Implement /proc/net/udp.

PiperOrigin-RevId: 266229756

14 files changed, 633 insertions, 101 deletions

diff --git a/pkg/sentry/fs/proc/BUILD b/pkg/sentry/fs/proc/BUILD
index 70ed854a8..c7599d1f6 100644
--- a/pkg/sentry/fs/proc/BUILD
+++ b/pkg/sentry/fs/proc/BUILD
@@ -31,7 +31,6 @@ go_library(
     visibility = ["//pkg/sentry:internal"],
     deps = [
         "//pkg/abi/linux",
-        "//pkg/binary",
         "//pkg/log",
         "//pkg/sentry/context",
         "//pkg/sentry/fs",
diff --git a/pkg/sentry/fs/proc/net.go b/pkg/sentry/fs/proc/net.go
index 9adb23608..5e28982c5 100644
--- a/pkg/sentry/fs/proc/net.go
+++ b/pkg/sentry/fs/proc/net.go
@@ -17,10 +17,10 @@ package proc
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"time"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
-	"gvisor.dev/gvisor/pkg/binary"
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/sentry/context"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
@@ -28,9 +28,11 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/fs/ramfs"
 	"gvisor.dev/gvisor/pkg/sentry/inet"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/socket"
 	"gvisor.dev/gvisor/pkg/sentry/socket/unix"
 	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
+	"gvisor.dev/gvisor/pkg/sentry/usermem"
 )
 
 // newNet creates a new proc net entry.
@@ -57,9 +59,8 @@ func (p *proc) newNetDir(ctx context.Context, k *kernel.Kernel, msrc *fs.MountSo
 			"ptype":  newStaticProcInode(ctx, msrc, []byte("Type Device      Function")),
 			"route":  newStaticProcInode(ctx, msrc, []byte("Iface   Destination     Gateway         Flags   RefCnt  Use     Metric  Mask            MTU     Window  IRTT")),
 			"tcp":    seqfile.NewSeqFileInode(ctx, &netTCP{k: k}, msrc),
-			"udp":    newStaticProcInode(ctx, msrc, []byte("  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode ref pointer drops")),
-
-			"unix": seqfile.NewSeqFileInode(ctx, &netUnix{k: k}, msrc),
+			"udp":    seqfile.NewSeqFileInode(ctx, &netUDP{k: k}, msrc),
+			"unix":   seqfile.NewSeqFileInode(ctx, &netUnix{k: k}, msrc),
 		}
 
 		if s.SupportsIPv6() {
@@ -216,7 +217,7 @@ func (n *netUnix) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]s
 	for _, se := range n.k.ListSockets() {
 		s := se.Sock.Get()
 		if s == nil {
-			log.Debugf("Couldn't resolve weakref %v in socket table, racing with destruction?", se.Sock)
+			log.Debugf("Couldn't resolve weakref with ID %v in socket table, racing with destruction?", se.ID)
 			continue
 		}
 		sfile := s.(*fs.File)
@@ -297,6 +298,42 @@ func (n *netUnix) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]s
 	return data, 0
 }
 
+func networkToHost16(n uint16) uint16 {
+	// n is in network byte order, so is big-endian. The most-significant byte
+	// should be stored in the lower address.
+	//
+	// We manually inline binary.BigEndian.Uint16() because Go does not support
+	// non-primitive consts, so binary.BigEndian is a (mutable) var, so calls to
+	// binary.BigEndian.Uint16() require a read of binary.BigEndian and an
+	// interface method call, defeating inlining.
+	buf := [2]byte{byte(n >> 8 & 0xff), byte(n & 0xff)}
+	return usermem.ByteOrder.Uint16(buf[:])
+}
+
+func writeInetAddr(w io.Writer, a linux.SockAddrInet) {
+	// linux.SockAddrInet.Port is stored in the network byte order and is
+	// printed like a number in host byte order. Note that all numbers in host
+	// byte order are printed with the most-significant byte first when
+	// formatted with %X. See get_tcp4_sock() and udp4_format_sock() in Linux.
+	port := networkToHost16(a.Port)
+
+	// linux.SockAddrInet.Addr is stored as a byte slice in big-endian order
+	// (i.e. most-significant byte in index 0). Linux represents this as a
+	// __be32 which is a typedef for an unsigned int, and is printed with
+	// %X. This means that for a little-endian machine, Linux prints the
+	// least-significant byte of the address first. To emulate this, we first
+	// invert the byte order for the address using usermem.ByteOrder.Uint32,
+	// which makes it have the equivalent encoding to a __be32 on a little
+	// endian machine. Note that this operation is a no-op on a big endian
+	// machine. Then similar to Linux, we format it with %X, which will print
+	// the most-significant byte of the __be32 address first, which is now
+	// actually the least-significant byte of the original address in
+	// linux.SockAddrInet.Addr on little endian machines, due to the conversion.
+	addr := usermem.ByteOrder.Uint32(a.Addr[:])
+
+	fmt.Fprintf(w, "%08X:%04X ", addr, port)
+}
+
 // netTCP implements seqfile.SeqSource for /proc/net/tcp.
 //
 // +stateify savable
@@ -311,6 +348,9 @@ func (*netTCP) NeedsUpdate(generation int64) bool {
 
 // ReadSeqFileData implements seqfile.SeqSource.ReadSeqFileData.
 func (n *netTCP) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]seqfile.SeqData, int64) {
+	// t may be nil here if our caller is not part of a task goroutine. This can
+	// happen for example if we're here for "sentryctl cat". When t is nil,
+	// degrade gracefully and retrieve what we can.
 	t := kernel.TaskFromContext(ctx)
 
 	if h != nil {
@@ -321,7 +361,7 @@ func (n *netTCP) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]se
 	for _, se := range n.k.ListSockets() {
 		s := se.Sock.Get()
 		if s == nil {
-			log.Debugf("Couldn't resolve weakref %+v in socket table, racing with destruction?", se.Sock)
+			log.Debugf("Couldn't resolve weakref with ID %v in socket table, racing with destruction?", se.ID)
 			continue
 		}
 		sfile := s.(*fs.File)
@@ -343,27 +383,23 @@ func (n *netTCP) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]se
 		// Field: sl; entry number.
 		fmt.Fprintf(&buf, "%4d: ", se.ID)
 
