Make UDP traceroute work.

Adds support to generate Port Unreachable messages for UDP
datagrams received on a port for which there is no valid
endpoint.

Fixes #703

PiperOrigin-RevId: 267034418

4 files changed, 179 insertions, 31 deletions

diff --git a/pkg/tcpip/header/icmpv4.go b/pkg/tcpip/header/icmpv4.go
index c52c0d851..0cac6c0a5 100644
--- a/pkg/tcpip/header/icmpv4.go
+++ b/pkg/tcpip/header/icmpv4.go
@@ -18,6 +18,7 @@ import (
 	"encoding/binary"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 )
 
 // ICMPv4 represents an ICMPv4 header stored in a byte array.
@@ -25,13 +26,29 @@ type ICMPv4 []byte
 
 const (
 	// ICMPv4PayloadOffset defines the start of ICMP payload.
-	ICMPv4PayloadOffset = 4
+	ICMPv4PayloadOffset = 8
 
 	// ICMPv4MinimumSize is the minimum size of a valid ICMP packet.
 	ICMPv4MinimumSize = 8
 
 	// ICMPv4ProtocolNumber is the ICMP transport protocol number.
 	ICMPv4ProtocolNumber tcpip.TransportProtocolNumber = 1
+
+	// icmpv4ChecksumOffset is the offset of the checksum field
+	// in an ICMPv4 message.
+	icmpv4ChecksumOffset = 2
+
+	// icmpv4MTUOffset is the offset of the MTU field
+	// in a ICMPv4FragmentationNeeded message.
+	icmpv4MTUOffset = 6
+
+	// icmpv4IdentOffset is the offset of the ident field
+	// in a ICMPv4EchoRequest/Reply message.
+	icmpv4IdentOffset = 4
+
+	// icmpv4SequenceOffset is the offset of the sequence field
+	// in a ICMPv4EchoRequest/Reply message.
+	icmpv4SequenceOffset = 6
 )
 
 // ICMPv4Type is the ICMP type field described in RFC 792.
@@ -72,12 +89,12 @@ func (b ICMPv4) SetCode(c byte) { b[1] = c }
 
 // Checksum is the ICMP checksum field.
 func (b ICMPv4) Checksum() uint16 {
-	return binary.BigEndian.Uint16(b[2:])
+	return binary.BigEndian.Uint16(b[icmpv4ChecksumOffset:])
 }
 
 // SetChecksum sets the ICMP checksum field.
 func (b ICMPv4) SetChecksum(checksum uint16) {
-	binary.BigEndian.PutUint16(b[2:], checksum)
+	binary.BigEndian.PutUint16(b[icmpv4ChecksumOffset:], checksum)
 }
 
 // SourcePort implements Transport.SourcePort.
@@ -102,3 +119,51 @@ func (ICMPv4) SetDestinationPort(uint16) {
 func (b ICMPv4) Payload() []byte {
 	return b[ICMPv4PayloadOffset:]
 }
+
+// MTU retrieves the MTU field from an ICMPv4 message.
+func (b ICMPv4) MTU() uint16 {
+	return binary.BigEndian.Uint16(b[icmpv4MTUOffset:])
+}
+
+// SetMTU sets the MTU field from an ICMPv4 message.
+func (b ICMPv4) SetMTU(mtu uint16) {
+	binary.BigEndian.PutUint16(b[icmpv4MTUOffset:], mtu)
+}
+
+// Ident retrieves the Ident field from an ICMPv4 message.
+func (b ICMPv4) Ident() uint16 {
+	return binary.BigEndian.Uint16(b[icmpv4IdentOffset:])
+}
+
+// SetIdent sets the Ident field from an ICMPv4 message.
+func (b ICMPv4) SetIdent(ident uint16) {
+	binary.BigEndian.PutUint16(b[icmpv4IdentOffset:], ident)
+}
+
+// Sequence retrieves the Sequence field from an ICMPv4 message.
+func (b ICMPv4) Sequence() uint16 {
+	return binary.BigEndian.Uint16(b[icmpv4SequenceOffset:])
+}
+
+// SetSequence sets the Sequence field from an ICMPv4 message.
+func (b ICMPv4) SetSequence(sequence uint16) {
+	binary.BigEndian.PutUint16(b[icmpv4SequenceOffset:], sequence)
+}
+
+// ICMPv4Checksum calculates the ICMP checksum over the provided ICMP header,
+// and payload.
+func ICMPv4Checksum(h ICMPv4, vv buffer.VectorisedView) uint16 {
+	// Calculate the IPv6 pseudo-header upper-layer checksum.
+	xsum := uint16(0)
+	for _, v := range vv.Views() {
+		xsum = Checksum(v, xsum)
+	}
+
+	// h[2:4] is the checksum itself, set it aside to avoid checksumming the checksum.
+	h2, h3 := h[2], h[3]
+	h[2], h[3] = 0, 0
+	xsum = ^Checksum(h, xsum)
+	h[2], h[3] = h2, h3
+
+	return xsum
+}
diff --git a/pkg/tcpip/header/icmpv6.go b/pkg/tcpip/header/icmpv6.go
index 3cc57e234..1125a7d14 100644
--- a/pkg/tcpip/header/icmpv6.go
+++ b/pkg/tcpip/header/icmpv6.go
@@ -18,6 +18,7 @@ import (
 	"encoding/binary"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 )
 
