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// Copyright 2018 The gVisor 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.
// 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.NewProtocol() 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.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/buffer"
"gvisor.dev/gvisor/pkg/tcpip/header"
"gvisor.dev/gvisor/pkg/tcpip/stack"
)
const (
// 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
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) PrefixLen() int {
return 0
}
func (e *endpoint) MaxHeaderLength() uint16 {
return e.linkEP.MaxHeaderLength() + header.ARPSize
}
func (e *endpoint) Close() {}
func (e *endpoint) WritePacket(*stack.Route, *stack.GSO, stack.NetworkHeaderParams, stack.PacketBuffer) *tcpip.Error {
return tcpip.ErrNotSupported
}
// WritePackets implements stack.NetworkEndpoint.WritePackets.
func (e *endpoint) WritePackets(*stack.Route, *stack.GSO, []stack.PacketBuffer, stack.NetworkHeaderParams) (int, *tcpip.Error) {
return 0, tcpip.ErrNotSupported
}
func (e *endpoint) WriteHeaderIncludedPacket(r *stack.Route, pkt stack.PacketBuffer) *tcpip.Error {
return tcpip.ErrNotSupported
}
func (e *endpoint) HandlePacket(r *stack.Route, pkt stack.PacketBuffer) {
v := pkt.Data.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)
packet := header.ARP(hdr.Prepend(header.ARPSize))
packet.SetIPv4OverEthernet()
packet.SetOp(header.ARPReply)
copy(packet.HardwareAddressSender(), r.LocalLinkAddress[:])
copy(packet.ProtocolAddressSender(), h.ProtocolAddressTarget())
copy(packet.HardwareAddressTarget(), h.HardwareAddressSender())
copy(packet.ProtocolAddressTarget(), h.ProtocolAddressSender())
e.linkEP.WritePacket(r, nil /* gso */, ProtocolNumber, stack.PacketBuffer{
Header: hdr,
})
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 (p *protocol) DefaultPrefixLen() int { return 0 }
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, addrWithPrefix tcpip.AddressWithPrefix, linkAddrCache stack.LinkAddressCache, dispatcher stack.TransportDispatcher, sender stack.LinkEndpoint, st *stack.Stack) (stack.NetworkEndpoint, *tcpip.Error) {
if addrWithPrefix.Address != ProtocolAddress {
return nil, tcpip.ErrBadLocalAddress
}
return &endpoint{
nicID: nicID,
linkEP: sender,
linkAddrCache: linkAddrCache,
}, nil
}
// LinkAddressProtocol implements stack.LinkAddressResolver.LinkAddressProtocol.
func (*protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
return header.IPv4ProtocolNumber
}
// LinkAddressRequest implements stack.LinkAddressResolver.LinkAddressRequest.
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, nil /* gso */, ProtocolNumber, stack.PacketBuffer{
Header: hdr,
})
}
// ResolveStaticAddress implements stack.LinkAddressResolver.ResolveStaticAddress.
func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
if addr == header.IPv4Broadcast {
return broadcastMAC, true
}
if header.IsV4MulticastAddress(addr) {
return header.EthernetAddressFromMulticastIPv4Address(addr), true
}
return tcpip.LinkAddress([]byte(nil)), false
}
// SetOption implements stack.NetworkProtocol.SetOption.
func (*protocol) SetOption(option interface{}) *tcpip.Error {
return tcpip.ErrUnknownProtocolOption
}
// Option implements stack.NetworkProtocol.Option.
func (*protocol) Option(option interface{}) *tcpip.Error {
return tcpip.ErrUnknownProtocolOption
}
// Close implements stack.TransportProtocol.Close.
func (*protocol) Close() {}
// Wait implements stack.TransportProtocol.Wait.
func (*protocol) Wait() {}
var broadcastMAC = tcpip.LinkAddress([]byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff})
// NewProtocol returns an ARP network protocol.
func NewProtocol() stack.NetworkProtocol {
return &protocol{}
}
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