aboutsummaryrefslogtreecommitdiff
path: root/libpod/networking_slirp4netns.go
blob: cc1b3cfdc81568e8b8cd19d83b93325b2ab61075 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
// +build linux

package libpod

import (
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"syscall"
	"time"

	"github.com/containernetworking/plugins/pkg/ns"
	"github.com/containers/podman/v3/libpod/network/types"
	"github.com/containers/podman/v3/pkg/errorhandling"
	"github.com/containers/podman/v3/pkg/rootless"
	"github.com/containers/podman/v3/pkg/rootlessport"
	"github.com/containers/podman/v3/pkg/servicereaper"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
)

type slirpFeatures struct {
	HasDisableHostLoopback bool
	HasMTU                 bool
	HasEnableSandbox       bool
	HasEnableSeccomp       bool
	HasCIDR                bool
	HasOutboundAddr        bool
	HasIPv6                bool
}

type slirp4netnsCmdArg struct {
	Proto     string `json:"proto,omitempty"`
	HostAddr  string `json:"host_addr"`
	HostPort  uint16 `json:"host_port"`
	GuestAddr string `json:"guest_addr"`
	GuestPort uint16 `json:"guest_port"`
}

type slirp4netnsCmd struct {
	Execute string            `json:"execute"`
	Args    slirp4netnsCmdArg `json:"arguments"`
}

type slirp4netnsNetworkOptions struct {
	cidr                string
	disableHostLoopback bool
	enableIPv6          bool
	isSlirpHostForward  bool
	noPivotRoot         bool
	mtu                 int
	outboundAddr        string
	outboundAddr6       string
}

const ipv6ConfDefaultAcceptDadSysctl = "/proc/sys/net/ipv6/conf/default/accept_dad"

func checkSlirpFlags(path string) (*slirpFeatures, error) {
	cmd := exec.Command(path, "--help")
	out, err := cmd.CombinedOutput()
	if err != nil {
		return nil, errors.Wrapf(err, "slirp4netns %q", out)
	}
	return &slirpFeatures{
		HasDisableHostLoopback: strings.Contains(string(out), "--disable-host-loopback"),
		HasMTU:                 strings.Contains(string(out), "--mtu"),
		HasEnableSandbox:       strings.Contains(string(out), "--enable-sandbox"),
		HasEnableSeccomp:       strings.Contains(string(out), "--enable-seccomp"),
		HasCIDR:                strings.Contains(string(out), "--cidr"),
		HasOutboundAddr:        strings.Contains(string(out), "--outbound-addr"),
		HasIPv6:                strings.Contains(string(out), "--enable-ipv6"),
	}, nil
}

