Add loss recovery option for TCP.

/proc/sys/net/ipv4/tcp_recovery is used to enable RACK loss
recovery in TCP.

PiperOrigin-RevId: 325157807

pkg/sentry/fs/proc/sys_net.go

@@ -272,6 +272,96 @@ func (f *tcpSackFile) Write(ctx context.Context, _ *fs.File, src usermem.IOSeque
 	return n, f.tcpSack.stack.SetTCPSACKEnabled(*f.tcpSack.enabled)
 }
 
+// +stateify savable
+type tcpRecovery struct {
+	fsutil.SimpleFileInode
+
+	stack    inet.Stack `state:"wait"`
+	recovery inet.TCPLossRecovery
+}
+
+func newTCPRecoveryInode(ctx context.Context, msrc *fs.MountSource, s inet.Stack) *fs.Inode {
+	ts := &tcpRecovery{
+		SimpleFileInode: *fsutil.NewSimpleFileInode(ctx, fs.RootOwner, fs.FilePermsFromMode(0644), linux.PROC_SUPER_MAGIC),
+		stack:           s,
+	}
+	sattr := fs.StableAttr{
+		DeviceID:  device.ProcDevice.DeviceID(),
+		InodeID:   device.ProcDevice.NextIno(),
+		BlockSize: usermem.PageSize,
+		Type:      fs.SpecialFile,
+	}
+	return fs.NewInode(ctx, ts, msrc, sattr)
+}
+
+// Truncate implements fs.InodeOperations.Truncate.
+func (*tcpRecovery) Truncate(context.Context, *fs.Inode, int64) error {
+	return nil
+}
+
+// GetFile implements fs.InodeOperations.GetFile.
+func (r *tcpRecovery) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileFlags) (*fs.File, error) {
+	flags.Pread = true
+	flags.Pwrite = true
+	return fs.NewFile(ctx, dirent, flags, &tcpRecoveryFile{
+		tcpRecovery: r,
+		stack:       r.stack,
+	}), nil
+}
+
+// +stateify savable
+type tcpRecoveryFile struct {
+	fsutil.FileGenericSeek          `state:"nosave"`
+	fsutil.FileNoIoctl              `state:"nosave"`
+	fsutil.FileNoMMap               `state:"nosave"`
+	fsutil.FileNoSplice             `state:"nosave"`
+	fsutil.FileNoopRelease          `state:"nosave"`
+	fsutil.FileNoopFlush            `state:"nosave"`
+	fsutil.FileNoopFsync            `state:"nosave"`
+	fsutil.FileNotDirReaddir        `state:"nosave"`
+	fsutil.FileUseInodeUnstableAttr `state:"nosave"`
+	waiter.AlwaysReady              `state:"nosave"`
+
+	tcpRecovery *tcpRecovery
+
+	stack inet.Stack `state:"wait"`
+}
+
+// Read implements fs.FileOperations.Read.
+func (f *tcpRecoveryFile) Read(ctx context.Context, _ *fs.File, dst usermem.IOSequence, offset int64) (int64, error) {
+	if offset != 0 {
+		return 0, io.EOF
+	}
+
+	recovery, err := f.stack.TCPRecovery()
+	if err != nil {
+		return 0, err
+	}
+	f.tcpRecovery.recovery = recovery
+	s := fmt.Sprintf("%d\n", f.tcpRecovery.recovery)
+	n, err := dst.CopyOut(ctx, []byte(s))
+	return int64(n), err
+}
+
+// Write implements fs.FileOperations.Write.
+func (f *tcpRecoveryFile) Write(ctx context.Context, _ *fs.File, src usermem.IOSequence, offset int64) (int64, error) {
+	if src.NumBytes() == 0 {
+		return 0, nil
+	}
+	src = src.TakeFirst(usermem.PageSize - 1)
+
+	var v int32
+	n, err := usermem.CopyInt32StringInVec(ctx, src.IO, src.Addrs, &v, src.Opts)
+	if err != nil {
+		return 0, err
+	}
+	f.tcpRecovery.recovery = inet.TCPLossRecovery(v)
+	if err := f.tcpRecovery.stack.SetTCPRecovery(f.tcpRecovery.recovery); err != nil {
+		return 0, err
+	}
+	return n, nil
+}
+
 func (p *proc) newSysNetCore(ctx context.Context, msrc *fs.MountSource, s inet.Stack) *fs.Inode {
 	// The following files are simple stubs until they are implemented in
 	// netstack, most of these files are configuration related. We use the
@@ -351,6 +441,11 @@ func (p *proc) newSysNetIPv4Dir(ctx context.Context, msrc *fs.MountSource, s ine
 		contents["tcp_wmem"] = newTCPMemInode(ctx, msrc, s, tcpWMem)
 	}
 
