Enlarge port range and fix integer overflow

Also count failed TCP port allocations

PiperOrigin-RevId: 368939619

pkg/sentry/socket/netstack/netstack.go

@@ -242,6 +242,7 @@ var Metrics = tcpip.Stats{
 		FastRetransmit:                     mustCreateMetric("/netstack/tcp/fast_retransmit", "Number of TCP segments which were fast retransmitted."),
 		Timeouts:                           mustCreateMetric("/netstack/tcp/timeouts", "Number of times RTO expired."),
 		ChecksumErrors:                     mustCreateMetric("/netstack/tcp/checksum_errors", "Number of segments dropped due to bad checksums."),
+		FailedPortReservations:             mustCreateMetric("/netstack/tcp/failed_port_reservations", "Number of time TCP failed to reserve a port."),
 	},
 	UDP: tcpip.UDPStats{
 		PacketsReceived:          mustCreateMetric("/netstack/udp/packets_received", "Number of UDP datagrams received via HandlePacket."),

pkg/tcpip/ports/ports.go

@@ -17,6 +17,7 @@
 package ports
 
 import (
+	"math"
 	"math/rand"
 	"sync/atomic"
 
@@ -24,7 +25,10 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip"
 )
 
-const anyIPAddress tcpip.Address = ""
+const (
+	firstEphemeral               = 16000
+	anyIPAddress   tcpip.Address = ""
+)
 
 // Reservation describes a port reservation.
 type Reservation struct {
@@ -220,10 +224,8 @@ type PortManager struct {
 func NewPortManager() *PortManager {
 	return &PortManager{
 		allocatedPorts: make(map[portDescriptor]addrToDevice),
-		// Match Linux's default ephemeral range. See:
-		// https://github.com/torvalds/linux/blob/e54937963fa249595824439dc839c948188dea83/net/ipv4/af_inet.c#L1842
-		firstEphemeral: 32768,
-		numEphemeral:   28232,
+		firstEphemeral: firstEphemeral,
+		numEphemeral:   math.MaxUint16 - firstEphemeral + 1,
 	}
 }
 
@@ -242,13 +244,13 @@ func (pm *PortManager) PickEphemeralPort(testPort PortTester) (port uint16, err
 	numEphemeral := pm.numEphemeral
 	pm.ephemeralMu.RUnlock()
 
-	offset := uint16(rand.Int31n(int32(numEphemeral)))
+	offset := uint32(rand.Int31n(int32(numEphemeral)))
 	return pickEphemeralPort(offset, firstEphemeral, numEphemeral, testPort)
 }
 
 // portHint atomically reads and returns the pm.hint value.
-func (pm *PortManager) portHint() uint16 {
-	return uint16(atomic.LoadUint32(&pm.hint))
+func (pm *PortManager) portHint() uint32 {
+	return atomic.LoadUint32(&pm.hint)
 }
 
 // incPortHint atomically increments pm.hint by 1.
@@ -260,7 +262,7 @@ func (pm *PortManager) incPortHint() {
 // iterates over all ephemeral ports, allowing the caller to decide whether a
 // given port is suitable for its needs and stopping when a port is found or an
 // error occurs.
-func (pm *PortManager) PickEphemeralPortStable(offset uint16, testPort PortTester) (port uint16, err tcpip.Error) {
+func (pm *PortManager) PickEphemeralPortStable(offset uint32, testPort PortTester) (port uint16, err tcpip.Error) {
 	pm.ephemeralMu.RLock()
 	firstEphemeral := pm.firstEphemeral
 	numEphemeral := pm.numEphemeral
@@ -277,9 +279,9 @@ func (pm *PortManager) PickEphemeralPortStable(offset uint16, testPort PortTeste
 // and iterates over the number of ports specified by count and allows the
 // caller to decide whether a given port is suitable for its needs, and stopping
 // when a port is found or an error occurs.
-func pickEphemeralPort(offset, first, count uint16, testPort PortTester) (port uint16, err tcpip.Error) {
-	for i := uint16(0); i < count; i++ {
-		port = first + (offset+i)%count
+func pickEphemeralPort(offset uint32, first, count uint16, testPort PortTester) (port uint16, err tcpip.Error) {
+	for i := uint32(0); i < uint32(count); i++ {
+		port := uint16(uint32(first) + (offset+i)%uint32(count))
 		ok, err := testPort(port)
 		if err != nil {
 			return 0, err

pkg/tcpip/ports/ports_test.go

@@ -15,6 +15,7 @@
 package ports
 
 import (
+	"math"
 	"math/rand"
 	"testing"
 
