Pass NetworkInterface to LinkAddressRequest

Previously a link endpoint was passed to
stack.LinkAddressResolver.LinkAddressRequest. With this change,
implementations that want a route for the link address request may
find one through the stack. Other implementations that want to send
a packet without a route may continue to do so using the network
interface directly.

Test: - arp_test.TestLinkAddressRequest
      - ipv6.TestLinkAddressRequest
PiperOrigin-RevId: 338577474

10 files changed, 33 insertions, 21 deletions

diff --git a/pkg/tcpip/stack/forwarding_test.go b/pkg/tcpip/stack/forwarding_test.go
index cf042309e..380688038 100644
--- a/pkg/tcpip/stack/forwarding_test.go
+++ b/pkg/tcpip/stack/forwarding_test.go
@@ -178,7 +178,7 @@ func (*fwdTestNetworkProtocol) Close() {}
 
 func (*fwdTestNetworkProtocol) Wait() {}
 
-func (f *fwdTestNetworkProtocol) LinkAddressRequest(addr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, linkEP LinkEndpoint) *tcpip.Error {
+func (f *fwdTestNetworkProtocol) LinkAddressRequest(addr, _ tcpip.Address, remoteLinkAddr tcpip.LinkAddress, _ NetworkInterface) *tcpip.Error {
 	if f.onLinkAddressResolved != nil {
 		time.AfterFunc(f.addrResolveDelay, func() {
 			f.onLinkAddressResolved(f.addrCache, f.neigh, addr, remoteLinkAddr)
diff --git a/pkg/tcpip/stack/linkaddrcache.go b/pkg/tcpip/stack/linkaddrcache.go
index 6f73a0ce4..c9b13cd0e 100644
--- a/pkg/tcpip/stack/linkaddrcache.go
+++ b/pkg/tcpip/stack/linkaddrcache.go
@@ -180,7 +180,7 @@ func (c *linkAddrCache) getOrCreateEntryLocked(k tcpip.FullAddress) *linkAddrEnt
 }
 
 // get reports any known link address for k.
-func (c *linkAddrCache) get(k tcpip.FullAddress, linkRes LinkAddressResolver, localAddr tcpip.Address, linkEP LinkEndpoint, waker *sleep.Waker) (tcpip.LinkAddress, <-chan struct{}, *tcpip.Error) {
+func (c *linkAddrCache) get(k tcpip.FullAddress, linkRes LinkAddressResolver, localAddr tcpip.Address, nic NetworkInterface, waker *sleep.Waker) (tcpip.LinkAddress, <-chan struct{}, *tcpip.Error) {
 	if linkRes != nil {
 		if addr, ok := linkRes.ResolveStaticAddress(k.Addr); ok {
 			return addr, nil, nil
@@ -221,7 +221,7 @@ func (c *linkAddrCache) get(k tcpip.FullAddress, linkRes LinkAddressResolver, lo
 			}
 
 			entry.done = make(chan struct{})
-			go c.startAddressResolution(k, linkRes, localAddr, linkEP, entry.done) // S/R-SAFE: link non-savable; wakers dropped synchronously.
+			go c.startAddressResolution(k, linkRes, localAddr, nic, entry.done) // S/R-SAFE: link non-savable; wakers dropped synchronously.
 		}
 
 		return entry.linkAddr, entry.done, tcpip.ErrWouldBlock
@@ -240,11 +240,11 @@ func (c *linkAddrCache) removeWaker(k tcpip.FullAddress, waker *sleep.Waker) {
 	}
 }
 
-func (c *linkAddrCache) startAddressResolution(k tcpip.FullAddress, linkRes LinkAddressResolver, localAddr tcpip.Address, linkEP LinkEndpoint, done <-chan struct{}) {
+func (c *linkAddrCache) startAddressResolution(k tcpip.FullAddress, linkRes LinkAddressResolver, localAddr tcpip.Address, nic NetworkInterface, done <-chan struct{}) {
 	for i := 0; ; i++ {
 		// Send link request, then wait for the timeout limit and check
 		// whether the request succeeded.
-		linkRes.LinkAddressRequest(k.Addr, localAddr, "" /* linkAddr */, linkEP)
+		linkRes.LinkAddressRequest(k.Addr, localAddr, "" /* linkAddr */, nic)
 
 		select {
 		case now := <-time.After(c.resolutionTimeout):
diff --git a/pkg/tcpip/stack/linkaddrcache_test.go b/pkg/tcpip/stack/linkaddrcache_test.go
index 33806340e..d2e37f38d 100644
--- a/pkg/tcpip/stack/linkaddrcache_test.go
+++ b/pkg/tcpip/stack/linkaddrcache_test.go
@@ -49,8 +49,8 @@ type testLinkAddressResolver struct {
 	onLinkAddressRequest func()
 }
 
