conn: introduce new package that splits out the Bind and Endpoint types

The sticky socket code stays in the device package for now,
as it reaches deeply into the peer list.

This is the first step in an effort to split some code out of
the very busy device package.

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>

1 files changed, 571 insertions, 0 deletions

diff --git a/conn/conn_linux.go b/conn/conn_linux.go
new file mode 100644
index 0000000..523da4a
--- /dev/null
+++ b/conn/conn_linux.go
@@ -0,0 +1,571 @@
+// +build !android
+
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2017-2019 WireGuard LLC. All Rights Reserved.
+ */
+
+package conn
+
+import (
+	"errors"
+	"net"
+	"strconv"
+	"sync"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+const (
+	FD_ERR = -1
+)
+
+type IPv4Source struct {
+	Src     [4]byte
+	Ifindex int32
+}
+
+type IPv6Source struct {
+	src [16]byte
+	//ifindex belongs in dst.ZoneId
+}
+
+type NativeEndpoint struct {
+	sync.Mutex
+	dst  [unsafe.Sizeof(unix.SockaddrInet6{})]byte
+	src  [unsafe.Sizeof(IPv6Source{})]byte
+	isV6 bool
+}
+
+func (endpoint *NativeEndpoint) Src4() *IPv4Source         { return endpoint.src4() }
+func (endpoint *NativeEndpoint) Dst4() *unix.SockaddrInet4 { return endpoint.dst4() }
+func (endpoint *NativeEndpoint) IsV6() bool                { return endpoint.isV6 }
+
+func (endpoint *NativeEndpoint) src4() *IPv4Source {
+	return (*IPv4Source)(unsafe.Pointer(&endpoint.src[0]))
+}
+
+func (endpoint *NativeEndpoint) src6() *IPv6Source {
+	return (*IPv6Source)(unsafe.Pointer(&endpoint.src[0]))
+}
+
+func (endpoint *NativeEndpoint) dst4() *unix.SockaddrInet4 {
+	return (*unix.SockaddrInet4)(unsafe.Pointer(&endpoint.dst[0]))
+}
+
+func (endpoint *NativeEndpoint) dst6() *unix.SockaddrInet6 {
+	return (*unix.SockaddrInet6)(unsafe.Pointer(&endpoint.dst[0]))
+}
+
+type nativeBind struct {
+	sock4    int
+	sock6    int
+	lastMark uint32
+}
+
+var _ Endpoint = (*NativeEndpoint)(nil)
+var _ Bind = (*nativeBind)(nil)
+
+func CreateEndpoint(s string) (Endpoint, error) {
+	var end NativeEndpoint
+	addr, err := parseEndpoint(s)
+	if err != nil {
+		return nil, err
+	}
+
+	ipv4 := addr.IP.To4()
+	if ipv4 != nil {
+		dst := end.dst4()
+		end.isV6 = false
+		dst.Port = addr.Port
+		copy(dst.Addr[:], ipv4)
+		end.ClearSrc()
+		return &end, nil
+	}
+
+	ipv6 := addr.IP.To16()
+	if ipv6 != nil {
+		zone, err := zoneToUint32(addr.Zone)
+		if err != nil {
+			return nil, err
+		}
+		dst := end.dst6()
+		end.isV6 = true
+		dst.Port = addr.Port
+		dst.ZoneId = zone
+		copy(dst.Addr[:], ipv6[:])
+		end.ClearSrc()
+		return &end, nil
+	}
+
+	return nil, errors.New("Invalid IP address")
+}
+
+func createBind(port uint16) (Bind, uint16, error) {
+	var err error
+	var bind nativeBind
+	var newPort uint16
+
+	// Attempt ipv6 bind, update port if successful.
+	bind.sock6, newPort, err = create6(port)
+	if err != nil {
+		if err != syscall.EAFNOSUPPORT {
+			return nil, 0, err
+		}
+	} else {
+		port = newPort
+	}
+
+	// Attempt ipv4 bind, update port if successful.