func parseSlirp4netnsNetworkOptions(r *Runtime, extraOptions []string) (*slirp4netnsNetworkOptions, error) {
	slirpOptions := append(r.config.Engine.NetworkCmdOptions, extraOptions...)
	slirp4netnsOpts := &slirp4netnsNetworkOptions{
		// overwrite defaults
		disableHostLoopback: true,
		mtu:                 slirp4netnsMTU,
		noPivotRoot:         r.config.Engine.NoPivotRoot,
	}
	for _, o := range slirpOptions {
		parts := strings.SplitN(o, "=", 2)
		if len(parts) < 2 {
			return nil, errors.Errorf("unknown option for slirp4netns: %q", o)
		}
		option, value := parts[0], parts[1]
		switch option {
		case "cidr":
			ipv4, _, err := net.ParseCIDR(value)
			if err != nil || ipv4.To4() == nil {
				return nil, errors.Errorf("invalid cidr %q", value)
			}
			slirp4netnsOpts.cidr = value
		case "port_handler":
			switch value {
			case "slirp4netns":
				slirp4netnsOpts.isSlirpHostForward = true
			case "rootlesskit":
				slirp4netnsOpts.isSlirpHostForward = false
			default:
				return nil, errors.Errorf("unknown port_handler for slirp4netns: %q", value)
			}
		case "allow_host_loopback":
			switch value {
			case "true":
				slirp4netnsOpts.disableHostLoopback = false
			case "false":
				slirp4netnsOpts.disableHostLoopback = true
			default:
				return nil, errors.Errorf("invalid value of allow_host_loopback for slirp4netns: %q", value)
			}
		case "enable_ipv6":
			switch value {
			case "true":
				slirp4netnsOpts.enableIPv6 = true
			case "false":
				slirp4netnsOpts.enableIPv6 = false
			default:
				return nil, errors.Errorf("invalid value of enable_ipv6 for slirp4netns: %q", value)
			}
		case "outbound_addr":
			ipv4 := net.ParseIP(value)
			if ipv4 == nil || ipv4.To4() == nil {
				_, err := net.InterfaceByName(value)
				if err != nil {
					return nil, errors.Errorf("invalid outbound_addr %q", value)
				}
			}
			slirp4netnsOpts.outboundAddr = value
		case "outbound_addr6":
			ipv6 := net.ParseIP(value)
			if ipv6 == nil || ipv6.To4() != nil {
				_, err := net.InterfaceByName(value)
				if err != nil {
					return nil, errors.Errorf("invalid outbound_addr6: %q", value)
				}
			}
			slirp4netnsOpts.outboundAddr6 = value
		case "mtu":
			var err error
			slirp4netnsOpts.mtu, err = strconv.Atoi(value)
			if slirp4netnsOpts.mtu < 68 || err != nil {
				return nil, errors.Errorf("invalid mtu %q", value)
			}
		default:
			return nil, errors.Errorf("unknown option for slirp4netns: %q", o)
		}
	}
	return slirp4netnsOpts, nil
}

func createBasicSlirp4netnsCmdArgs(options *slirp4netnsNetworkOptions, features *slirpFeatures) ([]string, error) {
	cmdArgs := []string{}
	if options.disableHostLoopback && features.HasDisableHostLoopback {
		cmdArgs = append(cmdArgs, "--disable-host-loopback")
	}
	if options.mtu > -1 && features.HasMTU {
		cmdArgs = append(cmdArgs, fmt.Sprintf("--mtu=%d", options.mtu))
	}
	if !options.noPivotRoot && features.HasEnableSandbox {
		cmdArgs = append(cmdArgs, "--enable-sandbox")
	}
	if features.HasEnableSeccomp {
		cmdArgs = append(cmdArgs, "--enable-seccomp")
	}

	if options.cidr != "" {
		if !features.HasCIDR {
			return nil, errors.Errorf("cidr not supported")
		}
		cmdArgs = append(cmdArgs, fmt.Sprintf("--cidr=%s", options.cidr))
	}

	if options.enableIPv6 {
		if !features.HasIPv6 {
			return nil, errors.Errorf("enable_ipv6 not supported")
		}
		cmdArgs = append(cmdArgs, "--enable-ipv6")
	}

	if options.outboundAddr != "" {
		if !features.HasOutboundAddr {
			return nil, errors.Errorf("outbound_addr not supported")
		}
		cmdArgs = append(cmdArgs, fmt.Sprintf("--outbound-addr=%s", options.outboundAddr))
	}

	if options.outboundAddr6 != "" {
		if !features.HasOutboundAddr || !features.HasIPv6 {
			return nil, errors.Errorf("outbound_addr6 not supported")
		}
		if !options.enableIPv6 {
			return nil, errors.Errorf("enable_ipv6=true is required for outbound_addr6")
		}
		cmdArgs = append(cmdArgs, fmt.Sprintf("--outbound-addr6=%s", options.outboundAddr6))
	}

	return cmdArgs, nil
}

// setupSlirp4netns can be called in rootful as well as in rootless
func (r *Runtime) setupSlirp4netns(ctr *Container, netns ns.NetNS) error {
	path := r.config.Engine.NetworkCmdPath
	if path == "" {
		var err error
		path, err = exec.LookPath("slirp4netns")
		if err != nil {
			logrus.Errorf("Could not find slirp4netns, the network namespace won't be configured: %v", err)
			return nil
		}
	}

