Use common parsing utilities when sniffing

Extract parsing utilities so they can be used by the sniffer.

Fixes #3930

PiperOrigin-RevId: 332401880

pkg/tcpip/header/parse/BUILD

@@ -0,0 +1,15 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+    name = "parse",
+    srcs = ["parse.go"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//pkg/tcpip",
+        "//pkg/tcpip/buffer",
+        "//pkg/tcpip/header",
+        "//pkg/tcpip/stack",
+    ],
+)

pkg/tcpip/header/parse/parse.go

@@ -0,0 +1,166 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package parse provides utilities to parse packets.
+package parse
+
+import (
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+)
+
+// ARP populates pkt's network header with an ARP header found in
+// pkt.Data.
+//
+// Returns true if the header was successfully parsed.
+func ARP(pkt *stack.PacketBuffer) bool {
+	_, ok := pkt.NetworkHeader().Consume(header.ARPSize)
+	if ok {
+		pkt.NetworkProtocolNumber = header.ARPProtocolNumber
+	}
+	return ok
+}
+
+// IPv4 parses an IPv4 packet found in pkt.Data and populates pkt's network
+// header with the IPv4 header.
+//
+// Returns true if the header was successfully parsed.
+func IPv4(pkt *stack.PacketBuffer) bool {
+	hdr, ok := pkt.Data.PullUp(header.IPv4MinimumSize)
+	if !ok {
+		return false
+	}
+	ipHdr := header.IPv4(hdr)
+
+	// Header may have options, determine the true header length.
+	headerLen := int(ipHdr.HeaderLength())
+	if headerLen < header.IPv4MinimumSize {
+		// TODO(gvisor.dev/issue/2404): Per RFC 791, IHL needs to be at least 5 in
+		// order for the packet to be valid. Figure out if we want to reject this
+		// case.
+		headerLen = header.IPv4MinimumSize
+	}
+	hdr, ok = pkt.NetworkHeader().Consume(headerLen)
+	if !ok {
+		return false
+	}
+	ipHdr = header.IPv4(hdr)
+
+	pkt.NetworkProtocolNumber = header.IPv4ProtocolNumber
+	pkt.Data.CapLength(int(ipHdr.TotalLength()) - len(hdr))
+	return true
+}
+
+// IPv6 parses an IPv6 packet found in pkt.Data and populates pkt's network
+// header with the IPv6 header.
+func IPv6(pkt *stack.PacketBuffer) (proto tcpip.TransportProtocolNumber, fragID uint32, fragOffset uint16, fragMore bool, ok bool) {
+	hdr, ok := pkt.Data.PullUp(header.IPv6MinimumSize)
+	if !ok {
+		return 0, 0, 0, false, false
+	}
+	ipHdr := header.IPv6(hdr)
+
+	// dataClone consists of:
+	// - Any IPv6 header bytes after the first 40 (i.e. extensions).
+	// - The transport header, if present.
+	// - Any other payload data.
+	views := [8]buffer.View{}
+	dataClone := pkt.Data.Clone(views[:])
+	dataClone.TrimFront(header.IPv6MinimumSize)
