summaryrefslogtreecommitdiff
path: root/pkg/rootless/rootless_linux.go
blob: 6089ad73aea90cbbb51a0966ff8bd6b8464bb90f (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
// +build linux

package rootless

import (
	"fmt"
	"io/ioutil"
	"os"
	"os/exec"
	gosignal "os/signal"
	"runtime"
	"strconv"
	"syscall"

	"github.com/containers/storage/pkg/idtools"
	"github.com/docker/docker/pkg/signal"
	"github.com/pkg/errors"
)

/*
extern int reexec_in_user_namespace(int ready);
extern int reexec_in_user_namespace_wait(int pid);
*/
import "C"

func runInUser() error {
	os.Setenv("_LIBPOD_USERNS_CONFIGURED", "done")
	return nil
}

// IsRootless tells us if we are running in rootless mode
func IsRootless() bool {
	return os.Getuid() != 0 || os.Getenv("_LIBPOD_USERNS_CONFIGURED") != ""
}

// GetRootlessUID returns the UID of the user in the parent userNS
func GetRootlessUID() int {
	uidEnv := os.Getenv("_LIBPOD_ROOTLESS_UID")
	if uidEnv != "" {
		u, _ := strconv.Atoi(uidEnv)
		return u
	}
	return os.Getuid()
}

func tryMappingTool(tool string, pid int, hostID int, mappings []idtools.IDMap) error {
	path, err := exec.LookPath(tool)
	if err != nil {
		return err
	}

	appendTriplet := func(l []string, a, b, c int) []string {
		return append(l, fmt.Sprintf("%d", a), fmt.Sprintf("%d", b), fmt.Sprintf("%d", c))
	}

	args := []string{path, fmt.Sprintf("%d", pid)}
	args = appendTriplet(args, 0, hostID, 1)
	if mappings != nil {
		for _, i := range mappings {
			args = appendTriplet(args, i.ContainerID+1, i.HostID, i.Size)
		}
	}
	cmd := exec.Cmd{
		Path: path,
		Args: args,
	}
	return cmd.Run()
}

// BecomeRootInUserNS re-exec podman in a new userNS.  It returns whether podman was re-executed
// into a new user namespace and the return code from the re-executed podman process.
// If podman was re-executed the caller needs to propagate the error code returned by the child
// process.
func BecomeRootInUserNS() (bool, int, error) {
	if os.Getuid() == 0 || os.Getenv("_LIBPOD_USERNS_CONFIGURED") != "" {
		if os.Getenv("_LIBPOD_USERNS_CONFIGURED") == "init" {
			return false, 0, runInUser()
		}
		return false, 0, nil
	}

	runtime.LockOSThread()
	defer runtime.UnlockOSThread()

	r, w, err := os.Pipe()
	if err != nil {
		return false, -1, err
	}
	defer r.Close()
	defer w.Close()

	pidC := C.reexec_in_user_namespace(C.int(r.Fd()))
	pid := int(pidC)
	if pid < 0 {
		return false, -1, errors.Errorf("cannot re-exec process")
	}

	setgroups := fmt.Sprintf("/proc/%d/setgroups", pid)
	err = ioutil.WriteFile(setgroups, []byte("deny\n"), 0666)
	if err != nil {
		return false, -1, errors.Wrapf(err, "cannot write setgroups file")
	}

	var uids, gids []idtools.IDMap
	username := os.Getenv("USER")
	mappings, err := idtools.NewIDMappings(username, username)
	if err == nil {
		uids = mappings.UIDs()
		gids = mappings.GIDs()
	}

	uidsMapped := false
	if mappings != nil && uids != nil {
		uidsMapped = tryMappingTool("newuidmap", pid, os.Getuid(), uids) == nil
	}
	if !uidsMapped {
		uidMap := fmt.Sprintf("/proc/%d/uid_map", pid)
		err = ioutil.WriteFile(uidMap, []byte(fmt.Sprintf("%d %d 1\n", 0, os.Getuid())), 0666)
		if err != nil {
			return false, -1, errors.Wrapf(err, "cannot write uid_map")
		}
	}

	gidsMapped := false
	if mappings != nil && gids != nil {
		gidsMapped = tryMappingTool("newgidmap", pid, os.Getgid(), gids) == nil
	}
	if !gidsMapped {
		gidMap := fmt.Sprintf("/proc/%d/gid_map", pid)
		err = ioutil.WriteFile(gidMap, []byte(fmt.Sprintf("%d %d 1\n", 0, os.Getgid())), 0666)
		if err != nil {
			return false, -1, errors.Wrapf(err, "cannot write gid_map")
		}
	}

	_, err = w.Write([]byte("1"))
	if err != nil {
		return false, -1, errors.Wrapf(err, "write to sync pipe")
	}

	c := make(chan os.Signal, 1)

	gosignal.Notify(c)
	defer gosignal.Reset()
	go func() {
		for s := range c {
			if s == signal.SIGCHLD || s == signal.SIGPIPE {
				continue
			}

			syscall.Kill(int(pidC), s.(syscall.Signal))
		}
	}()

	ret := C.reexec_in_user_namespace_wait(pidC)
	if ret < 0 {
		return false, -1, errors.Wrapf(err, "error waiting for the re-exec process")
	}

	return true, int(ret), nil
}