	syncR, syncW, err := os.Pipe()
	if err != nil {
		return errors.Wrapf(err, "failed to open pipe")
	}
	defer errorhandling.CloseQuiet(syncR)
	defer errorhandling.CloseQuiet(syncW)

	havePortMapping := len(ctr.config.PortMappings) > 0
	logPath := filepath.Join(ctr.runtime.config.Engine.TmpDir, fmt.Sprintf("slirp4netns-%s.log", ctr.config.ID))

	ctrNetworkSlipOpts := []string{}
	if ctr.config.NetworkOptions != nil {
		ctrNetworkSlipOpts = append(ctrNetworkSlipOpts, ctr.config.NetworkOptions["slirp4netns"]...)
	}
	netOptions, err := parseSlirp4netnsNetworkOptions(r, ctrNetworkSlipOpts)
	if err != nil {
		return err
	}
	slirpFeatures, err := checkSlirpFlags(path)
	if err != nil {
		return errors.Wrapf(err, "error checking slirp4netns binary %s: %q", path, err)
	}
	cmdArgs, err := createBasicSlirp4netnsCmdArgs(netOptions, slirpFeatures)
	if err != nil {
		return err
	}

	// the slirp4netns arguments being passed are describes as follows:
	// from the slirp4netns documentation: https://github.com/rootless-containers/slirp4netns
	// -c, --configure Brings up the tap interface
	// -e, --exit-fd=FD specify the FD for terminating slirp4netns
	// -r, --ready-fd=FD specify the FD to write to when the initialization steps are finished
	cmdArgs = append(cmdArgs, "-c", "-e", "3", "-r", "4")

	var apiSocket string
	if havePortMapping && netOptions.isSlirpHostForward {
		apiSocket = filepath.Join(ctr.runtime.config.Engine.TmpDir, fmt.Sprintf("%s.net", ctr.config.ID))
		cmdArgs = append(cmdArgs, "--api-socket", apiSocket)
	}
	netnsPath := ""
	if !ctr.config.PostConfigureNetNS {
		ctr.rootlessSlirpSyncR, ctr.rootlessSlirpSyncW, err = os.Pipe()
		if err != nil {
			return errors.Wrapf(err, "failed to create rootless network sync pipe")
		}
		netnsPath = netns.Path()
		cmdArgs = append(cmdArgs, "--netns-type=path", netnsPath, "tap0")
	} else {
		defer errorhandling.CloseQuiet(ctr.rootlessSlirpSyncR)
		defer errorhandling.CloseQuiet(ctr.rootlessSlirpSyncW)
		netnsPath = fmt.Sprintf("/proc/%d/ns/net", ctr.state.PID)
		// we don't use --netns-path here (unavailable for slirp4netns < v0.4)
		cmdArgs = append(cmdArgs, fmt.Sprintf("%d", ctr.state.PID), "tap0")
	}

	cmd := exec.Command(path, cmdArgs...)
	logrus.Debugf("slirp4netns command: %s", strings.Join(cmd.Args, " "))
	cmd.SysProcAttr = &syscall.SysProcAttr{
		Setpgid: true,
	}

	// workaround for https://github.com/rootless-containers/slirp4netns/pull/153
	if !netOptions.noPivotRoot && slirpFeatures.HasEnableSandbox {
		cmd.SysProcAttr.Cloneflags = syscall.CLONE_NEWNS
		cmd.SysProcAttr.Unshareflags = syscall.CLONE_NEWNS
	}

	// Leak one end of the pipe in slirp4netns, the other will be sent to conmon
	cmd.ExtraFiles = append(cmd.ExtraFiles, ctr.rootlessSlirpSyncR, syncW)

	logFile, err := os.Create(logPath)
	if err != nil {
		return errors.Wrapf(err, "failed to open slirp4netns log file %s", logPath)
	}
	defer logFile.Close()
	// Unlink immediately the file so we won't need to worry about cleaning it up later.
	// It is still accessible through the open fd logFile.
	if err := os.Remove(logPath); err != nil {
		return errors.Wrapf(err, "delete file %s", logPath)
	}
	cmd.Stdout = logFile
	cmd.Stderr = logFile

	var slirpReadyChan (chan struct{})

