Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

[1.1] rootfs: fix 'can we mount on top of /proc' check #4334

Merged
merged 1 commit into from
Jul 5, 2024
Merged
Show file tree
Hide file tree
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension

Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion libcontainer/container_linux.go
Original file line number Diff line number Diff line change
Expand Up @@ -1300,7 +1300,7 @@ func (c *linuxContainer) makeCriuRestoreMountpoints(m *configs.Mount) error {
if err != nil {
return err
}
if err := checkProcMount(c.config.Rootfs, dest, ""); err != nil {
if err := checkProcMount(c.config.Rootfs, dest, m, ""); err != nil {
return err
}
if err := os.MkdirAll(dest, 0o755); err != nil {
Expand Down
65 changes: 42 additions & 23 deletions libcontainer/rootfs_linux.go
Original file line number Diff line number Diff line change
Expand Up @@ -244,7 +244,7 @@ func prepareBindMount(m *configs.Mount, rootfs string, mountFd *int) error {
if dest, err = securejoin.SecureJoin(rootfs, m.Destination); err != nil {
return err
}
if err := checkProcMount(rootfs, dest, source); err != nil {
if err := checkProcMount(rootfs, dest, m, source); err != nil {
return err
}
if err := createIfNotExists(dest, stat.IsDir()); err != nil {
Expand Down Expand Up @@ -509,7 +509,7 @@ func mountToRootfs(m *configs.Mount, c *mountConfig) error {
}
return mountCgroupV1(m, c)
default:
if err := checkProcMount(rootfs, dest, m.Source); err != nil {
if err := checkProcMount(rootfs, dest, m, m.Source); err != nil {
return err
}
if err := os.MkdirAll(dest, 0o755); err != nil {
Expand Down Expand Up @@ -557,11 +557,17 @@ func getCgroupMounts(m *configs.Mount) ([]*configs.Mount, error) {
return binds, nil
}

// checkProcMount checks to ensure that the mount destination is not over the top of /proc.
// dest is required to be an abs path and have any symlinks resolved before calling this function.
// Taken from <include/linux/proc_ns.h>. If a file is on a filesystem of type
// PROC_SUPER_MAGIC, we're guaranteed that only the root of the superblock will
// have this inode number.
const procRootIno = 1

// checkProcMount checks to ensure that the mount destination is not over the
// top of /proc. dest is required to be an abs path and have any symlinks
// resolved before calling this function.
//
// if source is nil, don't stat the filesystem. This is used for restore of a checkpoint.
func checkProcMount(rootfs, dest, source string) error {
// source is "" when doing criu restores.
cyphar marked this conversation as resolved.
Show resolved Hide resolved
func checkProcMount(rootfs, dest string, m *configs.Mount, source string) error {
cyphar marked this conversation as resolved.
Show resolved Hide resolved
const procPath = "/proc"
path, err := filepath.Rel(filepath.Join(rootfs, procPath), dest)
if err != nil {
Expand All @@ -572,18 +578,39 @@ func checkProcMount(rootfs, dest, source string) error {
return nil
}
if path == "." {
// an empty source is pasted on restore
// Skip this check for criu restores.
// NOTE: This is a special case kept from the original implementation,
// only present for the 1.1.z branch to avoid any possible breakage in
// a patch release. This check was removed in commit cdff09ab8751
// ("rootfs: fix 'can we mount on top of /proc' check") in 1.2, because
// it doesn't make sense with the new IsBind()-based checks.
if source == "" {
return nil
}
// only allow a mount on-top of proc if it's source is "proc"
isproc, err := isProc(source)
if err != nil {
return err
}
// pass if the mount is happening on top of /proc and the source of
// the mount is a proc filesystem
if isproc {
// Only allow bind-mounts on top of /proc, and only if the source is a
// procfs mount.
if m.IsBind() {
var fsSt unix.Statfs_t
if err := unix.Statfs(source, &fsSt); err != nil {
return &os.PathError{Op: "statfs", Path: source, Err: err}
}
if fsSt.Type == unix.PROC_SUPER_MAGIC {
var uSt unix.Stat_t
if err := unix.Stat(source, &uSt); err != nil {
return &os.PathError{Op: "stat", Path: source, Err: err}
}
if uSt.Ino != procRootIno {
// We cannot error out in this case, because we've
// supported these kinds of mounts for a long time.
// However, we would expect users to bind-mount the root of
// a real procfs on top of /proc in the container. We might
// want to block this in the future.
logrus.Warnf("bind-mount %v (source %v) is of type procfs but is not the root of a procfs (inode %d). Future versions of runc might block this configuration -- please report an issue to <https://github.com/opencontainers/runc> if you see this warning.", dest, source, uSt.Ino)
}
return nil
}
} else if m.Device == "proc" {
// Fresh procfs-type mounts are always safe to mount on top of /proc.
return nil
}
return fmt.Errorf("%q cannot be mounted because it is not of type proc", dest)
Expand Down Expand Up @@ -617,14 +644,6 @@ func checkProcMount(rootfs, dest, source string) error {
return fmt.Errorf("%q cannot be mounted because it is inside /proc", dest)
}

func isProc(path string) (bool, error) {
var s unix.Statfs_t
if err := unix.Statfs(path, &s); err != nil {
return false, &os.PathError{Op: "statfs", Path: path, Err: err}
}
return s.Type == unix.PROC_SUPER_MAGIC, nil
}

func setupDevSymlinks(rootfs string) error {
links := [][2]string{
{"/proc/self/fd", "/dev/fd"},
Expand Down
99 changes: 88 additions & 11 deletions libcontainer/rootfs_linux_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -3,52 +3,129 @@ package libcontainer
import (
"testing"

