fix(unikontainers): reject OCI specs with missing root section

pkg/unikontainers/unikontainers.go

@@ -63,15 +63,28 @@ type Unikontainer struct {
 	Conn     *net.UnixConn
 }
 
+// requireLinuxAndRoot ensures the OCI spec has the sections urunc later
+// dereferences. Matching the shim's Root check keeps create/start validation
+// consistent across entry points.
+func requireLinuxAndRoot(spec *specs.Spec) error {
+	if spec == nil || spec.Linux == nil {
+		return fmt.Errorf("invalid OCI spec: linux section is required")
+	}
+	if spec.Root == nil {
+		return fmt.Errorf("invalid OCI spec: root section is required")
+	}
+	return nil
+}
+
 // New parses the bundle and creates a new Unikontainer object
 func New(bundlePath string, containerID string, rootDir string, cfg *UruncConfig) (*Unikontainer, error) {
 	spec, err := loadSpec(bundlePath)
 	if err != nil {
 		return nil, err
 	}
 
-	if spec == nil || spec.Linux == nil {
-		return nil, fmt.Errorf("invalid OCI spec: linux section is required")
+	if err := requireLinuxAndRoot(spec); err != nil {
+		return nil, err
 	}
 
 	containerName := spec.Annotations["io.kubernetes.cri.container-name"]
@@ -129,8 +142,8 @@ func Get(containerID string, rootDir string) (*Unikontainer, error) {
 	if err != nil {
 		return nil, err
 	}
-	if spec == nil || spec.Linux == nil {
-		return nil, fmt.Errorf("invalid OCI spec: linux section is required")
+	if err := requireLinuxAndRoot(spec); err != nil {
+		return nil, err
 	}
 	u.BaseDir = containerDir
 	u.RootDir = rootDir

pkg/unikontainers/unikontainers_test.go

@@ -0,0 +1,107 @@
+// Copyright (c) 2023-2026, Nubificus LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package unikontainers
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/stretchr/testify/assert"
+)
+
+func writeBundleConfig(t *testing.T, bundleDir string, configJSON string) {
+	t.Helper()
+	err := os.WriteFile(filepath.Join(bundleDir, configFilename), []byte(configJSON), 0o600)
+	assert.NoError(t, err)
+}
+
+func TestNewRejectsMissingRoot(t *testing.T) {
+	cfg := UruncConfigFromMap(map[string]string{})
+
+	t.Run("linux present without root returns root validation error", func(t *testing.T) {
+		t.Parallel()
+		bundleDir := t.TempDir()
+		writeBundleConfig(t, bundleDir, `{"linux":{}}`)
+
+		u, err := New(bundleDir, "test-container", t.TempDir(), cfg)
+		assert.Nil(t, u)
+		assert.Error(t, err)
+		assert.EqualError(t, err, "invalid OCI spec: root section is required")
+	})
+
+	t.Run("valid annotations cannot bypass missing root validation", func(t *testing.T) {
+		t.Parallel()
+		bundleDir := t.TempDir()
+		writeBundleConfig(t, bundleDir, `{
+			"linux": {},
+			"annotations": {
+				"com.urunc.unikernel.unikernelType": "unikraft",
+				"com.urunc.unikernel.hypervisor": "qemu",
+				"com.urunc.unikernel.binary": "/kernel"
+			}
+		}`)
+
+		u, err := New(bundleDir, "test-container", t.TempDir(), cfg)
+		assert.Nil(t, u)
+		assert.Error(t, err)
+		assert.EqualError(t, err, "invalid OCI spec: root section is required")
+	})
+
+	t.Run("missing linux still returns linux validation error", func(t *testing.T) {
+		t.Parallel()
+		bundleDir := t.TempDir()
+		writeBundleConfig(t, bundleDir, `{"root":{"path":"rootfs"}}`)
+
+		u, err := New(bundleDir, "test-container", t.TempDir(), cfg)
+		assert.Nil(t, u)
+		assert.Error(t, err)
+		assert.EqualError(t, err, "invalid OCI spec: linux section is required")
+	})
+}
+
+func TestGetRejectsMissingRoot(t *testing.T) {
+	t.Parallel()
+
+	bundleDir := t.TempDir()
+	writeBundleConfig(t, bundleDir, `{"linux":{}}`)
+
+	rootDir := t.TempDir()
+	containerID := "test-container"
+	containerDir := filepath.Join(rootDir, containerID)
+	err := os.MkdirAll(containerDir, 0o755)
+	assert.NoError(t, err)
+
+	state := specs.State{
+		Version: "1.0.0",
+		ID:      containerID,
+		Status:  "created",
+		Bundle:  bundleDir,
+		Annotations: map[string]string{
+			annotType: "unikraft",
+		},
+	}
+	stateData, err := json.Marshal(state)
+	assert.NoError(t, err)
+	err = os.WriteFile(filepath.Join(containerDir, stateFilename), stateData, 0o600)
+	assert.NoError(t, err)
+
+	u, err := Get(containerID, rootDir)
+	assert.Nil(t, u)
+	assert.Error(t, err)
+	assert.EqualError(t, err, "invalid OCI spec: root section is required")
+}