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Diffstat (limited to 'pkg/tcpip/header/eth.go')
-rw-r--r-- | pkg/tcpip/header/eth.go | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/pkg/tcpip/header/eth.go b/pkg/tcpip/header/eth.go new file mode 100644 index 000000000..b1e92d2d7 --- /dev/null +++ b/pkg/tcpip/header/eth.go @@ -0,0 +1,177 @@ +// 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 header + +import ( + "encoding/binary" + + "gvisor.dev/gvisor/pkg/tcpip" +) + +const ( + dstMAC = 0 + srcMAC = 6 + ethType = 12 +) + +// EthernetFields contains the fields of an ethernet frame header. It is used to +// describe the fields of a frame that needs to be encoded. +type EthernetFields struct { + // SrcAddr is the "MAC source" field of an ethernet frame header. + SrcAddr tcpip.LinkAddress + + // DstAddr is the "MAC destination" field of an ethernet frame header. + DstAddr tcpip.LinkAddress + + // Type is the "ethertype" field of an ethernet frame header. + Type tcpip.NetworkProtocolNumber +} + +// Ethernet represents an ethernet frame header stored in a byte array. +type Ethernet []byte + +const ( + // EthernetMinimumSize is the minimum size of a valid ethernet frame. + EthernetMinimumSize = 14 + + // EthernetAddressSize is the size, in bytes, of an ethernet address. + EthernetAddressSize = 6 + + // unspecifiedEthernetAddress is the unspecified ethernet address + // (all bits set to 0). + unspecifiedEthernetAddress = tcpip.LinkAddress("\x00\x00\x00\x00\x00\x00") + + // unicastMulticastFlagMask is the mask of the least significant bit in + // the first octet (in network byte order) of an ethernet address that + // determines whether the ethernet address is a unicast or multicast. If + // the masked bit is a 1, then the address is a multicast, unicast + // otherwise. + // + // See the IEEE Std 802-2001 document for more details. Specifically, + // section 9.2.1 of http://ieee802.org/secmail/pdfocSP2xXA6d.pdf: + // "A 48-bit universal address consists of two parts. The first 24 bits + // correspond to the OUI as assigned by the IEEE, expect that the + // assignee may set the LSB of the first octet to 1 for group addresses + // or set it to 0 for individual addresses." + unicastMulticastFlagMask = 1 + + // unicastMulticastFlagByteIdx is the byte that holds the + // unicast/multicast flag. See unicastMulticastFlagMask. + unicastMulticastFlagByteIdx = 0 +) + +const ( + // EthernetProtocolAll is a catch-all for all protocols carried inside + // an ethernet frame. It is mainly used to create packet sockets that + // capture all traffic. + EthernetProtocolAll tcpip.NetworkProtocolNumber = 0x0003 + + // EthernetProtocolPUP is the PARC Universial Packet protocol ethertype. + EthernetProtocolPUP tcpip.NetworkProtocolNumber = 0x0200 +) + +// Ethertypes holds the protocol numbers describing the payload of an ethernet +// frame. These types aren't necessarily supported by netstack, but can be used +// to catch all traffic of a type via packet endpoints. +var Ethertypes = []tcpip.NetworkProtocolNumber{ + EthernetProtocolAll, + EthernetProtocolPUP, +} + +// SourceAddress returns the "MAC source" field of the ethernet frame header. +func (b Ethernet) SourceAddress() tcpip.LinkAddress { + return tcpip.LinkAddress(b[srcMAC:][:EthernetAddressSize]) +} + +// DestinationAddress returns the "MAC destination" field of the ethernet frame +// header. +func (b Ethernet) DestinationAddress() tcpip.LinkAddress { + return tcpip.LinkAddress(b[dstMAC:][:EthernetAddressSize]) +} + +// Type returns the "ethertype" field of the ethernet frame header. +func (b Ethernet) Type() tcpip.NetworkProtocolNumber { + return tcpip.NetworkProtocolNumber(binary.BigEndian.Uint16(b[ethType:])) +} + +// Encode encodes all the fields of the ethernet frame header. +func (b Ethernet) Encode(e *EthernetFields) { + binary.BigEndian.PutUint16(b[ethType:], uint16(e.Type)) + copy(b[srcMAC:][:EthernetAddressSize], e.SrcAddr) + copy(b[dstMAC:][:EthernetAddressSize], e.DstAddr) +} + +// IsValidUnicastEthernetAddress returns true if addr is a valid unicast +// ethernet address. +func IsValidUnicastEthernetAddress(addr tcpip.LinkAddress) bool { + // Must be of the right length. + if len(addr) != EthernetAddressSize { + return false + } + + // Must not be unspecified. + if addr == unspecifiedEthernetAddress { + return false + } + + // Must not be a multicast. + if addr[unicastMulticastFlagByteIdx]&unicastMulticastFlagMask != 0 { + return false + } + + // addr is a valid unicast ethernet address. + return true +} + +// EthernetAddressFromMulticastIPv4Address returns a multicast Ethernet address +// for a multicast IPv4 address. +// +// addr MUST be a multicast IPv4 address. +func EthernetAddressFromMulticastIPv4Address(addr tcpip.Address) tcpip.LinkAddress { + var linkAddrBytes [EthernetAddressSize]byte + // 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). + linkAddrBytes[0] = 0x1 + linkAddrBytes[2] = 0x5e + linkAddrBytes[3] = addr[1] & 0x7F + copy(linkAddrBytes[4:], addr[IPv4AddressSize-2:]) + return tcpip.LinkAddress(linkAddrBytes[:]) +} + +// EthernetAddressFromMulticastIPv6Address returns a multicast Ethernet address +// for a multicast IPv6 address. +// +// addr MUST be a multicast IPv6 address. +func EthernetAddressFromMulticastIPv6Address(addr tcpip.Address) tcpip.LinkAddress { + // RFC 2464 Transmission of IPv6 Packets over Ethernet Networks + // + // 7. Address Mapping -- Multicast + // + // An IPv6 packet with a multicast destination address DST, + // consisting of the sixteen octets DST[1] through DST[16], is + // transmitted to the Ethernet multicast address whose first + // two octets are the value 3333 hexadecimal and whose last + // four octets are the last four octets of DST. + linkAddrBytes := []byte(addr[IPv6AddressSize-EthernetAddressSize:]) + linkAddrBytes[0] = 0x33 + linkAddrBytes[1] = 0x33 + return tcpip.LinkAddress(linkAddrBytes[:]) +} |