+	bind.sock4, newPort, err = create4(port)
+	if err != nil {
+		if err != syscall.EAFNOSUPPORT {
+			unix.Close(bind.sock6)
+			return nil, 0, err
+		}
+	} else {
+		port = newPort
+	}
+
+	if bind.sock4 == FD_ERR && bind.sock6 == FD_ERR {
+		return nil, 0, errors.New("ipv4 and ipv6 not supported")
+	}
+
+	return &bind, port, nil
+}
+
+func (bind *nativeBind) LastMark() uint32 {
+	return bind.lastMark
+}
+
+func (bind *nativeBind) SetMark(value uint32) error {
+	if bind.sock6 != -1 {
+		err := unix.SetsockoptInt(
+			bind.sock6,
+			unix.SOL_SOCKET,
+			unix.SO_MARK,
+			int(value),
+		)
+
+		if err != nil {
+			return err
+		}
+	}
+
+	if bind.sock4 != -1 {
+		err := unix.SetsockoptInt(
+			bind.sock4,
+			unix.SOL_SOCKET,
+			unix.SO_MARK,
+			int(value),
+		)
+
+		if err != nil {
+			return err
+		}
+	}
+
+	bind.lastMark = value
+	return nil
+}
+
+func closeUnblock(fd int) error {
+	// shutdown to unblock readers and writers
+	unix.Shutdown(fd, unix.SHUT_RDWR)
+	return unix.Close(fd)
+}
+
+func (bind *nativeBind) Close() error {
+	var err1, err2 error
+	if bind.sock6 != -1 {
+		err1 = closeUnblock(bind.sock6)
+	}
+	if bind.sock4 != -1 {
+		err2 = closeUnblock(bind.sock4)
+	}
+
+	if err1 != nil {
+		return err1
+	}
+	return err2
+}
+
+func (bind *nativeBind) ReceiveIPv6(buff []byte) (int, Endpoint, error) {
+	var end NativeEndpoint
+	if bind.sock6 == -1 {
+		return 0, nil, syscall.EAFNOSUPPORT
+	}
+	n, err := receive6(
+		bind.sock6,
+		buff,
+		&end,
+	)
+	return n, &end, err
+}
+
+func (bind *nativeBind) ReceiveIPv4(buff []byte) (int, Endpoint, error) {
+	var end NativeEndpoint
+	if bind.sock4 == -1 {
+		return 0, nil, syscall.EAFNOSUPPORT
+	}
+	n, err := receive4(
+		bind.sock4,
+		buff,
+		&end,
+	)
+	return n, &end, err
+}
+
+func (bind *nativeBind) Send(buff []byte, end Endpoint) error {
+	nend := end.(*NativeEndpoint)
+	if !nend.isV6 {
+		if bind.sock4 == -1 {
+			return syscall.EAFNOSUPPORT
+		}
+		return send4(bind.sock4, nend, buff)
+	} else {
+		if bind.sock6 == -1 {
+			return syscall.EAFNOSUPPORT
+		}
+		return send6(bind.sock6, nend, buff)
+	}
+}
+
+func (end *NativeEndpoint) SrcIP() net.IP {
+	if !end.isV6 {
+		return net.IPv4(
+			end.src4().Src[0],
+			end.src4().Src[1],
+			end.src4().Src[2],
+			end.src4().Src[3],
+		)
+	} else {
+		return end.src6().src[:]
+	}
+}
+
+func (end *NativeEndpoint) DstIP() net.IP {
+	if !end.isV6 {
+		return net.IPv4(
+			end.dst4().Addr[0],
+			end.dst4().Addr[1],
+			end.dst4().Addr[2],
+			end.dst4().Addr[3],
+		)
+	} else {
+		return end.dst6().Addr[:]
+	}
+}
+
+func (end *NativeEndpoint) DstToBytes() []byte {
+	if !end.isV6 {
+		return (*[unsafe.Offsetof(end.dst4().Addr) + unsafe.Sizeof(end.dst4().Addr)]byte)(unsafe.Pointer(end.dst4()))[:]
+	} else {
+		return (*[unsafe.Offsetof(end.dst6().Addr) + unsafe.Sizeof(end.dst6().Addr)]byte)(unsafe.Pointer(end.dst6()))[:]
+	}
+}
+
