conn: make binds replacable

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 580 insertions, 0 deletions

diff --git a/conn/bind_linux.go b/conn/bind_linux.go
new file mode 100644
index 0000000..4199809
--- /dev/null
+++ b/conn/bind_linux.go
@@ -0,0 +1,580 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
+ */
+
+package conn
+
+import (
+	"errors"
+	"net"
+	"strconv"
+	"sync"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+type ipv4Source struct {
+	Src     [4]byte
+	Ifindex int32
+}
+
+type ipv6Source struct {
+	src [16]byte
+	// ifindex belongs in dst.ZoneId
+}
+
+type LinuxSocketEndpoint struct {
+	sync.Mutex
+	dst  [unsafe.Sizeof(unix.SockaddrInet6{})]byte
+	src  [unsafe.Sizeof(ipv6Source{})]byte
+	isV6 bool
+}
+
+func (endpoint *LinuxSocketEndpoint) Src4() *ipv4Source         { return endpoint.src4() }
+func (endpoint *LinuxSocketEndpoint) Dst4() *unix.SockaddrInet4 { return endpoint.dst4() }
+func (endpoint *LinuxSocketEndpoint) IsV6() bool                { return endpoint.isV6 }
+
+func (endpoint *LinuxSocketEndpoint) src4() *ipv4Source {
+	return (*ipv4Source)(unsafe.Pointer(&endpoint.src[0]))
+}
+
+func (endpoint *LinuxSocketEndpoint) src6() *ipv6Source {
+	return (*ipv6Source)(unsafe.Pointer(&endpoint.src[0]))
+}
+
+func (endpoint *LinuxSocketEndpoint) dst4() *unix.SockaddrInet4 {
+	return (*unix.SockaddrInet4)(unsafe.Pointer(&endpoint.dst[0]))
+}
+
+func (endpoint *LinuxSocketEndpoint) dst6() *unix.SockaddrInet6 {
+	return (*unix.SockaddrInet6)(unsafe.Pointer(&endpoint.dst[0]))
+}
+
+// LinuxSocketBind uses sendmsg and recvmsg to implement a full bind with sticky sockets on Linux.
+type LinuxSocketBind struct {
+	sock4    int
+	sock6    int
+	lastMark uint32
+	closing  sync.RWMutex
+}
+
+func NewLinuxSocketBind() Bind { return &LinuxSocketBind{sock4: -1, sock6: -1} }
+func NewDefaultBind() Bind     { return NewLinuxSocketBind() }
+
+var _ Endpoint = (*LinuxSocketEndpoint)(nil)
+var _ Bind = (*LinuxSocketBind)(nil)
+
+func (*LinuxSocketBind) ParseEndpoint(s string) (Endpoint, error) {
+	var end LinuxSocketEndpoint
+	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 (bind *LinuxSocketBind) Open(port uint16) (uint16, error) {
+	var err error
+	var newPort uint16
+	var tries int
+
+	if bind.sock4 != -1 || bind.sock6 != -1 {
+		return 0, ErrBindAlreadyOpen
+	}
+
+	originalPort := port
+
+again:
+	port = originalPort
+	// Attempt ipv6 bind, update port if successful.
+	bind.sock6, newPort, err = create6(port)
+	if err != nil {
+		if err != syscall.EAFNOSUPPORT {
+			return 0, err
+		}
+	} else {
+		port = newPort
+	}
+
+	// Attempt ipv4 bind, update port if successful.
+	bind.sock4, newPort, err = create4(port)
+	if err != nil {
+		if originalPort == 0 && err == syscall.EADDRINUSE && tries < 100 {
+			unix.Close(bind.sock6)
+			tries++
+			goto again
+		}
+		if err != syscall.EAFNOSUPPORT {
+			unix.Close(bind.sock6)
+			return 0, err
+		}
+	} else {
+		port = newPort
+	}
+
+	if bind.sock4 == -1 && bind.sock6 == -1 {
+		return 0, syscall.EAFNOSUPPORT
+	}
+	return port, nil
+}
+
+func (bind *LinuxSocketBind) SetMark(value uint32) error {
+	bind.closing.RLock()
+	defer bind.closing.RUnlock()
+
+	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 (bind *LinuxSocketBind) Close() error {
+	var err1, err2 error
+	bind.closing.RLock()
+	if bind.sock6 != -1 {
+		unix.Shutdown(bind.sock6, unix.SHUT_RDWR)
+	}
+	if bind.sock4 != -1 {
+		unix.Shutdown(bind.sock4, unix.SHUT_RDWR)
+	}
+	bind.closing.RUnlock()
+	bind.closing.Lock()
+	if bind.sock6 != -1 {
+		err1 = unix.Close(bind.sock6)
+		bind.sock6 = -1
+	}
+	if bind.sock4 != -1 {
+		err2 = unix.Close(bind.sock4)
+		bind.sock4 = -1
+	}
+	bind.closing.Unlock()
+
+	if err1 != nil {
+		return err1
+	}
+	return err2
+}
+
+func (bind *LinuxSocketBind) ReceiveIPv6(buff []byte) (int, Endpoint, error) {
+	bind.closing.RLock()
+	defer bind.closing.RUnlock()
+
+	var end LinuxSocketEndpoint
+	if bind.sock6 == -1 {
+		return 0, nil, net.ErrClosed
+	}
+	n, err := receive6(
+		bind.sock6,
+		buff,
+		&end,
+	)
+	return n, &end, err
+}
+
+func (bind *LinuxSocketBind) ReceiveIPv4(buff []byte) (int, Endpoint, error) {
+	bind.closing.RLock()
+	defer bind.closing.RUnlock()
+
+	var end LinuxSocketEndpoint
+	if bind.sock4 == -1 {
+		return 0, nil, net.ErrClosed
+	}
+	n, err := receive4(
+		bind.sock4,
+		buff,
+		&end,
+	)
+	return n, &end, err
+}
+
+func (bind *LinuxSocketBind) Send(buff []byte, end Endpoint) error {
+	bind.closing.RLock()
+	defer bind.closing.RUnlock()
+
+	nend, ok := end.(*LinuxSocketEndpoint)
+	if !ok {
+		return ErrWrongEndpointType
+	}
+	if !nend.isV6 {
+		if bind.sock4 == -1 {
+			return net.ErrClosed
+		}
+		return send4(bind.sock4, nend, buff)
+	} else {
+		if bind.sock6 == -1 {
+			return net.ErrClosed
+		}
+		return send6(bind.sock6, nend, buff)
+	}
+}
+
+func (end *LinuxSocketEndpoint) 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 *LinuxSocketEndpoint) 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 *LinuxSocketEndpoint) 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 *LinuxSocketEndpoint) SrcToString() string {
+	return end.SrcIP().String()
+}
+
+func (end *LinuxSocketEndpoint) 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 *LinuxSocketEndpoint) ClearDst() {
+	for i := range end.dst {
+		end.dst[i] = 0
+	}
+}
+
+func (end *LinuxSocketEndpoint) 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 -1, 0, err
+	}
+
+	addr := unix.SockaddrInet4{
+		Port: int(port),
+	}
+
+	// set sockopts and bind
+
+	if err := func() error {
+		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 -1, 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 -1, 0, err
+	}
+
+	// set sockopts and bind
+
+	addr := unix.SockaddrInet6{
+		Port: int(port),
+	}
+
+	if err := func() error {
+		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 -1, 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 *LinuxSocketEndpoint, 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 *LinuxSocketEndpoint, 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 *LinuxSocketEndpoint) (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 *LinuxSocketEndpoint) (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
+}