Cap UDP payload size to length informed in UDP header

startblock:
  has LGTM from peterjohnston
  and then
  add reviewer ghanan,tamird
PiperOrigin-RevId: 346565589

4 files changed, 110 insertions, 29 deletions

diff --git a/pkg/tcpip/header/udp.go b/pkg/tcpip/header/udp.go
index 98bdd29db..a6d4fcd59 100644
--- a/pkg/tcpip/header/udp.go
+++ b/pkg/tcpip/header/udp.go
@@ -36,10 +36,10 @@ const (
 // UDPFields contains the fields of a UDP packet. It is used to describe the
 // fields of a packet that needs to be encoded.
 type UDPFields struct {
-	// SrcPort is the "source port" field of a UDP packet.
+	// SrcPort is the "Source Port" field of a UDP packet.
 	SrcPort uint16
 
-	// DstPort is the "destination port" field of a UDP packet.
+	// DstPort is the "Destination Port" field of a UDP packet.
 	DstPort uint16
 
 	// Length is the "length" field of a UDP packet.
@@ -64,52 +64,57 @@ const (
 	UDPProtocolNumber tcpip.TransportProtocolNumber = 17
 )
 
-// SourcePort returns the "source port" field of the udp header.
+// SourcePort returns the "Source Port" field of the UDP header.
 func (b UDP) SourcePort() uint16 {
 	return binary.BigEndian.Uint16(b[udpSrcPort:])
 }
 
-// DestinationPort returns the "destination port" field of the udp header.
+// DestinationPort returns the "Destination Port" field of the UDP header.
 func (b UDP) DestinationPort() uint16 {
 	return binary.BigEndian.Uint16(b[udpDstPort:])
 }
 
-// Length returns the "length" field of the udp header.
+// Length returns the "Length" field of the UDP header.
 func (b UDP) Length() uint16 {
 	return binary.BigEndian.Uint16(b[udpLength:])
 }
 
 // Payload returns the data contained in the UDP datagram.
 func (b UDP) Payload() []byte {
-	return b[UDPMinimumSize:]
+	return b[:b.Length()][UDPMinimumSize:]
 }
 
-// Checksum returns the "checksum" field of the udp header.
+// Checksum returns the "checksum" field of the UDP header.
 func (b UDP) Checksum() uint16 {
 	return binary.BigEndian.Uint16(b[udpChecksum:])
 }
 
-// SetSourcePort sets the "source port" field of the udp header.
+// SetSourcePort sets the "source port" field of the UDP header.
 func (b UDP) SetSourcePort(port uint16) {
 	binary.BigEndian.PutUint16(b[udpSrcPort:], port)
 }
 
-// SetDestinationPort sets the "destination port" field of the udp header.
+// SetDestinationPort sets the "destination port" field of the UDP header.
 func (b UDP) SetDestinationPort(port uint16) {
 	binary.BigEndian.PutUint16(b[udpDstPort:], port)
 }
 
-// SetChecksum sets the "checksum" field of the udp header.
+// SetChecksum sets the "checksum" field of the UDP header.
 func (b UDP) SetChecksum(checksum uint16) {
 	binary.BigEndian.PutUint16(b[udpChecksum:], checksum)
 }
 
-// SetLength sets the "length" field of the udp header.
+// SetLength sets the "length" field of the UDP header.
 func (b UDP) SetLength(length uint16) {
 	binary.BigEndian.PutUint16(b[udpLength:], length)
 }
 
-// CalculateChecksum calculates the checksum of the udp packet, given the
+// PayloadLength returns the length of the payload following the UDP header.
+func (b UDP) PayloadLength() uint16 {
+	return b.Length() - UDPMinimumSize
+}
+
+// CalculateChecksum calculates the checksum of the UDP packet, given the
 // checksum of the network-layer pseudo-header and the checksum of the payload.
 func (b UDP) CalculateChecksum(partialChecksum uint16) uint16 {
 	// Calculate the rest of the checksum.
diff --git a/pkg/tcpip/transport/udp/BUILD b/pkg/tcpip/transport/udp/BUILD
index 7ebae63d8..153e8c950 100644
--- a/pkg/tcpip/transport/udp/BUILD
+++ b/pkg/tcpip/transport/udp/BUILD
@@ -58,5 +58,6 @@ go_test(
         "//pkg/tcpip/stack",
         "//pkg/tcpip/transport/icmp",
         "//pkg/waiter",
+        "@com_github_google_go_cmp//cmp:go_default_library",
     ],
 )
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 5043e7aa5..ee1bb29f8 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -1267,7 +1267,6 @@ func verifyChecksum(hdr header.UDP, pkt *stack.PacketBuffer) bool {
 // HandlePacket is called by the stack when new packets arrive to this transport
 // endpoint.
 func (e *endpoint) HandlePacket(id stack.TransportEndpointID, pkt *stack.PacketBuffer) {
-	// Get the header then trim it from the view.
 	hdr := header.UDP(pkt.TransportHeader().View())
 	if int(hdr.Length()) > pkt.Data.Size()+header.UDPMinimumSize {
 		// Malformed packet.
@@ -1276,6 +1275,10 @@ func (e *endpoint) HandlePacket(id stack.TransportEndpointID, pkt *stack.PacketB
 		return
 	}
 