 // ICMPv6 represents an ICMPv6 header stored in a byte array.
@@ -25,14 +26,18 @@ type ICMPv6 []byte
 
 const (
 	// ICMPv6MinimumSize is the minimum size of a valid ICMP packet.
-	ICMPv6MinimumSize = 4
+	ICMPv6MinimumSize = 8
+
+	// ICMPv6PayloadOffset is the offset of the payload in an
+	// ICMP packet.
+	ICMPv6PayloadOffset = 8
 
 	// ICMPv6ProtocolNumber is the ICMP transport protocol number.
 	ICMPv6ProtocolNumber tcpip.TransportProtocolNumber = 58
 
 	// ICMPv6NeighborSolicitMinimumSize is the minimum size of a
 	// neighbor solicitation packet.
-	ICMPv6NeighborSolicitMinimumSize = ICMPv6MinimumSize + 4 + 16
+	ICMPv6NeighborSolicitMinimumSize = ICMPv6MinimumSize + 16
 
 	// ICMPv6NeighborAdvertSize is size of a neighbor advertisement.
 	ICMPv6NeighborAdvertSize = 32
@@ -42,11 +47,27 @@ const (
 
 	// ICMPv6DstUnreachableMinimumSize is the minimum size of a valid ICMP
 	// destination unreachable packet.
-	ICMPv6DstUnreachableMinimumSize = ICMPv6MinimumSize + 4
+	ICMPv6DstUnreachableMinimumSize = ICMPv6MinimumSize
 
 	// ICMPv6PacketTooBigMinimumSize is the minimum size of a valid ICMP
 	// packet-too-big packet.
-	ICMPv6PacketTooBigMinimumSize = ICMPv6MinimumSize + 4
+	ICMPv6PacketTooBigMinimumSize = ICMPv6MinimumSize
+
+	// icmpv6ChecksumOffset is the offset of the checksum field
+	// in an ICMPv6 message.
+	icmpv6ChecksumOffset = 2
+
+	// icmpv6MTUOffset is the offset of the MTU field in an ICMPv6
+	// PacketTooBig message.
+	icmpv6MTUOffset = 4
+
+	// icmpv6IdentOffset is the offset of the ident field
+	// in a ICMPv6 Echo Request/Reply message.
+	icmpv6IdentOffset = 4
+
+	// icmpv6SequenceOffset is the offset of the sequence field
+	// in a ICMPv6 Echo Request/Reply message.
+	icmpv6SequenceOffset = 6
 )
 
 // ICMPv6Type is the ICMP type field described in RFC 4443 and friends.
@@ -89,12 +110,12 @@ func (b ICMPv6) SetCode(c byte) { b[1] = c }
 
 // Checksum is the ICMP checksum field.
 func (b ICMPv6) Checksum() uint16 {
-	return binary.BigEndian.Uint16(b[2:])
+	return binary.BigEndian.Uint16(b[icmpv6ChecksumOffset:])
 }
 