-		portBuf := make([]byte, 2)
-
 		// Field: local_adddress.
 		var localAddr linux.SockAddrInet
-		if local, _, err := sops.GetSockName(t); err == nil {
-			localAddr = *local.(*linux.SockAddrInet)
+		if t != nil {
+			if local, _, err := sops.GetSockName(t); err == nil {
+				localAddr = *local.(*linux.SockAddrInet)
+			}
 		}
-		binary.LittleEndian.PutUint16(portBuf, localAddr.Port)
-		fmt.Fprintf(&buf, "%08X:%04X ",
-			binary.LittleEndian.Uint32(localAddr.Addr[:]),
-			portBuf)
+		writeInetAddr(&buf, localAddr)
 
 		// Field: rem_address.
 		var remoteAddr linux.SockAddrInet
-		if remote, _, err := sops.GetPeerName(t); err == nil {
-			remoteAddr = *remote.(*linux.SockAddrInet)
+		if t != nil {
+			if remote, _, err := sops.GetPeerName(t); err == nil {
+				remoteAddr = *remote.(*linux.SockAddrInet)
+			}
 		}
-		binary.LittleEndian.PutUint16(portBuf, remoteAddr.Port)
-		fmt.Fprintf(&buf, "%08X:%04X ",
-			binary.LittleEndian.Uint32(remoteAddr.Addr[:]),
-			portBuf)
+		writeInetAddr(&buf, remoteAddr)
 
 		// Field: state; socket state.
 		fmt.Fprintf(&buf, "%02X ", sops.State())
@@ -386,7 +422,8 @@ func (n *netTCP) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]se
 			log.Warningf("Failed to retrieve unstable attr for socket file: %v", err)
 			fmt.Fprintf(&buf, "%5d ", 0)
 		} else {
-			fmt.Fprintf(&buf, "%5d ", uint32(uattr.Owner.UID.In(t.UserNamespace()).OrOverflow()))
+			creds := auth.CredentialsFromContext(ctx)
+			fmt.Fprintf(&buf, "%5d ", uint32(uattr.Owner.UID.In(creds.UserNamespace).OrOverflow()))
 		}
 
 		// Field: timeout; number of unanswered 0-window probes.
@@ -438,3 +475,125 @@ func (n *netTCP) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]se
 	}
 	return data, 0
 }
+
+// netUDP implements seqfile.SeqSource for /proc/net/udp.
+//
+// +stateify savable
+type netUDP struct {
+	k *kernel.Kernel
+}
+
+// NeedsUpdate implements seqfile.SeqSource.NeedsUpdate.
+func (*netUDP) NeedsUpdate(generation int64) bool {
+	return true
+}
+
+// ReadSeqFileData implements seqfile.SeqSource.ReadSeqFileData.
+func (n *netUDP) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]seqfile.SeqData, int64) {
+	// t may be nil here if our caller is not part of a task goroutine. This can
+	// happen for example if we're here for "sentryctl cat". When t is nil,
+	// degrade gracefully and retrieve what we can.
+	t := kernel.TaskFromContext(ctx)
+
+	if h != nil {
+		return nil, 0
+	}
+
+	var buf bytes.Buffer
+	for _, se := range n.k.ListSockets() {
+		s := se.Sock.Get()
+		if s == nil {
+			log.Debugf("Couldn't resolve weakref with ID %v in socket table, racing with destruction?", se.ID)
+			continue
+		}
+		sfile := s.(*fs.File)
+		sops, ok := sfile.FileOperations.(socket.Socket)
+		if !ok {
+			panic(fmt.Sprintf("Found non-socket file in socket table: %+v", sfile))
+		}
+		if family, stype, _ := sops.Type(); family != linux.AF_INET || stype != linux.SOCK_DGRAM {
+			s.DecRef()
+			// Not udp4 socket.
+			continue
+		}
+
+		// For Linux's implementation, see net/ipv4/udp.c:udp4_format_sock().
+
+		// Field: sl; entry number.
+		fmt.Fprintf(&buf, "%5d: ", se.ID)
+
+		// Field: local_adddress.
+		var localAddr linux.SockAddrInet
+		if t != nil {
+			if local, _, err := sops.GetSockName(t); err == nil {
+				localAddr = *local.(*linux.SockAddrInet)
+			}
+		}
+		writeInetAddr(&buf, localAddr)
+
+		// Field: rem_address.
+		var remoteAddr linux.SockAddrInet
+		if t != nil {
+			if remote, _, err := sops.GetPeerName(t); err == nil {
+				remoteAddr = *remote.(*linux.SockAddrInet)
+			}
+		}
+		writeInetAddr(&buf, remoteAddr)
+
+		// Field: state; socket state.
+		fmt.Fprintf(&buf, "%02X ", sops.State())
+
+		// Field: tx_queue, rx_queue; number of packets in the transmit and
+		// receive queue. Unimplemented.
+		fmt.Fprintf(&buf, "%08X:%08X ", 0, 0)
+
+		// Field: tr, tm->when. Always 0 for UDP.
+		fmt.Fprintf(&buf, "%02X:%08X ", 0, 0)
+
+		// Field: retrnsmt. Always 0 for UDP.
+		fmt.Fprintf(&buf, "%08X ", 0)
+
+		// Field: uid.
+		uattr, err := sfile.Dirent.Inode.UnstableAttr(ctx)
+		if err != nil {
+			log.Warningf("Failed to retrieve unstable attr for socket file: %v", err)
+			fmt.Fprintf(&buf, "%5d ", 0)
+		} else {
+			creds := auth.CredentialsFromContext(ctx)
+			fmt.Fprintf(&buf, "%5d ", uint32(uattr.Owner.UID.In(creds.UserNamespace).OrOverflow()))
+		}
+
+		// Field: timeout. Always 0 for UDP.
+		fmt.Fprintf(&buf, "%8d ", 0)
+
+		// Field: inode.
+		fmt.Fprintf(&buf, "%8d ", sfile.InodeID())
+
+		// Field: ref; reference count on the socket inode. Don't count the ref
+		// we obtain while deferencing the weakref to this socket.
+		fmt.Fprintf(&buf, "%d ", sfile.ReadRefs()-1)
+
+		// Field: Socket struct address. Redacted due to the same reason as
+		// the 'Num' field in /proc/net/unix, see netUnix.ReadSeqFileData.
+		fmt.Fprintf(&buf, "%#016p ", (*socket.Socket)(nil))
+
+		// Field: drops; number of dropped packets. Unimplemented.
+		fmt.Fprintf(&buf, "%d", 0)
+
+		fmt.Fprintf(&buf, "\n")
+
+		s.DecRef()
+	}
+
+	data := []seqfile.SeqData{
+		{
+			Buf:    []byte("  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode ref pointer drops             \n"),
+			Handle: n,
+		},
+		{
+			Buf:    buf.Bytes(),
+			Handle: n,
+		},
+	}
+	return data, 0
+}
diff --git a/pkg/sentry/socket/epsocket/epsocket.go b/pkg/sentry/socket/epsocket/epsocket.go
index 635042263..def29646e 100644
--- a/pkg/sentry/socket/epsocket/epsocket.go
+++ b/pkg/sentry/socket/epsocket/epsocket.go
@@ -27,12 +27,14 @@ package epsocket
 import (
 	"bytes"
 	"math"
+	"reflect"
 	"sync"
 	"syscall"
 	"time"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/binary"
+	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/metric"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/context"
@@ -52,6 +54,7 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 	"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
+	"gvisor.dev/gvisor/pkg/tcpip/transport/udp"
 	"gvisor.dev/gvisor/pkg/waiter"
 )
 
