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726 lines
20 KiB
Go
726 lines
20 KiB
Go
// +build linux
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package libcontainer
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import (
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"fmt"
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"io"
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"io/ioutil"
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"os"
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"os/exec"
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"path"
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"path/filepath"
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"strings"
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"syscall"
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"time"
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"github.com/docker/docker/pkg/mount"
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"github.com/docker/docker/pkg/symlink"
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"github.com/opencontainers/runc/libcontainer/cgroups"
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"github.com/opencontainers/runc/libcontainer/configs"
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"github.com/opencontainers/runc/libcontainer/label"
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"github.com/opencontainers/runc/libcontainer/system"
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libcontainerUtils "github.com/opencontainers/runc/libcontainer/utils"
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)
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const defaultMountFlags = syscall.MS_NOEXEC | syscall.MS_NOSUID | syscall.MS_NODEV
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// needsSetupDev returns true if /dev needs to be set up.
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func needsSetupDev(config *configs.Config) bool {
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for _, m := range config.Mounts {
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if m.Device == "bind" && libcontainerUtils.CleanPath(m.Destination) == "/dev" {
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return false
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}
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}
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return true
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}
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// setupRootfs sets up the devices, mount points, and filesystems for use inside a
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// new mount namespace.
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func setupRootfs(config *configs.Config, console *linuxConsole, pipe io.ReadWriter) (err error) {
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if err := prepareRoot(config); err != nil {
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return newSystemErrorWithCause(err, "preparing rootfs")
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}
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setupDev := needsSetupDev(config)
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for _, m := range config.Mounts {
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for _, precmd := range m.PremountCmds {
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if err := mountCmd(precmd); err != nil {
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return newSystemErrorWithCause(err, "running premount command")
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}
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}
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if err := mountToRootfs(m, config.Rootfs, config.MountLabel); err != nil {
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return newSystemErrorWithCausef(err, "mounting %q to rootfs %q at %q", m.Source, config.Rootfs, m.Destination)
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}
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for _, postcmd := range m.PostmountCmds {
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if err := mountCmd(postcmd); err != nil {
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return newSystemErrorWithCause(err, "running postmount command")
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}
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}
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}
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if setupDev {
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if err := createDevices(config); err != nil {
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return newSystemErrorWithCause(err, "creating device nodes")
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}
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if err := setupPtmx(config, console); err != nil {
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return newSystemErrorWithCause(err, "setting up ptmx")
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}
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if err := setupDevSymlinks(config.Rootfs); err != nil {
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return newSystemErrorWithCause(err, "setting up /dev symlinks")
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}
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}
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// Signal the parent to run the pre-start hooks.
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// The hooks are run after the mounts are setup, but before we switch to the new
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// root, so that the old root is still available in the hooks for any mount
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// manipulations.
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if err := syncParentHooks(pipe); err != nil {
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return err
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}
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if err := syscall.Chdir(config.Rootfs); err != nil {
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return newSystemErrorWithCausef(err, "changing dir to %q", config.Rootfs)
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}
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if config.NoPivotRoot {
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err = msMoveRoot(config.Rootfs)
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} else {
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err = pivotRoot(config.Rootfs, config.PivotDir)
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}
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if err != nil {
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return newSystemErrorWithCause(err, "jailing process inside rootfs")
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}
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if setupDev {
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if err := reOpenDevNull(); err != nil {
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return newSystemErrorWithCause(err, "reopening /dev/null inside container")
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}
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}
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// remount dev as ro if specified
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for _, m := range config.Mounts {
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if libcontainerUtils.CleanPath(m.Destination) == "/dev" {
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if m.Flags&syscall.MS_RDONLY != 0 {
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if err := remountReadonly(m.Destination); err != nil {
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return newSystemErrorWithCausef(err, "remounting %q as readonly", m.Destination)
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}
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}
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break
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}
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}
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// set rootfs ( / ) as readonly
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if config.Readonlyfs {
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if err := setReadonly(); err != nil {
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return newSystemErrorWithCause(err, "setting rootfs as readonly")
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}
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}
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syscall.Umask(0022)
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return nil
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}
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func mountCmd(cmd configs.Command) error {
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command := exec.Command(cmd.Path, cmd.Args[:]...)