	if netOptions.enableIPv6 {
		slirpReadyChan = make(chan struct{})
		defer close(slirpReadyChan)
		go func() {
			err := ns.WithNetNSPath(netnsPath, func(_ ns.NetNS) error {
				// Duplicate Address Detection slows the ipv6 setup down for 1-2 seconds.
				// Since slirp4netns is run it is own namespace and not directly routed
				// we can skip this to make the ipv6 address immediately available.
				// We change the default to make sure the slirp tap interface gets the
				// correct value assigned so DAD is disabled for it
				// Also make sure to change this value back to the original after slirp4netns
				// is ready in case users rely on this sysctl.
				orgValue, err := ioutil.ReadFile(ipv6ConfDefaultAcceptDadSysctl)
				if err != nil {
					return err
				}
				err = ioutil.WriteFile(ipv6ConfDefaultAcceptDadSysctl, []byte("0"), 0644)
				if err != nil {
					return err
				}
				// wait for slirp to finish setup
				<-slirpReadyChan
				return ioutil.WriteFile(ipv6ConfDefaultAcceptDadSysctl, orgValue, 0644)
			})
			if err != nil {
				logrus.Warnf("failed to set net.ipv6.conf.default.accept_dad sysctl: %v", err)
			}
		}()
	}

	if err := cmd.Start(); err != nil {
		return errors.Wrapf(err, "failed to start slirp4netns process")
	}
	defer func() {
		servicereaper.AddPID(cmd.Process.Pid)
		if err := cmd.Process.Release(); err != nil {
			logrus.Errorf("Unable to release command process: %q", err)
		}
	}()

	if err := waitForSync(syncR, cmd, logFile, 1*time.Second); err != nil {
		return err
	}
	if slirpReadyChan != nil {
		slirpReadyChan <- struct{}{}
	}

	// Set a default slirp subnet. Parsing a string with the net helper is easier than building the struct myself
	_, ctr.slirp4netnsSubnet, _ = net.ParseCIDR(defaultSlirp4netnsSubnet)

	// Set slirp4netnsSubnet addresses now that we are pretty sure the command executed
	if netOptions.cidr != "" {
		ipv4, ipv4network, err := net.ParseCIDR(netOptions.cidr)
		if err != nil || ipv4.To4() == nil {
			return errors.Errorf("invalid cidr %q", netOptions.cidr)
		}
		ctr.slirp4netnsSubnet = ipv4network
	}

	if havePortMapping {
		if netOptions.isSlirpHostForward {
			return r.setupRootlessPortMappingViaSlirp(ctr, cmd, apiSocket)
		}
		return r.setupRootlessPortMappingViaRLK(ctr, netnsPath, nil)
	}

	return nil
}

// Get expected slirp ipv4 address based on subnet. If subnet is null use default subnet
// Reference: https://github.com/rootless-containers/slirp4netns/blob/master/slirp4netns.1.md#description
func GetSlirp4netnsIP(subnet *net.IPNet) (*net.IP, error) {
	_, slirpSubnet, _ := net.ParseCIDR(defaultSlirp4netnsSubnet)
	if subnet != nil {
		slirpSubnet = subnet
	}
	expectedIP, err := addToIP(slirpSubnet, uint32(100))
	if err != nil {
		return nil, errors.Wrapf(err, "error calculating expected ip for slirp4netns")
	}
	return expectedIP, nil
}

// Get expected slirp Gateway ipv4 address based on subnet
// Reference: https://github.com/rootless-containers/slirp4netns/blob/master/slirp4netns.1.md#description
func GetSlirp4netnsGateway(subnet *net.IPNet) (*net.IP, error) {
	_, slirpSubnet, _ := net.ParseCIDR(defaultSlirp4netnsSubnet)
	if subnet != nil {
		slirpSubnet = subnet
	}
	expectedGatewayIP, err := addToIP(slirpSubnet, uint32(2))
	if err != nil {
		return nil, errors.Wrapf(err, "error calculating expected gateway ip for slirp4netns")
	}
	return expectedGatewayIP, nil
}

