Support checkpoint/restore with pods

This adds support to checkpoint containers out of pods and restore
container into pods.

It is only possible to restore a container into a pod if it has been
checkpointed out of pod. It is also not possible to restore a non pod
container into a pod.

The main reason this does not work is the PID namespace. If a non pod
container is being restored in a pod with a shared PID namespace, at
least one process in the restored container uses PID 1 which is already
in use by the infrastructure container. If someone tries to restore
container from a pod with a shared PID namespace without a shared PID
namespace it will also fail because the resulting PID namespace will not
have a PID 1.

Signed-off-by: Adrian Reber <areber@redhat.com>

2 files changed, 107 insertions, 0 deletions

diff --git a/pkg/checkpoint/checkpoint_restore.go b/pkg/checkpoint/checkpoint_restore.go
index 0d45cab5f..9fdf04933 100644
--- a/pkg/checkpoint/checkpoint_restore.go
+++ b/pkg/checkpoint/checkpoint_restore.go
@@ -9,6 +9,9 @@ import (
 	"github.com/containers/common/libimage"
 	"github.com/containers/common/pkg/config"
 	"github.com/containers/podman/v3/libpod"
+	ann "github.com/containers/podman/v3/pkg/annotations"
+	"github.com/containers/podman/v3/pkg/checkpoint/crutils"
+	"github.com/containers/podman/v3/pkg/criu"
 	"github.com/containers/podman/v3/pkg/domain/entities"
 	"github.com/containers/podman/v3/pkg/errorhandling"
 	"github.com/containers/podman/v3/pkg/specgen/generate"
@@ -68,6 +71,14 @@ func CRImportCheckpoint(ctx context.Context, runtime *libpod.Runtime, restoreOpt
 		return nil, err
 	}
 
+	if ctrConfig.Pod != "" && restoreOptions.Pod == "" {
+		return nil, errors.New("cannot restore pod container without --pod")
+	}
+
+	if ctrConfig.Pod == "" && restoreOptions.Pod != "" {
+		return nil, errors.New("cannot restore non pod container into pod")
+	}
+
 	// This should not happen as checkpoints with these options are not exported.
 	if len(ctrConfig.Dependencies) > 0 {
 		return nil, errors.Errorf("Cannot import checkpoints of containers with dependencies")
@@ -96,6 +107,91 @@ func CRImportCheckpoint(ctx context.Context, runtime *libpod.Runtime, restoreOpt
 		newName = true
 	}
 