"golang.org/x/sys/unix"

"github.com/opencontainers/runc/libcontainer/configs"
)

func TestCheckMountDestOnProc(t *testing.T) {
func TestCheckMountDestInProc(t *testing.T) {
m := &configs.Mount{
Destination: "/proc/sys",
Source: "/proc/sys",
Device: "bind",
Flags: unix.MS_BIND,
}
dest := "/rootfs/proc/sys"
err := checkProcMount("/rootfs", dest, "")
err := checkProcMount("/rootfs", dest, m, m.Source)
if err == nil {
t.Fatal("destination inside proc should return an error")
}
}

func TestCheckMountDestOnProcChroot(t *testing.T) {
func TestCheckProcMountOnProc(t *testing.T) {
m := &configs.Mount{
Destination: "/proc",
Source: "foo",
Device: "proc",
}
dest := "/rootfs/proc/"
err := checkProcMount("/rootfs", dest, "/proc")
err := checkProcMount("/rootfs", dest, m, m.Source)
if err != nil {
t.Fatal("destination inside proc when using chroot should not return an error")
t.Fatalf("procfs type mount on /proc should not return an error: %v", err)
}
}

func TestCheckBindMountOnProc(t *testing.T) {
m := &configs.Mount{
Destination: "/proc",
Source: "/proc/self",
Device: "bind",
Flags: unix.MS_BIND,
}
dest := "/rootfs/proc/"
err := checkProcMount("/rootfs", dest, m, m.Source)
if err != nil {
t.Fatalf("bind-mount of procfs on top of /proc should not return an error (for now): %v", err)
}
}

func TestCheckTrickyMountOnProc(t *testing.T) {
// Make a non-bind mount that looks like a bit like a bind-mount.
m := &configs.Mount{
Destination: "/proc",
Source: "/proc",
Device: "overlay",
Data: "lowerdir=/tmp/fakeproc,upperdir=/tmp/fakeproc2,workdir=/tmp/work",
}
dest := "/rootfs/proc/"
err := checkProcMount("/rootfs", dest, m, m.Source)
if err == nil {
t.Fatalf("dodgy overlayfs mount on top of /proc should return an error")
}
}

func TestCheckTrickyBindMountOnProc(t *testing.T) {
// Make a bind mount that looks like it might be a procfs mount.
m := &configs.Mount{
Destination: "/proc",
Source: "/sys",
Device: "proc",
Flags: unix.MS_BIND,
}
dest := "/rootfs/proc/"
err := checkProcMount("/rootfs", dest, m, m.Source)
if err == nil {
t.Fatalf("dodgy bind-mount on top of /proc should return an error")
}
}

func TestCheckMountDestInSys(t *testing.T) {
m := &configs.Mount{
Destination: "/sys/fs/cgroup",
Source: "tmpfs",
Device: "tmpfs",
}
dest := "/rootfs//sys/fs/cgroup"
err := checkProcMount("/rootfs", dest, "")
err := checkProcMount("/rootfs", dest, m, m.Source)
if err != nil {
t.Fatal("destination inside /sys should not return an error")
t.Fatalf("destination inside /sys should not return an error: %v", err)
}
}

func TestCheckMountDestFalsePositive(t *testing.T) {
m := &configs.Mount{
Destination: "/sysfiles/fs/cgroup",
Source: "tmpfs",
Device: "tmpfs",
}
dest := "/rootfs/sysfiles/fs/cgroup"
err := checkProcMount("/rootfs", dest, "")
err := checkProcMount("/rootfs", dest, m, m.Source)
if err != nil {
t.Fatal(err)
}
}

func TestCheckMountDestNsLastPid(t *testing.T) {
m := &configs.Mount{
Destination: "/proc/sys/kernel/ns_last_pid",
Source: "lxcfs",
Device: "fuse.lxcfs",
}
dest := "/rootfs/proc/sys/kernel/ns_last_pid"
err := checkProcMount("/rootfs", dest, "/proc")
err := checkProcMount("/rootfs", dest, m, m.Source)
if err != nil {
t.Fatal("/proc/sys/kernel/ns_last_pid should not return an error")
t.Fatalf("/proc/sys/kernel/ns_last_pid should not return an error: %v", err)
}
}

func TestCheckCryptoFipsEnabled(t *testing.T) {
m := &configs.Mount{
Destination: "/proc/sys/crypto/fips_enabled",
Source: "tmpfs",
Device: "tmpfs",
}
dest := "/rootfs/proc/sys/crypto/fips_enabled"
err := checkProcMount("/rootfs", dest, "/proc")
err := checkProcMount("/rootfs", dest, m, m.Source)
if err != nil {
t.Fatalf("/proc/sys/crypto/fips_enabled should not return an error: %v", err)
}
Expand Down
Loading