-func (r *testLinkAddressResolver) LinkAddressRequest(addr, _ tcpip.Address, _ tcpip.LinkAddress, _ LinkEndpoint) *tcpip.Error {
-	time.AfterFunc(r.delay, func() { r.fakeRequest(addr) })
+func (r *testLinkAddressResolver) LinkAddressRequest(targetAddr, _ tcpip.Address, _ tcpip.LinkAddress, _ NetworkInterface) *tcpip.Error {
+	time.AfterFunc(r.delay, func() { r.fakeRequest(targetAddr) })
 	if f := r.onLinkAddressRequest; f != nil {
 		f()
 	}
diff --git a/pkg/tcpip/stack/neighbor_cache_test.go b/pkg/tcpip/stack/neighbor_cache_test.go
index fcd54ed83..a73f63896 100644
--- a/pkg/tcpip/stack/neighbor_cache_test.go
+++ b/pkg/tcpip/stack/neighbor_cache_test.go
@@ -195,10 +195,10 @@ type testNeighborResolver struct {
 
 var _ LinkAddressResolver = (*testNeighborResolver)(nil)
 
-func (r *testNeighborResolver) LinkAddressRequest(addr, localAddr tcpip.Address, linkAddr tcpip.LinkAddress, linkEP LinkEndpoint) *tcpip.Error {
+func (r *testNeighborResolver) LinkAddressRequest(targetAddr, _ tcpip.Address, _ tcpip.LinkAddress, _ NetworkInterface) *tcpip.Error {
 	// Delay handling the request to emulate network latency.
 	r.clock.AfterFunc(r.delay, func() {
-		r.fakeRequest(addr)
+		r.fakeRequest(targetAddr)
 	})
 
 	// Execute post address resolution action, if available.
diff --git a/pkg/tcpip/stack/neighbor_entry.go b/pkg/tcpip/stack/neighbor_entry.go
index be61a21af..ab3cf6e9d 100644
--- a/pkg/tcpip/stack/neighbor_entry.go
+++ b/pkg/tcpip/stack/neighbor_entry.go
@@ -236,7 +236,7 @@ func (e *neighborEntry) setStateLocked(next NeighborState) {
 				return
 			}
 
-			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, e.neigh.LocalAddr, "", e.nic.LinkEndpoint); err != nil {
+			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, e.neigh.LocalAddr, "", e.nic); err != nil {
 				// There is no need to log the error here; the NUD implementation may
 				// assume a working link. A valid link should be the responsibility of
 				// the NIC/stack.LinkEndpoint.
@@ -277,7 +277,7 @@ func (e *neighborEntry) setStateLocked(next NeighborState) {
 				return
 			}
 
-			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, e.neigh.LocalAddr, e.neigh.LinkAddr, e.nic.LinkEndpoint); err != nil {
+			if err := e.linkRes.LinkAddressRequest(e.neigh.Addr, e.neigh.LocalAddr, e.neigh.LinkAddr, e.nic); err != nil {
 				e.dispatchRemoveEventLocked()
 				e.setStateLocked(Failed)
 				return
diff --git a/pkg/tcpip/stack/neighbor_entry_test.go b/pkg/tcpip/stack/neighbor_entry_test.go
index 3ee2a3b31..ba4041487 100644
--- a/pkg/tcpip/stack/neighbor_entry_test.go
+++ b/pkg/tcpip/stack/neighbor_entry_test.go
@@ -202,9 +202,9 @@ func (p entryTestProbeInfo) String() string {
 
 // LinkAddressRequest sends a request for the LinkAddress of addr. Broadcasts
 // to the local network if linkAddr is the zero value.
-func (r *entryTestLinkResolver) LinkAddressRequest(addr, localAddr tcpip.Address, linkAddr tcpip.LinkAddress, linkEP LinkEndpoint) *tcpip.Error {
+func (r *entryTestLinkResolver) LinkAddressRequest(targetAddr, localAddr tcpip.Address, linkAddr tcpip.LinkAddress, _ NetworkInterface) *tcpip.Error {
 	p := entryTestProbeInfo{
-		RemoteAddress:     addr,
+		RemoteAddress:     targetAddr,
 		RemoteLinkAddress: linkAddr,
 		LocalAddress:      localAddr,
 	}
diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index dcd4319bf..b97f4380a 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -273,6 +273,15 @@ func (n *NIC) WritePacket(r *Route, gso *GSO, protocol tcpip.NetworkProtocolNumb
 	return n.writePacket(r, gso, protocol, pkt)
 }
 