+	// Add tcp_recovery.
+	if _, err := s.TCPRecovery(); err == nil {
+		contents["tcp_recovery"] = newTCPRecoveryInode(ctx, msrc, s)
+	}
+
 	d := ramfs.NewDir(ctx, contents, fs.RootOwner, fs.FilePermsFromMode(0555))
 	return newProcInode(ctx, d, msrc, fs.SpecialDirectory, nil)
 }

pkg/sentry/fsimpl/proc/tasks_sys.go

@@ -55,7 +55,8 @@ func (fs *filesystem) newSysNetDir(root *auth.Credentials, k *kernel.Kernel) *ke
 	if stack := k.RootNetworkNamespace().Stack(); stack != nil {
 		contents = map[string]*kernfs.Dentry{
 			"ipv4": kernfs.NewStaticDir(root, linux.UNNAMED_MAJOR, fs.devMinor, fs.NextIno(), 0555, map[string]*kernfs.Dentry{
-				"tcp_sack": fs.newDentry(root, fs.NextIno(), 0644, &tcpSackData{stack: stack}),
+				"tcp_recovery": fs.newDentry(root, fs.NextIno(), 0644, &tcpRecoveryData{stack: stack}),
+				"tcp_sack":     fs.newDentry(root, fs.NextIno(), 0644, &tcpSackData{stack: stack}),
 
 				// The following files are simple stubs until they are implemented in
 				// netstack, most of these files are configuration related. We use the
@@ -207,3 +208,49 @@ func (d *tcpSackData) Write(ctx context.Context, src usermem.IOSequence, offset
 	*d.enabled = v != 0
 	return n, d.stack.SetTCPSACKEnabled(*d.enabled)
 }
+
+// tcpRecoveryData implements vfs.WritableDynamicBytesSource for
+// /proc/sys/net/ipv4/tcp_recovery.
+//
+// +stateify savable
+type tcpRecoveryData struct {
+	kernfs.DynamicBytesFile
+
+	stack inet.Stack `state:"wait"`
+}
+
+var _ vfs.WritableDynamicBytesSource = (*tcpRecoveryData)(nil)
+
+// Generate implements vfs.DynamicBytesSource.
+func (d *tcpRecoveryData) Generate(ctx context.Context, buf *bytes.Buffer) error {
+	recovery, err := d.stack.TCPRecovery()
+	if err != nil {
+		return err
+	}
+
+	buf.WriteString(fmt.Sprintf("%d\n", recovery))
+	return nil
+}
+
+func (d *tcpRecoveryData) Write(ctx context.Context, src usermem.IOSequence, offset int64) (int64, error) {
+	if offset != 0 {
+		// No need to handle partial writes thus far.
+		return 0, syserror.EINVAL
+	}
+	if src.NumBytes() == 0 {
+		return 0, nil
+	}
+
+	// Limit the amount of memory allocated.
+	src = src.TakeFirst(usermem.PageSize - 1)
+
+	var v int32
+	n, err := usermem.CopyInt32StringInVec(ctx, src.IO, src.Addrs, &v, src.Opts)
+	if err != nil {
+		return 0, err
+	}
+	if err := d.stack.SetTCPRecovery(inet.TCPLossRecovery(v)); err != nil {
+		return 0, err
+	}
+	return n, nil
+}

pkg/sentry/inet/inet.go

@@ -56,6 +56,12 @@ type Stack interface {
 	// settings.
 	SetTCPSACKEnabled(enabled bool) error
 
+	// TCPRecovery returns the TCP loss detection algorithm.
+	TCPRecovery() (TCPLossRecovery, error)
+
+	// SetTCPRecovery attempts to change TCP loss detection algorithm.
+	SetTCPRecovery(recovery TCPLossRecovery) error
+
 	// Statistics reports stack statistics.
 	Statistics(stat interface{}, arg string) error
 
