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authorgVisor bot <gvisor-bot@google.com>2020-10-06 03:47:28 +0000
committergVisor bot <gvisor-bot@google.com>2020-10-06 03:47:28 +0000
commit8afb4bb7c716d2878834206a587ef5a81e53c1a2 (patch)
treef1a16cec3b986c4561fc593919b8ca33719b3dd6 /pkg/tcpip/header
parent1070297816ef242d77cffe161bfea993c97f84a7 (diff)
parent798cc6b04dc1206538b2cedb1af427e0d5468b46 (diff)
Merge release-20200928.0-50-g798cc6b04 (automated)
Diffstat (limited to 'pkg/tcpip/header')
-rw-r--r--pkg/tcpip/header/ipv4.go71
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)