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// Copyright 2020 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 parse provides utilities to parse packets.
package parse
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"
)
// ARP populates pkt's network header with an ARP header found in
// pkt.Data.
//
// Returns true if the header was successfully parsed.
func ARP(pkt *stack.PacketBuffer) bool {
_, ok := pkt.NetworkHeader().Consume(header.ARPSize)
if ok {
pkt.NetworkProtocolNumber = header.ARPProtocolNumber
}
return ok
}
// IPv4 parses an IPv4 packet found in pkt.Data and populates pkt's network
// header with the IPv4 header.
//
// Returns true if the header was successfully parsed.
func IPv4(pkt *stack.PacketBuffer) bool {
hdr, ok := pkt.Data.PullUp(header.IPv4MinimumSize)
if !ok {
return false
}
ipHdr := header.IPv4(hdr)
// Header may have options, determine the true header length.
headerLen := int(ipHdr.HeaderLength())
if headerLen < header.IPv4MinimumSize {
// TODO(gvisor.dev/issue/2404): Per RFC 791, IHL needs to be at least 5 in
// order for the packet to be valid. Figure out if we want to reject this
// case.
headerLen = header.IPv4MinimumSize
}
hdr, ok = pkt.NetworkHeader().Consume(headerLen)
if !ok {
return false
}
ipHdr = header.IPv4(hdr)
pkt.NetworkProtocolNumber = header.IPv4ProtocolNumber
pkt.Data.CapLength(int(ipHdr.TotalLength()) - len(hdr))
return true
}
// IPv6 parses an IPv6 packet found in pkt.Data and populates pkt's network
// header with the IPv6 header.
func IPv6(pkt *stack.PacketBuffer) (proto tcpip.TransportProtocolNumber, fragID uint32, fragOffset uint16, fragMore bool, ok bool) {
hdr, ok := pkt.Data.PullUp(header.IPv6MinimumSize)
if !ok {
return 0, 0, 0, false, false
}
ipHdr := header.IPv6(hdr)
// dataClone consists of:
// - Any IPv6 header bytes after the first 40 (i.e. extensions).
// - The transport header, if present.
// - Any other payload data.
views := [8]buffer.View{}
dataClone := pkt.Data.Clone(views[:])
dataClone.TrimFront(header.IPv6MinimumSize)
it := header.MakeIPv6PayloadIterator(header.IPv6ExtensionHeaderIdentifier(ipHdr.NextHeader()), dataClone)
// Iterate over the IPv6 extensions to find their length.
var nextHdr tcpip.TransportProtocolNumber
var extensionsSize int
traverseExtensions:
for {
extHdr, done, err := it.Next()
if err != nil {
break
}
// If we exhaust the extension list, the entire packet is the IPv6 header
// and (possibly) extensions.
if done {
extensionsSize = dataClone.Size()
break
}
switch extHdr := extHdr.(type) {
case header.IPv6FragmentExtHdr:
if fragID == 0 && fragOffset == 0 && !fragMore {
fragID = extHdr.ID()
fragOffset = extHdr.FragmentOffset()
fragMore = extHdr.More()
}
rawPayload := it.AsRawHeader(true /* consume */)
extensionsSize = dataClone.Size() - rawPayload.Buf.Size()
break traverseExtensions
case header.IPv6RawPayloadHeader:
// We've found the payload after any extensions.
extensionsSize = dataClone.Size() - extHdr.Buf.Size()
nextHdr = tcpip.TransportProtocolNumber(extHdr.Identifier)
break traverseExtensions
default:
// Any other extension is a no-op, keep looping until we find the payload.
}
}
// Put the IPv6 header with extensions in pkt.NetworkHeader().
hdr, ok = pkt.NetworkHeader().Consume(header.IPv6MinimumSize + extensionsSize)
if !ok {
panic(fmt.Sprintf("pkt.Data should have at least %d bytes, but only has %d.", header.IPv6MinimumSize+extensionsSize, pkt.Data.Size()))
}
ipHdr = header.IPv6(hdr)
pkt.Data.CapLength(int(ipHdr.PayloadLength()))
pkt.NetworkProtocolNumber = header.IPv6ProtocolNumber
return nextHdr, fragID, fragOffset, fragMore, true
}
// UDP parses a UDP packet found in pkt.Data and populates pkt's transport
// header with the UDP header.
//
// Returns true if the header was successfully parsed.
func UDP(pkt *stack.PacketBuffer) bool {
_, ok := pkt.TransportHeader().Consume(header.UDPMinimumSize)
pkt.TransportProtocolNumber = header.UDPProtocolNumber
return ok
}
// TCP parses a TCP packet found in pkt.Data and populates pkt's transport
// header with the TCP header.
//
// Returns true if the header was successfully parsed.
func TCP(pkt *stack.PacketBuffer) bool {
// TCP header is variable length, peek at it first.
hdrLen := header.TCPMinimumSize
hdr, ok := pkt.Data.PullUp(hdrLen)
if !ok {
return false
}
// If the header has options, pull those up as well.
if offset := int(header.TCP(hdr).DataOffset()); offset > header.TCPMinimumSize && offset <= pkt.Data.Size() {
// TODO(gvisor.dev/issue/2404): Figure out whether to reject this kind of
// packets.
hdrLen = offset
}
_, ok = pkt.TransportHeader().Consume(hdrLen)
pkt.TransportProtocolNumber = header.TCPProtocolNumber
return ok
}
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