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run_linux.go
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run_linux.go
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//go:build linux
// +build linux
package chroot
import (
"errors"
"fmt"
"os"
"os/exec"
"path/filepath"
"strings"
"syscall"
"time"
"github.com/containers/buildah/copier"
"github.com/containers/storage/pkg/mount"
"github.com/containers/storage/pkg/unshare"
"github.com/opencontainers/runc/libcontainer/apparmor"
"github.com/opencontainers/runtime-spec/specs-go"
"github.com/sirupsen/logrus"
"github.com/syndtr/gocapability/capability"
"golang.org/x/sys/unix"
)
var (
rlimitsMap = map[string]int{
"RLIMIT_AS": unix.RLIMIT_AS,
"RLIMIT_CORE": unix.RLIMIT_CORE,
"RLIMIT_CPU": unix.RLIMIT_CPU,
"RLIMIT_DATA": unix.RLIMIT_DATA,
"RLIMIT_FSIZE": unix.RLIMIT_FSIZE,
"RLIMIT_LOCKS": unix.RLIMIT_LOCKS,
"RLIMIT_MEMLOCK": unix.RLIMIT_MEMLOCK,
"RLIMIT_MSGQUEUE": unix.RLIMIT_MSGQUEUE,
"RLIMIT_NICE": unix.RLIMIT_NICE,
"RLIMIT_NOFILE": unix.RLIMIT_NOFILE,
"RLIMIT_NPROC": unix.RLIMIT_NPROC,
"RLIMIT_RSS": unix.RLIMIT_RSS,
"RLIMIT_RTPRIO": unix.RLIMIT_RTPRIO,
"RLIMIT_RTTIME": unix.RLIMIT_RTTIME,
"RLIMIT_SIGPENDING": unix.RLIMIT_SIGPENDING,
"RLIMIT_STACK": unix.RLIMIT_STACK,
}
rlimitsReverseMap = map[int]string{}
)
type runUsingChrootSubprocOptions struct {
Spec *specs.Spec
BundlePath string
UIDMappings []syscall.SysProcIDMap
GIDMappings []syscall.SysProcIDMap
}
func setPlatformUnshareOptions(spec *specs.Spec, cmd *unshare.Cmd) error {
// If we have configured ID mappings, set them here so that they can apply to the child.
hostUidmap, hostGidmap, err := unshare.GetHostIDMappings("")
if err != nil {
return err
}
uidmap, gidmap := spec.Linux.UIDMappings, spec.Linux.GIDMappings
if len(uidmap) == 0 {
// No UID mappings are configured for the container. Borrow our parent's mappings.
uidmap = append([]specs.LinuxIDMapping{}, hostUidmap...)
for i := range uidmap {
uidmap[i].HostID = uidmap[i].ContainerID
}
}
if len(gidmap) == 0 {
// No GID mappings are configured for the container. Borrow our parent's mappings.
gidmap = append([]specs.LinuxIDMapping{}, hostGidmap...)
for i := range gidmap {
gidmap[i].HostID = gidmap[i].ContainerID
}
}
cmd.UnshareFlags = syscall.CLONE_NEWUTS | syscall.CLONE_NEWNS
requestedUserNS := false
for _, ns := range spec.Linux.Namespaces {
if ns.Type == specs.UserNamespace {
requestedUserNS = true
}
}
if len(spec.Linux.UIDMappings) > 0 || len(spec.Linux.GIDMappings) > 0 || requestedUserNS {
cmd.UnshareFlags = cmd.UnshareFlags | syscall.CLONE_NEWUSER
cmd.UidMappings = uidmap
cmd.GidMappings = gidmap
cmd.GidMappingsEnableSetgroups = true
}
cmd.OOMScoreAdj = spec.Process.OOMScoreAdj
return nil
}
func setContainerHostname(name string) {
if err := unix.Sethostname([]byte(name)); err != nil {
logrus.Debugf("failed to set hostname %q for process: %v", name, err)
}
}
// logNamespaceDiagnostics knows which namespaces we want to create.