+	// TODO(gvisor.dev/issues/5033): We should mirror the Network layer and cap
+	// packets at "Parse" instead of when handling a packet.
+	pkt.Data.CapLength(int(hdr.PayloadLength()))
+
 	if !verifyChecksum(hdr, pkt) {
 		// Checksum Error.
 		e.stack.Stats().UDP.ChecksumErrors.Increment()
@@ -1309,7 +1312,7 @@ func (e *endpoint) HandlePacket(id stack.TransportEndpointID, pkt *stack.PacketB
 		senderAddress: tcpip.FullAddress{
 			NIC:  pkt.NICID,
 			Addr: id.RemoteAddress,
-			Port: header.UDP(hdr).SourcePort(),
+			Port: hdr.SourcePort(),
 		},
 	}
 	packet.data = pkt.Data
diff --git a/pkg/tcpip/transport/udp/udp_test.go b/pkg/tcpip/transport/udp/udp_test.go
index e384f52dd..b0b9b2773 100644
--- a/pkg/tcpip/transport/udp/udp_test.go
+++ b/pkg/tcpip/transport/udp/udp_test.go
@@ -22,6 +22,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/google/go-cmp/cmp"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/checker"
@@ -1827,27 +1828,31 @@ func TestV4UnknownDestination(t *testing.T) {
 			icmpPkt := header.ICMPv4(hdr.Payload())
 			payloadIPHeader := header.IPv4(icmpPkt.Payload())
 			incomingHeaderLength := header.IPv4MinimumSize + header.UDPMinimumSize
-			wantLen := len(payload)
+			wantPayloadLen := len(payload)
 			if tc.largePayload {
 				// To work out the data size we need to simulate what the sender would
 				// have done. The wanted size is the total available minus the sum of
 				// the headers in the UDP AND ICMP packets, given that we know the test
 				// had only a minimal IP header but the ICMP sender will have allowed
 				// for a maximally sized packet header.
-				wantLen = header.IPv4MinimumProcessableDatagramSize - header.IPv4MaximumHeaderSize - header.ICMPv4MinimumSize - incomingHeaderLength
+				wantPayloadLen = header.IPv4MinimumProcessableDatagramSize - header.IPv4MaximumHeaderSize - header.ICMPv4MinimumSize - incomingHeaderLength
 			}
 
 			// In the case of large payloads the IP packet may be truncated. Update
 			// the length field before retrieving the udp datagram payload.
 			// Add back the two headers within the payload.
-			payloadIPHeader.SetTotalLength(uint16(wantLen + incomingHeaderLength))
-
+			payloadIPHeader.SetTotalLength(uint16(wantPayloadLen + incomingHeaderLength))
 			origDgram := header.UDP(payloadIPHeader.Payload())
-			if got, want := len(origDgram.Payload()), wantLen; got != want {
-				t.Fatalf("unexpected payload length got: %d, want: %d", got, want)
+			wantDgramLen := wantPayloadLen + header.UDPMinimumSize
+
+			if got, want := len(origDgram), wantDgramLen; got != want {
+				t.Fatalf("got len(origDgram) = %d, want = %d", got, want)
 			}
-			if got, want := origDgram.Payload(), payload[:wantLen]; !bytes.Equal(got, want) {
-				t.Fatalf("unexpected payload got: %d, want: %d", got, want)
+			// Correct UDP length to access payload.
+			origDgram.SetLength(uint16(wantDgramLen))
+
+			if got, want := origDgram.Payload(), payload[:wantPayloadLen]; !bytes.Equal(got, want) {
+				t.Fatalf("got origDgram.Payload() = %x, want = %x", got, want)
 			}
 		})
 	}
@@ -1922,20 +1927,23 @@ func TestV6UnknownDestination(t *testing.T) {
 