@@ -2421,7 +2424,8 @@ func (s *SocketOperations) State() uint32 {
 		return 0
 	}
 
-	if !s.isPacketBased() {
+	switch {
+	case s.skType == linux.SOCK_STREAM && s.protocol == 0 || s.protocol == syscall.IPPROTO_TCP:
 		// TCP socket.
 		switch tcp.EndpointState(s.Endpoint.State()) {
 		case tcp.StateEstablished:
@@ -2450,9 +2454,26 @@ func (s *SocketOperations) State() uint32 {
 			// Internal or unknown state.
 			return 0
 		}
+	case s.skType == linux.SOCK_DGRAM && s.protocol == 0 || s.protocol == syscall.IPPROTO_UDP:
+		// UDP socket.
+		switch udp.EndpointState(s.Endpoint.State()) {
+		case udp.StateInitial, udp.StateBound, udp.StateClosed:
+			return linux.TCP_CLOSE
+		case udp.StateConnected:
+			return linux.TCP_ESTABLISHED
+		default:
+			return 0
+		}
+	case s.skType == linux.SOCK_DGRAM && s.protocol == syscall.IPPROTO_ICMP || s.protocol == syscall.IPPROTO_ICMPV6:
+		// TODO(b/112063468): Export states for ICMP sockets.
+	case s.skType == linux.SOCK_RAW:
+		// TODO(b/112063468): Export states for raw sockets.
+	default:
+		// Unknown transport protocol, how did we make this socket?
+		log.Warningf("Unknown transport protocol for an existing socket: family=%v, type=%v, protocol=%v, internal type %v", s.family, s.skType, s.protocol, reflect.TypeOf(s.Endpoint).Elem())
+		return 0
 	}
 
-	// TODO(b/112063468): Export states for UDP, ICMP, and raw sockets.
 	return 0
 }
 
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index ac5905772..66455ef46 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -37,13 +37,17 @@ type udpPacket struct {
 	views [8]buffer.View `state:"nosave"`
 }
 
-type endpointState int
+// EndpointState represents the state of a UDP endpoint.
+type EndpointState uint32
 
+// Endpoint states. Note that are represented in a netstack-specific manner and
+// may not be meaningful externally. Specifically, they need to be translated to
+// Linux's representation for these states if presented to userspace.
 const (
-	stateInitial endpointState = iota
-	stateBound
-	stateConnected
-	stateClosed
+	StateInitial EndpointState = iota
+	StateBound
+	StateConnected
+	StateClosed
 )
 
 // endpoint represents a UDP endpoint. This struct serves as the interface
@@ -74,7 +78,7 @@ type endpoint struct {
 	mu             sync.RWMutex `state:"nosave"`
 	sndBufSize     int
 	id             stack.TransportEndpointID
-	state          endpointState
+	state          EndpointState
 	bindNICID      tcpip.NICID
 	regNICID       tcpip.NICID
 	route          stack.Route `state:"manual"`
@@ -140,7 +144,7 @@ func (e *endpoint) Close() {
 	e.shutdownFlags = tcpip.ShutdownRead | tcpip.ShutdownWrite
 
 	switch e.state {
-	case stateBound, stateConnected:
+	case StateBound, StateConnected:
 		e.stack.UnregisterTransportEndpoint(e.regNICID, e.effectiveNetProtos, ProtocolNumber, e.id, e)
 		e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, e.id.LocalAddress, e.id.LocalPort)
 	}
@@ -163,7 +167,7 @@ func (e *endpoint) Close() {
 	e.route.Release()
 
 	// Update the state.
-	e.state = stateClosed
+	e.state = StateClosed
 
 	e.mu.Unlock()
 
@@ -211,11 +215,11 @@ func (e *endpoint) Read(addr *tcpip.FullAddress) (buffer.View, tcpip.ControlMess
 // Returns true for retry if preparation should be retried.
 func (e *endpoint) prepareForWrite(to *tcpip.FullAddress) (retry bool, err *tcpip.Error) {
 	switch e.state {
-	case stateInitial:
-	case stateConnected:
+	case StateInitial:
+	case StateConnected:
 		return false, nil
 
-	case stateBound:
+	case StateBound:
 		if to == nil {
 			return false, tcpip.ErrDestinationRequired
 		}
@@ -232,7 +236,7 @@ func (e *endpoint) prepareForWrite(to *tcpip.FullAddress) (retry bool, err *tcpi
 
 	// The state changed when we released the shared locked and re-acquired
 	// it in exclusive mode. Try again.
-	if e.state != stateInitial {
+	if e.state != StateInitial {
 		return true, nil
 	}
 
@@ -322,7 +326,7 @@ func (e *endpoint) Write(p tcpip.Payload, opts tcpip.WriteOptions) (int64, <-cha
 			defer e.mu.Unlock()
 
