net: relax IP interface address determination on linux

Linux allows to have a peer IP address on IP interface over ethernet
link encapsulation, though it only installs a static route with the peer
address as an on-link nexthop.

Fixes #11338.

Change-Id: Ie2583737e4c7cec39baabb89dd732463d3f10a61
Reviewed-on: https://go-review.googlesource.com/11352
Reviewed-by: Russ Cox <rsc@golang.org>

4 files changed, 56 insertions, 35 deletions

diff --git a/src/net/interface_bsd_test.go b/src/net/interface_bsd_test.go
index 88daf73935..43ccc89f43 100644
--- a/src/net/interface_bsd_test.go
+++ b/src/net/interface_bsd_test.go
@@ -28,10 +28,8 @@ func (ti *testInterface) setBroadcast(suffix int) error {
 	return nil
 }
 
-func (ti *testInterface) setPointToPoint(suffix int, local, remote string) error {
+func (ti *testInterface) setPointToPoint(suffix int) error {
 	ti.name = fmt.Sprintf("gif%d", suffix)
-	ti.local = local
-	ti.remote = remote
 	xname, err := exec.LookPath("ifconfig")
 	if err != nil {
 		return err
diff --git a/src/net/interface_linux.go b/src/net/interface_linux.go
index 6551a3562e..ef2042920e 100644
--- a/src/net/interface_linux.go
+++ b/src/net/interface_linux.go
@@ -176,17 +176,15 @@ func newAddr(ifi *Interface, ifam *syscall.IfAddrmsg, attrs []syscall.NetlinkRou
 	var ipPointToPoint bool
 	// Seems like we need to make sure whether the IP interface
 	// stack consists of IP point-to-point numbered or unnumbered
-	// addressing over point-to-point link encapsulation.
-	if ifi.Flags&FlagPointToPoint != 0 {
-		for _, a := range attrs {
-			if a.Attr.Type == syscall.IFA_LOCAL {
-				ipPointToPoint = true
-				break
-			}
+	// addressing.
+	for _, a := range attrs {
+		if a.Attr.Type == syscall.IFA_LOCAL {
+			ipPointToPoint = true
+			break
 		}
 	}
 	for _, a := range attrs {
-		if ipPointToPoint && a.Attr.Type == syscall.IFA_ADDRESS || !ipPointToPoint && a.Attr.Type == syscall.IFA_LOCAL {
+		if ipPointToPoint && a.Attr.Type == syscall.IFA_ADDRESS {
 			continue
 		}
 		switch ifam.Family {
diff --git a/src/net/interface_linux_test.go b/src/net/interface_linux_test.go
index 059bde11c6..6251b2674c 100644
--- a/src/net/interface_linux_test.go
+++ b/src/net/interface_linux_test.go
@@ -20,6 +20,14 @@ func (ti *testInterface) setBroadcast(suffix int) error {
 		Path: xname,
 		Args: []string{"ip", "link", "add", ti.name, "type", "dummy"},
 	})
+	ti.setupCmds = append(ti.setupCmds, &exec.Cmd{
+		Path: xname,
+		Args: []string{"ip", "address", "add", ti.local, "peer", ti.remote, "dev", ti.name},
+	})
+	ti.teardownCmds = append(ti.teardownCmds, &exec.Cmd{
+		Path: xname,
+		Args: []string{"ip", "address", "del", ti.local, "peer", ti.remote, "dev", ti.name},
+	})
 	ti.teardownCmds = append(ti.teardownCmds, &exec.Cmd{
 		Path: xname,
 		Args: []string{"ip", "link", "delete", ti.name, "type", "dummy"},
@@ -27,29 +35,27 @@ func (ti *testInterface) setBroadcast(suffix int) error {
 	return nil
 }
 
