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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 ipv4
import (
"fmt"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/buffer"
"gvisor.dev/gvisor/pkg/tcpip/header"
"gvisor.dev/gvisor/pkg/tcpip/stack"
)
// handleControl handles the case when an ICMP packet contains the headers of
// the original packet that caused the ICMP one to be sent. This information is
// used to find out which transport endpoint must be notified about the ICMP
// packet.
func (e *endpoint) handleControl(typ stack.ControlType, extra uint32, pkt *stack.PacketBuffer) {
h, ok := pkt.Data.PullUp(header.IPv4MinimumSize)
if !ok {
return
}
hdr := header.IPv4(h)
// We don't use IsValid() here because ICMP only requires that the IP
// header plus 8 bytes of the transport header be included. So it's
// likely that it is truncated, which would cause IsValid to return
// false.
//
// Drop packet if it doesn't have the basic IPv4 header or if the
// original source address doesn't match an address we own.
src := hdr.SourceAddress()
if e.protocol.stack.CheckLocalAddress(e.nic.ID(), ProtocolNumber, src) == 0 {
return
}
hlen := int(hdr.HeaderLength())
if pkt.Data.Size() < hlen || hdr.FragmentOffset() != 0 {
// We won't be able to handle this if it doesn't contain the
// full IPv4 header, or if it's a fragment not at offset 0
// (because it won't have the transport header).
return
}
// Skip the ip header, then deliver control message.
pkt.Data.TrimFront(hlen)
p := hdr.TransportProtocol()
e.dispatcher.DeliverTransportControlPacket(src, hdr.DestinationAddress(), ProtocolNumber, p, typ, extra, pkt)
}
func (e *endpoint) handleICMP(r *stack.Route, pkt *stack.PacketBuffer) {
stats := r.Stats()
received := stats.ICMP.V4PacketsReceived
// TODO(gvisor.dev/issue/170): ICMP packets don't have their
// TransportHeader fields set. See icmp/protocol.go:protocol.Parse for a
// full explanation.
v, ok := pkt.Data.PullUp(header.ICMPv4MinimumSize)
if !ok {
received.Invalid.Increment()
return
}
h := header.ICMPv4(v)
// TODO(b/112892170): Meaningfully handle all ICMP types.
switch h.Type() {
case header.ICMPv4Echo:
received.Echo.Increment()
// Only send a reply if the checksum is valid.
headerChecksum := h.Checksum()
h.SetChecksum(0)
calculatedChecksum := ^header.ChecksumVV(pkt.Data, 0 /* initial */)
h.SetChecksum(headerChecksum)
if calculatedChecksum != headerChecksum {
// It's possible that a raw socket still expects to receive this.
e.dispatcher.DeliverTransportPacket(r, header.ICMPv4ProtocolNumber, pkt)
received.Invalid.Increment()
return
}
// DeliverTransportPacket will take ownership of pkt so don't use it beyond
// this point. Make a deep copy of the data before pkt gets sent as we will
// be modifying fields.
//
// TODO(gvisor.dev/issue/4399): The copy may not be needed if there are no
// waiting endpoints. Consider moving responsibility for doing the copy to
// DeliverTransportPacket so that is is only done when needed.
replyData := pkt.Data.ToOwnedView()
replyIPHdr := header.IPv4(append(buffer.View(nil), pkt.NetworkHeader().View()...))
e.dispatcher.DeliverTransportPacket(r, header.ICMPv4ProtocolNumber, pkt)
// As per RFC 1122 section 3.2.1.3, when a host sends any datagram, the IP
// source address MUST be one of its own IP addresses (but not a broadcast
// or multicast address).
localAddr := r.LocalAddress
if r.IsInboundBroadcast() || header.IsV4MulticastAddress(localAddr) {
localAddr = ""
}
r, err := r.Stack().FindRoute(e.nic.ID(), localAddr, r.RemoteAddress, ProtocolNumber, false /* multicastLoop */)
if err != nil {
// If we cannot find a route to the destination, silently drop the packet.
return
}
defer r.Release()
// TODO(gvisor.dev/issue/3810:) When adding protocol numbers into the
// header information, we may have to change this code to handle the
// ICMP header no longer being in the data buffer.
// Because IP and ICMP are so closely intertwined, we need to handcraft our
// IP header to be able to follow RFC 792. The wording on page 13 is as
// follows:
// IP Fields:
// Addresses
// The address of the source in an echo message will be the
// destination of the echo reply message. To form an echo reply
// message, the source and destination addresses are simply reversed,
// the type code changed to 0, and the checksum recomputed.
//
// This was interpreted by early implementors to mean that all options must
// be copied from the echo request IP header to the echo reply IP header
// and this behaviour is still relied upon by some applications.
//
// Create a copy of the IP header we received, options and all, and change
// The fields we need to alter.
