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nl_linux.go
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nl_linux.go
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// Package nl has low level primitives for making Netlink calls.
package nl
import (
"bytes"
"encoding/binary"
"fmt"
"net"
"sync/atomic"
"syscall"
"unsafe"
)
const (
// Family type definitions
FAMILY_ALL = syscall.AF_UNSPEC
FAMILY_V4 = syscall.AF_INET
FAMILY_V6 = syscall.AF_INET6
)
var nextSeqNr uint32
// GetIPFamily returns the family type of a net.IP.
func GetIPFamily(ip net.IP) int {
if len(ip) <= net.IPv4len {
return FAMILY_V4
}
if ip.To4() != nil {
return FAMILY_V4
}
return FAMILY_V6
}
var nativeEndian binary.ByteOrder
// Get native endianness for the system
func NativeEndian() binary.ByteOrder {
if nativeEndian == nil {
var x uint32 = 0x01020304
if *(*byte)(unsafe.Pointer(&x)) == 0x01 {
nativeEndian = binary.BigEndian
} else {
nativeEndian = binary.LittleEndian
}
}
return nativeEndian
}
// Byte swap a 16 bit value if we aren't big endian
func Swap16(i uint16) uint16 {
if NativeEndian() == binary.BigEndian {
return i
}
return (i&0xff00)>>8 | (i&0xff)<<8
}
// Byte swap a 32 bit value if aren't big endian
func Swap32(i uint32) uint32 {
if NativeEndian() == binary.BigEndian {
return i
}
return (i&0xff000000)>>24 | (i&0xff0000)>>8 | (i&0xff00)<<8 | (i&0xff)<<24
}
type NetlinkRequestData interface {
Len() int
Serialize() []byte
}
// IfInfomsg is related to links, but it is used for list requests as well
type IfInfomsg struct {
syscall.IfInfomsg
}
// Create an IfInfomsg with family specified
func NewIfInfomsg(family int) *IfInfomsg {
return &IfInfomsg{
IfInfomsg: syscall.IfInfomsg{
Family: uint8(family),
},
}
}
func DeserializeIfInfomsg(b []byte) *IfInfomsg {
return (*IfInfomsg)(unsafe.Pointer(&b[0:syscall.SizeofIfInfomsg][0]))
}
func (msg *IfInfomsg) Serialize() []byte {
return (*(*[syscall.SizeofIfInfomsg]byte)(unsafe.Pointer(msg)))[:]
}
func (msg *IfInfomsg) Len() int {
return syscall.SizeofIfInfomsg
}
func rtaAlignOf(attrlen int) int {
return (attrlen + syscall.RTA_ALIGNTO - 1) & ^(syscall.RTA_ALIGNTO - 1)
}
func NewIfInfomsgChild(parent *RtAttr, family int) *IfInfomsg {
msg := NewIfInfomsg(family)
parent.children = append(parent.children, msg)
return msg
}
// Extend RtAttr to handle data and children
type RtAttr struct {
syscall.RtAttr
Data []byte
children []NetlinkRequestData
}
// Create a new Extended RtAttr object
func NewRtAttr(attrType int, data []byte) *RtAttr {
return &RtAttr{
RtAttr: syscall.RtAttr{
Type: uint16(attrType),
},
children: []NetlinkRequestData{},
Data: data,
}
}
// Create a new RtAttr obj anc add it as a child of an existing object
func NewRtAttrChild(parent *RtAttr, attrType int, data []byte) *RtAttr {
attr := NewRtAttr(attrType, data)
parent.children = append(parent.children, attr)
return attr
}
func (a *RtAttr) Len() int {
if len(a.children) == 0 {
return (syscall.SizeofRtAttr + len(a.Data))
}
l := 0
for _, child := range a.children {
l += rtaAlignOf(child.Len())
}
l += syscall.SizeofRtAttr
return rtaAlignOf(l + len(a.Data))
}
// Serialize the RtAttr into a byte array
// This can't just unsafe.cast because it must iterate through children.