 			// Recheck state after lock was re-acquired.
-			if e.state != stateConnected {
+			if e.state != StateConnected {
 				return 0, nil, tcpip.ErrInvalidEndpointState
 			}
 		}
@@ -400,7 +404,7 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 		defer e.mu.Unlock()
 
 		// We only allow this to be set when we're in the initial state.
-		if e.state != stateInitial {
+		if e.state != StateInitial {
 			return tcpip.ErrInvalidEndpointState
 		}
 
@@ -726,7 +730,7 @@ func (e *endpoint) Disconnect() *tcpip.Error {
 	e.mu.Lock()
 	defer e.mu.Unlock()
 
-	if e.state != stateConnected {
+	if e.state != StateConnected {
 		return nil
 	}
 	id := stack.TransportEndpointID{}
@@ -741,9 +745,9 @@ func (e *endpoint) Disconnect() *tcpip.Error {
 		if err != nil {
 			return err
 		}
-		e.state = stateBound
+		e.state = StateBound
 	} else {
-		e.state = stateInitial
+		e.state = StateInitial
 	}
 
 	e.stack.UnregisterTransportEndpoint(e.regNICID, e.effectiveNetProtos, ProtocolNumber, e.id, e)
@@ -772,8 +776,8 @@ func (e *endpoint) Connect(addr tcpip.FullAddress) *tcpip.Error {
 	nicid := addr.NIC
 	var localPort uint16
 	switch e.state {
-	case stateInitial:
-	case stateBound, stateConnected:
+	case StateInitial:
+	case StateBound, StateConnected:
 		localPort = e.id.LocalPort
 		if e.bindNICID == 0 {
 			break
@@ -801,7 +805,7 @@ func (e *endpoint) Connect(addr tcpip.FullAddress) *tcpip.Error {
 		RemoteAddress: r.RemoteAddress,
 	}
 
-	if e.state == stateInitial {
+	if e.state == StateInitial {
 		id.LocalAddress = r.LocalAddress
 	}
 
@@ -832,7 +836,7 @@ func (e *endpoint) Connect(addr tcpip.FullAddress) *tcpip.Error {
 	e.regNICID = nicid
 	e.effectiveNetProtos = netProtos
 
-	e.state = stateConnected
+	e.state = StateConnected
 
 	e.rcvMu.Lock()
 	e.rcvReady = true
@@ -854,7 +858,7 @@ func (e *endpoint) Shutdown(flags tcpip.ShutdownFlags) *tcpip.Error {
 
 	// A socket in the bound state can still receive multicast messages,
 	// so we need to notify waiters on shutdown.
-	if e.state != stateBound && e.state != stateConnected {
+	if e.state != StateBound && e.state != StateConnected {
 		return tcpip.ErrNotConnected
 	}
 
@@ -903,7 +907,7 @@ func (e *endpoint) registerWithStack(nicid tcpip.NICID, netProtos []tcpip.Networ
 func (e *endpoint) bindLocked(addr tcpip.FullAddress) *tcpip.Error {
 	// Don't allow binding once endpoint is not in the initial state
 	// anymore.
-	if e.state != stateInitial {
+	if e.state != StateInitial {
 		return tcpip.ErrInvalidEndpointState
 	}
 
@@ -946,7 +950,7 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) *tcpip.Error {
 	e.effectiveNetProtos = netProtos
 
 	// Mark endpoint as bound.
-	e.state = stateBound
+	e.state = StateBound
 
 	e.rcvMu.Lock()
 	e.rcvReady = true
@@ -989,7 +993,7 @@ func (e *endpoint) GetRemoteAddress() (tcpip.FullAddress, *tcpip.Error) {
 	e.mu.RLock()
 	defer e.mu.RUnlock()
 
-	if e.state != stateConnected {
+	if e.state != StateConnected {
 		return tcpip.FullAddress{}, tcpip.ErrNotConnected
 	}
 
@@ -1069,10 +1073,11 @@ func (e *endpoint) HandlePacket(r *stack.Route, id stack.TransportEndpointID, vv
 func (e *endpoint) HandleControlPacket(id stack.TransportEndpointID, typ stack.ControlType, extra uint32, vv buffer.VectorisedView) {
 }
 
-// State implements socket.Socket.State.
+// State implements tcpip.Endpoint.State.
 func (e *endpoint) State() uint32 {
-	// TODO(b/112063468): Translate internal state to values returned by Linux.
-	return 0
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	return uint32(e.state)
 }
 
 func isBroadcastOrMulticast(a tcpip.Address) bool {
diff --git a/pkg/tcpip/transport/udp/endpoint_state.go b/pkg/tcpip/transport/udp/endpoint_state.go
index 5cbb56120..be46e6d4e 100644
--- a/pkg/tcpip/transport/udp/endpoint_state.go
+++ b/pkg/tcpip/transport/udp/endpoint_state.go
@@ -77,7 +77,7 @@ func (e *endpoint) Resume(s *stack.Stack) {
 		}
 	}
 
-	if e.state != stateBound && e.state != stateConnected {
+	if e.state != StateBound && e.state != StateConnected {
 		return
 	}
 
@@ -92,7 +92,7 @@ func (e *endpoint) Resume(s *stack.Stack) {
 	}
 
 	var err *tcpip.Error
-	if e.state == stateConnected {
+	if e.state == StateConnected {
 		e.route, err = e.stack.FindRoute(e.regNICID, e.id.LocalAddress, e.id.RemoteAddress, netProto, e.multicastLoop)
 		if err != nil {
 			panic(err)
diff --git a/pkg/tcpip/transport/udp/forwarder.go b/pkg/tcpip/transport/udp/forwarder.go
index a874fc9fd..a9edc2c8d 100644
--- a/pkg/tcpip/transport/udp/forwarder.go
+++ b/pkg/tcpip/transport/udp/forwarder.go
@@ -84,7 +84,7 @@ func (r *ForwarderRequest) CreateEndpoint(queue *waiter.Queue) (tcpip.Endpoint,
 	ep.dstPort = r.id.RemotePort
 	ep.regNICID = r.route.NICID()
 
-	ep.state = stateConnected
+	ep.state = StateConnected
 
 	ep.rcvMu.Lock()
 	ep.rcvReady = true
diff --git a/test/syscalls/BUILD b/test/syscalls/BUILD
index ccae4925f..6947ddc25 100644
--- a/test/syscalls/BUILD
+++ b/test/syscalls/BUILD
@@ -691,6 +691,10 @@ syscall_test(
 
 syscall_test(test = "//test/syscalls/linux:proc_net_unix_test")
 