// Output debug messages when that differs from what we're being asked to do.
func logNamespaceDiagnostics(spec *specs.Spec) {
sawMountNS := false
sawUTSNS := false
for _, ns := range spec.Linux.Namespaces {
switch ns.Type {
case specs.CgroupNamespace:
if ns.Path != "" {
logrus.Debugf("unable to join cgroup namespace, sorry about that")
} else {
logrus.Debugf("unable to create cgroup namespace, sorry about that")
}
case specs.IPCNamespace:
if ns.Path != "" {
logrus.Debugf("unable to join IPC namespace, sorry about that")
} else {
logrus.Debugf("unable to create IPC namespace, sorry about that")
}
case specs.MountNamespace:
if ns.Path != "" {
logrus.Debugf("unable to join mount namespace %q, creating a new one", ns.Path)
}
sawMountNS = true
case specs.NetworkNamespace:
if ns.Path != "" {
logrus.Debugf("unable to join network namespace, sorry about that")
} else {
logrus.Debugf("unable to create network namespace, sorry about that")
}
case specs.PIDNamespace:
if ns.Path != "" {
logrus.Debugf("unable to join PID namespace, sorry about that")
} else {
logrus.Debugf("unable to create PID namespace, sorry about that")
}
case specs.UserNamespace:
if ns.Path != "" {
logrus.Debugf("unable to join user namespace, sorry about that")
}
case specs.UTSNamespace:
if ns.Path != "" {
logrus.Debugf("unable to join UTS namespace %q, creating a new one", ns.Path)
}
sawUTSNS = true
}
}
if !sawMountNS {
logrus.Debugf("mount namespace not requested, but creating a new one anyway")
}
if !sawUTSNS {
logrus.Debugf("UTS namespace not requested, but creating a new one anyway")
}
}
// setApparmorProfile sets the apparmor profile for ourselves, and hopefully any child processes that we'll start.
func setApparmorProfile(spec *specs.Spec) error {
if !apparmor.IsEnabled() || spec.Process.ApparmorProfile == "" {
return nil
}
if err := apparmor.ApplyProfile(spec.Process.ApparmorProfile); err != nil {
return fmt.Errorf("setting apparmor profile to %q: %w", spec.Process.ApparmorProfile, err)
}
return nil
}
// setCapabilities sets capabilities for ourselves, to be more or less inherited by any processes that we'll start.
func setCapabilities(spec *specs.Spec, keepCaps ...string) error {
currentCaps, err := capability.NewPid2(0)
if err != nil {
return fmt.Errorf("reading capabilities of current process: %w", err)
}
if err := currentCaps.Load(); err != nil {
return fmt.Errorf("loading capabilities: %w", err)
}
caps, err := capability.NewPid2(0)
if err != nil {
return fmt.Errorf("reading capabilities of current process: %w", err)
}
capMap := map[capability.CapType][]string{
capability.BOUNDING: spec.Process.Capabilities.Bounding,
capability.EFFECTIVE: spec.Process.Capabilities.Effective,
capability.INHERITABLE: []string{},
capability.PERMITTED: spec.Process.Capabilities.Permitted,
capability.AMBIENT: spec.Process.Capabilities.Ambient,
}
knownCaps := capability.List()
noCap := capability.Cap(-1)
for capType, capList := range capMap {
for _, capToSet := range capList {
cap := noCap
for _, c := range knownCaps {
if strings.EqualFold("CAP_"+c.String(), capToSet) {
cap = c
break
}
}
if cap == noCap {
return fmt.Errorf("mapping capability %q to a number", capToSet)
}
caps.Set(capType, cap)
}
for _, capToSet := range keepCaps {
cap := noCap
for _, c := range knownCaps {
if strings.EqualFold("CAP_"+c.String(), capToSet) {
cap = c
break
}
}
if cap == noCap {
return fmt.Errorf("mapping capability %q to a number", capToSet)
}
if currentCaps.Get(capType, cap) {
caps.Set(capType, cap)
}
}
}
if err = caps.Apply(capability.CAPS | capability.BOUNDS | capability.AMBS); err != nil {
return fmt.Errorf("setting capabilities: %w", err)
}
return nil
}
func makeRlimit(limit specs.POSIXRlimit) unix.Rlimit {
return unix.Rlimit{Cur: limit.Soft, Max: limit.Hard}
}
func createPlatformContainer(options runUsingChrootExecSubprocOptions) error {
return errors.New("unsupported createPlatformContainer")
}
func makeReadOnly(mntpoint string, flags uintptr) error {
var fs unix.Statfs_t
// Make sure it's read-only.