+	it := header.MakeIPv6PayloadIterator(header.IPv6ExtensionHeaderIdentifier(ipHdr.NextHeader()), dataClone)
+
+	// Iterate over the IPv6 extensions to find their length.
+	var nextHdr tcpip.TransportProtocolNumber
+	var extensionsSize int
+
+traverseExtensions:
+	for {
+		extHdr, done, err := it.Next()
+		if err != nil {
+			break
+		}
+
+		// If we exhaust the extension list, the entire packet is the IPv6 header
+		// and (possibly) extensions.
+		if done {
+			extensionsSize = dataClone.Size()
+			break
+		}
+
+		switch extHdr := extHdr.(type) {
+		case header.IPv6FragmentExtHdr:
+			if fragID == 0 && fragOffset == 0 && !fragMore {
+				fragID = extHdr.ID()
+				fragOffset = extHdr.FragmentOffset()
+				fragMore = extHdr.More()
+			}
+
+		case header.IPv6RawPayloadHeader:
+			// We've found the payload after any extensions.
+			extensionsSize = dataClone.Size() - extHdr.Buf.Size()
+			nextHdr = tcpip.TransportProtocolNumber(extHdr.Identifier)
+			break traverseExtensions
+
+		default:
+			// Any other extension is a no-op, keep looping until we find the payload.
+		}
+	}
+
+	// Put the IPv6 header with extensions in pkt.NetworkHeader().
+	hdr, ok = pkt.NetworkHeader().Consume(header.IPv6MinimumSize + extensionsSize)
+	if !ok {
+		panic(fmt.Sprintf("pkt.Data should have at least %d bytes, but only has %d.", header.IPv6MinimumSize+extensionsSize, pkt.Data.Size()))
+	}
+	ipHdr = header.IPv6(hdr)
+	pkt.Data.CapLength(int(ipHdr.PayloadLength()))
+	pkt.NetworkProtocolNumber = header.IPv6ProtocolNumber
+
+	return nextHdr, fragID, fragOffset, fragMore, true
+}
+
+// UDP parses a UDP packet found in pkt.Data and populates pkt's transport
+// header with the UDP header.
+//
+// Returns true if the header was successfully parsed.
+func UDP(pkt *stack.PacketBuffer) bool {
+	_, ok := pkt.TransportHeader().Consume(header.UDPMinimumSize)
+	return ok
+}
+
+// TCP parses a TCP packet found in pkt.Data and populates pkt's transport
+// header with the TCP header.
+//
+// Returns true if the header was successfully parsed.
+func TCP(pkt *stack.PacketBuffer) bool {
+	// TCP header is variable length, peek at it first.
+	hdrLen := header.TCPMinimumSize
+	hdr, ok := pkt.Data.PullUp(hdrLen)
+	if !ok {
+		return false
+	}
+
+	// If the header has options, pull those up as well.
+	if offset := int(header.TCP(hdr).DataOffset()); offset > header.TCPMinimumSize && offset <= pkt.Data.Size() {
+		// TODO(gvisor.dev/issue/2404): Figure out whether to reject this kind of
+		// packets.
+		hdrLen = offset
+	}
+
+	_, ok = pkt.TransportHeader().Consume(hdrLen)
+	return ok
+}

