docker-cli/components/engine/pkg/libcontainer/devices/devices.go

package devices

import (
	"fmt"
	"os"
	"syscall"
)

const (
	Wildcard = -1
)

type Device struct {
	Type              rune        `json:"type,omitempty"`
	Path              string      `json:"path,omitempty"`               // It is fine if this is an empty string in the case that you are using Wildcards
	MajorNumber       int64       `json:"major_number,omitempty"`       // Use the wildcard constant for wildcards.
	MinorNumber       int64       `json:"minor_number,omitempty"`       // Use the wildcard constant for wildcards.
	CgroupPermissions string      `json:"cgroup_permissions,omitempty"` // Typically just "rwm"
	FileMode          os.FileMode `json:"file_mode,omitempty"`          // The permission bits of the file's mode
}

func GetDeviceNumberString(deviceNumber int64) string {
	if deviceNumber == Wildcard {
		return "*"
	} else {
		return fmt.Sprintf("%d", deviceNumber)
	}
}

func (device Device) GetCgroupAllowString() string {
	return fmt.Sprintf("%c %s:%s %s", device.Type, GetDeviceNumberString(device.MajorNumber), GetDeviceNumberString(device.MinorNumber), device.CgroupPermissions)
}

// Given the path to a device and it's cgroup_permissions(which cannot be easilly queried) look up the information about a linux device and return that information as a Device struct.
func GetDevice(path string, cgroupPermissions string) (Device, error) {
	var (
		err                    error
		fileInfo               os.FileInfo
		mode                   os.FileMode
		fileModePermissionBits os.FileMode
		devType                rune
		devNumber              int
		stat_t                 *syscall.Stat_t
		ok                     bool
		device                 Device
	)

	fileInfo, err = os.Stat(path)
	if err != nil {
		return Device{}, err
	}

	mode = fileInfo.Mode()
	fileModePermissionBits = os.FileMode.Perm(mode)
	switch {
	case (mode & os.ModeDevice) == 0:
		return Device{}, fmt.Errorf("%s is not a device", path)
	case (mode & os.ModeCharDevice) != 0:
		fileModePermissionBits |= syscall.S_IFCHR
		devType = 'c'
	default:
		fileModePermissionBits |= syscall.S_IFBLK
		devType = 'b'
	}

	stat_t, ok = fileInfo.Sys().(*syscall.Stat_t)
	if !ok {
		return Device{}, fmt.Errorf("cannot determine the device number for device %s", path)
	}
	devNumber = int(stat_t.Rdev)

	device = Device{
		Type:              devType,
		Path:              path,
		MajorNumber:       Major(devNumber),
		MinorNumber:       Minor(devNumber),
		CgroupPermissions: cgroupPermissions,
		FileMode:          fileModePermissionBits,
	}
	return device, nil
}

var (
	// These are devices that are to be both allowed and created.

	DefaultSimpleDevices = []Device{
		// /dev/null and zero
		{
			Path:              "/dev/null",
			Type:              'c',
			MajorNumber:       1,
			MinorNumber:       3,
			CgroupPermissions: "rwm",
			FileMode:          0666,
		},
		{
			Path:              "/dev/zero",
			Type:              'c',
			MajorNumber:       1,
			MinorNumber:       5,
			CgroupPermissions: "rwm",
			FileMode:          0666,
		},

		{
			Path:              "/dev/full",
			Type:              'c',
			MajorNumber:       1,
			MinorNumber:       7,
			CgroupPermissions: "rwm",
			FileMode:          0666,
		},

		// consoles and ttys
		{
			Path:              "/dev/tty",
			Type:              'c',
			MajorNumber:       5,
			MinorNumber:       0,
			CgroupPermissions: "rwm",
			FileMode:          0666,
		},

		// /dev/urandom,/dev/random
		{
			Path:              "/dev/urandom",
			Type:              'c',
			MajorNumber:       1,
			MinorNumber:       9,
			CgroupPermissions: "rwm",
			FileMode:          0666,
		},
		{
			Path:              "/dev/random",
			Type:              'c',
			MajorNumber:       1,
			MinorNumber:       8,
			CgroupPermissions: "rwm",
			FileMode:          0666,
		},
	}

	DefaultAllowedDevices = append([]Device{
		// allow mknod for any device
		{
			Type:              'c',
			MajorNumber:       Wildcard,
			MinorNumber:       Wildcard,
			CgroupPermissions: "m",
		},
		{
			Type:              'b',
			MajorNumber:       Wildcard,
			MinorNumber:       Wildcard,
			CgroupPermissions: "m",
		},

		{
			Path:              "/dev/console",
			Type:              'c',
			MajorNumber:       5,
			MinorNumber:       1,
			CgroupPermissions: "rwm",
		},
		{
			Path:              "/dev/tty0",
			Type:              'c',
			MajorNumber:       4,
			MinorNumber:       0,
			CgroupPermissions: "rwm",
		},
		{
			Path:              "/dev/tty1",
			Type:              'c',
			MajorNumber:       4,
			MinorNumber:       1,
			CgroupPermissions: "rwm",
		},
		// /dev/pts/ - pts namespaces are "coming soon"
		{
			Path:              "",
			Type:              'c',
			MajorNumber:       136,
			MinorNumber:       Wildcard,
			CgroupPermissions: "rwm",
		},
		{
			Path:              "",
			Type:              'c',
			MajorNumber:       5,
			MinorNumber:       2,
			CgroupPermissions: "rwm",
		},

		// tuntap
		{
			Path:              "",
			Type:              'c',
			MajorNumber:       10,
			MinorNumber:       200,
			CgroupPermissions: "rwm",
		},

		/*// fuse
		   {
		    Path: "",
		    Type: 'c',
		    MajorNumber: 10,
		    MinorNumber: 229,
		    CgroupPermissions: "rwm",
		   },

		// rtc
		   {
		    Path: "",
		    Type: 'c',
		    MajorNumber: 254,
		    MinorNumber: 0,
		    CgroupPermissions: "rwm",
		   },
		*/
	}, DefaultSimpleDevices...)

	DefaultAutoCreatedDevices = append([]Device{
		{
			// /dev/fuse is created but not allowed.
			// This is to allow java to work.  Because java
			// Insists on there being a /dev/fuse
			// https://github.com/dotcloud/docker/issues/514
			// https://github.com/dotcloud/docker/issues/2393
			//
			Path:              "/dev/fuse",
			Type:              'c',
			MajorNumber:       10,
			MinorNumber:       229,
			CgroupPermissions: "rwm",
		},
	}, DefaultSimpleDevices...)
)