+syscall_test(test = "//test/syscalls/linux:proc_net_tcp_test")
+
+syscall_test(test = "//test/syscalls/linux:proc_net_udp_test")
+
 go_binary(
     name = "syscall_test_runner",
     srcs = ["syscall_test_runner.go"],
diff --git a/test/syscalls/linux/BUILD b/test/syscalls/linux/BUILD
index 88f3bfcb3..1ce38c929 100644
--- a/test/syscalls/linux/BUILD
+++ b/test/syscalls/linux/BUILD
@@ -3472,3 +3472,18 @@ cc_binary(
         "@com_google_googletest//:gtest",
     ],
 )
+
+cc_binary(
+    name = "proc_net_udp_test",
+    testonly = 1,
+    srcs = ["proc_net_udp.cc"],
+    linkstatic = 1,
+    deps = [
+        ":ip_socket_test_util",
+        "//test/util:file_descriptor",
+        "//test/util:test_main",
+        "//test/util:test_util",
+        "@com_google_absl//absl/strings",
+        "@com_google_googletest//:gtest",
+    ],
+)
diff --git a/test/syscalls/linux/ip_socket_test_util.cc b/test/syscalls/linux/ip_socket_test_util.cc
index c73262e72..410b42a47 100644
--- a/test/syscalls/linux/ip_socket_test_util.cc
+++ b/test/syscalls/linux/ip_socket_test_util.cc
@@ -23,6 +23,16 @@
 namespace gvisor {
 namespace testing {
 
+uint32_t IPFromInetSockaddr(const struct sockaddr* addr) {
+  auto* in_addr = reinterpret_cast<const struct sockaddr_in*>(addr);
+  return in_addr->sin_addr.s_addr;
+}
+
+uint16_t PortFromInetSockaddr(const struct sockaddr* addr) {
+  auto* in_addr = reinterpret_cast<const struct sockaddr_in*>(addr);
+  return ntohs(in_addr->sin_port);
+}
+
 PosixErrorOr<int> InterfaceIndex(std::string name) {
   // TODO(igudger): Consider using netlink.
   ifreq req = {};
diff --git a/test/syscalls/linux/ip_socket_test_util.h b/test/syscalls/linux/ip_socket_test_util.h
index b498a053d..3d36b9620 100644
--- a/test/syscalls/linux/ip_socket_test_util.h
+++ b/test/syscalls/linux/ip_socket_test_util.h
@@ -26,6 +26,31 @@
 namespace gvisor {
 namespace testing {
 
+// Possible values of the "st" field in a /proc/net/{tcp,udp} entry. Source:
+// Linux kernel, include/net/tcp_states.h.
+enum {
+  TCP_ESTABLISHED = 1,
+  TCP_SYN_SENT,
+  TCP_SYN_RECV,
+  TCP_FIN_WAIT1,
+  TCP_FIN_WAIT2,
+  TCP_TIME_WAIT,
+  TCP_CLOSE,
+  TCP_CLOSE_WAIT,
+  TCP_LAST_ACK,
+  TCP_LISTEN,
+  TCP_CLOSING,
+  TCP_NEW_SYN_RECV,
+
+  TCP_MAX_STATES
+};
+
+// Extracts the IP address from an inet sockaddr in network byte order.
+uint32_t IPFromInetSockaddr(const struct sockaddr* addr);
+
+// Extracts the port from an inet sockaddr in host byte order.
+uint16_t PortFromInetSockaddr(const struct sockaddr* addr);
+
 // InterfaceIndex returns the index of the named interface.
 PosixErrorOr<int> InterfaceIndex(std::string name);
 
diff --git a/test/syscalls/linux/proc_net_tcp.cc b/test/syscalls/linux/proc_net_tcp.cc
index 498f62d9c..f6d7ad0bb 100644
--- a/test/syscalls/linux/proc_net_tcp.cc
+++ b/test/syscalls/linux/proc_net_tcp.cc
@@ -38,25 +38,6 @@ constexpr char kProcNetTCPHeader[] =
     "retrnsmt   uid  timeout inode                                             "
     "        ";
 
-// Possible values of the "st" field in a /proc/net/tcp entry. Source: Linux
-// kernel, include/net/tcp_states.h.
-enum {
-  TCP_ESTABLISHED = 1,
-  TCP_SYN_SENT,
-  TCP_SYN_RECV,
-  TCP_FIN_WAIT1,
-  TCP_FIN_WAIT2,
-  TCP_TIME_WAIT,
-  TCP_CLOSE,
-  TCP_CLOSE_WAIT,
-  TCP_LAST_ACK,
-  TCP_LISTEN,
-  TCP_CLOSING,
-  TCP_NEW_SYN_RECV,
-
-  TCP_MAX_STATES
-};
-
 // TCPEntry represents a single entry from /proc/net/tcp.
 struct TCPEntry {
   uint32_t local_addr;
@@ -70,42 +51,35 @@ struct TCPEntry {
   uint64_t inode;
 };
 
-uint32_t IP(const struct sockaddr* addr) {
-  auto* in_addr = reinterpret_cast<const struct sockaddr_in*>(addr);
-  return in_addr->sin_addr.s_addr;
-}
-
-uint16_t Port(const struct sockaddr* addr) {
-  auto* in_addr = reinterpret_cast<const struct sockaddr_in*>(addr);
-  return ntohs(in_addr->sin_port);
-}
-
 // Finds the first entry in 'entries' for which 'predicate' returns true.
-// Returns true on match, and sets 'match' to point to the matching entry.
-bool FindBy(std::vector<TCPEntry> entries, TCPEntry* match,
+// Returns true on match, and sets 'match' to a copy of the matching entry. If
+// 'match' is null, it's ignored.
+bool FindBy(const std::vector<TCPEntry>& entries, TCPEntry* match,
             std::function<bool(const TCPEntry&)> predicate) {
-  for (int i = 0; i < entries.size(); ++i) {
-    if (predicate(entries[i])) {
-      *match = entries[i];
+  for (const TCPEntry& entry : entries) {
+    if (predicate(entry)) {
+      if (match != nullptr) {
+        *match = entry;
+      }
       return true;
     }
   }
   return false;
 }
 
