1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
|
// Copyright 2012 Google, Inc. All rights reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file in the root of the source
// tree.
// +build linux
// Package routing provides a very basic but mostly functional implementation of
// a routing table for IPv4/IPv6 addresses. It uses a routing table pulled from
// the kernel via netlink to find the correct interface, gateway, and preferred
// source IP address for packets destined to a particular location.
//
// The routing package is meant to be used with applications that are sending
// raw packet data, which don't have the benefit of having the kernel route
// packets for them.
package routing
import (
"bytes"
"errors"
"fmt"
"net"
"sort"
"strings"
"syscall"
"unsafe"
)
// Pulled from http://man7.org/linux/man-pages/man7/rtnetlink.7.html
// See the section on RTM_NEWROUTE, specifically 'struct rtmsg'.
type routeInfoInMemory struct {
Family byte
DstLen byte
SrcLen byte
TOS byte
Table byte
Protocol byte
Scope byte
Type byte
Flags uint32
}
// rtInfo contains information on a single route.
type rtInfo struct {
Src, Dst *net.IPNet
Gateway, PrefSrc net.IP
// We currently ignore the InputIface.
InputIface, OutputIface uint32
Priority uint32
}
// routeSlice implements sort.Interface to sort routes by Priority.
type routeSlice []*rtInfo
func (r routeSlice) Len() int {
return len(r)
}
func (r routeSlice) Less(i, j int) bool {
return r[i].Priority < r[j].Priority
}
func (r routeSlice) Swap(i, j int) {
r[i], r[j] = r[j], r[i]
}
type router struct {
ifaces []net.Interface
addrs []ipAddrs
v4, v6 routeSlice
}
func (r *router) String() string {
strs := []string{"ROUTER", "--- V4 ---"}
for _, route := range r.v4 {
strs = append(strs, fmt.Sprintf("%+v", *route))
}
strs = append(strs, "--- V6 ---")
for _, route := range r.v6 {
strs = append(strs, fmt.Sprintf("%+v", *route))
}
return strings.Join(strs, "\n")
}
type ipAddrs struct {
v4, v6 net.IP
}
func (r *router) Route(dst net.IP) (iface *net.Interface, gateway, preferredSrc net.IP, err error) {
return r.RouteWithSrc(nil, nil, dst)
}
func (r *router) RouteWithSrc(input net.HardwareAddr, src, dst net.IP) (iface *net.Interface, gateway, preferredSrc net.IP, err error) {
var ifaceIndex int
switch {
case dst.To4() != nil:
ifaceIndex, gateway, preferredSrc, err = r.route(r.v4, input, src, dst)
case dst.To16() != nil:
ifaceIndex, gateway, preferredSrc, err = r.route(r.v6, input, src, dst)
default:
err = errors.New("IP is not valid as IPv4 or IPv6")
return
}
// Interfaces are 1-indexed, but we store them in a 0-indexed array.
ifaceIndex--
iface = &r.ifaces[ifaceIndex]
if preferredSrc == nil {
switch {
case dst.To4() != nil:
preferredSrc = r.addrs[ifaceIndex].v4
case dst.To16() != nil:
preferredSrc = r.addrs[ifaceIndex].v6
}
}
return
}
func (r *router) route(routes routeSlice, input net.HardwareAddr, src, dst net.IP) (iface int, gateway, preferredSrc net.IP, err error) {
var inputIndex uint32
if input != nil {
for i, iface := range r.ifaces {
if bytes.Equal(input, iface.HardwareAddr) {
// Convert from zero- to one-indexed.
inputIndex = uint32(i + 1)
break
}
}
}
for _, rt := range routes {
if rt.InputIface != 0 && rt.InputIface != inputIndex {
continue
}
if rt.Src != nil && !rt.Src.Contains(src) {
continue
}
if rt.Dst != nil && !rt.Dst.Contains(dst) {
continue
}
return int(rt.OutputIface), rt.Gateway, rt.PrefSrc, nil
}
err = fmt.Errorf("no route found for %v", dst)
return
}
// New creates a new router object. The router returned by New currently does
// not update its routes after construction... care should be taken for
// long-running programs to call New() regularly to take into account any
// changes to the routing table which have occurred since the last New() call.
func New() (Router, error) {
rtr := &router{}
tab, err := syscall.NetlinkRIB(syscall.RTM_GETROUTE, syscall.AF_UNSPEC)
if err != nil {
return nil, err
}
msgs, err := syscall.ParseNetlinkMessage(tab)
if err != nil {
return nil, err
}
loop:
for _, m := range msgs {
switch m.Header.Type {
case syscall.NLMSG_DONE:
break loop
case syscall.RTM_NEWROUTE:
rt := (*routeInfoInMemory)(unsafe.Pointer(&m.Data[0]))
routeInfo := rtInfo{}
attrs, err := syscall.ParseNetlinkRouteAttr(&m)
if err != nil {
return nil, err
}
switch rt.Family {
case syscall.AF_INET:
rtr.v4 = append(rtr.v4, &routeInfo)
case syscall.AF_INET6:
rtr.v6 = append(rtr.v6, &routeInfo)
default:
continue loop
}
for _, attr := range attrs {
switch attr.Attr.Type {
case syscall.RTA_DST:
routeInfo.Dst = &net.IPNet{
IP: net.IP(attr.Value),
Mask: net.CIDRMask(int(rt.DstLen), len(attr.Value)*8),
}
case syscall.RTA_SRC:
routeInfo.Src = &net.IPNet{
IP: net.IP(attr.Value),
Mask: net.CIDRMask(int(rt.SrcLen), len(attr.Value)*8),
}
case syscall.RTA_GATEWAY:
routeInfo.Gateway = net.IP(attr.Value)
case syscall.RTA_PREFSRC:
routeInfo.PrefSrc = net.IP(attr.Value)
case syscall.RTA_IIF:
routeInfo.InputIface = *(*uint32)(unsafe.Pointer(&attr.Value[0]))
case syscall.RTA_OIF:
routeInfo.OutputIface = *(*uint32)(unsafe.Pointer(&attr.Value[0]))
case syscall.RTA_PRIORITY:
routeInfo.Priority = *(*uint32)(unsafe.Pointer(&attr.Value[0]))
}
}
}
}
sort.Sort(rtr.v4)
sort.Sort(rtr.v6)
ifaces, err := net.Interfaces()
if err != nil {
return nil, err
}
for i, iface := range ifaces {
if i != iface.Index-1 {
return nil, fmt.Errorf("out of order iface %d = %v", i, iface)
}
rtr.ifaces = append(rtr.ifaces, iface)
var addrs ipAddrs
ifaceAddrs, err := iface.Addrs()
if err != nil {
return nil, err
}
for _, addr := range ifaceAddrs {
if inet, ok := addr.(*net.IPNet); ok {
// Go has a nasty habit of giving you IPv4s as ::ffff:1.2.3.4 instead of 1.2.3.4.
// We want to use mapped v4 addresses as v4 preferred addresses, never as v6
// preferred addresses.
if v4 := inet.IP.To4(); v4 != nil {
if addrs.v4 == nil {
addrs.v4 = v4
}
} else if addrs.v6 == nil {
addrs.v6 = inet.IP
}
}
}
rtr.addrs = append(rtr.addrs, addrs)
}
return rtr, nil
}
|
