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// Copyright 2018 Google LLC
//
// 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.
// Package arp implements the ARP network protocol. It is used to resolve
// IPv4 addresses into link-local MAC addresses, and advertises IPv4
// addresses of its stack with the local network.
//
// To use it in the networking stack, pass arp.ProtocolName as one of the
// network protocols when calling stack.New. Then add an "arp" address to
// every NIC on the stack that should respond to ARP requests. That is:
//
// if err := s.AddAddress(1, arp.ProtocolNumber, "arp"); err != nil {
// // handle err
// }
package arp
import (
"gvisor.googlesource.com/gvisor/pkg/tcpip"
"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
"gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
)
const (
// ProtocolName is the string representation of the ARP protocol name.
ProtocolName = "arp"
// ProtocolNumber is the ARP protocol number.
ProtocolNumber = header.ARPProtocolNumber
// ProtocolAddress is the address expected by the ARP endpoint.
ProtocolAddress = tcpip.Address("arp")
)
// endpoint implements stack.NetworkEndpoint.
type endpoint struct {
nicid tcpip.NICID
addr tcpip.Address
linkEP stack.LinkEndpoint
linkAddrCache stack.LinkAddressCache
}
// DefaultTTL is unused for ARP. It implements stack.NetworkEndpoint.
func (e *endpoint) DefaultTTL() uint8 {
return 0
}
func (e *endpoint) MTU() uint32 {
lmtu := e.linkEP.MTU()
return lmtu - uint32(e.MaxHeaderLength())
}
func (e *endpoint) NICID() tcpip.NICID {
return e.nicid
}
func (e *endpoint) Capabilities() stack.LinkEndpointCapabilities {
return e.linkEP.Capabilities()
}
func (e *endpoint) ID() *stack.NetworkEndpointID {
return &stack.NetworkEndpointID{ProtocolAddress}
}
func (e *endpoint) MaxHeaderLength() uint16 {
return e.linkEP.MaxHeaderLength() + header.ARPSize
}
func (e *endpoint) Close() {}
func (e *endpoint) WritePacket(*stack.Route, buffer.Prependable, buffer.VectorisedView, tcpip.TransportProtocolNumber, uint8, stack.PacketLooping) *tcpip.Error {
return tcpip.ErrNotSupported
}
func (e *endpoint) HandlePacket(r *stack.Route, vv buffer.VectorisedView) {
v := vv.First()
h := header.ARP(v)
if !h.IsValid() {
return
}
switch h.Op() {
case header.ARPRequest:
localAddr := tcpip.Address(h.ProtocolAddressTarget())
if e.linkAddrCache.CheckLocalAddress(e.nicid, header.IPv4ProtocolNumber, localAddr) == 0 {
return // we have no useful answer, ignore the request
}
hdr := buffer.NewPrependable(int(e.linkEP.MaxHeaderLength()) + header.ARPSize)
pkt := header.ARP(hdr.Prepend(header.ARPSize))
pkt.SetIPv4OverEthernet()
pkt.SetOp(header.ARPReply)
copy(pkt.HardwareAddressSender(), r.LocalLinkAddress[:])
copy(pkt.ProtocolAddressSender(), h.ProtocolAddressTarget())
copy(pkt.ProtocolAddressTarget(), h.ProtocolAddressSender())
e.linkEP.WritePacket(r, hdr, buffer.VectorisedView{}, ProtocolNumber)
fallthrough // also fill the cache from requests
case header.ARPReply:
addr := tcpip.Address(h.ProtocolAddressSender())
linkAddr := tcpip.LinkAddress(h.HardwareAddressSender())
e.linkAddrCache.AddLinkAddress(e.nicid, addr, linkAddr)
}
}
// protocol implements stack.NetworkProtocol and stack.LinkAddressResolver.
type protocol struct {
}
func (p *protocol) Number() tcpip.NetworkProtocolNumber { return ProtocolNumber }
func (p *protocol) MinimumPacketSize() int { return header.ARPSize }
func (*protocol) ParseAddresses(v buffer.View) (src, dst tcpip.Address) {
h := header.ARP(v)
return tcpip.Address(h.ProtocolAddressSender()), ProtocolAddress
}
func (p *protocol) NewEndpoint(nicid tcpip.NICID, addr tcpip.Address, linkAddrCache stack.LinkAddressCache, dispatcher stack.TransportDispatcher, sender stack.LinkEndpoint) (stack.NetworkEndpoint, *tcpip.Error) {
if addr != ProtocolAddress {
return nil, tcpip.ErrBadLocalAddress
}
return &endpoint{
nicid: nicid,
addr: addr,
linkEP: sender,
linkAddrCache: linkAddrCache,
}, nil
}
// LinkAddressProtocol implements stack.LinkAddressResolver.
func (*protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
return header.IPv4ProtocolNumber
}
// LinkAddressRequest implements stack.LinkAddressResolver.
func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.LinkEndpoint) *tcpip.Error {
r := &stack.Route{
RemoteLinkAddress: broadcastMAC,
}
hdr := buffer.NewPrependable(int(linkEP.MaxHeaderLength()) + header.ARPSize)
h := header.ARP(hdr.Prepend(header.ARPSize))
h.SetIPv4OverEthernet()
h.SetOp(header.ARPRequest)
copy(h.HardwareAddressSender(), linkEP.LinkAddress())
copy(h.ProtocolAddressSender(), localAddr)
copy(h.ProtocolAddressTarget(), addr)
return linkEP.WritePacket(r, hdr, buffer.VectorisedView{}, ProtocolNumber)
}
// ResolveStaticAddress implements stack.LinkAddressResolver.
func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
if addr == header.IPv4Broadcast {
return broadcastMAC, true
}
if header.IsV4MulticastAddress(addr) {
// RFC 1112 Host Extensions for IP Multicasting
//
// 6.4. Extensions to an Ethernet Local Network Module:
//
// An IP host group address is mapped to an Ethernet multicast
// address by placing the low-order 23-bits of the IP address
// into the low-order 23 bits of the Ethernet multicast address
// 01-00-5E-00-00-00 (hex).
return tcpip.LinkAddress([]byte{
0x01,
0x00,
0x5e,
addr[header.IPv4AddressSize-3] & 0x7f,
addr[header.IPv4AddressSize-2],
addr[header.IPv4AddressSize-1],
}), true
}
return "", false
}
// SetOption implements NetworkProtocol.
func (p *protocol) SetOption(option interface{}) *tcpip.Error {
return tcpip.ErrUnknownProtocolOption
}
// Option implements NetworkProtocol.
func (p *protocol) Option(option interface{}) *tcpip.Error {
return tcpip.ErrUnknownProtocolOption
}
var broadcastMAC = tcpip.LinkAddress([]byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff})
func init() {
stack.RegisterNetworkProtocolFactory(ProtocolName, func() stack.NetworkProtocol {
return &protocol{}
})
}
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