From a8943325db43d04be8a10157f6d3f3180e5170a5 Mon Sep 17 00:00:00 2001
From: Ghanan Gowripalan <ghanan@google.com>
Date: Mon, 9 Sep 2019 12:04:33 -0700
Subject: Join IPv6 all-nodes and solicited-node multicast addresses where
 appropriate.

The IPv6 all-nodes multicast address will be joined on NIC enable, and the
appropriate IPv6 solicited-node multicast address will be joined when IPv6
addresses are added.

Tests: Test receiving packets destined to the IPv6 link-local all-nodes
multicast address and the IPv6 solicted node address of an added IPv6 address.
PiperOrigin-RevId: 268047073
---
 pkg/tcpip/stack/nic.go   | 69 ++++++++++++++++++++++++++++++++++++++++++++----
 pkg/tcpip/stack/stack.go |  6 ++---
 2 files changed, 66 insertions(+), 9 deletions(-)

(limited to 'pkg/tcpip/stack')

diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index 43719085e..249a19946 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -102,6 +102,25 @@ func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint, loopback
 	}
 }
 
+// enable enables the NIC. enable will attach the link to its LinkEndpoint and
+// join the IPv6 All-Nodes Multicast address (ff02::1).
+func (n *NIC) enable() *tcpip.Error {
+	n.attachLinkEndpoint()
+
+	// Join the IPv6 All-Nodes Multicast group if the stack is configured to
+	// use IPv6. This is required to ensure that this node properly receives
+	// and responds to the various NDP messages that are destined to the
+	// all-nodes multicast address. An example is the Neighbor Advertisement
+	// when we perform Duplicate Address Detection, or Router Advertisement
+	// when we do Router Discovery. See RFC 4862, section 5.4.2 and RFC 4861
+	// section 4.2 for more information.
+	if _, ok := n.stack.networkProtocols[header.IPv6ProtocolNumber]; ok {
+		return n.joinGroup(header.IPv6ProtocolNumber, header.IPv6AllNodesMulticastAddress)
+	}
+
+	return nil
+}
+
 // attachLinkEndpoint attaches the NIC to the endpoint, which will enable it
 // to start delivering packets.
 func (n *NIC) attachLinkEndpoint() {
@@ -339,6 +358,15 @@ func (n *NIC) addAddressLocked(protocolAddress tcpip.ProtocolAddress, peb Primar
 		}
 	}
 
+	// If we are adding an IPv6 address, join the solicited-node multicast
+	// address for a unicast protocolAddress.
+	if protocolAddress.Protocol == header.IPv6ProtocolNumber && !header.IsV6MulticastAddress(protocolAddress.AddressWithPrefix.Address) {
+		snmc := header.SolicitedNodeAddr(protocolAddress.AddressWithPrefix.Address)
+		if err := n.joinGroupLocked(protocolAddress.Protocol, snmc); err != nil {
+			return nil, err
+		}
+	}
+
 	n.endpoints[id] = ref
 
 	l, ok := n.primary[protocolAddress.Protocol]
@@ -467,13 +495,27 @@ func (n *NIC) removeEndpoint(r *referencedNetworkEndpoint) {
 }
 
 func (n *NIC) removePermanentAddressLocked(addr tcpip.Address) *tcpip.Error {
-	r := n.endpoints[NetworkEndpointID{addr}]
-	if r == nil || r.getKind() != permanent {
+	r, ok := n.endpoints[NetworkEndpointID{addr}]
+	if !ok || r.getKind() != permanent {
 		return tcpip.ErrBadLocalAddress
 	}
 
 	r.setKind(permanentExpired)
-	r.decRefLocked()
+	if !r.decRefLocked() {
+		// The endpoint still has references to it.
+		return nil
+	}
+
+	// At this point the endpoint is deleted.
+
+	// If we are removing an IPv6 address, leave the solicited-node
+	// multicast address for a unicast addr.
+	if r.protocol == header.IPv6ProtocolNumber && !header.IsV6MulticastAddress(addr) {
+		snmc := header.SolicitedNodeAddr(addr)
+		if err := n.leaveGroupLocked(snmc); err != nil {
+			return err
+		}
+	}
 
 	return nil
 }
@@ -491,6 +533,13 @@ func (n *NIC) joinGroup(protocol tcpip.NetworkProtocolNumber, addr tcpip.Address
 	n.mu.Lock()
 	defer n.mu.Unlock()
 
+	return n.joinGroupLocked(protocol, addr)
+}
+
+// joinGroupLocked adds a new endpoint for the given multicast address, if none
+// exists yet. Otherwise it just increments its count. n MUST be locked before
+// joinGroupLocked is called.
+func (n *NIC) joinGroupLocked(protocol tcpip.NetworkProtocolNumber, addr tcpip.Address) *tcpip.Error {
 	id := NetworkEndpointID{addr}
 	joins := n.mcastJoins[id]
 	if joins == 0 {
@@ -518,6 +567,13 @@ func (n *NIC) leaveGroup(addr tcpip.Address) *tcpip.Error {
 	n.mu.Lock()
 	defer n.mu.Unlock()
 
+	return n.leaveGroupLocked(addr)
+}
+
+// leaveGroupLocked decrements the count for the given multicast address, and
+// when it reaches zero removes the endpoint for this address. n MUST be locked
+// before leaveGroupLocked is called.
+func (n *NIC) leaveGroupLocked(addr tcpip.Address) *tcpip.Error {
 	id := NetworkEndpointID{addr}
 	joins := n.mcastJoins[id]
 	switch joins {
@@ -802,11 +858,14 @@ func (r *referencedNetworkEndpoint) decRef() {
 }
 
 // decRefLocked is the same as decRef but assumes that the NIC.mu mutex is
-// locked.
-func (r *referencedNetworkEndpoint) decRefLocked() {
+// locked. Returns true if the endpoint was removed.
+func (r *referencedNetworkEndpoint) decRefLocked() bool {
 	if atomic.AddInt32(&r.refs, -1) == 0 {
 		r.nic.removeEndpointLocked(r)
+		return true
 	}
+
+	return false
 }
 
 // incRef increments the ref count. It must only be called when the caller is
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index a961e8ebe..1fe21b68e 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -633,7 +633,7 @@ func (s *Stack) createNIC(id tcpip.NICID, name string, ep LinkEndpoint, enabled,
 
 	s.nics[id] = n
 	if enabled {
-		n.attachLinkEndpoint()
+		return n.enable()
 	}
 
 	return nil
@@ -680,9 +680,7 @@ func (s *Stack) EnableNIC(id tcpip.NICID) *tcpip.Error {
 		return tcpip.ErrUnknownNICID
 	}
 
-	nic.attachLinkEndpoint()
-
-	return nil
+	return nic.enable()
 }
 
 // CheckNIC checks if a NIC is usable.
-- 
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