// Get expected slirp DNS ipv4 address based on subnet
// Reference: https://github.com/rootless-containers/slirp4netns/blob/master/slirp4netns.1.md#description
func GetSlirp4netnsDNS(subnet *net.IPNet) (*net.IP, error) {
	_, slirpSubnet, _ := net.ParseCIDR(defaultSlirp4netnsSubnet)
	if subnet != nil {
		slirpSubnet = subnet
	}
	expectedDNSIP, err := addToIP(slirpSubnet, uint32(3))
	if err != nil {
		return nil, errors.Wrapf(err, "error calculating expected dns ip for slirp4netns")
	}
	return expectedDNSIP, nil
}

// Helper function to calculate slirp ip address offsets
// Adapted from: https://github.com/signalsciences/ipv4/blob/master/int.go#L12-L24
func addToIP(subnet *net.IPNet, offset uint32) (*net.IP, error) {
	// I have no idea why I have to do this, but if I don't ip is 0
	ipFixed := subnet.IP.To4()

	ipInteger := uint32(ipFixed[3]) | uint32(ipFixed[2])<<8 | uint32(ipFixed[1])<<16 | uint32(ipFixed[0])<<24
	ipNewRaw := ipInteger + offset
	// Avoid overflows
	if ipNewRaw < ipInteger {
		return nil, errors.Errorf("integer overflow while calculating ip address offset, %s + %d", ipFixed, offset)
	}
	ipNew := net.IPv4(byte(ipNewRaw>>24), byte(ipNewRaw>>16&0xFF), byte(ipNewRaw>>8)&0xFF, byte(ipNewRaw&0xFF))
	if !subnet.Contains(ipNew) {
		return nil, errors.Errorf("calculated ip address %s is not within given subnet %s", ipNew.String(), subnet.String())
	}
	return &ipNew, nil
}

func waitForSync(syncR *os.File, cmd *exec.Cmd, logFile io.ReadSeeker, timeout time.Duration) error {
	prog := filepath.Base(cmd.Path)
	if len(cmd.Args) > 0 {
		prog = cmd.Args[0]
	}
	b := make([]byte, 16)
	for {
		if err := syncR.SetDeadline(time.Now().Add(timeout)); err != nil {
			return errors.Wrapf(err, "error setting %s pipe timeout", prog)
		}
		// FIXME: return err as soon as proc exits, without waiting for timeout
		if _, err := syncR.Read(b); err == nil {
			break
		} else {
			if os.IsTimeout(err) {
				// Check if the process is still running.
				var status syscall.WaitStatus
				pid, err := syscall.Wait4(cmd.Process.Pid, &status, syscall.WNOHANG, nil)
				if err != nil {
					return errors.Wrapf(err, "failed to read %s process status", prog)
				}
				if pid != cmd.Process.Pid {
					continue
				}
				if status.Exited() {
					// Seek at the beginning of the file and read all its content
					if _, err := logFile.Seek(0, 0); err != nil {
						logrus.Errorf("Could not seek log file: %q", err)
					}
					logContent, err := ioutil.ReadAll(logFile)
					if err != nil {
						return errors.Wrapf(err, "%s failed", prog)
					}
					return errors.Errorf("%s failed: %q", prog, logContent)
				}
				if status.Signaled() {
					return errors.Errorf("%s killed by signal", prog)
				}
				continue
			}
			return errors.Wrapf(err, "failed to read from %s sync pipe", prog)
		}
	}
	return nil
}

func (r *Runtime) setupRootlessPortMappingViaRLK(ctr *Container, netnsPath string, netStatus map[string]types.StatusBlock) error {
	syncR, syncW, err := os.Pipe()
	if err != nil {
		return errors.Wrapf(err, "failed to open pipe")
	}
	defer errorhandling.CloseQuiet(syncR)
	defer errorhandling.CloseQuiet(syncW)

