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

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merged 1 commit into from
Jul 5, 2024
Merged

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

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2 changes: 1 addition & 1 deletion libcontainer/container_linux.go
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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
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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.
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func checkProcMount(rootfs, dest string, m *configs.Mount, source string) error {
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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
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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
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