pkg/tcpip/link/sniffer/BUILD

@@ -14,6 +14,7 @@ go_library(
         "//pkg/tcpip",
         "//pkg/tcpip/buffer",
         "//pkg/tcpip/header",
+        "//pkg/tcpip/header/parse",
         "//pkg/tcpip/link/nested",
         "//pkg/tcpip/stack",
     ],

pkg/tcpip/link/sniffer/sniffer.go

@@ -31,6 +31,7 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/header/parse"
 	"gvisor.dev/gvisor/pkg/tcpip/link/nested"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 )
@@ -195,49 +196,52 @@ func logPacket(prefix string, protocol tcpip.NetworkProtocolNumber, pkt *stack.P
 	var transProto uint8
 	src := tcpip.Address("unknown")
 	dst := tcpip.Address("unknown")
-	id := 0
+	var size uint16
-	size := uint16(0)
+	var id uint32
 	var fragmentOffset uint16
 	var moreFragments bool
 
-	// Examine the packet using a new VV. Backing storage must not be written.
+	// Clone the packet buffer to not modify the original.
-	vv := buffer.NewVectorisedView(pkt.Size(), pkt.Views())
+	//
-
+	// We don't clone the original packet buffer so that the new packet buffer
+	// does not have any of its headers set.
+	pkt = stack.NewPacketBuffer(stack.PacketBufferOptions{Data: buffer.NewVectorisedView(pkt.Size(), pkt.Views())})
 	switch protocol {
 	case header.IPv4ProtocolNumber:
-		hdr, ok := vv.PullUp(header.IPv4MinimumSize)
+		if ok := parse.IPv4(pkt); !ok {
-		if !ok {
 			return
 		}
-		ipv4 := header.IPv4(hdr)
+
+		ipv4 := header.IPv4(pkt.NetworkHeader().View())
 		fragmentOffset = ipv4.FragmentOffset()
 		moreFragments = ipv4.Flags()&header.IPv4FlagMoreFragments == header.IPv4FlagMoreFragments
 		src = ipv4.SourceAddress()
 		dst = ipv4.DestinationAddress()
 		transProto = ipv4.Protocol()
 		size = ipv4.TotalLength() - uint16(ipv4.HeaderLength())
-		vv.TrimFront(int(ipv4.HeaderLength()))
+		id = uint32(ipv4.ID())
-		id = int(ipv4.ID())
 
 	case header.IPv6ProtocolNumber:
-		hdr, ok := vv.PullUp(header.IPv6MinimumSize)
+		proto, fragID, fragOffset, fragMore, ok := parse.IPv6(pkt)
 		if !ok {
 			return
 		}
-		ipv6 := header.IPv6(hdr)
+
+		ipv6 := header.IPv6(pkt.NetworkHeader().View())
 		src = ipv6.SourceAddress()
 		dst = ipv6.DestinationAddress()
-		transProto = ipv6.NextHeader()
+		transProto = uint8(proto)
 		size = ipv6.PayloadLength()
-		vv.TrimFront(header.IPv6MinimumSize)
+		id = fragID
+		moreFragments = fragMore
+		fragmentOffset = fragOffset
 
 	case header.ARPProtocolNumber:
-		hdr, ok := vv.PullUp(header.ARPSize)
+		if parse.ARP(pkt) {
-		if !ok {
 			return
 		}
-		vv.TrimFront(header.ARPSize)
+
-		arp := header.ARP(hdr)
+		arp := header.ARP(pkt.NetworkHeader().View())
 		log.Infof(
 			"%s arp %s (%s) -> %s (%s) valid:%t",
 			prefix,
@@ -259,7 +263,7 @@ func logPacket(prefix string, protocol tcpip.NetworkProtocolNumber, pkt *stack.P
 	switch tcpip.TransportProtocolNumber(transProto) {
 	case header.ICMPv4ProtocolNumber:
 		transName = "icmp"
-		hdr, ok := vv.PullUp(header.ICMPv4MinimumSize)
+		hdr, ok := pkt.Data.PullUp(header.ICMPv4MinimumSize)
 		if !ok {
 			break
 		}
@@ -296,7 +300,7 @@ func logPacket(prefix string, protocol tcpip.NetworkProtocolNumber, pkt *stack.P
 
 	case header.ICMPv6ProtocolNumber:
 		transName = "icmp"
-		hdr, ok := vv.PullUp(header.ICMPv6MinimumSize)
+		hdr, ok := pkt.Data.PullUp(header.ICMPv6MinimumSize)
 		if !ok {
 			break
 		}
@@ -331,11 +335,11 @@ func logPacket(prefix string, protocol tcpip.NetworkProtocolNumber, pkt *stack.P
 
 	case header.UDPProtocolNumber:
 		transName = "udp"
-		hdr, ok := vv.PullUp(header.UDPMinimumSize)
+		if ok := parse.UDP(pkt); !ok {
-		if !ok {
 			break
 		}
-		udp := header.UDP(hdr)
+
+		udp := header.UDP(pkt.TransportHeader().View())
 		if fragmentOffset == 0 {
 			srcPort = udp.SourcePort()
 			dstPort = udp.DestinationPort()
@@ -345,19 +349,19 @@ func logPacket(prefix string, protocol tcpip.NetworkProtocolNumber, pkt *stack.P
 