+func (end *NativeEndpoint) SrcToString() string {
+	return end.SrcIP().String()
+}
+
+func (end *NativeEndpoint) DstToString() string {
+	var udpAddr net.UDPAddr
+	udpAddr.IP = end.DstIP()
+	if !end.isV6 {
+		udpAddr.Port = end.dst4().Port
+	} else {
+		udpAddr.Port = end.dst6().Port
+	}
+	return udpAddr.String()
+}
+
+func (end *NativeEndpoint) ClearDst() {
+	for i := range end.dst {
+		end.dst[i] = 0
+	}
+}
+
+func (end *NativeEndpoint) ClearSrc() {
+	for i := range end.src {
+		end.src[i] = 0
+	}
+}
+
+func zoneToUint32(zone string) (uint32, error) {
+	if zone == "" {
+		return 0, nil
+	}
+	if intr, err := net.InterfaceByName(zone); err == nil {
+		return uint32(intr.Index), nil
+	}
+	n, err := strconv.ParseUint(zone, 10, 32)
+	return uint32(n), err
+}
+
+func create4(port uint16) (int, uint16, error) {
+
+	// create socket
+
+	fd, err := unix.Socket(
+		unix.AF_INET,
+		unix.SOCK_DGRAM,
+		0,
+	)
+
+	if err != nil {
+		return FD_ERR, 0, err
+	}
+
+	addr := unix.SockaddrInet4{
+		Port: int(port),
+	}
+
+	// set sockopts and bind
+
+	if err := func() error {
+		if err := unix.SetsockoptInt(
+			fd,
+			unix.SOL_SOCKET,
+			unix.SO_REUSEADDR,
+			1,
+		); err != nil {
+			return err
+		}
+
+		if err := unix.SetsockoptInt(
+			fd,
+			unix.IPPROTO_IP,
+			unix.IP_PKTINFO,
+			1,
+		); err != nil {
+			return err
+		}
+
+		return unix.Bind(fd, &addr)
+	}(); err != nil {
+		unix.Close(fd)
+		return FD_ERR, 0, err
+	}
+
+	sa, err := unix.Getsockname(fd)
+	if err == nil {
+		addr.Port = sa.(*unix.SockaddrInet4).Port
+	}
+
+	return fd, uint16(addr.Port), err
+}
+
+func create6(port uint16) (int, uint16, error) {
+
+	// create socket
+
+	fd, err := unix.Socket(
+		unix.AF_INET6,
+		unix.SOCK_DGRAM,
+		0,
+	)
+
+	if err != nil {
+		return FD_ERR, 0, err
+	}
+
+	// set sockopts and bind
+
+	addr := unix.SockaddrInet6{
+		Port: int(port),
+	}
+
+	if err := func() error {
+
+		if err := unix.SetsockoptInt(
+			fd,
+			unix.SOL_SOCKET,
+			unix.SO_REUSEADDR,
+			1,
+		); err != nil {
+			return err
+		}
+
+		if err := unix.SetsockoptInt(
+			fd,
+			unix.IPPROTO_IPV6,
+			unix.IPV6_RECVPKTINFO,
+			1,
+		); err != nil {
+			return err
+		}
+
+		if err := unix.SetsockoptInt(
+			fd,
+			unix.IPPROTO_IPV6,
+			unix.IPV6_V6ONLY,
+			1,
+		); err != nil {
+			return err
+		}
+
+		return unix.Bind(fd, &addr)
+
+	}(); err != nil {
+		unix.Close(fd)
+		return FD_ERR, 0, err
+	}
+
+	sa, err := unix.Getsockname(fd)
+	if err == nil {
+		addr.Port = sa.(*unix.SockaddrInet6).Port
+	}
+
+	return fd, uint16(addr.Port), err
+}
+
+func send4(sock int, end *NativeEndpoint, buff []byte) error {
+
+	// construct message header
+
+	cmsg := struct {
+		cmsghdr unix.Cmsghdr
+		pktinfo unix.Inet4Pktinfo
+	}{
+		unix.Cmsghdr{
+			Level: unix.IPPROTO_IP,
+			Type:  unix.IP_PKTINFO,
+			Len:   unix.SizeofInet4Pktinfo + unix.SizeofCmsghdr,
+		},
+		unix.Inet4Pktinfo{
+			Spec_dst: end.src4().Src,
