diff options
Diffstat (limited to 'pkg/tcpip/header')
| -rw-r--r-- | pkg/tcpip/header/ipv4.go | 71 |
1 files changed, 67 insertions, 4 deletions
diff --git a/pkg/tcpip/header/ipv4.go b/pkg/tcpip/header/ipv4.go index b07d9991d..4c6e4be64 100644 --- a/pkg/tcpip/header/ipv4.go +++ b/pkg/tcpip/header/ipv4.go @@ -16,10 +16,29 @@ package header import ( "encoding/binary" + "fmt" "gvisor.dev/gvisor/pkg/tcpip" ) +// RFC 971 defines the fields of the IPv4 header on page 11 using the following +// diagram: ("Figure 4") +// 0 1 2 3 +// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +// |Version| IHL |Type of Service| Total Length | +// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +// | Identification |Flags| Fragment Offset | +// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +// | Time to Live | Protocol | Header Checksum | +// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +// | Source Address | +// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +// | Destination Address | +// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +// | Options | Padding | +// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +// const ( versIHL = 0 tos = 1 @@ -33,6 +52,7 @@ const ( checksum = 10 srcAddr = 12 dstAddr = 16 + options = 20 ) // IPv4Fields contains the fields of an IPv4 packet. It is used to describe the @@ -76,7 +96,8 @@ type IPv4Fields struct { // IPv4 represents an ipv4 header stored in a byte array. // Most of the methods of IPv4 access to the underlying slice without // checking the boundaries and could panic because of 'index out of range'. -// Always call IsValid() to validate an instance of IPv4 before using other methods. +// Always call IsValid() to validate an instance of IPv4 before using other +// methods. type IPv4 []byte const ( @@ -151,13 +172,44 @@ func IPVersion(b []byte) int { if len(b) < versIHL+1 { return -1 } - return int(b[versIHL] >> 4) + return int(b[versIHL] >> ipVersionShift) } +// RFC 791 page 11 shows the header length (IHL) is in the lower 4 bits +// of the first byte, and is counted in multiples of 4 bytes. +// +// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +// |Version| IHL |Type of Service| Total Length | +// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +// (...) +// Version: 4 bits +// The Version field indicates the format of the internet header. This +// document describes version 4. +// +// IHL: 4 bits +// Internet Header Length is the length of the internet header in 32 +// bit words, and thus points to the beginning of the data. Note that +// the minimum value for a correct header is 5. +// +const ( + ipVersionShift = 4 + ipIHLMask = 0x0f + IPv4IHLStride = 4 +) + // HeaderLength returns the value of the "header length" field of the ipv4 // header. The length returned is in bytes. func (b IPv4) HeaderLength() uint8 { - return (b[versIHL] & 0xf) * 4 + return (b[versIHL] & ipIHLMask) * IPv4IHLStride +} + +// SetHeaderLength sets the value of the "Internet Header Length" field. +func (b IPv4) SetHeaderLength(hdrLen uint8) { + if hdrLen > IPv4MaximumHeaderSize { + panic(fmt.Sprintf("got IPv4 Header size = %d, want <= %d", hdrLen, IPv4MaximumHeaderSize)) + } + b[versIHL] = (IPv4Version << ipVersionShift) | ((hdrLen / IPv4IHLStride) & ipIHLMask) } // ID returns the value of the identifier field of the ipv4 header. @@ -211,6 +263,12 @@ func (b IPv4) DestinationAddress() tcpip.Address { return tcpip.Address(b[dstAddr : dstAddr+IPv4AddressSize]) } +// Options returns a a buffer holding the options. +func (b IPv4) Options() []byte { + hdrLen := b.HeaderLength() + return b[options:hdrLen:hdrLen] +} + // TransportProtocol implements Network.TransportProtocol. func (b IPv4) TransportProtocol() tcpip.TransportProtocolNumber { return tcpip.TransportProtocolNumber(b.Protocol()) @@ -236,6 +294,11 @@ func (b IPv4) SetTOS(v uint8, _ uint32) { b[tos] = v } +// SetTTL sets the "Time to Live" field of the IPv4 header. +func (b IPv4) SetTTL(v byte) { + b[ttl] = v +} + // SetTotalLength sets the "total length" field of the ipv4 header. func (b IPv4) SetTotalLength(totalLength uint16) { binary.BigEndian.PutUint16(b[IPv4TotalLenOffset:], totalLength) @@ -276,7 +339,7 @@ func (b IPv4) CalculateChecksum() uint16 { // Encode encodes all the fields of the ipv4 header. func (b IPv4) Encode(i *IPv4Fields) { - b[versIHL] = (4 << 4) | ((i.IHL / 4) & 0xf) + b.SetHeaderLength(i.IHL) b[tos] = i.TOS b.SetTotalLength(i.TotalLength) binary.BigEndian.PutUint16(b[id:], i.ID) |