 	case header.TCPProtocolNumber:
 		transName = "tcp"
-		hdr, ok := vv.PullUp(header.TCPMinimumSize)
+		if ok := parse.TCP(pkt); !ok {
-		if !ok {
 			break
 		}
-		tcp := header.TCP(hdr)
+
+		tcp := header.TCP(pkt.TransportHeader().View())
 		if fragmentOffset == 0 {
 			offset := int(tcp.DataOffset())
 			if offset < header.TCPMinimumSize {
 				details += fmt.Sprintf("invalid packet: tcp data offset too small %d", offset)
 				break
 			}
-			if offset > vv.Size() && !moreFragments {
+			if size := pkt.Data.Size() + len(tcp); offset > size && !moreFragments {
-				details += fmt.Sprintf("invalid packet: tcp data offset %d larger than packet buffer length %d", offset, vv.Size())
+				details += fmt.Sprintf("invalid packet: tcp data offset %d larger than tcp packet length %d", offset, size)
 				break
 			}
 

pkg/tcpip/network/arp/BUILD

@@ -10,6 +10,7 @@ go_library(
         "//pkg/tcpip",
         "//pkg/tcpip/buffer",
         "//pkg/tcpip/header",
+        "//pkg/tcpip/header/parse",
         "//pkg/tcpip/stack",
     ],
 )

pkg/tcpip/network/arp/arp.go

@@ -29,6 +29,7 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/header/parse"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 )
 
@@ -234,11 +235,7 @@ func (*protocol) Wait() {}
 
 // Parse implements stack.NetworkProtocol.Parse.
 func (*protocol) Parse(pkt *stack.PacketBuffer) (proto tcpip.TransportProtocolNumber, hasTransportHdr bool, ok bool) {
-	_, ok = pkt.NetworkHeader().Consume(header.ARPSize)
+	return 0, false, parse.ARP(pkt)
-	if !ok {
-		return 0, false, false
-	}
-	return 0, false, true
 }
 
 // NewProtocol returns an ARP network protocol.

pkg/tcpip/network/ipv4/BUILD

@@ -13,6 +13,7 @@ go_library(
         "//pkg/tcpip",
         "//pkg/tcpip/buffer",
         "//pkg/tcpip/header",
+        "//pkg/tcpip/header/parse",
         "//pkg/tcpip/network/fragmentation",
         "//pkg/tcpip/network/hash",
         "//pkg/tcpip/stack",

pkg/tcpip/network/ipv4/ipv4.go

@@ -26,6 +26,7 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/header/parse"
 	"gvisor.dev/gvisor/pkg/tcpip/network/fragmentation"
 	"gvisor.dev/gvisor/pkg/tcpip/network/hash"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
@@ -529,37 +530,14 @@ func (*protocol) Close() {}
 // Wait implements stack.TransportProtocol.Wait.
 func (*protocol) Wait() {}
 
-// Parse implements stack.TransportProtocol.Parse.
+// Parse implements stack.NetworkProtocol.Parse.
 func (*protocol) Parse(pkt *stack.PacketBuffer) (proto tcpip.TransportProtocolNumber, hasTransportHdr bool, ok bool) {
-	hdr, ok := pkt.Data.PullUp(header.IPv4MinimumSize)
+	if ok := parse.IPv4(pkt); !ok {
-	if !ok {
 		return 0, false, false
 	}
-	ipHdr := header.IPv4(hdr)
 