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command.Env = cmd.Env
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command.Dir = cmd.Dir
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if out, err := command.CombinedOutput(); err != nil {
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return fmt.Errorf("%#v failed: %s: %v", cmd, string(out), err)
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}
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return nil
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}
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func mountToRootfs(m *configs.Mount, rootfs, mountLabel string) error {
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var (
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dest = m.Destination
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)
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if !strings.HasPrefix(dest, rootfs) {
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dest = filepath.Join(rootfs, dest)
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}
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switch m.Device {
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case "proc", "sysfs":
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if err := os.MkdirAll(dest, 0755); err != nil {
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return err
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}
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// Selinux kernels do not support labeling of /proc or /sys
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return mountPropagate(m, rootfs, "")
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case "mqueue":
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if err := os.MkdirAll(dest, 0755); err != nil {
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return err
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}
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if err := mountPropagate(m, rootfs, mountLabel); err != nil {
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// older kernels do not support labeling of /dev/mqueue
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if err := mountPropagate(m, rootfs, ""); err != nil {
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return err
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}
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return label.SetFileLabel(dest, mountLabel)
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}
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return nil
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case "tmpfs":
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stat, err := os.Stat(dest)
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if err != nil {
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if err := os.MkdirAll(dest, 0755); err != nil {
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return err
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}
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}
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if err := mountPropagate(m, rootfs, mountLabel); err != nil {
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return err
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}
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if stat != nil {
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if err = os.Chmod(dest, stat.Mode()); err != nil {
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return err
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}
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}
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return nil
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case "bind":
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stat, err := os.Stat(m.Source)
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if err != nil {
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// error out if the source of a bind mount does not exist as we will be
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// unable to bind anything to it.
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return err
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}
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// ensure that the destination of the bind mount is resolved of symlinks at mount time because
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// any previous mounts can invalidate the next mount's destination.
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// this can happen when a user specifies mounts within other mounts to cause breakouts or other
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// evil stuff to try to escape the container's rootfs.
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if dest, err = symlink.FollowSymlinkInScope(filepath.Join(rootfs, m.Destination), rootfs); err != nil {
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return err
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}
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if err := checkMountDestination(rootfs, dest); err != nil {
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return err
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}
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// update the mount with the correct dest after symlinks are resolved.
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m.Destination = dest
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if err := createIfNotExists(dest, stat.IsDir()); err != nil {
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return err
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}
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if err := mountPropagate(m, rootfs, mountLabel); err != nil {
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return err
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}
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// bind mount won't change mount options, we need remount to make mount options effective.
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// first check that we have non-default options required before attempting a remount
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if m.Flags&^(syscall.MS_REC|syscall.MS_REMOUNT|syscall.MS_BIND) != 0 {
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// only remount if unique mount options are set
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if err := remount(m, rootfs); err != nil {
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return err
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}
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}
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if m.Relabel != "" {
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if err := label.Validate(m.Relabel); err != nil {
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return err
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}
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shared := label.IsShared(m.Relabel)
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if err := label.Relabel(m.Source, mountLabel, shared); err != nil {
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return err
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}
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}
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case "cgroup":
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binds, err := getCgroupMounts(m)
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if err != nil {
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return err
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}
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var merged []string
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for _, b := range binds {
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ss := filepath.Base(b.Destination)
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if strings.Contains(ss, ",") {
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merged = append(merged, ss)
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}
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}
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tmpfs := &configs.Mount{
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Source: "tmpfs",
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Device: "tmpfs",
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Destination: m.Destination,
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Flags: defaultMountFlags,
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Data: "mode=755",
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PropagationFlags: m.PropagationFlags,
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}
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if err := mountToRootfs(tmpfs, rootfs, mountLabel); err != nil {
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return err
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}
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for _, b := range binds {
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if err := mountToRootfs(b, rootfs, mountLabel); err != nil {
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return err
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}
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}
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for _, mc := range merged {
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for _, ss := range strings.Split(mc, ",") {
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// symlink(2) is very dumb, it will just shove the path into
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// the link and doesn't do any checks or relative path
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// conversion. Also, don't error out if the cgroup already exists.
