From 99decaadd6da0df2d8ec70ddea9d754c9d71a584 Mon Sep 17 00:00:00 2001
From: Julian Elischer <jrelis@google.com>
Date: Wed, 23 Sep 2020 02:26:50 -0700
Subject: Extract ICMP error sender from UDP

Store transport protocol number on packet buffers for use in ICMP error
generation.

Updates #2211.

PiperOrigin-RevId: 333252762
---
 pkg/tcpip/header/icmpv6.go | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

(limited to 'pkg/tcpip/header/icmpv6.go')

diff --git a/pkg/tcpip/header/icmpv6.go b/pkg/tcpip/header/icmpv6.go
index 20b01d8f4..4eb5abd79 100644
--- a/pkg/tcpip/header/icmpv6.go
+++ b/pkg/tcpip/header/icmpv6.go
@@ -54,9 +54,17 @@ const (
 	// address.
 	ICMPv6NeighborAdvertSize = ICMPv6HeaderSize + NDPNAMinimumSize + NDPLinkLayerAddressSize
 
-	// ICMPv6EchoMinimumSize is the minimum size of a valid ICMP echo packet.
+	// ICMPv6EchoMinimumSize is the minimum size of a valid echo packet.
 	ICMPv6EchoMinimumSize = 8
 
+	// ICMPv6ErrorHeaderSize is the size of an ICMP error packet header,
+	// as per RFC 4443, Apendix A, item 4 and the errata.
+	//   ... all ICMP error messages shall have exactly
+	//   32 bits of type-specific data, so that receivers can reliably find
+	//   the embedded invoking packet even when they don't recognize the
+	//   ICMP message Type.
+	ICMPv6ErrorHeaderSize = 8
+
 	// ICMPv6DstUnreachableMinimumSize is the minimum size of a valid ICMP
 	// destination unreachable packet.
 	ICMPv6DstUnreachableMinimumSize = ICMPv6MinimumSize
@@ -69,6 +77,10 @@ const (
 	// in an ICMPv6 message.
 	icmpv6ChecksumOffset = 2
 
+	// icmpv6PointerOffset is the offset of the pointer
+	// in an ICMPv6 Parameter problem message.
+	icmpv6PointerOffset = 4
+
 	// icmpv6MTUOffset is the offset of the MTU field in an ICMPv6
 	// PacketTooBig message.
 	icmpv6MTUOffset = 4
@@ -89,9 +101,10 @@ const (
 	NDPHopLimit = 255
 )
 
-// ICMPv6Type is the ICMP type field described in RFC 4443 and friends.
+// ICMPv6Type is the ICMP type field described in RFC 4443.
 type ICMPv6Type byte
 
+// Values for use in the Type field of ICMPv6 packet from RFC 4433.
 const (
 	ICMPv6DstUnreachable ICMPv6Type = 1
 	ICMPv6PacketTooBig   ICMPv6Type = 2
@@ -109,7 +122,18 @@ const (
 	ICMPv6RedirectMsg     ICMPv6Type = 137
 )
 
-// ICMPv6Code is the ICMP code field described in RFC 4443.
+// IsErrorType returns true if the receiver is an ICMP error type.
+func (typ ICMPv6Type) IsErrorType() bool {
+	// Per RFC 4443 section 2.1:
+	//   ICMPv6 messages are grouped into two classes: error messages and
+	//   informational messages.  Error messages are identified as such by a
+	//   zero in the high-order bit of their message Type field values.  Thus,
+	//   error messages have message types from 0 to 127; informational
+	//   messages have message types from 128 to 255.
+	return typ&0x80 == 0
+}
+
+// ICMPv6Code is the ICMP Code field described in RFC 4443.
 type ICMPv6Code byte
 
 // ICMP codes used with Destination Unreachable (Type 1). As per RFC 4443
@@ -153,6 +177,11 @@ func (b ICMPv6) Code() ICMPv6Code { return ICMPv6Code(b[1]) }
 // SetCode sets the ICMP code field.
 func (b ICMPv6) SetCode(c ICMPv6Code) { b[1] = byte(c) }
 
+// SetTypeSpecific sets the full 32 bit type specific data field.
+func (b ICMPv6) SetTypeSpecific(val uint32) {
+	binary.BigEndian.PutUint32(b[icmpv6PointerOffset:], val)
+}
+
 // Checksum is the ICMP checksum field.
 func (b ICMPv6) Checksum() uint16 {
 	return binary.BigEndian.Uint16(b[icmpv6ChecksumOffset:])
-- 
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