//
// We need to produce the entire packet in the data segment in order to
// use WriteHeaderIncludedPacket().
replyIPHdr.SetSourceAddress(r.LocalAddress)
replyIPHdr.SetDestinationAddress(r.RemoteAddress)
replyIPHdr.SetTTL(r.DefaultTTL())
replyICMPHdr := header.ICMPv4(replyData)
replyICMPHdr.SetType(header.ICMPv4EchoReply)
replyICMPHdr.SetChecksum(0)
replyICMPHdr.SetChecksum(^header.Checksum(replyData, 0))
replyVV := buffer.View(replyIPHdr).ToVectorisedView()
replyVV.AppendView(replyData)
replyPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
ReserveHeaderBytes: int(r.MaxHeaderLength()),
Data: replyVV,
})
replyPkt.TransportProtocolNumber = header.ICMPv4ProtocolNumber
// The checksum will be calculated so we don't need to do it here.
sent := stats.ICMP.V4PacketsSent
if err := r.WriteHeaderIncludedPacket(replyPkt); err != nil {
sent.Dropped.Increment()
return
}
sent.EchoReply.Increment()
case header.ICMPv4EchoReply:
received.EchoReply.Increment()
e.dispatcher.DeliverTransportPacket(r, header.ICMPv4ProtocolNumber, pkt)
case header.ICMPv4DstUnreachable:
received.DstUnreachable.Increment()
pkt.Data.TrimFront(header.ICMPv4MinimumSize)
switch h.Code() {
case header.ICMPv4HostUnreachable:
e.handleControl(stack.ControlNoRoute, 0, pkt)
case header.ICMPv4PortUnreachable:
e.handleControl(stack.ControlPortUnreachable, 0, pkt)
case header.ICMPv4FragmentationNeeded:
networkMTU, err := calculateNetworkMTU(uint32(h.MTU()), header.IPv4MinimumSize)
if err != nil {
networkMTU = 0
}
e.handleControl(stack.ControlPacketTooBig, networkMTU, pkt)
}
case header.ICMPv4SrcQuench:
received.SrcQuench.Increment()
case header.ICMPv4Redirect:
received.Redirect.Increment()
case header.ICMPv4TimeExceeded:
received.TimeExceeded.Increment()
case header.ICMPv4ParamProblem:
received.ParamProblem.Increment()
case header.ICMPv4Timestamp:
received.Timestamp.Increment()
case header.ICMPv4TimestampReply:
received.TimestampReply.Increment()
case header.ICMPv4InfoRequest:
received.InfoRequest.Increment()
case header.ICMPv4InfoReply:
received.InfoReply.Increment()
default:
received.Invalid.Increment()
}
}
// ======= ICMP Error packet generation =========
// icmpReason is a marker interface for IPv4 specific ICMP errors.
type icmpReason interface {
isICMPReason()
}
// icmpReasonPortUnreachable is an error where the transport protocol has no
// listener and no alternative means to inform the sender.
type icmpReasonPortUnreachable struct{}
func (*icmpReasonPortUnreachable) isICMPReason() {}
// icmpReasonProtoUnreachable is an error where the transport protocol is
// not supported.
type icmpReasonProtoUnreachable struct{}
func (*icmpReasonProtoUnreachable) isICMPReason() {}
// returnError takes an error descriptor and generates the appropriate ICMP
// error packet for IPv4 and sends it back to the remote device that sent
// the problematic packet. It incorporates as much of that packet as
// possible as well as any error metadata as is available. returnError
// expects pkt to hold a valid IPv4 packet as per the wire format.
func (p *protocol) returnError(r *stack.Route, reason icmpReason, pkt *stack.PacketBuffer) *tcpip.Error {
// We check we are responding only when we are allowed to.
// See RFC 1812 section 4.3.2.7 (shown below).
//
// =========
// 4.3.2.7 When Not to Send ICMP Errors
//
// An ICMP error message MUST NOT be sent as the result of receiving:
//
// o An ICMP error message, or
//
// o A packet which fails the IP header validation tests described in
// Section [5.2.2] (except where that section specifically permits
// the sending of an ICMP error message), or
//
// o A packet destined to an IP broadcast or IP multicast address, or
//
// o A packet sent as a Link Layer broadcast or multicast, or
//
// o Any fragment of a datagram other then the first fragment (i.e., a
// packet for which the fragment offset in the IP header is nonzero).