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if err := os.Symlink(mc, filepath.Join(rootfs, m.Destination, ss)); err != nil && !os.IsExist(err) {
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return err
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}
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}
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}
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if m.Flags&syscall.MS_RDONLY != 0 {
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// remount cgroup root as readonly
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mcgrouproot := &configs.Mount{
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Source: m.Destination,
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Device: "bind",
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Destination: m.Destination,
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Flags: defaultMountFlags | syscall.MS_RDONLY | syscall.MS_BIND,
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}
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if err := remount(mcgrouproot, rootfs); err != nil {
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return err
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}
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}
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default:
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if err := os.MkdirAll(dest, 0755); err != nil {
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return err
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}
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return mountPropagate(m, rootfs, mountLabel)
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}
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return nil
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}
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func getCgroupMounts(m *configs.Mount) ([]*configs.Mount, error) {
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mounts, err := cgroups.GetCgroupMounts(false)
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if err != nil {
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return nil, err
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}
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cgroupPaths, err := cgroups.ParseCgroupFile("/proc/self/cgroup")
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if err != nil {
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return nil, err
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}
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var binds []*configs.Mount
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for _, mm := range mounts {
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dir, err := mm.GetThisCgroupDir(cgroupPaths)
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if err != nil {
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return nil, err
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}
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relDir, err := filepath.Rel(mm.Root, dir)
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if err != nil {
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return nil, err
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}
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binds = append(binds, &configs.Mount{
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Device: "bind",
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Source: filepath.Join(mm.Mountpoint, relDir),
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Destination: filepath.Join(m.Destination, strings.Join(mm.Subsystems, ",")),
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Flags: syscall.MS_BIND | syscall.MS_REC | m.Flags,
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PropagationFlags: m.PropagationFlags,
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})
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}
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return binds, nil
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}
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// checkMountDestination checks to ensure that the mount destination is not over the top of /proc.
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// dest is required to be an abs path and have any symlinks resolved before calling this function.
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func checkMountDestination(rootfs, dest string) error {
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invalidDestinations := []string{
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"/proc",
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}
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// White list, it should be sub directories of invalid destinations
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validDestinations := []string{
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// These entries can be bind mounted by files emulated by fuse,
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// so commands like top, free displays stats in container.
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"/proc/cpuinfo",
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"/proc/diskstats",
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"/proc/meminfo",
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"/proc/stat",
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"/proc/swaps",
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"/proc/uptime",
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"/proc/net/dev",
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}
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for _, valid := range validDestinations {
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path, err := filepath.Rel(filepath.Join(rootfs, valid), dest)
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if err != nil {
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return err
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}
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if path == "." {
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return nil
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}
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}
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for _, invalid := range invalidDestinations {
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path, err := filepath.Rel(filepath.Join(rootfs, invalid), dest)
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if err != nil {
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return err
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}
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if path == "." || !strings.HasPrefix(path, "..") {
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return fmt.Errorf("%q cannot be mounted because it is located inside %q", dest, invalid)
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}
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}
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return nil
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}
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func setupDevSymlinks(rootfs string) error {
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var links = [][2]string{
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{"/proc/self/fd", "/dev/fd"},
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{"/proc/self/fd/0", "/dev/stdin"},
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{"/proc/self/fd/1", "/dev/stdout"},
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{"/proc/self/fd/2", "/dev/stderr"},
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}
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// kcore support can be toggled with CONFIG_PROC_KCORE; only create a symlink
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// in /dev if it exists in /proc.
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if _, err := os.Stat("/proc/kcore"); err == nil {
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links = append(links, [2]string{"/proc/kcore", "/dev/core"})
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}
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for _, link := range links {
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var (
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src = link[0]
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dst = filepath.Join(rootfs, link[1])
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)
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if err := os.Symlink(src, dst); err != nil && !os.IsExist(err) {
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return fmt.Errorf("symlink %s %s %s", src, dst, err)
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}
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}
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return nil
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}
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// If stdin, stdout, and/or stderr are pointing to `/dev/null` in the parent's rootfs
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// this method will make them point to `/dev/null` in this container's rootfs. This
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// needs to be called after we chroot/pivot into the container's rootfs so that any
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// symlinks are resolved locally.