if err := unix.Statfs(mntpoint, &fs); err != nil {
return fmt.Errorf("checking if directory %q was bound read-only: %w", mntpoint, err)
}
if fs.Flags&unix.ST_RDONLY == 0 {
if err := unix.Mount(mntpoint, mntpoint, "bind", flags|unix.MS_REMOUNT, ""); err != nil {
return fmt.Errorf("remounting %s in mount namespace read-only: %w", mntpoint, err)
}
}
return nil
}
// setupChrootBindMounts actually bind mounts things under the rootfs, and returns a
// callback that will clean up its work.
func setupChrootBindMounts(spec *specs.Spec, bundlePath string) (undoBinds func() error, err error) {
var fs unix.Statfs_t
undoBinds = func() error {
if err2 := unix.Unmount(spec.Root.Path, unix.MNT_DETACH); err2 != nil {
retries := 0
for (err2 == unix.EBUSY || err2 == unix.EAGAIN) && retries < 50 {
time.Sleep(50 * time.Millisecond)
err2 = unix.Unmount(spec.Root.Path, unix.MNT_DETACH)
retries++
}
if err2 != nil {
logrus.Warnf("pkg/chroot: error unmounting %q (retried %d times): %v", spec.Root.Path, retries, err2)
if err == nil {
err = err2
}
}
}
return err
}
// Now bind mount all of those things to be under the rootfs's location in this
// mount namespace.
commonFlags := uintptr(unix.MS_BIND | unix.MS_REC | unix.MS_PRIVATE)
bindFlags := commonFlags | unix.MS_NODEV
devFlags := commonFlags | unix.MS_NOEXEC | unix.MS_NOSUID | unix.MS_RDONLY
procFlags := devFlags | unix.MS_NODEV
sysFlags := devFlags | unix.MS_NODEV
// Bind /dev read-only.
subDev := filepath.Join(spec.Root.Path, "/dev")
if err := unix.Mount("/dev", subDev, "bind", devFlags, ""); err != nil {
if errors.Is(err, os.ErrNotExist) {
err = os.Mkdir(subDev, 0755)
if err == nil {
err = unix.Mount("/dev", subDev, "bind", devFlags, "")
}
}
if err != nil {
return undoBinds, fmt.Errorf("bind mounting /dev from host into mount namespace: %w", err)
}
}
// Make sure it's read-only.
if err = unix.Statfs(subDev, &fs); err != nil {
return undoBinds, fmt.Errorf("checking if directory %q was bound read-only: %w", subDev, err)
}
if fs.Flags&unix.ST_RDONLY == 0 {
if err := unix.Mount(subDev, subDev, "bind", devFlags|unix.MS_REMOUNT, ""); err != nil {
return undoBinds, fmt.Errorf("remounting /dev in mount namespace read-only: %w", err)
}
}
logrus.Debugf("bind mounted %q to %q", "/dev", filepath.Join(spec.Root.Path, "/dev"))
// Bind /proc read-only.