-	// Header may have options, determine the true header length.
+	ipHdr := header.IPv4(pkt.NetworkHeader().View())
-	headerLen := int(ipHdr.HeaderLength())
+	return ipHdr.TransportProtocol(), !ipHdr.More() && ipHdr.FragmentOffset() == 0, true
-	if headerLen < header.IPv4MinimumSize {
-		// TODO(gvisor.dev/issue/2404): Per RFC 791, IHL needs to be at least 5 in
-		// order for the packet to be valid. Figure out if we want to reject this
-		// case.
-		headerLen = header.IPv4MinimumSize
-	}
-	hdr, ok = pkt.NetworkHeader().Consume(headerLen)
-	if !ok {
-		return 0, false, false
-	}
-	ipHdr = header.IPv4(hdr)
-
-	// If this is a fragment, don't bother parsing the transport header.
-	parseTransportHeader := true
-	if ipHdr.More() || ipHdr.FragmentOffset() != 0 {
-		parseTransportHeader = false
-	}
-
-	pkt.NetworkProtocolNumber = header.IPv4ProtocolNumber
-	pkt.Data.CapLength(int(ipHdr.TotalLength()) - len(hdr))
-	return ipHdr.TransportProtocol(), parseTransportHeader, true
 }
 
 // calculateMTU calculates the network-layer payload MTU based on the link-layer

pkg/tcpip/network/ipv6/BUILD

@@ -13,6 +13,7 @@ go_library(
         "//pkg/tcpip",
         "//pkg/tcpip/buffer",
         "//pkg/tcpip/header",
+        "//pkg/tcpip/header/parse",
         "//pkg/tcpip/network/fragmentation",
         "//pkg/tcpip/stack",
     ],

pkg/tcpip/network/ipv6/ipv6.go

@@ -27,6 +27,7 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/header/parse"
 	"gvisor.dev/gvisor/pkg/tcpip/network/fragmentation"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 )
@@ -574,75 +575,14 @@ func (*protocol) Close() {}
 // Wait implements stack.TransportProtocol.Wait.
 func (*protocol) Wait() {}
 
-// Parse implements stack.TransportProtocol.Parse.
+// Parse implements stack.NetworkProtocol.Parse.
 func (*protocol) Parse(pkt *stack.PacketBuffer) (proto tcpip.TransportProtocolNumber, hasTransportHdr bool, ok bool) {
-	hdr, ok := pkt.Data.PullUp(header.IPv6MinimumSize)
+	proto, _, fragOffset, fragMore, ok := parse.IPv6(pkt)
 	if !ok {
 		return 0, false, false
 	}
-	ipHdr := header.IPv6(hdr)
 
-	// dataClone consists of:
+	return proto, !fragMore && fragOffset == 0, true
-	// - Any IPv6 header bytes after the first 40 (i.e. extensions).
-	// - The transport header, if present.
-	// - Any other payload data.
-	views := [8]buffer.View{}
-	dataClone := pkt.Data.Clone(views[:])
-	dataClone.TrimFront(header.IPv6MinimumSize)
-	it := header.MakeIPv6PayloadIterator(header.IPv6ExtensionHeaderIdentifier(ipHdr.NextHeader()), dataClone)
-
-	// Iterate over the IPv6 extensions to find their length.
-	//
-	// Parsing occurs again in HandlePacket because we don't track the
-	// extensions in PacketBuffer. Unfortunately, that means HandlePacket
-	// has to do the parsing work again.
-	var nextHdr tcpip.TransportProtocolNumber
-	foundNext := true
-	extensionsSize := 0
-traverseExtensions:
-	for extHdr, done, err := it.Next(); ; extHdr, done, err = it.Next() {
-		if err != nil {
-			break
-		}
-		// If we exhaust the extension list, the entire packet is the IPv6 header
-		// and (possibly) extensions.
-		if done {
-			extensionsSize = dataClone.Size()
-			foundNext = false
-			break
-		}
-
-		switch extHdr := extHdr.(type) {
-		case header.IPv6FragmentExtHdr:
-			// If this is an atomic fragment, we don't have to treat it specially.
-			if !extHdr.More() && extHdr.FragmentOffset() == 0 {
-				continue
-			}
-			// This is a non-atomic fragment and has to be re-assembled before we can
-			// examine the payload for a transport header.
-			foundNext = false
-
-		case header.IPv6RawPayloadHeader:
-			// We've found the payload after any extensions.
-			extensionsSize = dataClone.Size() - extHdr.Buf.Size()
-			nextHdr = tcpip.TransportProtocolNumber(extHdr.Identifier)
-			break traverseExtensions
-
-		default:
-			// Any other extension is a no-op, keep looping until we find the payload.
-		}
-	}
-
-	// Put the IPv6 header with extensions in pkt.NetworkHeader().
-	hdr, ok = pkt.NetworkHeader().Consume(header.IPv6MinimumSize + extensionsSize)
-	if !ok {
-		panic(fmt.Sprintf("pkt.Data should have at least %d bytes, but only has %d.", header.IPv6MinimumSize+extensionsSize, pkt.Data.Size()))
-	}
-	ipHdr = header.IPv6(hdr)
-	pkt.Data.CapLength(int(ipHdr.PayloadLength()))
-	pkt.NetworkProtocolNumber = header.IPv6ProtocolNumber
-
-	return nextHdr, foundNext, true
 }
 