+	if restoreOptions.Pod != "" {
+		// Restoring into a Pod requires much newer versions of CRIU
+		if !criu.CheckForCriu(criu.PodCriuVersion) {
+			return nil, errors.Errorf("restoring containers into pods requires at least CRIU %d", criu.PodCriuVersion)
+		}
+		// The runtime also has to support it
+		if !crutils.CRRuntimeSupportsPodCheckpointRestore(runtime.GetOCIRuntimePath()) {
+			return nil, errors.Errorf("runtime %s does not support pod restore", runtime.GetOCIRuntimePath())
+		}
+		// Restoring into an existing Pod
+		ctrConfig.Pod = restoreOptions.Pod
+
+		// According to podman pod create a pod can share the following namespaces:
+		// cgroup, ipc, net, pid, uts
+		// Let's make sure we a restoring into a pod with the same shared namespaces.
+		pod, err := runtime.LookupPod(ctrConfig.Pod)
+		if err != nil {
+			return nil, errors.Wrapf(err, "pod %q cannot be retrieved", ctrConfig.Pod)
+		}
+
+		infraContainer, err := pod.InfraContainer()
+		if err != nil {
+			return nil, errors.Wrapf(err, "cannot retrieve infra container from pod %q", ctrConfig.Pod)
+		}
+
+		// If a namespaces was shared (!= "") it needs to be set to the new infrastructure container
+		// If the infrastructure container does not share the same namespaces as the to be restored
+		// container we abort.
+		if ctrConfig.IPCNsCtr != "" {
+			if !pod.SharesIPC() {
+				return nil, errors.Errorf("pod %s does not share the IPC namespace", ctrConfig.Pod)
+			}
+			ctrConfig.IPCNsCtr = infraContainer.ID()
+		}
+
+		if ctrConfig.NetNsCtr != "" {
+			if !pod.SharesNet() {
+				return nil, errors.Errorf("pod %s does not share the network namespace", ctrConfig.Pod)
+			}
+			ctrConfig.NetNsCtr = infraContainer.ID()
+		}
+
+		if ctrConfig.PIDNsCtr != "" {
+			if !pod.SharesPID() {
+				return nil, errors.Errorf("pod %s does not share the PID namespace", ctrConfig.Pod)
+			}
+			ctrConfig.PIDNsCtr = infraContainer.ID()
+		}
+
+		if ctrConfig.UTSNsCtr != "" {
+			if !pod.SharesUTS() {
+				return nil, errors.Errorf("pod %s does not share the UTS namespace", ctrConfig.Pod)
+			}
+			ctrConfig.UTSNsCtr = infraContainer.ID()
+		}
+
+		if ctrConfig.CgroupNsCtr != "" {
+			if !pod.SharesCgroup() {
+				return nil, errors.Errorf("pod %s does not share the cgroup namespace", ctrConfig.Pod)
+			}
+			ctrConfig.CgroupNsCtr = infraContainer.ID()
+		}
+
+		// Change SELinux labels to infrastructure container labels
+		ctrConfig.MountLabel = infraContainer.MountLabel()
+		ctrConfig.ProcessLabel = infraContainer.ProcessLabel()
+
+		// Fix parent cgroup
+		cgroupPath, err := pod.CgroupPath()
+		if err != nil {
+			return nil, errors.Wrapf(err, "cannot retrieve cgroup path from pod %q", ctrConfig.Pod)
+		}
+		ctrConfig.CgroupParent = cgroupPath
+
+		oldPodID := dumpSpec.Annotations[ann.SandboxID]
+		// Fix up SandboxID in the annotations
+		dumpSpec.Annotations[ann.SandboxID] = ctrConfig.Pod
+		// Fix up CreateCommand
+		for i, c := range ctrConfig.CreateCommand {
+			if c == oldPodID {
+				ctrConfig.CreateCommand[i] = ctrConfig.Pod
+			}
+		}
+	}
+
 	if len(restoreOptions.PublishPorts) > 0 {
 		ports, _, _, err := generate.ParsePortMapping(restoreOptions.PublishPorts)
 		if err != nil {
diff --git a/pkg/checkpoint/crutils/checkpoint_restore_utils.go b/pkg/checkpoint/crutils/checkpoint_restore_utils.go
index 53ff55865..3b77368bb 100644
--- a/pkg/checkpoint/crutils/checkpoint_restore_utils.go
+++ b/pkg/checkpoint/crutils/checkpoint_restore_utils.go
@@ -1,6 +1,7 @@
 package crutils
 
 import (
+	"bytes"
 	"io"
 	"os"
 	"os/exec"
@@ -189,3 +190,13 @@ func CRRuntimeSupportsCheckpointRestore(runtimePath string) bool {
 	}
 	return false
 }
+
+// CRRuntimeSupportsCheckpointRestore tests if the runtime at 'runtimePath'
+// supports restoring into existing Pods. The runtime needs to support
+// the CRIU option --lsm-mount-context and the existence of this is checked
+// by this function. In addition it is necessary to at least have CRIU 3.16.
+func CRRuntimeSupportsPodCheckpointRestore(runtimePath string) bool {
+	cmd := exec.Command(runtimePath, "restore", "--lsm-mount-context")
+	out, _ := cmd.CombinedOutput()
+	return bytes.Contains(out, []byte("flag needs an argument"))
+}