 // SetChecksum calculates and sets the ICMP checksum field.
 func (b ICMPv6) SetChecksum(checksum uint16) {
-	binary.BigEndian.PutUint16(b[2:], checksum)
+	binary.BigEndian.PutUint16(b[icmpv6ChecksumOffset:], checksum)
 }
 
 // SourcePort implements Transport.SourcePort.
@@ -115,7 +136,60 @@ func (ICMPv6) SetSourcePort(uint16) {
 func (ICMPv6) SetDestinationPort(uint16) {
 }
 
+// MTU retrieves the MTU field from an ICMPv6 message.
+func (b ICMPv6) MTU() uint32 {
+	return binary.BigEndian.Uint32(b[icmpv6MTUOffset:])
+}
+
+// SetMTU sets the MTU field from an ICMPv6 message.
+func (b ICMPv6) SetMTU(mtu uint32) {
+	binary.BigEndian.PutUint32(b[icmpv6MTUOffset:], mtu)
+}
+
+// Ident retrieves the Ident field from an ICMPv6 message.
+func (b ICMPv6) Ident() uint16 {
+	return binary.BigEndian.Uint16(b[icmpv6IdentOffset:])
+}
+
+// SetIdent sets the Ident field from an ICMPv6 message.
+func (b ICMPv6) SetIdent(ident uint16) {
+	binary.BigEndian.PutUint16(b[icmpv6IdentOffset:], ident)
+}
+
+// Sequence retrieves the Sequence field from an ICMPv6 message.
+func (b ICMPv6) Sequence() uint16 {
+	return binary.BigEndian.Uint16(b[icmpv6SequenceOffset:])
+}
+
+// SetSequence sets the Sequence field from an ICMPv6 message.
+func (b ICMPv6) SetSequence(sequence uint16) {
+	binary.BigEndian.PutUint16(b[icmpv6SequenceOffset:], sequence)
+}
+
 // Payload implements Transport.Payload.
 func (b ICMPv6) Payload() []byte {
-	return b[ICMPv6MinimumSize:]
+	return b[ICMPv6PayloadOffset:]
+}
+
+// ICMPv6Checksum calculates the ICMP checksum over the provided ICMP header,
+// IPv6 src/dst addresses and the payload.
+func ICMPv6Checksum(h ICMPv6, src, dst tcpip.Address, vv buffer.VectorisedView) uint16 {
+	// Calculate the IPv6 pseudo-header upper-layer checksum.
+	xsum := Checksum([]byte(src), 0)
+	xsum = Checksum([]byte(dst), xsum)
+	var upperLayerLength [4]byte
+	binary.BigEndian.PutUint32(upperLayerLength[:], uint32(len(h)+vv.Size()))
+	xsum = Checksum(upperLayerLength[:], xsum)
+	xsum = Checksum([]byte{0, 0, 0, uint8(ICMPv6ProtocolNumber)}, xsum)
+	for _, v := range vv.Views() {
+		xsum = Checksum(v, xsum)
+	}
+
+	// h[2:4] is the checksum itself, set it aside to avoid checksumming the checksum.
+	h2, h3 := h[2], h[3]
+	h[2], h[3] = 0, 0
+	xsum = ^Checksum(h, xsum)
+	h[2], h[3] = h2, h3
+
+	return xsum
 }
diff --git a/pkg/tcpip/header/ipv4.go b/pkg/tcpip/header/ipv4.go
index 17fc9c68e..554632a64 100644
--- a/pkg/tcpip/header/ipv4.go
+++ b/pkg/tcpip/header/ipv4.go
@@ -21,16 +21,18 @@ import (
 )
 
 const (
-	versIHL  = 0
-	tos      = 1
-	totalLen = 2
-	id       = 4
-	flagsFO  = 6
-	ttl      = 8
-	protocol = 9
-	checksum = 10
-	srcAddr  = 12
-	dstAddr  = 16
+	versIHL = 0
+	tos     = 1
+	// IPv4TotalLenOffset is the offset of the total length field in the
+	// IPv4 header.
+	IPv4TotalLenOffset = 2
+	id                 = 4
+	flagsFO            = 6
+	ttl                = 8
+	protocol           = 9
+	checksum           = 10
+	srcAddr            = 12
+	dstAddr            = 16
 )
 
