3 files changed, 86 insertions, 5 deletions
diff --git a/pkg/tcpip/ports/ports.go b/pkg/tcpip/ports/ports.go
index 40e202717..30cea8996 100644
--- a/pkg/tcpip/ports/ports.go
+++ b/pkg/tcpip/ports/ports.go
@@ -19,6 +19,7 @@ import (
 	"math"
 	"math/rand"
 	"sync"
+	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
 )
@@ -27,6 +28,10 @@ const (
 	// FirstEphemeral is the first ephemeral port.
 	FirstEphemeral = 16000
 
+	// numEphemeralPorts it the mnumber of available ephemeral ports to
+	// Netstack.
+	numEphemeralPorts = math.MaxUint16 - FirstEphemeral + 1
+
 	anyIPAddress tcpip.Address = ""
 )
 
@@ -40,6 +45,13 @@ type portDescriptor struct {
 type PortManager struct {
 	mu             sync.RWMutex
 	allocatedPorts map[portDescriptor]bindAddresses
+
+	// hint is used to pick ports ephemeral ports in a stable order for
+	// a given port offset.
+	//
+	// hint must be accessed using the portHint/incPortHint helpers.
+	// TODO(gvisor.dev/issue/940): S/R this field.
+	hint uint32
 }
 
 type portNode struct {
@@ -130,11 +142,40 @@ func NewPortManager() *PortManager {
 // is suitable for its needs, and stopping when a port is found or an error
 // occurs.
 func (s *PortManager) PickEphemeralPort(testPort func(p uint16) (bool, *tcpip.Error)) (port uint16, err *tcpip.Error) {
-	count := uint16(math.MaxUint16 - FirstEphemeral + 1)
-	offset := uint16(rand.Int31n(int32(count)))
+	offset := uint32(rand.Int31n(numEphemeralPorts))
+	return s.pickEphemeralPort(offset, numEphemeralPorts, testPort)
+}
+
+// portHint atomically reads and returns the s.hint value.
+func (s *PortManager) portHint() uint32 {
+	return atomic.LoadUint32(&s.hint)
+}
+
+// incPortHint atomically increments s.hint by 1.
+func (s *PortManager) incPortHint() {
+	atomic.AddUint32(&s.hint, 1)
+}
+
+// PickEphemeralPortStable starts at the specified offset + s.portHint and
+// 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 (s *PortManager) PickEphemeralPortStable(offset uint32, testPort func(p uint16) (bool, *tcpip.Error)) (port uint16, err *tcpip.Error) {
+	p, err := s.pickEphemeralPort(s.portHint()+offset, numEphemeralPorts, testPort)
+	if err == nil {
+		s.incPortHint()
+	}
+	return p, err
+
+}
 
-	for i := uint16(0); i < count; i++ {
-		port = FirstEphemeral + (offset+i)%count
+// pickEphemeralPort starts at the offset specified from the FirstEphemeral port
+// 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 (s *PortManager) pickEphemeralPort(offset, count uint32, testPort func(p uint16) (bool, *tcpip.Error)) (port uint16, err *tcpip.Error) {
+	for i := uint32(0); i < count; i++ {
+		port = uint16(FirstEphemeral + (offset+i)%count)
 		ok, err := testPort(port)
 		if err != nil {
 			return 0, err
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 6a8079823..90c2cf1be 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -20,10 +20,12 @@
 package stack
 
 import (
+	"encoding/binary"
 	"sync"
 	"time"
 
 	"golang.org/x/time/rate"
+	"gvisor.dev/gvisor/pkg/rand"
 	"gvisor.dev/gvisor/pkg/sleep"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
@@ -388,6 +390,12 @@ type Stack struct {
 	// icmpRateLimiter is a global rate limiter for all ICMP messages generated
 	// by the stack.
 	icmpRateLimiter *ICMPRateLimiter
+
+	// portSeed is a one-time random value initialized at stack startup
+	// and is used to seed the TCP port picking on active connections
+	//
+	// TODO(gvisor.dev/issues/940): S/R this field.
+	portSeed uint32
 }
 
 // Options contains optional Stack configuration.
@@ -440,6 +448,7 @@ func New(opts Options) *Stack {
 		stats:              opts.Stats.FillIn(),
 		handleLocal:        opts.HandleLocal,
 		icmpRateLimiter:    NewICMPRateLimiter(),
+		portSeed:           generateRandUint32(),
 	}
 
 	// Add specified network protocols.
@@ -1197,3 +1206,19 @@ func (s *Stack) SetICMPBurst(burst int) {
 func (s *Stack) AllowICMPMessage() bool {
 	return s.icmpRateLimiter.Allow()
 }
+
+// PortSeed returns a 32 bit value that can be used as a seed value for port
+// picking.
+//
+// NOTE: The seed is generated once during stack initialization only.
+func (s *Stack) PortSeed() uint32 {
+	return s.portSeed
+}
+
+func generateRandUint32() uint32 {
+	b := make([]byte, 4)
+	if _, err := rand.Read(b); err != nil {
+		panic(err)
+	}
+	return binary.LittleEndian.Uint32(b)
+}
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index a1cd0d481..f9d5e0085 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -15,6 +15,7 @@
 package tcp
 
 import (
+	"encoding/binary"
 	"fmt"
 	"math"
 	"strings"
@@ -26,6 +27,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sleep"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+	"gvisor.dev/gvisor/pkg/tcpip/hash/jenkins"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/pkg/tcpip/iptables"
 	"gvisor.dev/gvisor/pkg/tcpip/seqnum"
@@ -1504,7 +1506,20 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) (er
 		// address/port for both local and remote (otherwise this
 		// endpoint would be trying to connect to itself).
 		sameAddr := e.id.LocalAddress == e.id.RemoteAddress
-		if _, err := e.stack.PickEphemeralPort(func(p uint16) (bool, *tcpip.Error) {
+
+		// Calculate a port offset based on the destination IP/port and
+		// src IP to ensure that for a given tuple (srcIP, destIP,
+		// destPort) the offset used as a starting point is the same to
+		// ensure that we can cycle through the port space effectively.
+		h := jenkins.Sum32(e.stack.PortSeed())
+		h.Write([]byte(e.id.LocalAddress))
+		h.Write([]byte(e.id.RemoteAddress))
+		portBuf := make([]byte, 2)
+		binary.LittleEndian.PutUint16(portBuf, e.id.RemotePort)
+		h.Write(portBuf)
+		portOffset := h.Sum32()
+
+		if _, err := e.stack.PickEphemeralPortStable(portOffset, func(p uint16) (bool, *tcpip.Error) {
 			if sameAddr && p == e.id.RemotePort {
 				return false, nil
 			}