-bool FindByLocalAddr(std::vector<TCPEntry> entries, TCPEntry* match,
+bool FindByLocalAddr(const std::vector<TCPEntry>& entries, TCPEntry* match,
                      const struct sockaddr* addr) {
-  uint32_t host = IP(addr);
-  uint16_t port = Port(addr);
+  uint32_t host = IPFromInetSockaddr(addr);
+  uint16_t port = PortFromInetSockaddr(addr);
   return FindBy(entries, match, [host, port](const TCPEntry& e) {
     return (e.local_addr == host && e.local_port == port);
   });
 }
 
-bool FindByRemoteAddr(std::vector<TCPEntry> entries, TCPEntry* match,
+bool FindByRemoteAddr(const std::vector<TCPEntry>& entries, TCPEntry* match,
                       const struct sockaddr* addr) {
-  uint32_t host = IP(addr);
-  uint16_t port = Port(addr);
+  uint32_t host = IPFromInetSockaddr(addr);
+  uint16_t port = PortFromInetSockaddr(addr);
   return FindBy(entries, match, [host, port](const TCPEntry& e) {
     return (e.remote_addr == host && e.remote_port == port);
   });
@@ -120,7 +94,7 @@ PosixErrorOr<std::vector<TCPEntry>> ProcNetTCPEntries() {
   std::vector<TCPEntry> entries;
   std::vector<std::string> lines = StrSplit(content, '\n');
   std::cerr << "<contents of /proc/net/tcp>" << std::endl;
-  for (std::string line : lines) {
+  for (const std::string& line : lines) {
     std::cerr << line << std::endl;
 
     if (!found_header) {
@@ -204,9 +178,8 @@ TEST(ProcNetTCP, BindAcceptConnect) {
     EXPECT_EQ(entries.size(), 2);
   }
 
-  TCPEntry e;
-  EXPECT_TRUE(FindByLocalAddr(entries, &e, sockets->first_addr()));
-  EXPECT_TRUE(FindByRemoteAddr(entries, &e, sockets->first_addr()));
+  EXPECT_TRUE(FindByLocalAddr(entries, nullptr, sockets->first_addr()));
+  EXPECT_TRUE(FindByRemoteAddr(entries, nullptr, sockets->first_addr()));
 }
 
 TEST(ProcNetTCP, InodeReasonable) {
@@ -261,8 +234,8 @@ TEST(ProcNetTCP, State) {
   FileDescriptor accepted =
       ASSERT_NO_ERRNO_AND_VALUE(Accept(server->get(), nullptr, nullptr));
 
-  const uint32_t accepted_local_host = IP(&addr);
-  const uint16_t accepted_local_port = Port(&addr);
+  const uint32_t accepted_local_host = IPFromInetSockaddr(&addr);
+  const uint16_t accepted_local_port = PortFromInetSockaddr(&addr);
 