func (a *RtAttr) Serialize() []byte {
native := NativeEndian()
length := a.Len()
buf := make([]byte, rtaAlignOf(length))
if a.Data != nil {
copy(buf[4:], a.Data)
} else {
next := 4
for _, child := range a.children {
childBuf := child.Serialize()
copy(buf[next:], childBuf)
next += rtaAlignOf(len(childBuf))
}
}
if l := uint16(length); l != 0 {
native.PutUint16(buf[0:2], l)
}
native.PutUint16(buf[2:4], a.Type)
return buf
}
type NetlinkRequest struct {
syscall.NlMsghdr
Data []NetlinkRequestData
}
// Serialize the Netlink Request into a byte array
func (req *NetlinkRequest) Serialize() []byte {
length := syscall.SizeofNlMsghdr
dataBytes := make([][]byte, len(req.Data))
for i, data := range req.Data {
dataBytes[i] = data.Serialize()
length = length + len(dataBytes[i])
}
req.Len = uint32(length)
b := make([]byte, length)
hdr := (*(*[syscall.SizeofNlMsghdr]byte)(unsafe.Pointer(req)))[:]
next := syscall.SizeofNlMsghdr
copy(b[0:next], hdr)
for _, data := range dataBytes {
for _, dataByte := range data {
b[next] = dataByte
next = next + 1
}
}
return b
}
func (req *NetlinkRequest) AddData(data NetlinkRequestData) {
if data != nil {
req.Data = append(req.Data, data)
}
}
// Execute the request against a the given sockType.
// Returns a list of netlink messages in seriaized format, optionally filtered
// by resType.
func (req *NetlinkRequest) Execute(sockType int, resType uint16) ([][]byte, error) {
s, err := getNetlinkSocket(sockType)
if err != nil {
return nil, err
}
defer s.Close()
if err := s.Send(req); err != nil {
return nil, err
}
pid, err := s.GetPid()
if err != nil {
return nil, err
}
var res [][]byte
done:
for {
msgs, err := s.Receive()
if err != nil {
return nil, err
}
for _, m := range msgs {
if m.Header.Seq != req.Seq {
return nil, fmt.Errorf("Wrong Seq nr %d, expected 1", m.Header.Seq)
}
if m.Header.Pid != pid {
return nil, fmt.Errorf("Wrong pid %d, expected %d", m.Header.Pid, pid)
}
if m.Header.Type == syscall.NLMSG_DONE {
break done
}
if m.Header.Type == syscall.NLMSG_ERROR {
native := NativeEndian()
error := int32(native.Uint32(m.Data[0:4]))
if error == 0 {
break done
}
return nil, syscall.Errno(-error)
}
if resType != 0 && m.Header.Type != resType {
continue
}
res = append(res, m.Data)
if m.Header.Flags&syscall.NLM_F_MULTI == 0 {
break done
}
}
}
return res, nil
}
// Create a new netlink request from proto and flags
// Note the Len value will be inaccurate once data is added until
// the message is serialized
func NewNetlinkRequest(proto, flags int) *NetlinkRequest {
return &NetlinkRequest{
NlMsghdr: syscall.NlMsghdr{
Len: uint32(syscall.SizeofNlMsghdr),
Type: uint16(proto),
Flags: syscall.NLM_F_REQUEST | uint16(flags),
Seq: atomic.AddUint32(&nextSeqNr, 1),
},
}
}
type NetlinkSocket struct {
fd int
lsa syscall.SockaddrNetlink
}
func getNetlinkSocket(protocol int) (*NetlinkSocket, error) {
fd, err := syscall.Socket(syscall.AF_NETLINK, syscall.SOCK_RAW, protocol)
if err != nil {
return nil, err
}
s := &NetlinkSocket{
fd: fd,
}
s.lsa.Family = syscall.AF_NETLINK
if err := syscall.Bind(fd, &s.lsa); err != nil {
syscall.Close(fd)
return nil, err
}
return s, nil
}
// Create a netlink socket with a given protocol (e.g. NETLINK_ROUTE)
// and subscribe it to multicast groups passed in variable argument list.