@@ -482,7 +483,7 @@ func TestPickEphemeralPortStable(t *testing.T) {
 			if err := pm.SetPortRange(firstEphemeral, firstEphemeral+numEphemeralPorts); err != nil {
 				t.Fatalf("failed to set ephemeral port range: %s", err)
 			}
-			portOffset := uint16(rand.Int31n(int32(numEphemeralPorts)))
+			portOffset := uint32(rand.Int31n(int32(numEphemeralPorts)))
 			port, err := pm.PickEphemeralPortStable(portOffset, test.f)
 			if diff := cmp.Diff(test.wantErr, err); diff != "" {
 				t.Fatalf("unexpected error from PickEphemeralPort(..), (-want, +got):\n%s", diff)
@@ -493,3 +494,29 @@ func TestPickEphemeralPortStable(t *testing.T) {
 		})
 	}
 }
+
+// TestOverflow addresses b/183593432, wherein an overflowing uint16 causes a
+// port allocation failure.
+func TestOverflow(t *testing.T) {
+	// Use a small range and start at offsets that will cause an overflow.
+	count := uint16(50)
+	for offset := uint32(math.MaxUint16 - count); offset < math.MaxUint16; offset++ {
+		reservedPorts := make(map[uint16]struct{})
+		// Ensure we can reserve everything in the allowed range.
+		for i := uint16(0); i < count; i++ {
+			port, err := pickEphemeralPort(offset, firstEphemeral, count, func(port uint16) (bool, tcpip.Error) {
+				if _, ok := reservedPorts[port]; !ok {
+					reservedPorts[port] = struct{}{}
+					return true, nil
+				}
+				return false, nil
+			})
+			if err != nil {
+				t.Fatalf("port picking failed at iteration %d, for offset %d, len(reserved): %+v", i, offset, len(reservedPorts))
+			}
+			if port < firstEphemeral || port > firstEphemeral+count {
+				t.Fatalf("reserved port %d, which is not in range [%d, %d]", port, firstEphemeral, firstEphemeral+count-1)
+			}
+		}
+	}
+}

pkg/tcpip/tcpip.go

@@ -1732,6 +1732,10 @@ type TCPStats struct {
 
 	// ChecksumErrors is the number of segments dropped due to bad checksums.
 	ChecksumErrors *StatCounter
+
+	// FailedPortReservations is the number of times TCP failed to reserve
+	// a port.
+	FailedPortReservations *StatCounter
 }
 
 // UDPStats collects UDP-specific stats.

pkg/tcpip/transport/tcp/accept.go

@@ -455,6 +455,7 @@ func (e *endpoint) reserveTupleLocked() bool {
 		Dest:         dest,
 	}
 	if !e.stack.ReserveTuple(portRes) {
+		e.stack.Stats().TCP.FailedPortReservations.Increment()
 		return false
 	}
 

pkg/tcpip/transport/tcp/endpoint.go

@@ -2251,7 +2251,7 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) tcp
 				panic(err)
 			}
 		}
-		portOffset := uint16(h.Sum32())
+		portOffset := h.Sum32()
 
 		var twReuse tcpip.TCPTimeWaitReuseOption
 		if err := e.stack.TransportProtocolOption(ProtocolNumber, &twReuse); err != nil {
@@ -2362,6 +2362,7 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) tcp
 			e.boundDest = addr
 			return true, nil
 		}); err != nil {
+			e.stack.Stats().TCP.FailedPortReservations.Increment()
 			return err
 		}
 	}
@@ -2685,6 +2686,7 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) (err tcpip.Error) {
 		return true, nil
 	})
 	if err != nil {
+		e.stack.Stats().TCP.FailedPortReservations.Increment()
 		return err
 	}