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func reOpenDevNull() error {
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var stat, devNullStat syscall.Stat_t
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file, err := os.OpenFile("/dev/null", os.O_RDWR, 0)
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if err != nil {
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return fmt.Errorf("Failed to open /dev/null - %s", err)
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}
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defer file.Close()
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if err := syscall.Fstat(int(file.Fd()), &devNullStat); err != nil {
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return err
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}
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for fd := 0; fd < 3; fd++ {
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if err := syscall.Fstat(fd, &stat); err != nil {
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return err
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}
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if stat.Rdev == devNullStat.Rdev {
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// Close and re-open the fd.
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if err := syscall.Dup3(int(file.Fd()), fd, 0); err != nil {
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return err
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}
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}
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}
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return nil
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}
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// Create the device nodes in the container.
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func createDevices(config *configs.Config) error {
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useBindMount := system.RunningInUserNS() || config.Namespaces.Contains(configs.NEWUSER)
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oldMask := syscall.Umask(0000)
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for _, node := range config.Devices {
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// containers running in a user namespace are not allowed to mknod
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// devices so we can just bind mount it from the host.
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if err := createDeviceNode(config.Rootfs, node, useBindMount); err != nil {
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syscall.Umask(oldMask)
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return err
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}
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}
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syscall.Umask(oldMask)
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return nil
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}
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func bindMountDeviceNode(dest string, node *configs.Device) error {
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f, err := os.Create(dest)
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if err != nil && !os.IsExist(err) {
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return err
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}
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if f != nil {
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f.Close()
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}
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return syscall.Mount(node.Path, dest, "bind", syscall.MS_BIND, "")
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}
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// Creates the device node in the rootfs of the container.
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func createDeviceNode(rootfs string, node *configs.Device, bind bool) error {
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dest := filepath.Join(rootfs, node.Path)
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if err := os.MkdirAll(filepath.Dir(dest), 0755); err != nil {
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return err
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}
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if bind {
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return bindMountDeviceNode(dest, node)
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}
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if err := mknodDevice(dest, node); err != nil {
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if os.IsExist(err) {
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return nil
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} else if os.IsPermission(err) {
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return bindMountDeviceNode(dest, node)
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}
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return err
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}
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return nil
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}
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func mknodDevice(dest string, node *configs.Device) error {
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fileMode := node.FileMode
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switch node.Type {
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case 'c':
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fileMode |= syscall.S_IFCHR
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case 'b':
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fileMode |= syscall.S_IFBLK
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default:
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return fmt.Errorf("%c is not a valid device type for device %s", node.Type, node.Path)
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}
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if err := syscall.Mknod(dest, uint32(fileMode), node.Mkdev()); err != nil {
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return err
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}
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return syscall.Chown(dest, int(node.Uid), int(node.Gid))
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}
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func getMountInfo(mountinfo []*mount.Info, dir string) *mount.Info {
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for _, m := range mountinfo {
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if m.Mountpoint == dir {
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return m
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}
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}
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return nil
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}
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// Get the parent mount point of directory passed in as argument. Also return
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// optional fields.
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func getParentMount(rootfs string) (string, string, error) {
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var path string
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mountinfos, err := mount.GetMounts()
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if err != nil {
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return "", "", err
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}
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mountinfo := getMountInfo(mountinfos, rootfs)
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if mountinfo != nil {
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return rootfs, mountinfo.Optional, nil
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}
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path = rootfs
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for {
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path = filepath.Dir(path)
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mountinfo = getMountInfo(mountinfos, path)
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if mountinfo != nil {
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return path, mountinfo.Optional, nil
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}
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if path == "/" {
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break
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}
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}
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// If we are here, we did not find parent mount. Something is wrong.
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return "", "", fmt.Errorf("Could not find parent mount of %s", rootfs)
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}
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// Make parent mount private if it was shared
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func rootfsParentMountPrivate(rootfs string) error {
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sharedMount := false
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parentMount, optionalOpts, err := getParentMount(rootfs)
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if err != nil {
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return err
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}
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optsSplit := strings.Split(optionalOpts, " ")
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for _, opt := range optsSplit {
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if strings.HasPrefix(opt, "shared:") {
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sharedMount = true
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break
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}
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}
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|
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// Make parent mount PRIVATE if it was shared. It is needed for two
|
|
// reasons. First of all pivot_root() will fail if parent mount is
|
|
// shared. Secondly when we bind mount rootfs it will propagate to
|
|
// parent namespace and we don't want that to happen.