// Returns the netlink socket on which Receive() method can be called
// to retrieve the messages from the kernel.
func Subscribe(protocol int, groups ...uint) (*NetlinkSocket, error) {
fd, err := syscall.Socket(syscall.AF_NETLINK, syscall.SOCK_RAW, protocol)
if err != nil {
return nil, err
}
s := &NetlinkSocket{
fd: fd,
}
s.lsa.Family = syscall.AF_NETLINK
for _, g := range groups {
s.lsa.Groups |= (1 << (g - 1))
}
if err := syscall.Bind(fd, &s.lsa); err != nil {
syscall.Close(fd)
return nil, err
}
return s, nil
}
func (s *NetlinkSocket) Close() {
syscall.Close(s.fd)
}
func (s *NetlinkSocket) Send(request *NetlinkRequest) error {
if err := syscall.Sendto(s.fd, request.Serialize(), 0, &s.lsa); err != nil {
return err
}
return nil
}
func (s *NetlinkSocket) Receive() ([]syscall.NetlinkMessage, error) {
rb := make([]byte, syscall.Getpagesize())
nr, _, err := syscall.Recvfrom(s.fd, rb, 0)
if err != nil {
return nil, err
}
if nr < syscall.NLMSG_HDRLEN {
return nil, fmt.Errorf("Got short response from netlink")
}
rb = rb[:nr]
return syscall.ParseNetlinkMessage(rb)
}
func (s *NetlinkSocket) GetPid() (uint32, error) {
lsa, err := syscall.Getsockname(s.fd)
if err != nil {
return 0, err
}
switch v := lsa.(type) {
case *syscall.SockaddrNetlink:
return v.Pid, nil
}
return 0, fmt.Errorf("Wrong socket type")
}
func ZeroTerminated(s string) []byte {
bytes := make([]byte, len(s)+1)
for i := 0; i < len(s); i++ {
bytes[i] = s[i]
}
bytes[len(s)] = 0
return bytes
}
func NonZeroTerminated(s string) []byte {
bytes := make([]byte, len(s))
for i := 0; i < len(s); i++ {
bytes[i] = s[i]
}
return bytes
}
func BytesToString(b []byte) string {
n := bytes.Index(b, []byte{0})
return string(b[:n])
}
func Uint8Attr(v uint8) []byte {
return []byte{byte(v)}
}
func Uint16Attr(v uint16) []byte {
native := NativeEndian()
bytes := make([]byte, 2)
native.PutUint16(bytes, v)
return bytes
}
func Uint32Attr(v uint32) []byte {
native := NativeEndian()
bytes := make([]byte, 4)
native.PutUint32(bytes, v)
return bytes
}
func ParseRouteAttr(b []byte) ([]syscall.NetlinkRouteAttr, error) {
var attrs []syscall.NetlinkRouteAttr
for len(b) >= syscall.SizeofRtAttr {
a, vbuf, alen, err := netlinkRouteAttrAndValue(b)
if err != nil {
return nil, err
}
ra := syscall.NetlinkRouteAttr{Attr: *a, Value: vbuf[:int(a.Len)-syscall.SizeofRtAttr]}
attrs = append(attrs, ra)
b = b[alen:]
}
return attrs, nil
}
func netlinkRouteAttrAndValue(b []byte) (*syscall.RtAttr, []byte, int, error) {
a := (*syscall.RtAttr)(unsafe.Pointer(&b[0]))
if int(a.Len) < syscall.SizeofRtAttr || int(a.Len) > len(b) {
return nil, nil, 0, syscall.EINVAL
}
return a, b[syscall.SizeofRtAttr:], rtaAlignOf(int(a.Len)), nil
}