (p *protocol) setForwarding(v bool) bool {
 	if v {
-		return atomic.SwapUint32(&p.forwarding, 1) == 0
+		return atomic.CompareAndSwapUint32(&p.forwarding, 0 /* old */, 1 /* new */)
 	}
-	return atomic.SwapUint32(&p.forwarding, 0) == 1
+	return atomic.CompareAndSwapUint32(&p.forwarding, 1 /* old */, 0 /* new */)
 }
 
 // SetForwarding implements stack.ForwardingNetworkProtocol.
diff --git a/pkg/tcpip/network/ipv6/mld.go b/pkg/tcpip/network/ipv6/mld.go
index 538590baf..165b7d2d2 100644
--- a/pkg/tcpip/network/ipv6/mld.go
+++ b/pkg/tcpip/network/ipv6/mld.go
@@ -76,7 +76,7 @@ func (mld *mldState) SendReport(groupAddress tcpip.Address) (bool, tcpip.Error)
 //
 // Precondition: mld.ep.mu must be read locked.
 func (mld *mldState) SendLeave(groupAddress tcpip.Address) tcpip.Error {
-	_, err := mld.writePacket(header.IPv6AllRoutersMulticastAddress, groupAddress, header.ICMPv6MulticastListenerDone)
+	_, err := mld.writePacket(header.IPv6AllRoutersLinkLocalMulticastAddress, groupAddress, header.ICMPv6MulticastListenerDone)
 	return err
 }
 
diff --git a/pkg/tcpip/network/ipv6/mld_test.go b/pkg/tcpip/network/ipv6/mld_test.go
index 1e611aca1..146b300f1 100644
--- a/pkg/tcpip/network/ipv6/mld_test.go
+++ b/pkg/tcpip/network/ipv6/mld_test.go
@@ -93,7 +93,7 @@ func TestIPv6JoinLeaveSolicitedNodeAddressPerformsMLD(t *testing.T) {
 	if p, ok := e.Read(); !ok {
 		t.Fatal("expected a done message to be sent")
 	} else {
-		validateMLDPacket(t, stack.PayloadSince(p.Pkt.NetworkHeader()), header.IPv6Any, header.IPv6AllRoutersMulticastAddress, header.ICMPv6MulticastListenerDone, linkLocalAddrSNMC)
+		validateMLDPacket(t, stack.PayloadSince(p.Pkt.NetworkHeader()), header.IPv6Any, header.IPv6AllRoutersLinkLocalMulticastAddress, header.ICMPv6MulticastListenerDone, linkLocalAddrSNMC)
 	}
 }
 
diff --git a/pkg/tcpip/network/ipv6/ndp.go b/pkg/tcpip/network/ipv6/ndp.go
index 536493f87..dd7f6a126 100644
--- a/pkg/tcpip/network/ipv6/ndp.go
+++ b/pkg/tcpip/network/ipv6/ndp.go
@@ -1703,7 +1703,7 @@ func (ndp *ndpState) startSolicitingRouters() {
 			//       the unspecified address if no address is assigned
 			//       to the sending interface.
 			localAddr := header.IPv6Any
-			if addressEndpoint := ndp.ep.AcquireOutgoingPrimaryAddress(header.IPv6AllRoutersMulticastAddress, false); addressEndpoint != nil {
+			if addressEndpoint := ndp.ep.AcquireOutgoingPrimaryAddress(header.IPv6AllRoutersLinkLocalMulticastAddress, false); addressEndpoint != nil {
 				localAddr = addressEndpoint.AddressWithPrefix().Address
 				addressEndpoint.DecRef()
 			}
@@ -1730,7 +1730,7 @@ func (ndp *ndpState) startSolicitingRouters() {
 			icmpData.SetChecksum(header.ICMPv6Checksum(header.ICMPv6ChecksumParams{
 				Header: icmpData,
 				Src:    localAddr,
-				Dst:    header.IPv6AllRoutersMulticastAddress,
+				Dst:    header.IPv6AllRoutersLinkLocalMulticastAddress,
 			}))
 
 			pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
@@ -1739,14 +1739,14 @@ func (ndp *ndpState) startSolicitingRouters() {
 			})
 
 			sent := ndp.ep.stats.icmp.packetsSent
-			if err := addIPHeader(localAddr, header.IPv6AllRoutersMulticastAddress, pkt, stack.NetworkHeaderParams{
+			if err := addIPHeader(localAddr, header.IPv6AllRoutersLinkLocalMulticastAddress, pkt, stack.NetworkHeaderParams{
 				Protocol: header.ICMPv6ProtocolNumber,
 				TTL:      header.NDPHopLimit,
 			}, nil /* extensionHeaders */); err != nil {
 				panic(fmt.Sprintf("failed to add IP header: %s", err))
 			}
 
-			if err := ndp.ep.nic.WritePacketToRemote(header.EthernetAddressFromMulticastIPv6Address(header.IPv6AllRoutersMulticastAddress), nil /* gso */, ProtocolNumber, pkt); err != nil {
+			if err := ndp.ep.nic.WritePacketToRemote(header.EthernetAddressFromMulticastIPv6Address(header.IPv6AllRoutersLinkLocalMulticastAddress), nil /* gso */, ProtocolNumber, pkt); err != nil {
 				sent.dropped.Increment()
 				// Don't send any more messages if we had an error.
 				remaining = 0