	logPath := filepath.Join(ctr.runtime.config.Engine.TmpDir, fmt.Sprintf("rootlessport-%s.log", ctr.config.ID))
	logFile, err := os.Create(logPath)
	if err != nil {
		return errors.Wrapf(err, "failed to open rootlessport log file %s", logPath)
	}
	defer logFile.Close()
	// Unlink immediately the file so we won't need to worry about cleaning it up later.
	// It is still accessible through the open fd logFile.
	if err := os.Remove(logPath); err != nil {
		return errors.Wrapf(err, "delete file %s", logPath)
	}

	if !ctr.config.PostConfigureNetNS {
		ctr.rootlessPortSyncR, ctr.rootlessPortSyncW, err = os.Pipe()
		if err != nil {
			return errors.Wrapf(err, "failed to create rootless port sync pipe")
		}
	}

	childIP := getRootlessPortChildIP(ctr, netStatus)
	cfg := rootlessport.Config{
		Mappings:    ctr.convertPortMappings(),
		NetNSPath:   netnsPath,
		ExitFD:      3,
		ReadyFD:     4,
		TmpDir:      ctr.runtime.config.Engine.TmpDir,
		ChildIP:     childIP,
		ContainerID: ctr.config.ID,
		RootlessCNI: ctr.config.NetMode.IsBridge() && rootless.IsRootless(),
	}
	cfgJSON, err := json.Marshal(cfg)
	if err != nil {
		return err
	}
	cfgR := bytes.NewReader(cfgJSON)
	var stdout bytes.Buffer
	path, err := r.config.FindHelperBinary(rootlessport.BinaryName, false)
	if err != nil {
		return err
	}
	cmd := exec.Command(path)
	cmd.Args = []string{rootlessport.BinaryName}

	// Leak one end of the pipe in rootlessport process, the other will be sent to conmon
	defer errorhandling.CloseQuiet(ctr.rootlessPortSyncR)

	cmd.ExtraFiles = append(cmd.ExtraFiles, ctr.rootlessPortSyncR, syncW)
	cmd.Stdin = cfgR
	// stdout is for human-readable error, stderr is for debug log
	cmd.Stdout = &stdout
	cmd.Stderr = io.MultiWriter(logFile, &logrusDebugWriter{"rootlessport: "})
	cmd.SysProcAttr = &syscall.SysProcAttr{
		Setpgid: true,
	}
	if err := cmd.Start(); err != nil {
		return errors.Wrapf(err, "failed to start rootlessport process")
	}
	defer func() {
		servicereaper.AddPID(cmd.Process.Pid)
		if err := cmd.Process.Release(); err != nil {
			logrus.Errorf("Unable to release rootlessport process: %q", err)
		}
	}()
	if err := waitForSync(syncR, cmd, logFile, 3*time.Second); err != nil {
		stdoutStr := stdout.String()
		if stdoutStr != "" {
			// err contains full debug log and too verbose, so return stdoutStr
			logrus.Debug(err)
			return errors.Errorf("rootlessport " + strings.TrimSuffix(stdoutStr, "\n"))
		}
		return err
	}
	logrus.Debug("rootlessport is ready")
	return nil
}

func (r *Runtime) setupRootlessPortMappingViaSlirp(ctr *Container, cmd *exec.Cmd, apiSocket string) (err error) {
	const pidWaitTimeout = 60 * time.Second
	chWait := make(chan error)
	go func() {
		interval := 25 * time.Millisecond
		for i := time.Duration(0); i < pidWaitTimeout; i += interval {
			// Check if the process is still running.
			var status syscall.WaitStatus
			pid, err := syscall.Wait4(cmd.Process.Pid, &status, syscall.WNOHANG, nil)
			if err != nil {
				break
			}
			if pid != cmd.Process.Pid {
				continue
			}
			if status.Exited() || status.Signaled() {
				chWait <- fmt.Errorf("slirp4netns exited with status %d", status.ExitStatus())
			}
			time.Sleep(interval)
		}
	}()
	defer close(chWait)

	// wait that API socket file appears before trying to use it.
	if _, err := WaitForFile(apiSocket, chWait, pidWaitTimeout); err != nil {
		return errors.Wrapf(err, "waiting for slirp4nets to create the api socket file %s", apiSocket)
	}