subProc := filepath.Join(spec.Root.Path, "/proc")
if err := unix.Mount("/proc", subProc, "bind", procFlags, ""); err != nil {
if errors.Is(err, os.ErrNotExist) {
err = os.Mkdir(subProc, 0755)
if err == nil {
err = unix.Mount("/proc", subProc, "bind", procFlags, "")
}
}
if err != nil {
return undoBinds, fmt.Errorf("bind mounting /proc from host into mount namespace: %w", err)
}
}
logrus.Debugf("bind mounted %q to %q", "/proc", filepath.Join(spec.Root.Path, "/proc"))
// Bind /sys read-only.
subSys := filepath.Join(spec.Root.Path, "/sys")
if err := unix.Mount("/sys", subSys, "bind", sysFlags, ""); err != nil {
if errors.Is(err, os.ErrNotExist) {
err = os.Mkdir(subSys, 0755)
if err == nil {
err = unix.Mount("/sys", subSys, "bind", sysFlags, "")
}
}
if err != nil {
return undoBinds, fmt.Errorf("bind mounting /sys from host into mount namespace: %w", err)
}
}
if err := makeReadOnly(subSys, sysFlags); err != nil {
return undoBinds, err
}
mnts, _ := mount.GetMounts()
for _, m := range mnts {
if !strings.HasPrefix(m.Mountpoint, "/sys/") &&
m.Mountpoint != "/sys" {
continue
}
subSys := filepath.Join(spec.Root.Path, m.Mountpoint)
if err := unix.Mount(m.Mountpoint, subSys, "bind", sysFlags, ""); err != nil {
msg := fmt.Sprintf("could not bind mount %q, skipping: %v", m.Mountpoint, err)
if strings.HasPrefix(m.Mountpoint, "/sys") {
logrus.Infof(msg)
} else {
logrus.Warningf(msg)
}
continue
}
if err := makeReadOnly(subSys, sysFlags); err != nil {
return undoBinds, err
}
}
logrus.Debugf("bind mounted %q to %q", "/sys", filepath.Join(spec.Root.Path, "/sys"))
// Bind mount in everything we've been asked to mount.
for _, m := range spec.Mounts {
// Skip anything that we just mounted.
switch m.Destination {
case "/dev", "/proc", "/sys":
logrus.Debugf("already bind mounted %q on %q", m.Destination, filepath.Join(spec.Root.Path, m.Destination))
continue
default:
if strings.HasPrefix(m.Destination, "/dev/") {
continue
}
if strings.HasPrefix(m.Destination, "/proc/") {
continue
}
if strings.HasPrefix(m.Destination, "/sys/") {
continue
}
}
// Skip anything that isn't a bind or tmpfs mount.
if m.Type != "bind" && m.Type != "tmpfs" && m.Type != "overlay" {
logrus.Debugf("skipping mount of type %q on %q", m.Type, m.Destination)
continue
}
// If the target is there, we can just mount it.
var srcinfo os.FileInfo
switch m.Type {
case "bind":
srcinfo, err = os.Stat(m.Source)
if err != nil {
return undoBinds, fmt.Errorf("examining %q for mounting in mount namespace: %w", m.Source, err)
}
case "overlay":
fallthrough
case "tmpfs":
srcinfo, err = os.Stat("/")
if err != nil {
return undoBinds, fmt.Errorf("examining / to use as a template for a %s: %w", m.Type, err)
}
}
target := filepath.Join(spec.Root.Path, m.Destination)
// Check if target is a symlink
stat, err := os.Lstat(target)
// If target is a symlink, follow the link and ensure the destination exists
if err == nil && stat != nil && (stat.Mode()&os.ModeSymlink != 0) {
target, err = copier.Eval(spec.Root.Path, m.Destination, copier.EvalOptions{})
if err != nil {
return nil, fmt.Errorf("evaluating symlink %q: %w", target, err)
}
// Stat the destination of the evaluated symlink
_, err = os.Stat(target)
}
if err != nil {
// If the target can't be stat()ted, check the error.
