Add NIC.isLoopback()

...enabling us to remove the "CreateNamedLoopbackNIC" variant of
CreateNIC and all the plumbing to connect it through to where the value
is read in FindRoute.

PiperOrigin-RevId: 288713093

3 files changed, 23 insertions, 26 deletions

diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index 5726c3642..4144d5d0f 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -27,11 +27,10 @@ import (
 // NIC represents a "network interface card" to which the networking stack is
 // attached.
 type NIC struct {
-	stack    *Stack
-	id       tcpip.NICID
-	name     string
-	linkEP   LinkEndpoint
-	loopback bool
+	stack  *Stack
+	id     tcpip.NICID
+	name   string
+	linkEP LinkEndpoint
 
 	mu            sync.RWMutex
 	spoofing      bool
@@ -85,7 +84,7 @@ const (
 )
 
 // newNIC returns a new NIC using the default NDP configurations from stack.
-func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint, loopback bool) *NIC {
+func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint) *NIC {
 	// TODO(b/141011931): Validate a LinkEndpoint (ep) is valid. For
 	// example, make sure that the link address it provides is a valid
 	// unicast ethernet address.
@@ -99,7 +98,6 @@ func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint, loopback
 		id:         id,
 		name:       name,
 		linkEP:     ep,
-		loopback:   loopback,
 		primary:    make(map[tcpip.NetworkProtocolNumber][]*referencedNetworkEndpoint),
 		endpoints:  make(map[NetworkEndpointID]*referencedNetworkEndpoint),
 		mcastJoins: make(map[NetworkEndpointID]int32),
@@ -175,7 +173,7 @@ func (n *NIC) enable() *tcpip.Error {
 	}
 
 	// Do not auto-generate an IPv6 link-local address for loopback devices.
-	if !n.stack.autoGenIPv6LinkLocal || n.loopback {
+	if !n.stack.autoGenIPv6LinkLocal || n.isLoopback() {
 		return nil
 	}
 
@@ -240,6 +238,10 @@ func (n *NIC) isPromiscuousMode() bool {
 	return rv
 }
 
+func (n *NIC) isLoopback() bool {
+	return n.linkEP.Capabilities()&CapabilityLoopback != 0
+}
+
 // setSpoofing enables or disables address spoofing.
 func (n *NIC) setSpoofing(enable bool) {
 	n.mu.Lock()
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 583ede3e5..807f910f6 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -798,7 +798,7 @@ func (s *Stack) NewPacketEndpoint(cooked bool, netProto tcpip.NetworkProtocolNum
 
 // createNIC creates a NIC with the provided id and link-layer endpoint, and
 // optionally enable it.
-func (s *Stack) createNIC(id tcpip.NICID, name string, ep LinkEndpoint, enabled, loopback bool) *tcpip.Error {
+func (s *Stack) createNIC(id tcpip.NICID, name string, ep LinkEndpoint, enabled bool) *tcpip.Error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
@@ -807,7 +807,7 @@ func (s *Stack) createNIC(id tcpip.NICID, name string, ep LinkEndpoint, enabled,
 		return tcpip.ErrDuplicateNICID
 	}
 
-	n := newNIC(s, id, name, ep, loopback)
+	n := newNIC(s, id, name, ep)
 
 	s.nics[id] = n
 	if enabled {
@@ -819,32 +819,26 @@ func (s *Stack) createNIC(id tcpip.NICID, name string, ep LinkEndpoint, enabled,
 
 // CreateNIC creates a NIC with the provided id and link-layer endpoint.
 func (s *Stack) CreateNIC(id tcpip.NICID, ep LinkEndpoint) *tcpip.Error {
-	return s.createNIC(id, "", ep, true, false)
+	return s.createNIC(id, "", ep, true)
 }
 
 // CreateNamedNIC creates a NIC with the provided id and link-layer endpoint,
 // and a human-readable name.
 func (s *Stack) CreateNamedNIC(id tcpip.NICID, name string, ep LinkEndpoint) *tcpip.Error {
-	return s.createNIC(id, name, ep, true, false)
-}
-
-// CreateNamedLoopbackNIC creates a NIC with the provided id and link-layer
-// endpoint, and a human-readable name.
-func (s *Stack) CreateNamedLoopbackNIC(id tcpip.NICID, name string, ep LinkEndpoint) *tcpip.Error {
-	return s.createNIC(id, name, ep, true, true)
+	return s.createNIC(id, name, ep, true)
 }
 