	// for each port we want to add we need to open a connection to the slirp4netns control socket
	// and send the add_hostfwd command.
	for _, i := range ctr.convertPortMappings() {
		conn, err := net.Dial("unix", apiSocket)
		if err != nil {
			return errors.Wrapf(err, "cannot open connection to %s", apiSocket)
		}
		defer func() {
			if err := conn.Close(); err != nil {
				logrus.Errorf("Unable to close connection: %q", err)
			}
		}()
		hostIP := i.HostIP
		if hostIP == "" {
			hostIP = "0.0.0.0"
		}
		apiCmd := slirp4netnsCmd{
			Execute: "add_hostfwd",
			Args: slirp4netnsCmdArg{
				Proto:     i.Protocol,
				HostAddr:  hostIP,
				HostPort:  i.HostPort,
				GuestPort: i.ContainerPort,
			},
		}
		// create the JSON payload and send it.  Mark the end of request shutting down writes
		// to the socket, as requested by slirp4netns.
		data, err := json.Marshal(&apiCmd)
		if err != nil {
			return errors.Wrapf(err, "cannot marshal JSON for slirp4netns")
		}
		if _, err := conn.Write([]byte(fmt.Sprintf("%s\n", data))); err != nil {
			return errors.Wrapf(err, "cannot write to control socket %s", apiSocket)
		}
		if err := conn.(*net.UnixConn).CloseWrite(); err != nil {
			return errors.Wrapf(err, "cannot shutdown the socket %s", apiSocket)
		}
		buf := make([]byte, 2048)
		readLength, err := conn.Read(buf)
		if err != nil {
			return errors.Wrapf(err, "cannot read from control socket %s", apiSocket)
		}
		// if there is no 'error' key in the received JSON data, then the operation was
		// successful.
		var y map[string]interface{}
		if err := json.Unmarshal(buf[0:readLength], &y); err != nil {
			return errors.Wrapf(err, "error parsing error status from slirp4netns")
		}
		if e, found := y["error"]; found {
			return errors.Errorf("error from slirp4netns while setting up port redirection: %v", e)
		}
	}
	logrus.Debug("slirp4netns port-forwarding setup via add_hostfwd is ready")
	return nil
}

func getRootlessPortChildIP(c *Container, netStatus map[string]types.StatusBlock) string {
	if c.config.NetMode.IsSlirp4netns() {
		slirp4netnsIP, err := GetSlirp4netnsIP(c.slirp4netnsSubnet)
		if err != nil {
			return ""
		}
		return slirp4netnsIP.String()
	}

	var ipv6 net.IP
	for _, status := range netStatus {
		for _, netInt := range status.Interfaces {
			for _, netAddress := range netInt.Subnets {
				ipv4 := netAddress.IPNet.IP.To4()
				if ipv4 != nil {
					return ipv4.String()
				}
				ipv6 = netAddress.IPNet.IP
			}
		}
	}
	if ipv6 != nil {
		return ipv6.String()
	}
	return ""
}

// reloadRootlessRLKPortMapping will trigger a reload for the port mappings in the rootlessport process.
// This should only be called by network connect/disconnect and only as rootless.
func (c *Container) reloadRootlessRLKPortMapping() error {
	if len(c.config.PortMappings) == 0 {
		return nil
	}
	childIP := getRootlessPortChildIP(c, c.state.NetworkStatus)
	logrus.Debugf("reloading rootless ports for container %s, childIP is %s", c.config.ID, childIP)

	conn, err := openUnixSocket(filepath.Join(c.runtime.config.Engine.TmpDir, "rp", c.config.ID))
	if err != nil {
		return errors.Wrap(err, "could not reload rootless port mappings, port forwarding may no longer work correctly")
	}
	defer conn.Close()
	enc := json.NewEncoder(conn)
	err = enc.Encode(childIP)
	if err != nil {
		return errors.Wrap(err, "port reloading failed")
	}
	b, err := ioutil.ReadAll(conn)
	if err != nil {
		return errors.Wrap(err, "port reloading failed")
	}
	data := string(b)
	if data != "OK" {
		return errors.Errorf("port reloading failed: %s", data)
	}
	return nil
}