 // IPv4Fields contains the fields of an IPv4 packet. It is used to describe the
@@ -103,6 +105,11 @@ const (
 
 	// IPv4Any is the non-routable IPv4 "any" meta address.
 	IPv4Any tcpip.Address = "\x00\x00\x00\x00"
+
+	// IPv4MinimumProcessableDatagramSize is the minimum size of an IP
+	// packet that every IPv4 capable host must be able to
+	// process/reassemble.
+	IPv4MinimumProcessableDatagramSize = 576
 )
 
 // Flags that may be set in an IPv4 packet.
@@ -163,7 +170,7 @@ func (b IPv4) FragmentOffset() uint16 {
 
 // TotalLength returns the "total length" field of the ipv4 header.
 func (b IPv4) TotalLength() uint16 {
-	return binary.BigEndian.Uint16(b[totalLen:])
+	return binary.BigEndian.Uint16(b[IPv4TotalLenOffset:])
 }
 
 // Checksum returns the checksum field of the ipv4 header.
@@ -209,7 +216,7 @@ func (b IPv4) SetTOS(v uint8, _ uint32) {
 
 // SetTotalLength sets the "total length" field of the ipv4 header.
 func (b IPv4) SetTotalLength(totalLength uint16) {
-	binary.BigEndian.PutUint16(b[totalLen:], totalLength)
+	binary.BigEndian.PutUint16(b[IPv4TotalLenOffset:], totalLength)
 }
 
 // SetChecksum sets the checksum field of the ipv4 header.
@@ -265,7 +272,7 @@ func (b IPv4) Encode(i *IPv4Fields) {
 // packets are produced.
 func (b IPv4) EncodePartial(partialChecksum, totalLength uint16) {
 	b.SetTotalLength(totalLength)
-	checksum := Checksum(b[totalLen:totalLen+2], partialChecksum)
+	checksum := Checksum(b[IPv4TotalLenOffset:IPv4TotalLenOffset+2], partialChecksum)
 	b.SetChecksum(^checksum)
 }
 
diff --git a/pkg/tcpip/header/ipv6.go b/pkg/tcpip/header/ipv6.go
index bc4e56535..093850e25 100644
--- a/pkg/tcpip/header/ipv6.go
+++ b/pkg/tcpip/header/ipv6.go
@@ -22,12 +22,14 @@ import (
 )
 
 const (
-	versTCFL   = 0
-	payloadLen = 4
-	nextHdr    = 6
-	hopLimit   = 7
-	v6SrcAddr  = 8
-	v6DstAddr  = v6SrcAddr + IPv6AddressSize
+	versTCFL = 0
+	// IPv6PayloadLenOffset is the offset of the PayloadLength field in
+	// IPv6 header.
+	IPv6PayloadLenOffset = 4
+	nextHdr              = 6
+	hopLimit             = 7
+	v6SrcAddr            = 8
+	v6DstAddr            = v6SrcAddr + IPv6AddressSize
 )
 
 // IPv6Fields contains the fields of an IPv6 packet. It is used to describe the
@@ -94,7 +96,7 @@ var IPv6EmptySubnet = func() tcpip.Subnet {
 // PayloadLength returns the value of the "payload length" field of the ipv6
 // header.
 func (b IPv6) PayloadLength() uint16 {
-	return binary.BigEndian.Uint16(b[payloadLen:])
+	return binary.BigEndian.Uint16(b[IPv6PayloadLenOffset:])
 }
 
 // HopLimit returns the value of the "hop limit" field of the ipv6 header.
@@ -148,7 +150,7 @@ func (b IPv6) SetTOS(t uint8, l uint32) {
 
 // SetPayloadLength sets the "payload length" field of the ipv6 header.
 func (b IPv6) SetPayloadLength(payloadLength uint16) {
-	binary.BigEndian.PutUint16(b[payloadLen:], payloadLength)
+	binary.BigEndian.PutUint16(b[IPv6PayloadLenOffset:], payloadLength)
 }
 
 // SetSourceAddress sets the "source address" field of the ipv6 header.