|
|
if sharedMount {
|
|
return syscall.Mount("", parentMount, "", syscall.MS_PRIVATE, "")
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
func prepareRoot(config *configs.Config) error {
|
|
flag := syscall.MS_SLAVE | syscall.MS_REC
|
|
if config.RootPropagation != 0 {
|
|
flag = config.RootPropagation
|
|
}
|
|
if err := syscall.Mount("", "/", "", uintptr(flag), ""); err != nil {
|
|
return err
|
|
}
|
|
if config.NoPivotRoot {
|
|
if err := rootfsParentMountPrivate(config.Rootfs); err != nil {
|
|
return err
|
|
}
|
|
}
|
|
|
|
return syscall.Mount(config.Rootfs, config.Rootfs, "bind", syscall.MS_BIND|syscall.MS_REC, "")
|
|
}
|
|
|
|
func setReadonly() error {
|
|
return syscall.Mount("/", "/", "bind", syscall.MS_BIND|syscall.MS_REMOUNT|syscall.MS_RDONLY|syscall.MS_REC, "")
|
|
}
|
|
|
|
func setupPtmx(config *configs.Config, console *linuxConsole) error {
|
|
ptmx := filepath.Join(config.Rootfs, "dev/ptmx")
|
|
if err := os.Remove(ptmx); err != nil && !os.IsNotExist(err) {
|
|
return err
|
|
}
|
|
if err := os.Symlink("pts/ptmx", ptmx); err != nil {
|
|
return fmt.Errorf("symlink dev ptmx %s", err)
|
|
}
|
|
if console != nil {
|
|
return console.mount(config.Rootfs, config.MountLabel)
|
|
}
|
|
return nil
|
|
}
|
|
|
|
func pivotRoot(rootfs, pivotBaseDir string) (err error) {
|
|
if pivotBaseDir == "" {
|
|
pivotBaseDir = "/"
|
|
}
|
|
tmpDir := filepath.Join(rootfs, pivotBaseDir)
|
|
if err := os.MkdirAll(tmpDir, 0755); err != nil {
|
|
return fmt.Errorf("can't create tmp dir %s, error %v", tmpDir, err)
|
|
}
|
|
pivotDir, err := ioutil.TempDir(tmpDir, ".pivot_root")
|
|
if err != nil {
|
|
return fmt.Errorf("can't create pivot_root dir %s, error %v", pivotDir, err)
|
|
}
|
|
defer func() {
|
|
errVal := os.Remove(pivotDir)
|
|
if err == nil {
|
|
err = errVal
|
|
}
|
|
}()
|
|
if err := syscall.PivotRoot(rootfs, pivotDir); err != nil {
|
|
// Make the parent mount private
|
|
if err := rootfsParentMountPrivate(rootfs); err != nil {
|
|
return err
|
|
}
|
|
// Try again
|
|
if err := syscall.PivotRoot(rootfs, pivotDir); err != nil {
|
|
return fmt.Errorf("pivot_root %s", err)
|
|
}
|
|
}
|
|
if err := syscall.Chdir("/"); err != nil {
|
|
return fmt.Errorf("chdir / %s", err)
|
|
}
|
|
// path to pivot dir now changed, update
|
|
pivotDir = filepath.Join(pivotBaseDir, filepath.Base(pivotDir))
|
|
|
|
// Make pivotDir rprivate to make sure any of the unmounts don't
|
|
// propagate to parent.
|
|
if err := syscall.Mount("", pivotDir, "", syscall.MS_PRIVATE|syscall.MS_REC, ""); err != nil {
|
|
return err
|
|
}
|
|
|
|
if err := syscall.Unmount(pivotDir, syscall.MNT_DETACH); err != nil {
|
|
return fmt.Errorf("unmount pivot_root dir %s", err)
|
|
}
|
|
return nil
|
|
}
|
|
|
|
func msMoveRoot(rootfs string) error {
|
|
if err := syscall.Mount(rootfs, "/", "", syscall.MS_MOVE, ""); err != nil {
|
|
return err
|
|
}
|
|
if err := syscall.Chroot("."); err != nil {
|
|
return err
|
|
}
|
|
return syscall.Chdir("/")
|
|
}
|
|
|
|
// createIfNotExists creates a file or a directory only if it does not already exist.
