Merge release-20201030.0-91-g6c0f53002 (automated)

pkg/tcpip/header/ipv6.go

@@ -54,7 +54,7 @@ type IPv6Fields struct {
 	// NextHeader is the "next header" field of an IPv6 packet.
 	NextHeader uint8
 
-	// HopLimit is the "hop limit" field of an IPv6 packet.
+	// HopLimit is the "Hop Limit" field of an IPv6 packet.
 	HopLimit uint8
 
 	// SrcAddr is the "source ip address" of an IPv6 packet.
@@ -171,7 +171,7 @@ func (b IPv6) PayloadLength() uint16 {
 	return binary.BigEndian.Uint16(b[IPv6PayloadLenOffset:])
 }
 
-// HopLimit returns the value of the "hop limit" field of the ipv6 header.
+// HopLimit returns the value of the "Hop Limit" field of the ipv6 header.
 func (b IPv6) HopLimit() uint8 {
 	return b[hopLimit]
 }
@@ -236,6 +236,11 @@ func (b IPv6) SetDestinationAddress(addr tcpip.Address) {
 	copy(b[v6DstAddr:][:IPv6AddressSize], addr)
 }
 
+// SetHopLimit sets the value of the "Hop Limit" field.
+func (b IPv6) SetHopLimit(v uint8) {
+	b[hopLimit] = v
+}
+
 // SetNextHeader sets the value of the "next header" field of the ipv6 header.
 func (b IPv6) SetNextHeader(v uint8) {
 	b[IPv6NextHeaderOffset] = v

pkg/tcpip/network/ipv4/icmp.go

@@ -290,6 +290,13 @@ type icmpReasonProtoUnreachable struct{}
 
 func (*icmpReasonProtoUnreachable) isICMPReason() {}
 
+// icmpReasonTTLExceeded is an error where a packet's time to live exceeded in
+// transit to its final destination, as per RFC 792 page 6, Time Exceeded
+// Message.
+type icmpReasonTTLExceeded struct{}
+
+func (*icmpReasonTTLExceeded) isICMPReason() {}
+
 // icmpReasonReassemblyTimeout is an error where insufficient fragments are
 // received to complete reassembly of a packet within a configured time after
 // the reception of the first-arriving fragment of that packet.
@@ -342,11 +349,31 @@ func (p *protocol) returnError(reason icmpReason, pkt *stack.PacketBuffer) *tcpi
 		return nil
 	}
 
+	// If we hit a TTL Exceeded error, then we know we are operating as a router.
+	// As per RFC 792 page 6, Time Exceeded Message,
+	//
+	//   If the gateway processing a datagram finds the time to live field
+	//   is zero it must discard the datagram.  The gateway may also notify
+	//   the source host via the time exceeded message.
+	//
+	//   ...
+	//
+	//   Code 0 may be received from a gateway. ...
+	//
+	// Note, Code 0 is the TTL exceeded error.
+	//
+	// If we are operating as a router/gateway, don't use the packet's destination
+	// address as the response's source address as we should not not own the
+	// destination address of a packet we are forwarding.
+	localAddr := origIPHdrDst
+	if _, ok := reason.(*icmpReasonTTLExceeded); ok {
+		localAddr = ""
+	}
 	// Even if we were able to receive a packet from some remote, we may not have
 	// a route to it - the remote may be blocked via routing rules. We must always
 	// consult our routing table and find a route to the remote before sending any
 	// packet.
-	route, err := p.stack.FindRoute(pkt.NICID, origIPHdrDst, origIPHdrSrc, ProtocolNumber, false /* multicastLoop */)
+	route, err := p.stack.FindRoute(pkt.NICID, localAddr, origIPHdrSrc, ProtocolNumber, false /* multicastLoop */)
 	if err != nil {
 		return err
 	}
@@ -454,6 +481,10 @@ func (p *protocol) returnError(reason icmpReason, pkt *stack.PacketBuffer) *tcpi
 		icmpHdr.SetType(header.ICMPv4DstUnreachable)
 		icmpHdr.SetCode(header.ICMPv4ProtoUnreachable)
 		counter = sent.DstUnreachable
+	case *icmpReasonTTLExceeded:
+		icmpHdr.SetType(header.ICMPv4TimeExceeded)
+		icmpHdr.SetCode(header.ICMPv4TTLExceeded)
+		counter = sent.TimeExceeded
 	case *icmpReasonReassemblyTimeout:
 		icmpHdr.SetType(header.ICMPv4TimeExceeded)
 		icmpHdr.SetCode(header.ICMPv4ReassemblyTimeout)