+			Ifindex:  end.src4().Ifindex,
+		},
+	}
+
+	end.Lock()
+	_, err := unix.SendmsgN(sock, buff, (*[unsafe.Sizeof(cmsg)]byte)(unsafe.Pointer(&cmsg))[:], end.dst4(), 0)
+	end.Unlock()
+
+	if err == nil {
+		return nil
+	}
+
+	// clear src and retry
+
+	if err == unix.EINVAL {
+		end.ClearSrc()
+		cmsg.pktinfo = unix.Inet4Pktinfo{}
+		end.Lock()
+		_, err = unix.SendmsgN(sock, buff, (*[unsafe.Sizeof(cmsg)]byte)(unsafe.Pointer(&cmsg))[:], end.dst4(), 0)
+		end.Unlock()
+	}
+
+	return err
+}
+
+func send6(sock int, end *NativeEndpoint, buff []byte) error {
+
+	// construct message header
+
+	cmsg := struct {
+		cmsghdr unix.Cmsghdr
+		pktinfo unix.Inet6Pktinfo
+	}{
+		unix.Cmsghdr{
+			Level: unix.IPPROTO_IPV6,
+			Type:  unix.IPV6_PKTINFO,
+			Len:   unix.SizeofInet6Pktinfo + unix.SizeofCmsghdr,
+		},
+		unix.Inet6Pktinfo{
+			Addr:    end.src6().src,
+			Ifindex: end.dst6().ZoneId,
+		},
+	}
+
+	if cmsg.pktinfo.Addr == [16]byte{} {
+		cmsg.pktinfo.Ifindex = 0
+	}
+
+	end.Lock()
+	_, err := unix.SendmsgN(sock, buff, (*[unsafe.Sizeof(cmsg)]byte)(unsafe.Pointer(&cmsg))[:], end.dst6(), 0)
+	end.Unlock()
+
+	if err == nil {
+		return nil
+	}
+
+	// clear src and retry
+
+	if err == unix.EINVAL {
+		end.ClearSrc()
+		cmsg.pktinfo = unix.Inet6Pktinfo{}
+		end.Lock()
+		_, err = unix.SendmsgN(sock, buff, (*[unsafe.Sizeof(cmsg)]byte)(unsafe.Pointer(&cmsg))[:], end.dst6(), 0)
+		end.Unlock()
+	}
+
+	return err
+}
+
+func receive4(sock int, buff []byte, end *NativeEndpoint) (int, error) {
+
+	// construct message header
+
+	var cmsg struct {
+		cmsghdr unix.Cmsghdr
+		pktinfo unix.Inet4Pktinfo
+	}
+
+	size, _, _, newDst, err := unix.Recvmsg(sock, buff, (*[unsafe.Sizeof(cmsg)]byte)(unsafe.Pointer(&cmsg))[:], 0)
+
+	if err != nil {
+		return 0, err
+	}
+	end.isV6 = false
+
+	if newDst4, ok := newDst.(*unix.SockaddrInet4); ok {
+		*end.dst4() = *newDst4
+	}
+
+	// update source cache
+
+	if cmsg.cmsghdr.Level == unix.IPPROTO_IP &&
+		cmsg.cmsghdr.Type == unix.IP_PKTINFO &&
+		cmsg.cmsghdr.Len >= unix.SizeofInet4Pktinfo {
+		end.src4().Src = cmsg.pktinfo.Spec_dst
+		end.src4().Ifindex = cmsg.pktinfo.Ifindex
+	}
+
+	return size, nil
+}
+
+func receive6(sock int, buff []byte, end *NativeEndpoint) (int, error) {
+
+	// construct message header
+
+	var cmsg struct {
+		cmsghdr unix.Cmsghdr
+		pktinfo unix.Inet6Pktinfo
+	}
+
+	size, _, _, newDst, err := unix.Recvmsg(sock, buff, (*[unsafe.Sizeof(cmsg)]byte)(unsafe.Pointer(&cmsg))[:], 0)
+
+	if err != nil {
+		return 0, err
+	}
+	end.isV6 = true
+
+	if newDst6, ok := newDst.(*unix.SockaddrInet6); ok {
+		*end.dst6() = *newDst6
+	}
+
+	// update source cache
+
+	if cmsg.cmsghdr.Level == unix.IPPROTO_IPV6 &&
+		cmsg.cmsghdr.Type == unix.IPV6_PKTINFO &&
+		cmsg.cmsghdr.Len >= unix.SizeofInet6Pktinfo {
+		end.src6().src = cmsg.pktinfo.Addr
+		end.dst6().ZoneId = cmsg.pktinfo.Ifindex
+	}
+
+	return size, nil
+}