   entries = ASSERT_NO_ERRNO_AND_VALUE(ProcNetTCPEntries());
   TCPEntry accepted_entry;
diff --git a/test/syscalls/linux/proc_net_udp.cc b/test/syscalls/linux/proc_net_udp.cc
new file mode 100644
index 000000000..369df8e0e
--- /dev/null
+++ b/test/syscalls/linux/proc_net_udp.cc
@@ -0,0 +1,309 @@
+// Copyright 2019 Google LLC
+//
+// 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.
+
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "gtest/gtest.h"
+#include "gtest/gtest.h"
+#include "absl/strings/numbers.h"
+#include "absl/strings/str_join.h"
+#include "absl/strings/str_split.h"
+#include "test/syscalls/linux/ip_socket_test_util.h"
+#include "test/util/file_descriptor.h"
+#include "test/util/test_util.h"
+
+namespace gvisor {
+namespace testing {
+namespace {
+
+using absl::StrCat;
+using absl::StrFormat;
+using absl::StrSplit;
+
+constexpr char kProcNetUDPHeader[] =
+    "  sl  local_address rem_address   st tx_queue rx_queue tr tm->when "
+    "retrnsmt   uid  timeout inode ref pointer drops             ";
+
+// UDPEntry represents a single entry from /proc/net/udp.
+struct UDPEntry {
+  uint32_t local_addr;
+  uint16_t local_port;
+
+  uint32_t remote_addr;
+  uint16_t remote_port;
+
+  uint64_t state;
+  uint64_t uid;
+  uint64_t inode;
+};
+
+std::string DescribeFirstInetSocket(const SocketPair& sockets) {
+  const struct sockaddr* addr = sockets.first_addr();
+  return StrFormat("First test socket: fd:%d %8X:%4X", sockets.first_fd(),
+                   IPFromInetSockaddr(addr), PortFromInetSockaddr(addr));
+}
+
+std::string DescribeSecondInetSocket(const SocketPair& sockets) {
+  const struct sockaddr* addr = sockets.second_addr();
+  return StrFormat("Second test socket fd:%d %8X:%4X", sockets.second_fd(),
+                   IPFromInetSockaddr(addr), PortFromInetSockaddr(addr));
+}
+
+// Finds the first entry in 'entries' for which 'predicate' returns true.
+// Returns true on match, and set 'match' to a copy of the matching entry. If
+// 'match' is null, it's ignored.
+bool FindBy(const std::vector<UDPEntry>& entries, UDPEntry* match,
+            std::function<bool(const UDPEntry&)> predicate) {
+  for (const UDPEntry& entry : entries) {
+    if (predicate(entry)) {
+      if (match != nullptr) {
+        *match = entry;
+      }
+      return true;
+    }
+  }
+  return false;
+}
+
+bool FindByLocalAddr(const std::vector<UDPEntry>& entries, UDPEntry* match,
+                     const struct sockaddr* addr) {
+  uint32_t host = IPFromInetSockaddr(addr);
+  uint16_t port = PortFromInetSockaddr(addr);
+  return FindBy(entries, match, [host, port](const UDPEntry& e) {
+    return (e.local_addr == host && e.local_port == port);
+  });
+}
+
+bool FindByRemoteAddr(const std::vector<UDPEntry>& entries, UDPEntry* match,
+                      const struct sockaddr* addr) {
+  uint32_t host = IPFromInetSockaddr(addr);
+  uint16_t port = PortFromInetSockaddr(addr);
+  return FindBy(entries, match, [host, port](const UDPEntry& e) {
+    return (e.remote_addr == host && e.remote_port == port);
+  });
+}
+
+PosixErrorOr<uint64_t> InodeFromSocketFD(int fd) {
+  ASSIGN_OR_RETURN_ERRNO(struct stat s, Fstat(fd));
+  if (!S_ISSOCK(s.st_mode)) {
+    return PosixError(EINVAL, StrFormat("FD %d is not a socket", fd));
+  }
+  return s.st_ino;
+}
+
+PosixErrorOr<bool> FindByFD(const std::vector<UDPEntry>& entries,
+                            UDPEntry* match, int fd) {
+  ASSIGN_OR_RETURN_ERRNO(uint64_t inode, InodeFromSocketFD(fd));
+  return FindBy(entries, match,
+                [inode](const UDPEntry& e) { return (e.inode == inode); });
+}
+
+// Returns a parsed representation of /proc/net/udp entries.
+PosixErrorOr<std::vector<UDPEntry>> ProcNetUDPEntries() {
+  std::string content;
+  RETURN_IF_ERRNO(GetContents("/proc/net/udp", &content));
+
+  bool found_header = false;
+  std::vector<UDPEntry> entries;
+  std::vector<std::string> lines = StrSplit(content, '\n');
+  std::cerr << "<contents of /proc/net/udp>" << std::endl;
+  for (const std::string& line : lines) {
+    std::cerr << line << std::endl;
+
+    if (!found_header) {
+      EXPECT_EQ(line, kProcNetUDPHeader);
+      found_header = true;
+      continue;
+    }
+    if (line.empty()) {
+      continue;
+    }
+
+    // Parse a single entry from /proc/net/udp.
+    //
+    // Example entries:
+    //
+    // clang-format off
+    //
+    //  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode ref pointer drops
+    // 3503: 0100007F:0035 00000000:0000 07 00000000:00000000 00:00000000 00000000     0        0 33317 2 0000000000000000 0
+    // 3518: 00000000:0044 00000000:0000 07 00000000:00000000 00:00000000 00000000     0        0 40394 2 0000000000000000 0
+    //   ^     ^       ^     ^       ^   ^     ^       ^      ^     ^        ^         ^        ^   ^   ^      ^           ^
+    //   0     1       2     3       4   5     6       7      8     9       10        11       12  13  14     15           16
+    //
+    // clang-format on
+
+    UDPEntry entry;
+    std::vector<std::string> fields =
+        StrSplit(line, absl::ByAnyChar(": "), absl::SkipEmpty());
+
+    ASSIGN_OR_RETURN_ERRNO(entry.local_addr, AtoiBase(fields[1], 16));
+    ASSIGN_OR_RETURN_ERRNO(entry.local_port, AtoiBase(fields[2], 16));
+
+    ASSIGN_OR_RETURN_ERRNO(entry.remote_addr, AtoiBase(fields[3], 16));
+    ASSIGN_OR_RETURN_ERRNO(entry.remote_port, AtoiBase(fields[4], 16));
+
+    ASSIGN_OR_RETURN_ERRNO(entry.state, AtoiBase(fields[5], 16));
+    ASSIGN_OR_RETURN_ERRNO(entry.uid, Atoi<uint64_t>(fields[11]));
+    ASSIGN_OR_RETURN_ERRNO(entry.inode, Atoi<uint64_t>(fields[13]));
+
+    // Linux shares internal data structures between TCP and UDP sockets. The
+    // proc entries for UDP sockets share some fields with TCP sockets, but
+    // these fields should always be zero as they're not meaningful for UDP
+    // sockets.
+    EXPECT_EQ(fields[8], "00") << StrFormat("sl:%s, tr", fields[0]);
+    EXPECT_EQ(fields[9], "00000000") << StrFormat("sl:%s, tm->when", fields[0]);
+    EXPECT_EQ(fields[10], "00000000")
+        << StrFormat("sl:%s, retrnsmt", fields[0]);
+    EXPECT_EQ(fields[12], "0") << StrFormat("sl:%s, timeout", fields[0]);
+