if !errors.Is(err, os.ErrNotExist) {
return undoBinds, fmt.Errorf("examining %q for mounting in mount namespace: %w", target, err)
}
// The target isn't there yet, so create it.
if srcinfo.IsDir() {
if err = os.MkdirAll(target, 0755); err != nil {
return undoBinds, fmt.Errorf("creating mountpoint %q in mount namespace: %w", target, err)
}
} else {
if err = os.MkdirAll(filepath.Dir(target), 0755); err != nil {
return undoBinds, fmt.Errorf("ensuring parent of mountpoint %q (%q) is present in mount namespace: %w", target, filepath.Dir(target), err)
}
var file *os.File
if file, err = os.OpenFile(target, os.O_WRONLY|os.O_CREATE, 0755); err != nil {
return undoBinds, fmt.Errorf("creating mountpoint %q in mount namespace: %w", target, err)
}
file.Close()
}
}
requestFlags := uintptr(0)
expectedFlags := uintptr(0)
for _, option := range m.Options {
switch option {
case "nodev":
requestFlags |= unix.MS_NODEV
expectedFlags |= unix.ST_NODEV
case "dev":
requestFlags &= ^uintptr(unix.MS_NODEV)
expectedFlags &= ^uintptr(unix.ST_NODEV)
case "noexec":
requestFlags |= unix.MS_NOEXEC
expectedFlags |= unix.ST_NOEXEC
case "exec":
requestFlags &= ^uintptr(unix.MS_NOEXEC)
expectedFlags &= ^uintptr(unix.ST_NOEXEC)
case "nosuid":
requestFlags |= unix.MS_NOSUID
expectedFlags |= unix.ST_NOSUID
case "suid":
requestFlags &= ^uintptr(unix.MS_NOSUID)
expectedFlags &= ^uintptr(unix.ST_NOSUID)
case "ro":
requestFlags |= unix.MS_RDONLY
expectedFlags |= unix.ST_RDONLY
case "rw":
requestFlags &= ^uintptr(unix.MS_RDONLY)
expectedFlags &= ^uintptr(unix.ST_RDONLY)
}
}
switch m.Type {
case "bind":
// Do the bind mount.
logrus.Debugf("bind mounting %q on %q", m.Destination, filepath.Join(spec.Root.Path, m.Destination))
if err := unix.Mount(m.Source, target, "", bindFlags|requestFlags, ""); err != nil {
return undoBinds, fmt.Errorf("bind mounting %q from host to %q in mount namespace (%q): %w", m.Source, m.Destination, target, err)
}
if (requestFlags & unix.MS_RDONLY) != 0 {
if err = unix.Statfs(target, &fs); err != nil {
return undoBinds, fmt.Errorf("checking if directory %q was bound read-only: %w", target, err)
}
// we need to make sure these flags are maintained in the REMOUNT operation
additionalFlags := uintptr(fs.Flags) & (unix.MS_NOEXEC | unix.MS_NOSUID | unix.MS_NODEV)
if err := unix.Mount("", target, "", unix.MS_REMOUNT|unix.MS_BIND|unix.MS_RDONLY|additionalFlags, ""); err != nil {
return undoBinds, fmt.Errorf("setting flags on the bind mount %q from host to %q in mount namespace (%q): %w", m.Source, m.Destination, target, err)
}
}
logrus.Debugf("bind mounted %q to %q", m.Source, target)
case "tmpfs":
// Mount a tmpfs.
if err := mount.Mount(m.Source, target, m.Type, strings.Join(append(m.Options, "private"), ",")); err != nil {
return undoBinds, fmt.Errorf("mounting tmpfs to %q in mount namespace (%q, %q): %w", m.Destination, target, strings.Join(m.Options, ","), err)
}
logrus.Debugf("mounted a tmpfs to %q", target)
case "overlay":
// Mount a overlay.