//
// TODO(gvisor.dev/issues/4058): Make sure we don't send ICMP errors in
// response to a non-initial fragment, but it currently can not happen.
if r.IsInboundBroadcast() || header.IsV4MulticastAddress(r.LocalAddress) || r.RemoteAddress == header.IPv4Any {
return nil
}
// Even if we were able to receive a packet from some remote, we may not have
// a route to it - the remote may be blocked via routing rules. We must always
// consult our routing table and find a route to the remote before sending any
// packet.
route, err := p.stack.FindRoute(r.NICID(), r.LocalAddress, r.RemoteAddress, ProtocolNumber, false /* multicastLoop */)
if err != nil {
return err
}
defer route.Release()
// From this point on, the incoming route should no longer be used; route
// must be used to send the ICMP error.
r = nil
sent := p.stack.Stats().ICMP.V4PacketsSent
if !p.stack.AllowICMPMessage() {
sent.RateLimited.Increment()
return nil
}
networkHeader := pkt.NetworkHeader().View()
transportHeader := pkt.TransportHeader().View()
// Don't respond to icmp error packets.
if header.IPv4(networkHeader).Protocol() == uint8(header.ICMPv4ProtocolNumber) {
// TODO(gvisor.dev/issue/3810):
// Unfortunately the current stack pretty much always has ICMPv4 headers
// in the Data section of the packet but there is no guarantee that is the
// case. If this is the case grab the header to make it like all other
// packet types. When this is cleaned up the Consume should be removed.
if transportHeader.IsEmpty() {
var ok bool
transportHeader, ok = pkt.TransportHeader().Consume(header.ICMPv4MinimumSize)
if !ok {
return nil
}
} else if transportHeader.Size() < header.ICMPv4MinimumSize {
return nil
}
// We need to decide to explicitly name the packets we can respond to or
// the ones we can not respond to. The decision is somewhat arbitrary and
// if problems arise this could be reversed. It was judged less of a breach
// of protocol to not respond to unknown non-error packets than to respond
// to unknown error packets so we take the first approach.
switch header.ICMPv4(transportHeader).Type() {
case
header.ICMPv4EchoReply,
header.ICMPv4Echo,
header.ICMPv4Timestamp,
header.ICMPv4TimestampReply,
header.ICMPv4InfoRequest,
header.ICMPv4InfoReply:
default:
// Assume any type we don't know about may be an error type.
return nil
}
}
// Now work out how much of the triggering packet we should return.
// As per RFC 1812 Section 4.3.2.3
//
// ICMP datagram SHOULD contain as much of the original
// datagram as possible without the length of the ICMP
// datagram exceeding 576 bytes.
//
// NOTE: The above RFC referenced is different from the original
// recommendation in RFC 1122 and RFC 792 where it mentioned that at
// least 8 bytes of the payload must be included. Today linux and other
// systems implement the RFC 1812 definition and not the original
// requirement. We treat 8 bytes as the minimum but will try send more.
mtu := int(route.MTU())
if mtu > header.IPv4MinimumProcessableDatagramSize {
mtu = header.IPv4MinimumProcessableDatagramSize
}
headerLen := int(route.MaxHeaderLength()) + header.ICMPv4MinimumSize
available := int(mtu) - headerLen
if available < header.IPv4MinimumSize+header.ICMPv4MinimumErrorPayloadSize {
return nil
}
payloadLen := networkHeader.Size() + transportHeader.Size() + pkt.Data.Size()
if payloadLen > available {
payloadLen = available
}
// The buffers used by pkt may be used elsewhere in the system.
// For example, an AF_RAW or AF_PACKET socket may use what the transport
// protocol considers an unreachable destination. Thus we deep copy pkt to
// prevent multiple ownership and SR errors. The new copy is a vectorized
// view with the entire incoming IP packet reassembled and truncated as
// required. This is now the payload of the new ICMP packet and no longer
// considered a packet in its own right.
newHeader := append(buffer.View(nil), networkHeader...)
newHeader = append(newHeader, transportHeader...)
payload := newHeader.ToVectorisedView()
payload.AppendView(pkt.Data.ToView())
payload.CapLength(payloadLen)
icmpPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
ReserveHeaderBytes: headerLen,
Data: payload,
})
icmpPkt.TransportProtocolNumber = header.ICMPv4ProtocolNumber
icmpHdr := header.ICMPv4(icmpPkt.TransportHeader().Push(header.ICMPv4MinimumSize))
switch reason.(type) {
case *icmpReasonPortUnreachable:
icmpHdr.SetCode(header.ICMPv4PortUnreachable)
case *icmpReasonProtoUnreachable:
icmpHdr.SetCode(header.ICMPv4ProtoUnreachable)
default:
panic(fmt.Sprintf("unsupported ICMP type %T", reason))
}
icmpHdr.SetType(header.ICMPv4DstUnreachable)
icmpHdr.SetChecksum(header.ICMPv4Checksum(icmpHdr, icmpPkt.Data))
counter := sent.DstUnreachable
if err := route.WritePacket(
nil, /* gso */
stack.NetworkHeaderParams{
Protocol: header.ICMPv4ProtocolNumber,
TTL: route.DefaultTTL(),
TOS: stack.DefaultTOS,
},
icmpPkt,
); err != nil {
sent.Dropped.Increment()
return err
}
counter.Increment()
return nil
}
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