Remove generic ICMP errors

Generic ICMP errors were required because the transport dispatcher was
given the responsibility of sending ICMP errors in response to transport
packet delivery failures. Instead, the transport dispatcher should let
network layer know it failed to deliver a packet (and why) and let the
network layer make the decision as to what error to send (if any).

Fixes #4068

PiperOrigin-RevId: 333962333

2 files changed, 14 insertions, 11 deletions

diff --git a/pkg/tcpip/network/ipv4/icmp.go b/pkg/tcpip/network/ipv4/icmp.go
index 5fe73315f..3e5cf2ad9 100644
--- a/pkg/tcpip/network/ipv4/icmp.go
+++ b/pkg/tcpip/network/ipv4/icmp.go
@@ -200,16 +200,6 @@ func (e *endpoint) handleICMP(r *stack.Route, pkt *stack.PacketBuffer) {
 
 // ======= ICMP Error packet generation =========
 
-// ReturnError implements stack.TransportProtocol.ReturnError.
-func (p *protocol) ReturnError(r *stack.Route, reason tcpip.ICMPReason, pkt *stack.PacketBuffer) *tcpip.Error {
-	switch reason.(type) {
-	case *tcpip.ICMPReasonPortUnreachable:
-		return returnError(r, &icmpReasonPortUnreachable{}, pkt)
-	default:
-		return tcpip.ErrNotSupported
-	}
-}
-
 // icmpReason is a marker interface for IPv4 specific ICMP errors.
 type icmpReason interface {
 	isICMPReason()
diff --git a/pkg/tcpip/network/ipv4/ipv4.go b/pkg/tcpip/network/ipv4/ipv4.go
index 135444222..e589d923d 100644
--- a/pkg/tcpip/network/ipv4/ipv4.go
+++ b/pkg/tcpip/network/ipv4/ipv4.go
@@ -21,6 +21,7 @@
 package ipv4
 
 import (
+	"fmt"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -463,7 +464,19 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 		return
 	}
 	r.Stats().IP.PacketsDelivered.Increment()
-	e.dispatcher.DeliverTransportPacket(r, p, pkt)
+
+	switch res := e.dispatcher.DeliverTransportPacket(r, p, pkt); res {
+	case stack.TransportPacketHandled:
+	case stack.TransportPacketDestinationPortUnreachable:
+		// As per RFC: 1122 Section 3.2.2.1 A host SHOULD generate Destination
+		//   Unreachable messages with code:
+		//     3 (Port Unreachable), when the designated transport protocol
+		//     (e.g., UDP) is unable to demultiplex the datagram but has no
+		//     protocol mechanism to inform the sender.
+		_ = returnError(r, &icmpReasonPortUnreachable{}, pkt)
+	default:
+		panic(fmt.Sprintf("unrecognized result from DeliverTransportPacket = %d", res))
+	}
 }
 
 // Close cleans up resources associated with the endpoint.