pkg/tcpip/network/ipv4/ipv4.go

@@ -485,6 +485,16 @@ func (e *endpoint) WriteHeaderIncludedPacket(r *stack.Route, pkt *stack.PacketBu
 // forwardPacket attempts to forward a packet to its final destination.
 func (e *endpoint) forwardPacket(pkt *stack.PacketBuffer) *tcpip.Error {
 	h := header.IPv4(pkt.NetworkHeader().View())
+	ttl := h.TTL()
+	if ttl == 0 {
+		// As per RFC 792 page 6, Time Exceeded Message,
+		//
+		//  If the gateway processing a datagram finds the time to live field
+		//  is zero it must discard the datagram.  The gateway may also notify
+		//  the source host via the time exceeded message.
+		return e.protocol.returnError(&icmpReasonTTLExceeded{}, pkt)
+	}
+
 	dstAddr := h.DestinationAddress()
 
 	// Check if the destination is owned by the stack.
@@ -503,13 +513,22 @@ func (e *endpoint) forwardPacket(pkt *stack.PacketBuffer) *tcpip.Error {
 	}
 	defer r.Release()
 
-	// TODO(b/143425874) Decrease the TTL field in forwarded packets.
+	// We need to do a deep copy of the IP packet because
+	// WriteHeaderIncludedPacket takes ownership of the packet buffer, but we do
+	// not own it.
+	newHdr := header.IPv4(stack.PayloadSince(pkt.NetworkHeader()))
+
+	// As per RFC 791 page 30, Time to Live,
+	//
+	//   This field must be decreased at each point that the internet header
+	//   is processed to reflect the time spent processing the datagram.
+	//   Even if no local information is available on the time actually
+	//   spent, the field must be decremented by 1.
+	newHdr.SetTTL(ttl - 1)
+
 	return r.WriteHeaderIncludedPacket(stack.NewPacketBuffer(stack.PacketBufferOptions{
 		ReserveHeaderBytes: int(r.MaxHeaderLength()),
-		// We need to do a deep copy of the IP packet because
+		Data:               buffer.View(newHdr).ToVectorisedView(),
-		// WriteHeaderIncludedPacket takes ownership of the packet buffer, but we do
-		// not own it.
-		Data: stack.PayloadSince(pkt.NetworkHeader()).ToVectorisedView(),
 	}))
 }
 

pkg/tcpip/network/ipv6/icmp.go

@@ -750,6 +750,12 @@ type icmpReasonPortUnreachable struct{}
 
 func (*icmpReasonPortUnreachable) isICMPReason() {}
 
+// icmpReasonHopLimitExceeded is an error where a packet's hop limit exceeded in
+// transit to its final destination, as per RFC 4443 section 3.3.
+type icmpReasonHopLimitExceeded struct{}
+
+func (*icmpReasonHopLimitExceeded) isICMPReason() {}
+
 // icmpReasonReassemblyTimeout is an error where insufficient fragments are
 // received to complete reassembly of a packet within a configured time after
 // the reception of the first-arriving fragment of that packet.
@@ -794,11 +800,27 @@ func (p *protocol) returnError(reason icmpReason, pkt *stack.PacketBuffer) *tcpi
 		return nil
 	}
 
+	// If we hit a Hop Limit Exceeded error, then we know we are operating as a
+	// router. As per RFC 4443 section 3.3:
+	//
+	//   If a router receives a packet with a Hop Limit of zero, or if a
+	//   router decrements a packet's Hop Limit to zero, it MUST discard the
+	//   packet and originate an ICMPv6 Time Exceeded message with Code 0 to
+	//   the source of the packet.  This indicates either a routing loop or
+	//   too small an initial Hop Limit value.
+	//
+	// If we are operating as a router, do not use the packet's destination
+	// address as the response's source address as we should not own the
+	// destination address of a packet we are forwarding.
+	localAddr := origIPHdrDst
+	if _, ok := reason.(*icmpReasonHopLimitExceeded); ok {
+		localAddr = ""
+	}
 	// Even if we were able to receive a packet from some remote, we may not have
 	// a route to it - the remote may be blocked via routing rules. We must always
 	// consult our routing table and find a route to the remote before sending any
 	// packet.
-	route, err := p.stack.FindRoute(pkt.NICID, origIPHdrDst, origIPHdrSrc, ProtocolNumber, false /* multicastLoop */)
+	route, err := p.stack.FindRoute(pkt.NICID, localAddr, origIPHdrSrc, ProtocolNumber, false /* multicastLoop */)
 	if err != nil {
 		return err
 	}
@@ -811,8 +833,6 @@ func (p *protocol) returnError(reason icmpReason, pkt *stack.PacketBuffer) *tcpi
 		return nil
 	}
 