+// WritePacketToRemote implements NetworkInterface.
+func (n *NIC) WritePacketToRemote(remoteLinkAddr tcpip.LinkAddress, gso *GSO, protocol tcpip.NetworkProtocolNumber, pkt *PacketBuffer) *tcpip.Error {
+	r := Route{
+		NetProto:          protocol,
+		RemoteLinkAddress: remoteLinkAddr,
+	}
+	return n.writePacket(&r, gso, protocol, pkt)
+}
+
 func (n *NIC) writePacket(r *Route, gso *GSO, protocol tcpip.NetworkProtocolNumber, pkt *PacketBuffer) *tcpip.Error {
 	// WritePacket takes ownership of pkt, calculate numBytes first.
 	numBytes := pkt.Size()
diff --git a/pkg/tcpip/stack/nic_test.go b/pkg/tcpip/stack/nic_test.go
index 97a96af62..4af04846f 100644
--- a/pkg/tcpip/stack/nic_test.go
+++ b/pkg/tcpip/stack/nic_test.go
@@ -169,7 +169,7 @@ func (*testIPv6Protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
 }
 
 // LinkAddressRequest implements LinkAddressResolver.
-func (*testIPv6Protocol) LinkAddressRequest(_, _ tcpip.Address, _ tcpip.LinkAddress, _ LinkEndpoint) *tcpip.Error {
+func (*testIPv6Protocol) LinkAddressRequest(_, _ tcpip.Address, _ tcpip.LinkAddress, _ NetworkInterface) *tcpip.Error {
 	return nil
 }
 
diff --git a/pkg/tcpip/stack/registration.go b/pkg/tcpip/stack/registration.go
index defb9129b..203f3b51f 100644
--- a/pkg/tcpip/stack/registration.go
+++ b/pkg/tcpip/stack/registration.go
@@ -490,6 +490,9 @@ type NetworkInterface interface {
 
 	// Enabled returns true if the interface is enabled.
 	Enabled() bool
+
+	// WritePacketToRemote writes the packet to the given remote link address.
+	WritePacketToRemote(tcpip.LinkAddress, *GSO, tcpip.NetworkProtocolNumber, *PacketBuffer) *tcpip.Error
 }
 
 // NetworkEndpoint is the interface that needs to be implemented by endpoints
@@ -764,13 +767,13 @@ type InjectableLinkEndpoint interface {
 // A LinkAddressResolver is an extension to a NetworkProtocol that
 // can resolve link addresses.
 type LinkAddressResolver interface {
-	// LinkAddressRequest sends a request for the LinkAddress of addr. Broadcasts
-	// the request on the local network if remoteLinkAddr is the zero value. The
-	// request is sent on linkEP with localAddr as the source.
+	// LinkAddressRequest sends a request for the link address of the target
+	// address. The request is broadcasted on the local network if a remote link
+	// address is not provided.
 	//
-	// A valid response will cause the discovery protocol's network
-	// endpoint to call AddLinkAddress.
-	LinkAddressRequest(addr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, linkEP LinkEndpoint) *tcpip.Error
+	// The request is sent from the passed network interface. If the interface
+	// local address is unspecified, any interface local address may be used.
+	LinkAddressRequest(targetAddr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, nic NetworkInterface) *tcpip.Error
 
 	// ResolveStaticAddress attempts to resolve address without sending
 	// requests. It either resolves the name immediately or returns the
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 3a07577c8..d3f75cb36 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -1323,7 +1323,7 @@ func (s *Stack) GetLinkAddress(nicID tcpip.NICID, addr, localAddr tcpip.Address,
 
 	fullAddr := tcpip.FullAddress{NIC: nicID, Addr: addr}
 	linkRes := s.linkAddrResolvers[protocol]
-	return s.linkAddrCache.get(fullAddr, linkRes, localAddr, nic.LinkEndpoint, waker)
+	return s.linkAddrCache.get(fullAddr, linkRes, localAddr, nic, waker)
 }
 
 // Neighbors returns all IP to MAC address associations.