Add symlink follow into unmount util.

Signed-off-by: Lantao Liu <lantaol@google.com>

pkg/os/os.go

@@ -25,6 +25,7 @@ import (
 	containerdmount "github.com/containerd/containerd/mount"
 	"github.com/containerd/fifo"
 	"github.com/docker/docker/pkg/mount"
+	"github.com/docker/docker/pkg/symlink"
 	"golang.org/x/net/context"
 	"golang.org/x/sys/unix"
 )
@@ -37,6 +38,7 @@ type OS interface {
 	OpenFifo(ctx context.Context, fn string, flag int, perm os.FileMode) (io.ReadWriteCloser, error)
 	Stat(name string) (os.FileInfo, error)
 	ResolveSymbolicLink(name string) (string, error)
+	FollowSymlinkInScope(path, scope string) (string, error)
 	CopyFile(src, dest string, perm os.FileMode) error
 	WriteFile(filename string, data []byte, perm os.FileMode) error
 	Mount(source string, target string, fstype string, flags uintptr, data string) error
@@ -79,6 +81,11 @@ func (RealOS) ResolveSymbolicLink(path string) (string, error) {
 	return filepath.EvalSymlinks(path)
 }
 
+// FollowSymlinkInScope will call symlink.FollowSymlinkInScope.
+func (RealOS) FollowSymlinkInScope(path, scope string) (string, error) {
+	return symlink.FollowSymlinkInScope(path, scope)
+}
+
 // CopyFile will copy src file to dest file
 func (RealOS) CopyFile(src, dest string, perm os.FileMode) error {
 	in, err := os.Open(src)
@@ -107,17 +114,21 @@ func (RealOS) Mount(source string, target string, fstype string, flags uintptr,
 	return unix.Mount(source, target, fstype, flags, data)
 }
 
-// Unmount will call unix.Unmount to unmount the file. The function doesn't
+// Unmount will call Unmount to unmount the file.
-// return error if target is not mounted.
 func (RealOS) Unmount(target string, flags int) error {
-	// TODO(random-liu): Follow symlink to make sure the result is correct.
+	return Unmount(target, flags)
-	if mounted, err := mount.Mounted(target); err != nil || !mounted {
-		return err
-	}
-	return unix.Unmount(target, flags)
 }
 
 // LookupMount gets mount info of a given path.
 func (RealOS) LookupMount(path string) (containerdmount.Info, error) {
 	return containerdmount.Lookup(path)
 }
+
+// Unmount will call unix.Unmount to unmount the file. The function doesn't
+// return error if target is not mounted.
+func Unmount(target string, flags int) error {
+	if mounted, err := mount.Mounted(target); err != nil || !mounted {
+		return err
+	}
+	return unix.Unmount(target, flags)
+}

pkg/os/testing/fake_os.go

@@ -45,6 +45,7 @@ type FakeOS struct {
 	OpenFifoFn             func(context.Context, string, int, os.FileMode) (io.ReadWriteCloser, error)
 	StatFn                 func(string) (os.FileInfo, error)
 	ResolveSymbolicLinkFn  func(string) (string, error)
+	FollowSymlinkInScopeFn func(string, string) (string, error)
 	CopyFileFn             func(string, string, os.FileMode) error
 	WriteFileFn            func(string, []byte, os.FileMode) error
 	MountFn                func(source string, target string, fstype string, flags uintptr, data string) error
@@ -176,6 +177,19 @@ func (f *FakeOS) ResolveSymbolicLink(path string) (string, error) {
 	return path, nil
 }
 
+// FollowSymlinkInScope is a fake call that invokes FollowSymlinkInScope or returns its input
+func (f *FakeOS) FollowSymlinkInScope(path, scope string) (string, error) {
+	f.appendCalls("FollowSymlinkInScope", path, scope)
+	if err := f.getError("FollowSymlinkInScope"); err != nil {
+		return "", err
+	}
+
+	if f.FollowSymlinkInScopeFn != nil {
+		return f.FollowSymlinkInScopeFn(path, scope)
+	}
+	return path, nil
+}
+
 // CopyFile is a fake call that invokes CopyFileFn or just return nil.
 func (f *FakeOS) CopyFile(src, dest string, perm os.FileMode) error {
 	f.appendCalls("CopyFile", src, dest, perm)

pkg/server/sandbox_run.go

@@ -491,8 +491,12 @@ func parseDNSOptions(servers, searches, options []string) (string, error) {
 //  2) The mount point doesn't exist.
 func (c *criService) unmountSandboxFiles(id string, config *runtime.PodSandboxConfig) error {
 	if config.GetLinux().GetSecurityContext().GetNamespaceOptions().GetIpc() != runtime.NamespaceMode_NODE {
-		if err := c.os.Unmount(c.getSandboxDevShm(id), unix.MNT_DETACH); err != nil && !os.IsNotExist(err) {
+		path, err := c.os.FollowSymlinkInScope(c.getSandboxDevShm(id), "/")
-			return err
+		if err != nil {
+			return errors.Wrap(err, "failed to follow symlink")
+		}
+		if err := c.os.Unmount(path, unix.MNT_DETACH); err != nil && !os.IsNotExist(err) {
+			return errors.Wrapf(err, "failed to unmount %q", path)
 		}
 	}
 	return nil

pkg/store/sandbox/netns.go

@@ -21,10 +21,11 @@ import (
 	"sync"
 
 	cnins "github.com/containernetworking/plugins/pkg/ns"
-	"github.com/docker/docker/pkg/mount"
 	"github.com/docker/docker/pkg/symlink"
 	"github.com/pkg/errors"
 	"golang.org/x/sys/unix"
+
+	osinterface "github.com/containerd/cri/pkg/os"
 )
 
 // ErrClosedNetNS is the error returned when network namespace is closed.
@@ -81,7 +82,6 @@ func (n *NetNS) Remove() error {
 	}
 	if n.restored {
 		path := n.ns.Path()
-		// TODO(random-liu): Add util function for unmount.
 		// Check netns existence.
 		if _, err := os.Stat(path); err != nil {
 			if os.IsNotExist(err) {
@@ -93,16 +93,9 @@ func (n *NetNS) Remove() error {
 		if err != nil {
 			return errors.Wrap(err, "failed to follow symlink")
 		}
-		mounted, err := mount.Mounted(path)
+		if err := osinterface.Unmount(path, unix.MNT_DETACH); err != nil && !os.IsNotExist(err) {
-		if err != nil {
-			return errors.Wrap(err, "failed to check netns mounted")
-		}
-		if mounted {
-			err := unix.Unmount(path, unix.MNT_DETACH)
-			if err != nil && !os.IsNotExist(err) {
 			return errors.Wrap(err, "failed to umount netns")
 		}
-		}
 		if err := os.RemoveAll(path); err != nil {
 			return errors.Wrap(err, "failed to remove netns")
 		}