-	network, transport := pkt.NetworkHeader().View(), pkt.TransportHeader().View()
-
 	if pkt.TransportProtocolNumber == header.ICMPv6ProtocolNumber {
 		// TODO(gvisor.dev/issues/3810): Sort this out when ICMP headers are stored.
 		// Unfortunately at this time ICMP Packets do not have a transport
@@ -830,6 +850,8 @@ func (p *protocol) returnError(reason icmpReason, pkt *stack.PacketBuffer) *tcpi
 		}
 	}
 
+	network, transport := pkt.NetworkHeader().View(), pkt.TransportHeader().View()
+
 	// As per RFC 4443 section 2.4
 	//
 	//    (c) Every ICMPv6 error message (type < 128) MUST include
@@ -873,6 +895,10 @@ func (p *protocol) returnError(reason icmpReason, pkt *stack.PacketBuffer) *tcpi
 		icmpHdr.SetType(header.ICMPv6DstUnreachable)
 		icmpHdr.SetCode(header.ICMPv6PortUnreachable)
 		counter = sent.DstUnreachable
+	case *icmpReasonHopLimitExceeded:
+		icmpHdr.SetType(header.ICMPv6TimeExceeded)
+		icmpHdr.SetCode(header.ICMPv6HopLimitExceeded)
+		counter = sent.TimeExceeded
 	case *icmpReasonReassemblyTimeout:
 		icmpHdr.SetType(header.ICMPv6TimeExceeded)
 		icmpHdr.SetCode(header.ICMPv6ReassemblyTimeout)

pkg/tcpip/network/ipv6/ipv6.go

@@ -645,6 +645,18 @@ func (e *endpoint) WriteHeaderIncludedPacket(r *stack.Route, pkt *stack.PacketBu
 // forwardPacket attempts to forward a packet to its final destination.
 func (e *endpoint) forwardPacket(pkt *stack.PacketBuffer) *tcpip.Error {
 	h := header.IPv6(pkt.NetworkHeader().View())
+	hopLimit := h.HopLimit()
+	if hopLimit <= 1 {
+		// As per RFC 4443 section 3.3,
+		//
+		//   If a router receives a packet with a Hop Limit of zero, or if a
+		//   router decrements a packet's Hop Limit to zero, it MUST discard the
+		//   packet and originate an ICMPv6 Time Exceeded message with Code 0 to
+		//   the source of the packet.  This indicates either a routing loop or
+		//   too small an initial Hop Limit value.
+		return e.protocol.returnError(&icmpReasonHopLimitExceeded{}, pkt)
+	}
+
 	dstAddr := h.DestinationAddress()
 
 	// Check if the destination is owned by the stack.
@@ -663,13 +675,20 @@ func (e *endpoint) forwardPacket(pkt *stack.PacketBuffer) *tcpip.Error {
 	}
 	defer r.Release()
 
-	// TODO(b/143425874) Decrease the TTL field in forwarded packets.
+	// We need to do a deep copy of the IP packet because
+	// WriteHeaderIncludedPacket takes ownership of the packet buffer, but we do
+	// not own it.
+	newHdr := header.IPv6(stack.PayloadSince(pkt.NetworkHeader()))
+
+	// As per RFC 8200 section 3,
+	//
+	//   Hop Limit           8-bit unsigned integer. Decremented by 1 by
+	//                       each node that forwards the packet.
+	newHdr.SetHopLimit(hopLimit - 1)
+
 	return r.WriteHeaderIncludedPacket(stack.NewPacketBuffer(stack.PacketBufferOptions{
 		ReserveHeaderBytes: int(r.MaxHeaderLength()),
-		// We need to do a deep copy of the IP packet because
+		Data:               buffer.View(newHdr).ToVectorisedView(),
-		// WriteHeaderIncludedPacket takes ownership of the packet buffer, but we do
-		// not own it.
-		Data: stack.PayloadSince(pkt.NetworkHeader()).ToVectorisedView(),
 	}))
 }