if err := mount.Mount(m.Source, target, m.Type, strings.Join(append(m.Options, "private"), ",")); err != nil {
return undoBinds, fmt.Errorf("mounting overlay to %q in mount namespace (%q, %q): %w", m.Destination, target, strings.Join(m.Options, ","), err)
}
logrus.Debugf("mounted a overlay to %q", target)
}
if err = unix.Statfs(target, &fs); err != nil {
return undoBinds, fmt.Errorf("checking if directory %q was bound read-only: %w", target, err)
}
if uintptr(fs.Flags)&expectedFlags != expectedFlags {
if err := unix.Mount(target, target, "bind", requestFlags|unix.MS_REMOUNT, ""); err != nil {
return undoBinds, fmt.Errorf("remounting %q in mount namespace with expected flags: %w", target, err)
}
}
}
// Set up any read-only paths that we need to. If we're running inside
// of a container, some of these locations will already be read-only.
for _, roPath := range spec.Linux.ReadonlyPaths {
r := filepath.Join(spec.Root.Path, roPath)
target, err := filepath.EvalSymlinks(r)
if err != nil {
if errors.Is(err, os.ErrNotExist) {
// No target, no problem.
continue
}
return undoBinds, fmt.Errorf("checking %q for symlinks before marking it read-only: %w", r, err)
}
// Check if the location is already read-only.
var fs unix.Statfs_t
if err = unix.Statfs(target, &fs); err != nil {
if errors.Is(err, os.ErrNotExist) {
// No target, no problem.
continue
}
return undoBinds, fmt.Errorf("checking if directory %q is already read-only: %w", target, err)
}
if fs.Flags&unix.ST_RDONLY != 0 {
continue
}
// Mount the location over itself, so that we can remount it as read-only.
roFlags := uintptr(unix.MS_NODEV | unix.MS_NOEXEC | unix.MS_NOSUID | unix.MS_RDONLY)
if err := unix.Mount(target, target, "", roFlags|unix.MS_BIND|unix.MS_REC, ""); err != nil {
if errors.Is(err, os.ErrNotExist) {
// No target, no problem.
continue
}
return undoBinds, fmt.Errorf("bind mounting %q onto itself in preparation for making it read-only: %w", target, err)
}
// Remount the location read-only.
if err = unix.Statfs(target, &fs); err != nil {
return undoBinds, fmt.Errorf("checking if directory %q was bound read-only: %w", target, err)
}
if fs.Flags&unix.ST_RDONLY == 0 {
if err := unix.Mount(target, target, "", roFlags|unix.MS_BIND|unix.MS_REMOUNT, ""); err != nil {
return undoBinds, fmt.Errorf("remounting %q in mount namespace read-only: %w", target, err)
}
}
// Check again.
if err = unix.Statfs(target, &fs); err != nil {
return undoBinds, fmt.Errorf("checking if directory %q was remounted read-only: %w", target, err)
}
if fs.Flags&unix.ST_RDONLY == 0 {
return undoBinds, fmt.Errorf("verifying that %q in mount namespace was remounted read-only: %w", target, err)
}
}
// Create an empty directory for to use for masking directories.
roEmptyDir := filepath.Join(bundlePath, "empty")
if len(spec.Linux.MaskedPaths) > 0 {
if err := os.Mkdir(roEmptyDir, 0700); err != nil {
return undoBinds, fmt.Errorf("creating empty directory %q: %w", roEmptyDir, err)
}
}
// Set up any masked paths that we need to. If we're running inside of
// a container, some of these locations will already be read-only tmpfs
// filesystems or bind mounted to os.DevNull. If we're not running
// inside of a container, and nobody else has done that, we'll do it.
for _, masked := range spec.Linux.MaskedPaths {
t := filepath.Join(spec.Root.Path, masked)
target, err := filepath.EvalSymlinks(t)
if err != nil {
target = t
}
// Get some info about the target.
targetinfo, err := os.Stat(target)
if err != nil {
if errors.Is(err, os.ErrNotExist) {
// No target, no problem.
