diff options
Diffstat (limited to 'pkg/tcpip/header/ipv4.go')
| -rw-r--r-- | pkg/tcpip/header/ipv4.go | 45 |
1 files changed, 36 insertions, 9 deletions
diff --git a/pkg/tcpip/header/ipv4.go b/pkg/tcpip/header/ipv4.go index 961b77628..7e32b31b4 100644 --- a/pkg/tcpip/header/ipv4.go +++ b/pkg/tcpip/header/ipv4.go @@ -56,12 +56,9 @@ const ( ) // IPv4Fields contains the fields of an IPv4 packet. It is used to describe the -// fields of a packet that needs to be encoded. +// fields of a packet that needs to be encoded. The IHL field is not here as +// it is totally defined by the size of the options. type IPv4Fields struct { - // IHL is the "internet header length" field of an IPv4 packet. The value - // is in bytes. - IHL uint8 - // TOS is the "type of service" field of an IPv4 packet. TOS uint8 @@ -91,6 +88,9 @@ type IPv4Fields struct { // DstAddr is the "destination ip address" of an IPv4 packet. DstAddr tcpip.Address + + // Options is between 0 and 40 bytes or nil if empty. + Options IPv4Options } // IPv4 is an IPv4 header. @@ -118,7 +118,7 @@ const ( // Linux limits this to 65,515 octets (the max IP datagram size - the IPv4 // header size). But RFC 791 section 3.2 discusses the design of the IPv4 // fragment "allows 2**13 = 8192 fragments of 8 octets each for a total of - // 65,536 octets. Note that this is consistent with the the datagram total + // 65,536 octets. Note that this is consistent with the datagram total // length field (of course, the header is counted in the total length and not // in the fragments)." IPv4MaximumPayloadSize = 65536 @@ -275,10 +275,22 @@ func (b IPv4) DestinationAddress() tcpip.Address { // IPv4Options is a buffer that holds all the raw IP options. type IPv4Options []byte -// Options returns a buffer holding the options. +// AllocationSize implements stack.NetOptions. +// It reports the size to allocate for the Options. RFC 791 page 23 (end of +// section 3.1) says of the padding at the end of the options: +// The internet header padding is used to ensure that the internet +// header ends on a 32 bit boundary. +func (o IPv4Options) AllocationSize() int { + return (len(o) + IPv4IHLStride - 1) & ^(IPv4IHLStride - 1) +} + +// Options returns a buffer holding the options or nil. func (b IPv4) Options() IPv4Options { hdrLen := b.HeaderLength() - return IPv4Options(b[options:hdrLen:hdrLen]) + if hdrLen > IPv4MinimumSize { + return IPv4Options(b[options:hdrLen:hdrLen]) + } + return nil } // TransportProtocol implements Network.TransportProtocol. @@ -351,7 +363,22 @@ func (b IPv4) CalculateChecksum() uint16 { // Encode encodes all the fields of the IPv4 header. func (b IPv4) Encode(i *IPv4Fields) { - b.SetHeaderLength(i.IHL) + // The size of the options defines the size of the whole header and thus the + // IHL field. Options are rare and this is a heavily used function so it is + // worth a bit of optimisation here to keep the copy out of the fast path. + hdrLen := IPv4MinimumSize + if len(i.Options) != 0 { + // AllocationSize is always >= len(i.Options). + aLen := i.Options.AllocationSize() + hdrLen += aLen + if hdrLen > len(b) { + panic(fmt.Sprintf("encode received %d bytes, wanted >= %d", len(b), hdrLen)) + } + if aLen != copy(b[options:], i.Options) { + _ = copy(b[options+len(i.Options):options+aLen], []byte{0, 0, 0, 0}) + } + } + b.SetHeaderLength(uint8(hdrLen)) b[tos] = i.TOS b.SetTotalLength(i.TotalLength) binary.BigEndian.PutUint16(b[id:], i.ID) |