tuntap: use the owner / group parameters

Set the tuntap owner / group via syscall on the opened file
descriptor.

Signed-off-by: Miguel Duarte Barroso <mdbarroso@redhat.com>

link_linux.go

@@ -1074,8 +1074,6 @@ func (h *Handle) linkModify(link Link, flags int) error {
 	}
 
 	if isTuntap {
-		// TODO: support user
-		// TODO: support group
 		if tuntap.Mode < unix.IFF_TUN || tuntap.Mode > unix.IFF_TAP {
 			return fmt.Errorf("Tuntap.Mode %v unknown", tuntap.Mode)
 		}
@@ -1121,6 +1119,18 @@ func (h *Handle) linkModify(link Link, flags int) error {
 				return fmt.Errorf("Tuntap IOCTL TUNSETIFF failed [%d], errno %v", i, errno)
 			}
 
+			_, _, errno = syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), syscall.TUNSETOWNER, uintptr(tuntap.Owner))
+			if errno != 0 {
+				cleanupFds(fds)
+				return fmt.Errorf("Tuntap IOCTL TUNSETOWNER failed [%d], errno %v", i, errno)
+			}
+
+			_, _, errno = syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), syscall.TUNSETGROUP, uintptr(tuntap.Group))
+			if errno != 0 {
+				cleanupFds(fds)
+				return fmt.Errorf("Tuntap IOCTL TUNSETGROUP failed [%d], errno %v", i, errno)
+			}
+
 			// Set the tun device to non-blocking before use. The below comment
 			// taken from:
 			//

link_test.go

@@ -2191,6 +2191,28 @@ func TestLinkAddDelTuntapMq(t *testing.T) {
 		Flags:     TUNTAP_MULTI_QUEUE_DEFAULTS | TUNTAP_VNET_HDR})
 }
 
+func TestLinkAddDelTuntapOwnerGroup(t *testing.T) {
+	tearDown := setUpNetlinkTest(t)
+	defer tearDown()
+
+	if err := syscall.Mount("sysfs", "/sys", "sysfs", syscall.MS_RDONLY, ""); err != nil {
+		t.Fatal("Cannot mount sysfs")
+	}
+
+	defer func() {
+		if err := syscall.Unmount("/sys", 0); err != nil {
+			t.Fatal("Cannot umount /sys")
+		}
+	}()
+
+	testLinkAddDel(t, &Tuntap{
+		LinkAttrs: LinkAttrs{Name: "foo"},
+		Mode:      TUNTAP_MODE_TAP,
+		Owner:     0,
+		Group:     0,
+	})
+}
+
 func TestVethPeerIndex(t *testing.T) {
 	tearDown := setUpNetlinkTest(t)
 	defer tearDown()