continue
}
return undoBinds, fmt.Errorf("examining %q for masking in mount namespace: %w", target, err)
}
if targetinfo.IsDir() {
// The target's a directory. Check if it's a read-only filesystem.
var statfs unix.Statfs_t
if err = unix.Statfs(target, &statfs); err != nil {
return undoBinds, fmt.Errorf("checking if directory %q is a mountpoint: %w", target, err)
}
isReadOnly := statfs.Flags&unix.MS_RDONLY != 0
// Check if any of the IDs we're mapping could read it.
var stat unix.Stat_t
if err = unix.Stat(target, &stat); err != nil {
return undoBinds, fmt.Errorf("checking permissions on directory %q: %w", target, err)
}
isAccessible := false
if stat.Mode&unix.S_IROTH|unix.S_IXOTH != 0 {
isAccessible = true
}
if !isAccessible && stat.Mode&unix.S_IROTH|unix.S_IXOTH != 0 {
if len(spec.Linux.GIDMappings) > 0 {
for _, mapping := range spec.Linux.GIDMappings {
if stat.Gid >= mapping.ContainerID && stat.Gid < mapping.ContainerID+mapping.Size {
isAccessible = true
break
}
}
}
}
if !isAccessible && stat.Mode&unix.S_IRUSR|unix.S_IXUSR != 0 {
if len(spec.Linux.UIDMappings) > 0 {
for _, mapping := range spec.Linux.UIDMappings {
if stat.Uid >= mapping.ContainerID && stat.Uid < mapping.ContainerID+mapping.Size {
isAccessible = true
break
}
}
}
}
// Check if it's empty.
hasContent := false
directory, err := os.Open(target)
if err != nil {
if !os.IsPermission(err) {
return undoBinds, fmt.Errorf("opening directory %q: %w", target, err)
}
} else {
names, err := directory.Readdirnames(0)
directory.Close()
if err != nil {
return undoBinds, fmt.Errorf("reading contents of directory %q: %w", target, err)
}
hasContent = false
for _, name := range names {
switch name {
case ".", "..":
continue
default:
hasContent = true
}
if hasContent {
break
}
}
}
// The target's a directory, so read-only bind mount an empty directory on it.
roFlags := uintptr(syscall.MS_BIND | syscall.MS_NOSUID | syscall.MS_NODEV | syscall.MS_NOEXEC | syscall.MS_RDONLY)
if !isReadOnly || (hasContent && isAccessible) {
if err = unix.Mount(roEmptyDir, target, "bind", roFlags, ""); err != nil {
return undoBinds, fmt.Errorf("masking directory %q in mount namespace: %w", target, err)
}
if err = unix.Statfs(target, &fs); err != nil {
return undoBinds, fmt.Errorf("checking if directory %q was mounted read-only in mount namespace: %w", target, err)
}
if fs.Flags&unix.ST_RDONLY == 0 {
if err = unix.Mount(target, target, "", roFlags|syscall.MS_REMOUNT, ""); err != nil {
return undoBinds, fmt.Errorf("making sure directory %q in mount namespace is read only: %w", target, err)
}
}
}
} else {
// If the target's is not a directory or os.DevNull, bind mount os.DevNull over it.
if !isDevNull(targetinfo) {
if err = unix.Mount(os.DevNull, target, "", uintptr(syscall.MS_BIND|syscall.MS_RDONLY|syscall.MS_PRIVATE), ""); err != nil {
return undoBinds, fmt.Errorf("masking non-directory %q in mount namespace: %w", target, err)
}
}
}
}
return undoBinds, nil
}
// setPdeathsig sets a parent-death signal for the process
func setPdeathsig(cmd *exec.Cmd) {
if cmd.SysProcAttr == nil {
cmd.SysProcAttr = &syscall.SysProcAttr{}
}
cmd.SysProcAttr.Pdeathsig = syscall.SIGKILL
}