Ensure volumes can be removed when they fail to unmount

Also, ensure that we don't try to mount them without root - it
appears that it can somehow not error and report that mount was
successful when it clearly did not succeed, which can induce this
case.

We reuse the `--force` flag to indicate that a volume should be
removed even after unmount errors. It seems fairly natural to
expect that --force will remove a volume that is otherwise
presenting problems.

Finally, ignore EINVAL on unmount - if the mount point no longer
exists our job is done.

Fixes: #4247
Fixes: #4248

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

libpod/define/errors.go

@@ -65,6 +65,10 @@ var (
 	// CGroup.
 	ErrNoCgroups = errors.New("this container does not have a cgroup")
 
+	// ErrRootless indicates that the given command cannot but run without
+	// root.
+	ErrRootless = errors.New("operation requires root privileges")
+
 	// ErrRuntimeStopped indicates that the runtime has already been shut
 	// down and no further operations can be performed on it
 	ErrRuntimeStopped = errors.New("runtime has already been stopped")

libpod/runtime_volume_linux.go

@@ -157,7 +157,14 @@ func (r *Runtime) removeVolume(ctx context.Context, v *Volume, force bool) error
 
 	// If the volume is still mounted - force unmount it
 	if err := v.unmount(true); err != nil {
-		return errors.Wrapf(err, "error unmounting volume %s", v.Name())
+		if force {
+			// If force is set, evict the volume, even if errors
+			// occur. Otherwise we'll never be able to get rid of
+			// them.
+			logrus.Errorf("Error unmounting volume %s: %v", v.Name(), err)
+		} else {
+			return errors.Wrapf(err, "error unmounting volume %s", v.Name())
+		}
 	}
 
 	// Set volume as invalid so it can no longer be used

libpod/volume_internal_linux.go

@@ -6,6 +6,8 @@ import (
 	"io/ioutil"
 	"os/exec"
 
+	"github.com/containers/libpod/libpod/define"
+	"github.com/containers/libpod/pkg/rootless"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
@@ -24,6 +26,11 @@ func (v *Volume) mount() error {
 		return nil
 	}
 
+	// We cannot mount volumes as rootless.
+	if rootless.IsRootless() {
+		return errors.Wrapf(define.ErrRootless, "cannot mount volumes without root privileges")
+	}
+
 	// Update the volume from the DB to get an accurate mount counter.
 	if err := v.update(); err != nil {
 		return err
@@ -108,6 +115,20 @@ func (v *Volume) unmount(force bool) error {
 		return nil
 	}
 
+	// We cannot unmount volumes as rootless.
+	if rootless.IsRootless() {
+		// If force is set, just clear the counter and bail without
+		// error, so we can remove volumes from the state if they are in
+		// an awkward configuration.
+		if force {
+			logrus.Errorf("Volume %s is mounted despite being rootless - state is not sane", v.Name())
+			v.state.MountCount = 0
+			return v.save()
+		}
+
+		return errors.Wrapf(define.ErrRootless, "cannot mount or unmount volumes without root privileges")
+	}
+
 	if !force {
 		v.state.MountCount = v.state.MountCount - 1
 	} else {
@@ -119,6 +140,10 @@ func (v *Volume) unmount(force bool) error {
 	if v.state.MountCount == 0 {
 		// Unmount the volume
 		if err := unix.Unmount(v.config.MountPoint, unix.MNT_DETACH); err != nil {
+			if err == unix.EINVAL {
+				// Ignore EINVAL - the mount no longer exists.
+				return nil
+			}
 			return errors.Wrapf(err, "error unmounting volume %s", v.Name())
 		}
 		logrus.Debugf("Unmounted volume %s", v.Name())