From 6768e6c59ec252854a1633e184b69dc5723ac3f3 Mon Sep 17 00:00:00 2001
From: Ghanan Gowripalan <ghanan@google.com>
Date: Thu, 8 Oct 2020 16:14:01 -0700
Subject: Do not resolve routes immediately

When a response needs to be sent to an incoming packet, the stack should
consult its neighbour table to determine the remote address's link
address.

When an entry does not exist in the stack's neighbor table, the stack
should queue the packet while link resolution completes. See comments.

PiperOrigin-RevId: 336185457
---
 pkg/tcpip/link/tun/device.go | 42 +++++++++++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 13 deletions(-)

(limited to 'pkg/tcpip/link/tun/device.go')

diff --git a/pkg/tcpip/link/tun/device.go b/pkg/tcpip/link/tun/device.go
index b6ddbe81e..f94491026 100644
--- a/pkg/tcpip/link/tun/device.go
+++ b/pkg/tcpip/link/tun/device.go
@@ -76,13 +76,29 @@ func (d *Device) Release(ctx context.Context) {
 	}
 }
 
+// NICID returns the NIC ID of the device.
+//
+// Must only be called after the device has been attached to an endpoint.
+func (d *Device) NICID() tcpip.NICID {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+
+	if d.endpoint == nil {
+		panic("called NICID on a device that has not been attached")
+	}
+
+	return d.endpoint.nicID
+}
+
 // SetIff services TUNSETIFF ioctl(2) request.
-func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) error {
+//
+// Returns true if a new NIC was created; false if an existing one was attached.
+func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) (bool, error) {
 	d.mu.Lock()
 	defer d.mu.Unlock()
 
 	if d.endpoint != nil {
-		return syserror.EINVAL
+		return false, syserror.EINVAL
 	}
 
 	// Input validations.
@@ -90,7 +106,7 @@ func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) error {
 	isTap := flags&linux.IFF_TAP != 0
 	supportedFlags := uint16(linux.IFF_TUN | linux.IFF_TAP | linux.IFF_NO_PI)
 	if isTap && isTun || !isTap && !isTun || flags&^supportedFlags != 0 {
-		return syserror.EINVAL
+		return false, syserror.EINVAL
 	}
 
 	prefix := "tun"
@@ -103,32 +119,32 @@ func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) error {
 		linkCaps |= stack.CapabilityResolutionRequired
 	}
 
-	endpoint, err := attachOrCreateNIC(s, name, prefix, linkCaps)
+	endpoint, created, err := attachOrCreateNIC(s, name, prefix, linkCaps)
 	if err != nil {
-		return syserror.EINVAL
+		return false, syserror.EINVAL
 	}
 
 	d.endpoint = endpoint
 	d.notifyHandle = d.endpoint.AddNotify(d)
 	d.flags = flags
-	return nil
+	return created, nil
 }
 
-func attachOrCreateNIC(s *stack.Stack, name, prefix string, linkCaps stack.LinkEndpointCapabilities) (*tunEndpoint, error) {
+func attachOrCreateNIC(s *stack.Stack, name, prefix string, linkCaps stack.LinkEndpointCapabilities) (*tunEndpoint, bool, error) {
 	for {
 		// 1. Try to attach to an existing NIC.
 		if name != "" {
-			if nic, found := s.GetNICByName(name); found {
-				endpoint, ok := nic.LinkEndpoint().(*tunEndpoint)
+			if linkEP := s.GetLinkEndpointByName(name); linkEP != nil {
+				endpoint, ok := linkEP.(*tunEndpoint)
 				if !ok {
 					// Not a NIC created by tun device.
-					return nil, syserror.EOPNOTSUPP
+					return nil, false, syserror.EOPNOTSUPP
 				}
 				if !endpoint.TryIncRef() {
 					// Race detected: NIC got deleted in between.
 					continue
 				}
-				return endpoint, nil
+				return endpoint, false, nil
 			}
 		}
 
@@ -151,12 +167,12 @@ func attachOrCreateNIC(s *stack.Stack, name, prefix string, linkCaps stack.LinkE
 		})
 		switch err {
 		case nil:
-			return endpoint, nil
+			return endpoint, true, nil
 		case tcpip.ErrDuplicateNICID:
 			// Race detected: A NIC has been created in between.
 			continue
 		default:
-			return nil, syserror.EINVAL
+			return nil, false, syserror.EINVAL
 		}
 	}
 }
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