 // CreateDisabledNIC creates a NIC with the provided id and link-layer endpoint,
 // but leave it disable. Stack.EnableNIC must be called before the link-layer
 // endpoint starts delivering packets to it.
 func (s *Stack) CreateDisabledNIC(id tcpip.NICID, ep LinkEndpoint) *tcpip.Error {
-	return s.createNIC(id, "", ep, false, false)
+	return s.createNIC(id, "", ep, false)
 }
 
 // CreateDisabledNamedNIC is a combination of CreateNamedNIC and
 // CreateDisabledNIC.
 func (s *Stack) CreateDisabledNamedNIC(id tcpip.NICID, name string, ep LinkEndpoint) *tcpip.Error {
-	return s.createNIC(id, name, ep, false, false)
+	return s.createNIC(id, name, ep, false)
 }
 
 // EnableNIC enables the given NIC so that the link-layer endpoint can start
@@ -911,7 +905,7 @@ func (s *Stack) NICInfo() map[tcpip.NICID]NICInfo {
 			Up:          true, // Netstack interfaces are always up.
 			Running:     nic.linkEP.IsAttached(),
 			Promiscuous: nic.isPromiscuousMode(),
-			Loopback:    nic.linkEP.Capabilities()&CapabilityLoopback != 0,
+			Loopback:    nic.isLoopback(),
 		}
 		nics[id] = NICInfo{
 			Name:              nic.name,
@@ -1072,7 +1066,7 @@ func (s *Stack) FindRoute(id tcpip.NICID, localAddr, remoteAddr tcpip.Address, n
 	if id != 0 && !needRoute {
 		if nic, ok := s.nics[id]; ok {
 			if ref := s.getRefEP(nic, localAddr, netProto); ref != nil {
-				return makeRoute(netProto, ref.ep.ID().LocalAddress, remoteAddr, nic.linkEP.LinkAddress(), ref, s.handleLocal && !nic.loopback, multicastLoop && !nic.loopback), nil
+				return makeRoute(netProto, ref.ep.ID().LocalAddress, remoteAddr, nic.linkEP.LinkAddress(), ref, s.handleLocal && !nic.isLoopback(), multicastLoop && !nic.isLoopback()), nil
 			}
 		}
 	} else {
@@ -1088,7 +1082,7 @@ func (s *Stack) FindRoute(id tcpip.NICID, localAddr, remoteAddr tcpip.Address, n
 						remoteAddr = ref.ep.ID().LocalAddress
 					}
 
-					r := makeRoute(netProto, ref.ep.ID().LocalAddress, remoteAddr, nic.linkEP.LinkAddress(), ref, s.handleLocal && !nic.loopback, multicastLoop && !nic.loopback)
+					r := makeRoute(netProto, ref.ep.ID().LocalAddress, remoteAddr, nic.linkEP.LinkAddress(), ref, s.handleLocal && !nic.isLoopback(), multicastLoop && !nic.isLoopback())
 					if needRoute {
 						r.NextHop = route.Gateway
 					}
diff --git a/pkg/tcpip/stack/stack_test.go b/pkg/tcpip/stack/stack_test.go
index d970a4abb..bf057745e 100644
--- a/pkg/tcpip/stack/stack_test.go
+++ b/pkg/tcpip/stack/stack_test.go
@@ -32,6 +32,7 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/pkg/tcpip/link/channel"
+	"gvisor.dev/gvisor/pkg/tcpip/link/loopback"
 	"gvisor.dev/gvisor/pkg/tcpip/network/ipv6"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 )
@@ -2153,10 +2154,10 @@ func TestNoLinkLocalAutoGenForLoopbackNIC(t *testing.T) {
 				OpaqueIIDOpts:        test.opaqueIIDOpts,
 			}
 
-			e := channel.New(0, 1280, linkAddr1)
+			e := loopback.New()
 			s := stack.New(opts)
-			if err := s.CreateNamedLoopbackNIC(nicID, nicName, e); err != nil {
-				t.Fatalf("CreateNamedLoopbackNIC(%d, %q, _) = %s", nicID, nicName, err)
+			if err := s.CreateNamedNIC(nicID, nicName, e); err != nil {
+				t.Fatalf("CreateNamedNIC(%d, %q, _) = %s", nicID, nicName, err)
 			}
 
 			addr, err := s.GetMainNICAddress(nicID, header.IPv6ProtocolNumber)