-func (ti *testInterface) setPointToPoint(suffix int, local, remote string) error {
+func (ti *testInterface) setPointToPoint(suffix int) error {
 	ti.name = fmt.Sprintf("gotest%d", suffix)
-	ti.local = local
-	ti.remote = remote
 	xname, err := exec.LookPath("ip")
 	if err != nil {
 		return err
 	}
 	ti.setupCmds = append(ti.setupCmds, &exec.Cmd{
 		Path: xname,
-		Args: []string{"ip", "tunnel", "add", ti.name, "mode", "gre", "local", local, "remote", remote},
+		Args: []string{"ip", "tunnel", "add", ti.name, "mode", "gre", "local", ti.local, "remote", ti.remote},
+	})
+	ti.setupCmds = append(ti.setupCmds, &exec.Cmd{
+		Path: xname,
+		Args: []string{"ip", "address", "add", ti.local, "peer", ti.remote, "dev", ti.name},
 	})
 	ti.teardownCmds = append(ti.teardownCmds, &exec.Cmd{
 		Path: xname,
-		Args: []string{"ip", "tunnel", "del", ti.name, "mode", "gre", "local", local, "remote", remote},
+		Args: []string{"ip", "address", "del", ti.local, "peer", ti.remote, "dev", ti.name},
 	})
-	xname, err = exec.LookPath("ifconfig")
-	if err != nil {
-		return err
-	}
-	ti.setupCmds = append(ti.setupCmds, &exec.Cmd{
+	ti.teardownCmds = append(ti.teardownCmds, &exec.Cmd{
 		Path: xname,
-		Args: []string{"ifconfig", ti.name, "inet", local, "dstaddr", remote},
+		Args: []string{"ip", "tunnel", "del", ti.name, "mode", "gre", "local", ti.local, "remote", ti.remote},
 	})
 	return nil
 }
diff --git a/src/net/interface_unix_test.go b/src/net/interface_unix_test.go
index 84bf06cbce..93b3b79afd 100644
--- a/src/net/interface_unix_test.go
+++ b/src/net/interface_unix_test.go
@@ -54,8 +54,8 @@ func TestPointToPointInterface(t *testing.T) {
 	local, remote := "169.254.0.1", "169.254.0.254"
 	ip := ParseIP(remote)
 	for i := 0; i < 3; i++ {
-		ti := &testInterface{}
-		if err := ti.setPointToPoint(5963+i, local, remote); err != nil {
+		ti := &testInterface{local: local, remote: remote}
+		if err := ti.setPointToPoint(5963 + i); err != nil {
 			t.Skipf("test requries external command: %v", err)
 		}
 		if err := ti.setup(); err != nil {
@@ -69,17 +69,18 @@ func TestPointToPointInterface(t *testing.T) {
 			t.Fatal(err)
 		}
 		for _, ifi := range ift {
-			if ti.name == ifi.Name {
-				ifat, err := ifi.Addrs()
-				if err != nil {
+			if ti.name != ifi.Name {
+				continue
+			}
+			ifat, err := ifi.Addrs()
+			if err != nil {
+				ti.teardown()
+				t.Fatal(err)
+			}
+			for _, ifa := range ifat {
+				if ip.Equal(ifa.(*IPNet).IP) {
 					ti.teardown()
-					t.Fatal(err)
-				}
-				for _, ifa := range ifat {
-					if ip.Equal(ifa.(*IPNet).IP) {
-						ti.teardown()
-						t.Fatalf("got %v; want %v", ip, local)
-					}
+					t.Fatalf("got %v", ifa)
 				}
 			}
 		}
@@ -99,12 +100,14 @@ func TestInterfaceArrivalAndDeparture(t *testing.T) {
 		t.Skip("must be root")
 	}
 
+	local, remote := "169.254.0.1", "169.254.0.254"
+	ip := ParseIP(remote)
 	for i := 0; i < 3; i++ {
 		ift1, err := Interfaces()
 		if err != nil {
 			t.Fatal(err)
 		}
-		ti := &testInterface{}
+		ti := &testInterface{local: local, remote: remote}
 		if err := ti.setBroadcast(5682 + i); err != nil {
 			t.Skipf("test requires external command: %v", err)
 		}
@@ -128,6 +131,22 @@ func TestInterfaceArrivalAndDeparture(t *testing.T) {
 			ti.teardown()
 			t.Fatalf("got %v; want gt %v", len(ift2), len(ift1))
 		}
+		for _, ifi := range ift2 {
+			if ti.name != ifi.Name {
+				continue
+			}
+			ifat, err := ifi.Addrs()
+			if err != nil {
+				ti.teardown()
+				t.Fatal(err)
+			}
+			for _, ifa := range ifat {
+				if ip.Equal(ifa.(*IPNet).IP) {
+					ti.teardown()
+					t.Fatalf("got %v", ifa)
+				}
+			}
+		}
 		if err := ti.teardown(); err != nil {
 			t.Fatal(err)
 		} else {