// Copyright 2016 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//go:build linux
// +build linux
package netutil
import (
"bytes"
"encoding/binary"
"fmt"
"net"
"sort"
"syscall"
"go.etcd.io/etcd/pkg/v3/cpuutil"
)
var errNoDefaultRoute = fmt.Errorf("could not find default route")
var errNoDefaultHost = fmt.Errorf("could not find default host")
var errNoDefaultInterface = fmt.Errorf("could not find default interface")
// GetDefaultHost obtains the first IP address of machine from the routing table and returns the IP address as string.
// An IPv4 address is preferred to an IPv6 address for backward compatibility.
func GetDefaultHost() (string, error) {
rmsgs, rerr := getDefaultRoutes()
if rerr != nil {
return "", rerr
}
// prioritize IPv4
if rmsg, ok := rmsgs[syscall.AF_INET]; ok {
if host, err := chooseHost(syscall.AF_INET, rmsg); host != "" || err != nil {
return host, err
}
delete(rmsgs, syscall.AF_INET)
}
// sort so choice is deterministic
var families []int
for family := range rmsgs {
families = append(families, int(family))
}
sort.Ints(families)
for _, f := range families {
family := uint8(f)
if host, err := chooseHost(family, rmsgs[family]); host != "" || err != nil {
return host, err
}
}
return "", errNoDefaultHost
}
func chooseHost(family uint8, rmsg *syscall.NetlinkMessage) (string, error) {
host, oif, err := parsePREFSRC(rmsg)
if host != "" || err != nil {
return host, err
}
// prefsrc not detected, fall back to getting address from iface
ifmsg, ierr := getIfaceAddr(oif, family)
if ierr != nil {
return "", ierr
}
attrs, aerr := syscall.ParseNetlinkRouteAttr(ifmsg)
if aerr != nil {
return "", aerr
}
for _, attr := range attrs {
// search for RTA_DST because ipv6 doesn't have RTA_SRC
if attr.Attr.Type == syscall.RTA_DST {
return net.IP(attr.Value).String(), nil
}
}
return "", nil
}
func getDefaultRoutes() (map[uint8]*syscall.NetlinkMessage, error) {
dat, err := syscall.NetlinkRIB(syscall.RTM_GETROUTE, syscall.AF_UNSPEC)
if err != nil {
return nil, err
}
msgs, msgErr := syscall.ParseNetlinkMessage(dat)
if msgErr != nil {
return nil, msgErr
}
routes := make(map[uint8]*syscall.NetlinkMessage)
rtmsg := syscall.RtMsg{}
for _, m := range msgs {
if m.Header.Type != syscall.RTM_NEWROUTE {
continue
}
buf := bytes.NewBuffer(m.Data[:syscall.SizeofRtMsg])
if rerr := binary.Read(buf, cpuutil.ByteOrder(), &rtmsg); rerr != nil {
continue
}
if rtmsg.Dst_len == 0 && rtmsg.Table == syscall.RT_TABLE_MAIN {
// zero-length Dst_len implies default route
msg := m
routes[rtmsg.Family] = &msg
}
}
if len(routes) > 0 {
return routes, nil
}
return nil, errNoDefaultRoute
}
// Used to get an address of interface.
func getIfaceAddr(idx uint32, family uint8) (*syscall.NetlinkMessage, error) {
dat, err := syscall.NetlinkRIB(syscall.RTM_GETADDR, int(family))
if err != nil {
return nil, err
}
msgs, msgErr := syscall.ParseNetlinkMessage(dat)
if msgErr != nil {
return nil, msgErr
}
ifaddrmsg := syscall.IfAddrmsg{}
for _, m := range msgs {
if m.Header.Type != syscall.RTM_NEWADDR {
continue
}
buf := bytes.NewBuffer(m.Data[:syscall.SizeofIfAddrmsg])
if rerr := binary.Read(buf, cpuutil.ByteOrder(), &ifaddrmsg); rerr != nil {
continue
}
if ifaddrmsg.Index == idx {
return &m, nil
}
}
return nil, fmt.Errorf("could not find address for interface index %v", idx)
}
// Used to get a name of interface.
func getIfaceLink(idx uint32) (*syscall.NetlinkMessage, error) {
dat, err := syscall.NetlinkRIB(syscall.RTM_GETLINK, syscall.AF_UNSPEC)
if err != nil {
return nil, err
}
msgs, msgErr := syscall.ParseNetlinkMessage(dat)
if msgErr != nil {
return nil, msgErr
}
ifinfomsg := syscall.IfInfomsg{}
for _, m := range msgs {
if m.Header.Type != syscall.RTM_NEWLINK {
continue
}
buf := bytes.NewBuffer(m.Data[:syscall.SizeofIfInfomsg])
if rerr := binary.Read(buf, cpuutil.ByteOrder(), &ifinfomsg); rerr != nil {
continue
}
if ifinfomsg.Index == int32(idx) {
return &m, nil
}
}
return nil, fmt.Errorf("could not find link for interface index %v", idx)
}
// GetDefaultInterfaces gets names of interfaces and returns a map[interface]families.
func GetDefaultInterfaces() (map[string]uint8, error) {
interfaces := make(map[string]uint8)
rmsgs, rerr := getDefaultRoutes()
if rerr != nil {
return interfaces, rerr
}
for family, rmsg := range rmsgs {
_, oif, err := parsePREFSRC(rmsg)
if err != nil {
return interfaces, err
}
ifmsg, ierr := getIfaceLink(oif)
if ierr != nil {
return interfaces, ierr
}
attrs, aerr := syscall.ParseNetlinkRouteAttr(ifmsg)
if aerr != nil {
return interfaces, aerr
}
for _, attr := range attrs {
if attr.Attr.Type == syscall.IFLA_IFNAME {
// key is an interface name
// possible values: 2 - AF_INET, 10 - AF_INET6, 12 - dualstack
interfaces[string(attr.Value[:len(attr.Value)-1])] += family
}
}
}
if len(interfaces) > 0 {
return interfaces, nil
}
return interfaces, errNoDefaultInterface
}
// parsePREFSRC returns preferred source address and output interface index (RTA_OIF).
func parsePREFSRC(m *syscall.NetlinkMessage) (host string, oif uint32, err error) {
var attrs []syscall.NetlinkRouteAttr
attrs, err = syscall.ParseNetlinkRouteAttr(m)
if err != nil {
return "", 0, err
}
for _, attr := range attrs {
if attr.Attr.Type == syscall.RTA_PREFSRC {
host = net.IP(attr.Value).String()
}
if attr.Attr.Type == syscall.RTA_OIF {
oif = cpuutil.ByteOrder().Uint32(attr.Value)
}
if host != "" && oif != uint32(0) {
break
}
}
if oif == 0 {
err = errNoDefaultRoute
}
return host, oif, err
}
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