net/tstun: use unix.Ifreq type for Linux TAP interface configuration

Signed-off-by: Matt Layher <mdlayher@gmail.com>

cmd/tailscaled/depaware.txt

@@ -127,7 +127,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/net/tlsdial                                    from tailscale.com/control/controlclient+
         tailscale.com/net/tsaddr                                     from tailscale.com/ipn/ipnlocal+
      💣 tailscale.com/net/tshttpproxy                                from tailscale.com/control/controlclient+
-     💣 tailscale.com/net/tstun                                      from tailscale.com/cmd/tailscaled+
+        tailscale.com/net/tstun                                      from tailscale.com/cmd/tailscaled+
         tailscale.com/paths                                          from tailscale.com/cmd/tailscaled+
         tailscale.com/portlist                                       from tailscale.com/ipn/ipnlocal
         tailscale.com/safesocket                                     from tailscale.com/ipn/ipnserver+

go.mod

@@ -40,7 +40,7 @@ require (
 	golang.org/x/crypto v0.0.0-20210616213533-5ff15b29337e
 	golang.org/x/net v0.0.0-20210614182718-04defd469f4e
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
-	golang.org/x/sys v0.0.0-20210616094352-59db8d763f22
+	golang.org/x/sys v0.0.0-20210817190340-bfb29a6856f2
 	golang.org/x/term v0.0.0-20210503060354-a79de5458b56
 	golang.org/x/time v0.0.0-20210611083556-38a9dc6acbc6
 	golang.org/x/tools v0.1.2

go.sum

@@ -810,8 +810,9 @@ golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20210510120138-977fb7262007/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210525143221-35b2ab0089ea/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20210616094352-59db8d763f22 h1:RqytpXGR1iVNX7psjB3ff8y7sNFinVFvkx1c8SjBkio=
 golang.org/x/sys v0.0.0-20210616094352-59db8d763f22/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20210817190340-bfb29a6856f2 h1:c8PlLMqBbOHoqtjteWm5/kbe6rNY2pbRfbIMVnepueo=
+golang.org/x/sys v0.0.0-20210817190340-bfb29a6856f2/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210503060354-a79de5458b56 h1:b8jxX3zqjpqb2LklXPzKSGJhzyxCOZSz8ncv8Nv+y7w=
@@ -987,5 +988,3 @@ mvdan.cc/lint v0.0.0-20170908181259-adc824a0674b/go.mod h1:2odslEg/xrtNQqCYg2/jC
 mvdan.cc/unparam v0.0.0-20200501210554-b37ab49443f7 h1:kAREL6MPwpsk1/PQPFD3Eg7WAQR5mPTWZJaBiG5LDbY=
 mvdan.cc/unparam v0.0.0-20200501210554-b37ab49443f7/go.mod h1:HGC5lll35J70Y5v7vCGb9oLhHoScFwkHDJm/05RdSTc=
 rsc.io/binaryregexp v0.2.0/go.mod h1:qTv7/COck+e2FymRvadv62gMdZztPaShugOCi3I+8D8=
-rsc.io/goversion v1.2.0 h1:SPn+NLTiAG7w30IRK/DKp1BjvpWabYgxlLp/+kx5J8w=
-rsc.io/goversion v1.2.0/go.mod h1:Eih9y/uIBS3ulggl7KNJ09xGSLcuNaLgmvvqa07sgfo=

net/tstun/tap_linux.go

@@ -9,10 +9,9 @@ import (
 	"net"
 	"os"
 	"os/exec"
-	"syscall"
-	"unsafe"
 
 	"github.com/insomniacslk/dhcp/dhcpv4"
+	"golang.org/x/sys/unix"
 	"golang.zx2c4.com/wireguard/tun"
 	"inet.af/netaddr"
 	"inet.af/netstack/tcpip"
@@ -32,25 +31,30 @@ var ourMAC = net.HardwareAddr{0x30, 0x2D, 0x66, 0xEC, 0x7A, 0x93}
 
 func init() { createTAP = createTAPLinux }
 
-func createTAPLinux(tapName, bridgeName string) (dev tun.Device, err error) {
+func createTAPLinux(tapName, bridgeName string) (tun.Device, error) {
-	fd, err := syscall.Open("/dev/net/tun", syscall.O_RDWR, 0)
+	fd, err := unix.Open("/dev/net/tun", unix.O_RDWR, 0)
 	if err != nil {
 		return nil, err
 	}
-	var ifr struct {
+
-		name  [16]byte
+	dev, err := openDevice(fd, tapName, bridgeName)
-		flags uint16
+	if err != nil {
-		_     [22]byte
+		unix.Close(fd)
+		return nil, err
 	}
-	copy(ifr.name[:], tapName)
+
-	ifr.flags = syscall.IFF_TAP | syscall.IFF_NO_PI
+	return dev, nil
-	_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), syscall.TUNSETIFF, uintptr(unsafe.Pointer(&ifr)))
+}
-	if errno != 0 {
+
-		syscall.Close(fd)
+func openDevice(fd int, tapName, bridgeName string) (tun.Device, error) {
-		return nil, errno
+	ifr, err := unix.NewIfreq(tapName)
+	if err != nil {
+		return nil, err
 	}
-	if err = syscall.SetNonblock(fd, true); err != nil {
+
-		syscall.Close(fd)
+	// Flags are stored as a uint16 in the ifreq union.
+	ifr.SetUint16(unix.IFF_TAP | unix.IFF_NO_PI)
+	if err := unix.IoctlIfreq(fd, unix.TUNSETIFF, ifr); err != nil {
 		return nil, err
 	}
 
@@ -62,11 +66,13 @@ func createTAPLinux(tapName, bridgeName string) (dev tun.Device, err error) {
 			return nil, err
 		}
 	}
-	dev, _, err = tun.CreateUnmonitoredTUNFromFD(fd) // TODO: MTU
+
+	// Also sets non-blocking I/O on fd when creating tun.Device.
+	dev, _, err := tun.CreateUnmonitoredTUNFromFD(fd) // TODO: MTU
 	if err != nil {
-		syscall.Close(fd)
 		return nil, err
 	}
+
 	return dev, nil
 }