@@ -189,3 +195,14 @@ type StatSNMPUDP [8]uint64
 
 // StatSNMPUDPLite describes UdpLite line of /proc/net/snmp.
 type StatSNMPUDPLite [8]uint64
+
+// TCPLossRecovery indicates TCP loss detection and recovery methods to use.
+type TCPLossRecovery int32
+
+// Loss recovery constants from include/net/tcp.h which are used to set
+// /proc/sys/net/ipv4/tcp_recovery.
+const (
+	TCP_RACK_LOSS_DETECTION TCPLossRecovery = 1 << iota
+	TCP_RACK_STATIC_REO_WND
+	TCP_RACK_NO_DUPTHRESH
+)

pkg/sentry/inet/test_stack.go

@@ -25,6 +25,7 @@ type TestStack struct {
 	TCPRecvBufSize    TCPBufferSize
 	TCPSendBufSize    TCPBufferSize
 	TCPSACKFlag       bool
+	Recovery          TCPLossRecovery
 }
 
 // NewTestStack returns a TestStack with no network interfaces. The value of
@@ -91,6 +92,17 @@ func (s *TestStack) SetTCPSACKEnabled(enabled bool) error {
 	return nil
 }
 
+// TCPRecovery implements Stack.TCPRecovery.
+func (s *TestStack) TCPRecovery() (TCPLossRecovery, error) {
+	return s.Recovery, nil
+}
+
+// SetTCPRecovery implements Stack.SetTCPRecovery.
+func (s *TestStack) SetTCPRecovery(recovery TCPLossRecovery) error {
+	s.Recovery = recovery
+	return nil
+}
+
 // Statistics implements inet.Stack.Statistics.
 func (s *TestStack) Statistics(stat interface{}, arg string) error {
 	return nil

pkg/sentry/socket/hostinet/stack.go

@@ -53,6 +53,7 @@ type Stack struct {
 	interfaceAddrs map[int32][]inet.InterfaceAddr
 	routes         []inet.Route
 	supportsIPv6   bool
+	tcpRecovery    inet.TCPLossRecovery
 	tcpRecvBufSize inet.TCPBufferSize
 	tcpSendBufSize inet.TCPBufferSize
 	tcpSACKEnabled bool
@@ -350,6 +351,16 @@ func (s *Stack) SetTCPSACKEnabled(enabled bool) error {
 	return syserror.EACCES
 }
 
+// TCPRecovery implements inet.Stack.TCPRecovery.
+func (s *Stack) TCPRecovery() (inet.TCPLossRecovery, error) {
+	return s.tcpRecovery, nil
+}
+
+// SetTCPRecovery implements inet.Stack.SetTCPRecovery.
+func (s *Stack) SetTCPRecovery(recovery inet.TCPLossRecovery) error {
+	return syserror.EACCES
+}
+
 // getLine reads one line from proc file, with specified prefix.
 // The last argument, withHeader, specifies if it contains line header.
 func getLine(f *os.File, prefix string, withHeader bool) string {

pkg/sentry/socket/netstack/stack.go

@@ -207,6 +207,20 @@ func (s *Stack) SetTCPSACKEnabled(enabled bool) error {
 	return syserr.TranslateNetstackError(s.Stack.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.SACKEnabled(enabled))).ToError()
 }
 
+// TCPRecovery implements inet.Stack.TCPRecovery.
+func (s *Stack) TCPRecovery() (inet.TCPLossRecovery, error) {
+	var recovery tcp.Recovery
+	if err := s.Stack.TransportProtocolOption(tcp.ProtocolNumber, &recovery); err != nil {
+		return 0, syserr.TranslateNetstackError(err).ToError()
+	}
+	return inet.TCPLossRecovery(recovery), nil
+}
+
+// SetTCPRecovery implements inet.Stack.SetTCPRecovery.
+func (s *Stack) SetTCPRecovery(recovery inet.TCPLossRecovery) error {
+	return syserr.TranslateNetstackError(s.Stack.SetTransportProtocolOption(tcp.ProtocolNumber, tcp.Recovery(recovery))).ToError()
+}
+
 // Statistics implements inet.Stack.Statistics.
 func (s *Stack) Statistics(stat interface{}, arg string) error {
 	switch stats := stat.(type) {

pkg/tcpip/transport/tcp/protocol.go

@@ -80,6 +80,25 @@ const (
 // enable/disable SACK support in TCP. See: https://tools.ietf.org/html/rfc2018.
 type SACKEnabled bool
 