 			icmpPkt := header.ICMPv6(hdr.Payload())
 			payloadIPHeader := header.IPv6(icmpPkt.Payload())
-			wantLen := len(payload)
+			wantPayloadLen := len(payload)
 			if tc.largePayload {
-				wantLen = header.IPv6MinimumMTU - header.IPv6MinimumSize*2 - header.ICMPv6MinimumSize - header.UDPMinimumSize
+				wantPayloadLen = header.IPv6MinimumMTU - header.IPv6MinimumSize*2 - header.ICMPv6MinimumSize - header.UDPMinimumSize
 			}
+			wantDgramLen := wantPayloadLen + header.UDPMinimumSize
 			// In case of large payloads the IP packet may be truncated. Update
 			// the length field before retrieving the udp datagram payload.
-			payloadIPHeader.SetPayloadLength(uint16(wantLen + header.UDPMinimumSize))
+			payloadIPHeader.SetPayloadLength(uint16(wantDgramLen))
 
 			origDgram := header.UDP(payloadIPHeader.Payload())
-			if got, want := len(origDgram.Payload()), wantLen; got != want {
-				t.Fatalf("unexpected payload length got: %d, want: %d", got, want)
+			if got, want := len(origDgram), wantPayloadLen+header.UDPMinimumSize; got != want {
+				t.Fatalf("got len(origDgram) = %d, want = %d", got, want)
 			}
-			if got, want := origDgram.Payload(), payload[:wantLen]; !bytes.Equal(got, want) {
-				t.Fatalf("unexpected payload got: %v, want: %v", got, want)
+			// Correct UDP length to access payload.
+			origDgram.SetLength(uint16(wantPayloadLen + header.UDPMinimumSize))
+			if got, want := origDgram.Payload(), payload[:wantPayloadLen]; !bytes.Equal(got, want) {
+				t.Fatalf("got origDgram.Payload() = %x, want = %x", got, want)
 			}
 		})
 	}
@@ -2448,3 +2456,67 @@ func TestOutgoingSubnetBroadcast(t *testing.T) {
 		})
 	}
 }
+
+func TestReceiveShortLength(t *testing.T) {
+	flows := []testFlow{unicastV4, unicastV6}
+	for _, flow := range flows {
+		t.Run(flow.String(), func(t *testing.T) {
+			c := newDualTestContext(t, defaultMTU)
+			defer c.cleanup()
+
+			c.createEndpointForFlow(flow)
+
+			// Bind to wildcard.
+			bindAddr := tcpip.FullAddress{Port: stackPort}
+			if err := c.ep.Bind(bindAddr); err != nil {
+				c.t.Fatalf("c.ep.Bind(%#v): %s", bindAddr, err)
+			}
+
+			payload := newPayload()
+			extraBytes := []byte{1, 2, 3, 4}
+			h := flow.header4Tuple(incoming)
+			var buf buffer.View
+			var proto tcpip.NetworkProtocolNumber
+
+			// Build packets with extra bytes not accounted for in the UDP length
+			// field.
+			var udp header.UDP
+			if flow.isV4() {
+				buf = c.buildV4Packet(payload, &h)
+				buf = append(buf, extraBytes...)
+				ip := header.IPv4(buf)
+				ip.SetTotalLength(ip.TotalLength() + uint16(len(extraBytes)))
+				ip.SetChecksum(0)
+				ip.SetChecksum(^ip.CalculateChecksum())
+				proto = ipv4.ProtocolNumber
+				udp = ip.Payload()
+			} else {
+				buf = c.buildV6Packet(payload, &h)
+				buf = append(buf, extraBytes...)
+				ip := header.IPv6(buf)
+				ip.SetPayloadLength(ip.PayloadLength() + uint16(len(extraBytes)))
+				proto = ipv6.ProtocolNumber
+				udp = ip.Payload()
+			}
+
+			if diff := cmp.Diff(payload, udp.Payload()); diff != "" {
+				t.Errorf("udp.Payload() mismatch (-want +got):\n%s", diff)
+			}
+
+			c.linkEP.InjectInbound(proto, stack.NewPacketBuffer(stack.PacketBufferOptions{
+				Data: buf.ToVectorisedView(),
+			}))
+
+			// Try to receive the data.
+			v, _, err := c.ep.Read(nil)
+			if err != nil {
+				t.Fatalf("c.ep.Read(..): %s", err)
+			}
+
+			// Check the payload is read back without extra bytes.
+			if diff := cmp.Diff(buffer.View(payload), v); diff != "" {
+				t.Errorf("c.ep.Read(..) mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}