+    entries.push_back(entry);
+  }
+  std::cerr << "<end of /proc/net/udp>" << std::endl;
+
+  return entries;
+}
+
+TEST(ProcNetUDP, Exists) {
+  const std::string content =
+      ASSERT_NO_ERRNO_AND_VALUE(GetContents("/proc/net/udp"));
+  const std::string header_line = StrCat(kProcNetUDPHeader, "\n");
+  EXPECT_THAT(content, ::testing::StartsWith(header_line));
+}
+
+TEST(ProcNetUDP, EntryUID) {
+  auto sockets =
+      ASSERT_NO_ERRNO_AND_VALUE(IPv4UDPBidirectionalBindSocketPair(0).Create());
+  std::vector<UDPEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcNetUDPEntries());
+  UDPEntry e;
+  ASSERT_TRUE(FindByLocalAddr(entries, &e, sockets->first_addr()))
+      << DescribeFirstInetSocket(*sockets);
+  EXPECT_EQ(e.uid, geteuid());
+  ASSERT_TRUE(FindByRemoteAddr(entries, &e, sockets->first_addr()))
+      << DescribeSecondInetSocket(*sockets);
+  EXPECT_EQ(e.uid, geteuid());
+}
+
+TEST(ProcNetUDP, FindMutualEntries) {
+  auto sockets =
+      ASSERT_NO_ERRNO_AND_VALUE(IPv4UDPBidirectionalBindSocketPair(0).Create());
+  std::vector<UDPEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcNetUDPEntries());
+
+  EXPECT_TRUE(FindByLocalAddr(entries, nullptr, sockets->first_addr()))
+      << DescribeFirstInetSocket(*sockets);
+  EXPECT_TRUE(FindByRemoteAddr(entries, nullptr, sockets->first_addr()))
+      << DescribeSecondInetSocket(*sockets);
+
+  EXPECT_TRUE(FindByLocalAddr(entries, nullptr, sockets->second_addr()))
+      << DescribeSecondInetSocket(*sockets);
+  EXPECT_TRUE(FindByRemoteAddr(entries, nullptr, sockets->second_addr()))
+      << DescribeFirstInetSocket(*sockets);
+}
+
+TEST(ProcNetUDP, EntriesRemovedOnClose) {
+  auto sockets =
+      ASSERT_NO_ERRNO_AND_VALUE(IPv4UDPBidirectionalBindSocketPair(0).Create());
+  std::vector<UDPEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcNetUDPEntries());
+
+  EXPECT_TRUE(FindByLocalAddr(entries, nullptr, sockets->first_addr()))
+      << DescribeFirstInetSocket(*sockets);
+  EXPECT_TRUE(FindByLocalAddr(entries, nullptr, sockets->second_addr()))
+      << DescribeSecondInetSocket(*sockets);
+
+  EXPECT_THAT(close(sockets->release_first_fd()), SyscallSucceeds());
+  entries = ASSERT_NO_ERRNO_AND_VALUE(ProcNetUDPEntries());
+  // First socket's entry should be gone, but the second socket's entry should
+  // still exist.
+  EXPECT_FALSE(FindByLocalAddr(entries, nullptr, sockets->first_addr()))
+      << DescribeFirstInetSocket(*sockets);
+  EXPECT_TRUE(FindByLocalAddr(entries, nullptr, sockets->second_addr()))
+      << DescribeSecondInetSocket(*sockets);
+
+  EXPECT_THAT(close(sockets->release_second_fd()), SyscallSucceeds());
+  entries = ASSERT_NO_ERRNO_AND_VALUE(ProcNetUDPEntries());
+  // Both entries should be gone.
+  EXPECT_FALSE(FindByLocalAddr(entries, nullptr, sockets->first_addr()))
+      << DescribeFirstInetSocket(*sockets);
+  EXPECT_FALSE(FindByLocalAddr(entries, nullptr, sockets->second_addr()))
+      << DescribeSecondInetSocket(*sockets);
+}
+
+PosixErrorOr<std::unique_ptr<FileDescriptor>> BoundUDPSocket() {
+  ASSIGN_OR_RETURN_ERRNO(std::unique_ptr<FileDescriptor> socket,
+                         IPv4UDPUnboundSocket(0).Create());
+  struct sockaddr_in addr;
+  addr.sin_family = AF_INET;
+  addr.sin_addr.s_addr = htonl(INADDR_ANY);
+  addr.sin_port = 0;
+
+  int res = bind(socket->get(), reinterpret_cast<const struct sockaddr*>(&addr),
+                 sizeof(addr));
+  if (res) {
+    return PosixError(errno, "bind()");
+  }
+  return socket;
+}
+
+TEST(ProcNetUDP, BoundEntry) {
+  std::unique_ptr<FileDescriptor> socket =
+      ASSERT_NO_ERRNO_AND_VALUE(BoundUDPSocket());
+  struct sockaddr addr;
+  socklen_t len = sizeof(addr);
+  ASSERT_THAT(getsockname(socket->get(), &addr, &len), SyscallSucceeds());
+  uint16_t port = PortFromInetSockaddr(&addr);
+
+  std::vector<UDPEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcNetUDPEntries());
+  UDPEntry e;
+  ASSERT_TRUE(ASSERT_NO_ERRNO_AND_VALUE(FindByFD(entries, &e, socket->get())));
+  EXPECT_EQ(e.local_port, port);
+  EXPECT_EQ(e.remote_addr, 0);
+  EXPECT_EQ(e.remote_port, 0);
+}
+
+TEST(ProcNetUDP, BoundSocketStateClosed) {
+  std::unique_ptr<FileDescriptor> socket =
+      ASSERT_NO_ERRNO_AND_VALUE(BoundUDPSocket());
+  std::vector<UDPEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcNetUDPEntries());
+  UDPEntry e;
+  ASSERT_TRUE(ASSERT_NO_ERRNO_AND_VALUE(FindByFD(entries, &e, socket->get())));
+  EXPECT_EQ(e.state, TCP_CLOSE);
+}
+
+TEST(ProcNetUDP, ConnectedSocketStateEstablished) {
+  auto sockets =
+      ASSERT_NO_ERRNO_AND_VALUE(IPv4UDPBidirectionalBindSocketPair(0).Create());
+  std::vector<UDPEntry> entries =
+      ASSERT_NO_ERRNO_AND_VALUE(ProcNetUDPEntries());
+
+  UDPEntry e;
+  ASSERT_TRUE(FindByLocalAddr(entries, &e, sockets->first_addr()))
+      << DescribeFirstInetSocket(*sockets);
+  EXPECT_EQ(e.state, TCP_ESTABLISHED);
+
+  ASSERT_TRUE(FindByLocalAddr(entries, &e, sockets->second_addr()))
+      << DescribeSecondInetSocket(*sockets);
+  EXPECT_EQ(e.state, TCP_ESTABLISHED);
+}
+
+}  // namespace
+}  // namespace testing
+}  // namespace gvisor
diff --git a/test/util/fs_util.cc b/test/util/fs_util.cc
index ae49725a0..f7d231b14 100644
--- a/test/util/fs_util.cc
+++ b/test/util/fs_util.cc
@@ -105,6 +105,15 @@ PosixErrorOr<struct stat> Stat(absl::string_view path) {
   return stat_buf;
 }
 
+PosixErrorOr<struct stat> Fstat(int fd) {
+  struct stat stat_buf;
+  int res = fstat(fd, &stat_buf);
+  if (res < 0) {
+    return PosixError(errno, absl::StrCat("fstat ", fd));
+  }
+  return stat_buf;
+}
+
 PosixErrorOr<bool> Exists(absl::string_view path) {
   struct stat stat_buf;
   int res = stat(std::string(path).c_str(), &stat_buf);
diff --git a/test/util/fs_util.h b/test/util/fs_util.h
index 3969f8309..e5b555891 100644
--- a/test/util/fs_util.h
+++ b/test/util/fs_util.h
@@ -35,6 +35,9 @@ PosixErrorOr<bool> Exists(absl::string_view path);
 // Returns a stat structure for the given path or an error.
 PosixErrorOr<struct stat> Stat(absl::string_view path);
 
+// Returns a stat struct for the given fd.
+PosixErrorOr<struct stat> Fstat(int fd);
+
 // Deletes the file or directory at path or returns an error.
 PosixError Delete(absl::string_view path);