 // calculateMTU calculates the network-layer payload MTU based on the link-layer

pkg/tcpip/transport/tcp/BUILD

@@ -69,6 +69,7 @@ go_library(
         "//pkg/tcpip/buffer",
         "//pkg/tcpip/hash/jenkins",
         "//pkg/tcpip/header",
+        "//pkg/tcpip/header/parse",
         "//pkg/tcpip/ports",
         "//pkg/tcpip/seqnum",
         "//pkg/tcpip/stack",

pkg/tcpip/transport/tcp/protocol.go

@@ -29,6 +29,7 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/header/parse"
 	"gvisor.dev/gvisor/pkg/tcpip/seqnum"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 	"gvisor.dev/gvisor/pkg/tcpip/transport/raw"
@@ -506,22 +507,7 @@ func (p *protocol) SynRcvdCounter() *synRcvdCounter {
 
 // Parse implements stack.TransportProtocol.Parse.
 func (*protocol) Parse(pkt *stack.PacketBuffer) bool {
-	// TCP header is variable length, peek at it first.
+	return parse.TCP(pkt)
-	hdrLen := header.TCPMinimumSize
-	hdr, ok := pkt.Data.PullUp(hdrLen)
-	if !ok {
-		return false
-	}
-
-	// If the header has options, pull those up as well.
-	if offset := int(header.TCP(hdr).DataOffset()); offset > header.TCPMinimumSize && offset <= pkt.Data.Size() {
-		// TODO(gvisor.dev/issue/2404): Figure out whether to reject this kind of
-		// packets.
-		hdrLen = offset
-	}
-
-	_, ok = pkt.TransportHeader().Consume(hdrLen)
-	return ok
 }
 
 // NewProtocol returns a TCP transport protocol.

pkg/tcpip/transport/udp/BUILD

@@ -32,6 +32,7 @@ go_library(
         "//pkg/tcpip",
         "//pkg/tcpip/buffer",
         "//pkg/tcpip/header",
+        "//pkg/tcpip/header/parse",
         "//pkg/tcpip/ports",
         "//pkg/tcpip/stack",
         "//pkg/tcpip/transport/raw",

pkg/tcpip/transport/udp/protocol.go

@@ -24,6 +24,7 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/header/parse"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 	"gvisor.dev/gvisor/pkg/tcpip/transport/raw"
 	"gvisor.dev/gvisor/pkg/waiter"
@@ -219,8 +220,7 @@ func (*protocol) Wait() {}
 
 // Parse implements stack.TransportProtocol.Parse.
 func (*protocol) Parse(pkt *stack.PacketBuffer) bool {
-	_, ok := pkt.TransportHeader().Consume(header.UDPMinimumSize)
+	return parse.UDP(pkt)
-	return ok
 }
 
 // NewProtocol returns a UDP transport protocol.