+// Recovery is used by stack.(*Stack).TransportProtocolOption to
+// set loss detection algorithm in TCP.
+type Recovery int32
+
+const (
+	// RACKLossDetection indicates RACK is used for loss detection and
+	// recovery.
+	RACKLossDetection Recovery = 1 << iota
+
+	// RACKStaticReoWnd indicates the reordering window should not be
+	// adjusted when DSACK is received.
+	RACKStaticReoWnd
+
+	// RACKNoDupTh indicates RACK should not consider the classic three
+	// duplicate acknowledgements rule to mark the segments as lost. This
+	// is used when reordering is not detected.
+	RACKNoDupTh
+)
+
 // DelayEnabled is used by stack.(Stack*).TransportProtocolOption to
 // enable/disable Nagle's algorithm in TCP.
 type DelayEnabled bool
@@ -161,6 +180,7 @@ func (s *synRcvdCounter) Threshold() uint64 {
 type protocol struct {
 	mu                         sync.RWMutex
 	sackEnabled                bool
+	recovery                   Recovery
 	delayEnabled               bool
 	sendBufferSize             SendBufferSizeOption
 	recvBufferSize             ReceiveBufferSizeOption
@@ -280,6 +300,12 @@ func (p *protocol) SetOption(option interface{}) *tcpip.Error {
 		p.mu.Unlock()
 		return nil
 
+	case Recovery:
+		p.mu.Lock()
+		p.recovery = Recovery(v)
+		p.mu.Unlock()
+		return nil
+
 	case DelayEnabled:
 		p.mu.Lock()
 		p.delayEnabled = bool(v)
@@ -394,6 +420,12 @@ func (p *protocol) Option(option interface{}) *tcpip.Error {
 		p.mu.RUnlock()
 		return nil
 
+	case *Recovery:
+		p.mu.RLock()
+		*v = Recovery(p.recovery)
+		p.mu.RUnlock()
+		return nil
+
 	case *DelayEnabled:
 		p.mu.RLock()
 		*v = DelayEnabled(p.delayEnabled)
@@ -535,6 +567,7 @@ func NewProtocol() stack.TransportProtocol {
 		minRTO:                     MinRTO,
 		maxRTO:                     MaxRTO,
 		maxRetries:                 MaxRetries,
+		recovery:                   RACKLossDetection,
 	}
 	p.dispatcher.init(runtime.GOMAXPROCS(0))
 	return &p

test/syscalls/linux/proc_net.cc

@@ -477,6 +477,44 @@ TEST(ProcNetSnmp, CheckSnmp) {
   EXPECT_EQ(value_count, 1);
 }
 
+TEST(ProcSysNetIpv4Recovery, Exists) {
+  EXPECT_THAT(open("/proc/sys/net/ipv4/tcp_recovery", O_RDONLY),
+              SyscallSucceeds());
+}
+
+TEST(ProcSysNetIpv4Recovery, CanReadAndWrite) {
+  // TODO(b/162988252): Enable save/restore for this test after the bug is
+  // fixed.
+  DisableSave ds;
+
+  SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability((CAP_DAC_OVERRIDE))));
+
+  auto const fd = ASSERT_NO_ERRNO_AND_VALUE(
+      Open("/proc/sys/net/ipv4/tcp_recovery", O_RDWR));
+
+  char buf[10] = {'\0'};
+  char to_write = '2';
+
+  // Check initial value is set to 1.
+  EXPECT_THAT(PreadFd(fd.get(), &buf, sizeof(buf), 0),
+              SyscallSucceedsWithValue(sizeof(to_write) + 1));
+  EXPECT_EQ(strcmp(buf, "1\n"), 0);
+
+  // Set tcp_recovery to one of the allowed constants.
+  EXPECT_THAT(PwriteFd(fd.get(), &to_write, sizeof(to_write), 0),
+              SyscallSucceedsWithValue(sizeof(to_write)));
+  EXPECT_THAT(PreadFd(fd.get(), &buf, sizeof(buf), 0),
+              SyscallSucceedsWithValue(sizeof(to_write) + 1));
+  EXPECT_EQ(strcmp(buf, "2\n"), 0);
+
+  // Set tcp_recovery to any random value.
+  char kMessage[] = "100";
+  EXPECT_THAT(PwriteFd(fd.get(), kMessage, strlen(kMessage), 0),
+              SyscallSucceedsWithValue(strlen(kMessage)));
+  EXPECT_THAT(PreadFd(fd.get(), buf, sizeof(kMessage), 0),
+              SyscallSucceedsWithValue(sizeof(kMessage)));
+  EXPECT_EQ(strcmp(buf, "100\n"), 0);
+}
 }  // namespace
 }  // namespace testing
 }  // namespace gvisor