|
|
func createIfNotExists(path string, isDir bool) error {
|
|
if _, err := os.Stat(path); err != nil {
|
|
if os.IsNotExist(err) {
|
|
if isDir {
|
|
return os.MkdirAll(path, 0755)
|
|
}
|
|
if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
|
|
return err
|
|
}
|
|
f, err := os.OpenFile(path, os.O_CREATE, 0755)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
f.Close()
|
|
}
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// remountReadonly will bind over the top of an existing path and ensure that it is read-only.
|
|
func remountReadonly(path string) error {
|
|
for i := 0; i < 5; i++ {
|
|
if err := syscall.Mount("", path, "", syscall.MS_REMOUNT|syscall.MS_RDONLY, ""); err != nil && !os.IsNotExist(err) {
|
|
switch err {
|
|
case syscall.EINVAL:
|
|
// Probably not a mountpoint, use bind-mount
|
|
if err := syscall.Mount(path, path, "", syscall.MS_BIND, ""); err != nil {
|
|
return err
|
|
}
|
|
return syscall.Mount(path, path, "", syscall.MS_BIND|syscall.MS_REMOUNT|syscall.MS_RDONLY|syscall.MS_REC|defaultMountFlags, "")
|
|
case syscall.EBUSY:
|
|
time.Sleep(100 * time.Millisecond)
|
|
continue
|
|
default:
|
|
return err
|
|
}
|
|
}
|
|
return nil
|
|
}
|
|
return fmt.Errorf("unable to mount %s as readonly max retries reached", path)
|
|
}
|
|
|
|
// maskPath masks the top of the specified path inside a container to avoid
|
|
// security issues from processes reading information from non-namespace aware
|
|
// mounts ( proc/kcore ).
|
|
// For files, maskPath bind mounts /dev/null over the top of the specified path.
|
|
// For directories, maskPath mounts read-only tmpfs over the top of the specified path.
|
|
func maskPath(path string) error {
|
|
if err := syscall.Mount("/dev/null", path, "", syscall.MS_BIND, ""); err != nil && !os.IsNotExist(err) {
|
|
if err == syscall.ENOTDIR {
|
|
return syscall.Mount("tmpfs", path, "tmpfs", syscall.MS_RDONLY, "")
|
|
}
|
|
return err
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// writeSystemProperty writes the value to a path under /proc/sys as determined from the key.
|
|
// For e.g. net.ipv4.ip_forward translated to /proc/sys/net/ipv4/ip_forward.
|
|
func writeSystemProperty(key, value string) error {
|
|
keyPath := strings.Replace(key, ".", "/", -1)
|
|
return ioutil.WriteFile(path.Join("/proc/sys", keyPath), []byte(value), 0644)
|
|
}
|
|
|
|
func remount(m *configs.Mount, rootfs string) error {
|
|
var (
|
|
dest = m.Destination
|
|
)
|
|
if !strings.HasPrefix(dest, rootfs) {
|
|
dest = filepath.Join(rootfs, dest)
|
|
}
|
|
if err := syscall.Mount(m.Source, dest, m.Device, uintptr(m.Flags|syscall.MS_REMOUNT), ""); err != nil {
|
|
return err
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// Do the mount operation followed by additional mounts required to take care
|
|
// of propagation flags.
|
|
func mountPropagate(m *configs.Mount, rootfs string, mountLabel string) error {
|
|
var (
|
|
dest = m.Destination
|
|
data = label.FormatMountLabel(m.Data, mountLabel)
|
|
flags = m.Flags
|
|
)
|
|
if libcontainerUtils.CleanPath(dest) == "/dev" {
|
|
flags &= ^syscall.MS_RDONLY
|
|
}
|
|
if !strings.HasPrefix(dest, rootfs) {
|
|
dest = filepath.Join(rootfs, dest)
|
|
}
|
|
|
|
if err := syscall.Mount(m.Source, dest, m.Device, uintptr(flags), data); err != nil {
|
|
return err
|
|
}
|
|
|
|
for _, pflag := range m.PropagationFlags {
|
|
if err := syscall.Mount("", dest, "", uintptr(pflag), ""); err != nil {
|
|
return err
|
|
}
|
|
}
|
|
return nil
|
|
}
|