Drop effective and permitted cap for non-root user.

Signed-off-by: Lantao Liu <[email protected]>

integration/images/private-workdir/Dockerfile

@@ -0,0 +1,20 @@
+# Copyright 2018 The Kubernetes Authors.
+#
+# 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.
+
+FROM busybox
+
+RUN mkdir /workdir
+RUN chmod 700 /workdir
+RUN chown nobody /workdir
+WORKDIR /workdir

integration/images/private-workdir/Makefile

@@ -0,0 +1,27 @@
+# Copyright 2018 The Kubernetes Authors.
+#
+# 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.
+
+all: build
+
+PROJ=gcr.io/k8s-cri-containerd
+VERSION=1.0
+IMAGE=$(PROJ)/private-workdir:$(VERSION)
+
+build:
+	docker build -t $(IMAGE) .
+
+push:
+	gcloud docker -- push $(IMAGE)
+
+.PHONY: build push

integration/main_test.go

@@ -251,6 +251,19 @@ func WithSupplementalGroups(gids []int64) ContainerOpts {
 	}
 }
 
+// WithRunAsUser adds RunAsUser uid.
+func WithRunAsUser(uid int64) ContainerOpts {
+	return func(c *runtime.ContainerConfig) {
+		if c.Linux == nil {
+			c.Linux = &runtime.LinuxContainerConfig{}
+		}
+		if c.Linux.SecurityContext == nil {
+			c.Linux.SecurityContext = &runtime.LinuxContainerSecurityContext{}
+		}
+		c.Linux.SecurityContext.RunAsUser = &runtime.Int64Value{Value: uid}
+	}
+}
+
 // ContainerConfig creates a container config given a name and image name
 // and additional container config options
 func ContainerConfig(name, image string, opts ...ContainerOpts) *runtime.ContainerConfig {

integration/non_root_user_cap_test.go

@@ -0,0 +1,82 @@
+/*
+Copyright The containerd Authors.
+
+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 integration
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	runtime "k8s.io/cri-api/pkg/apis/runtime/v1alpha2"
+)
+
+func TestNonRootUserCap(t *testing.T) {
+	for name, test := range map[string]struct {
+		uid     int64
+		startOK bool
+	}{
+		"shouldn't be able to run container with a private workdir only accessible to nobody as a non-root user": {
+			uid:     1234,
+			startOK: false,
+		},
+		"shouldn be able to run container with a private workdir only accessible to nobody as root": {
+			uid:     0,
+			startOK: true,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Log("Create a sandbox")
+			sbConfig := PodSandboxConfig("sandbox", "non-root-user-cap")
+			sb, err := runtimeService.RunPodSandbox(sbConfig, *runtimeHandler)
+			require.NoError(t, err)
+			// Make sure the sandbox is cleaned up.
+			defer func() {
+				assert.NoError(t, runtimeService.StopPodSandbox(sb))
+				assert.NoError(t, runtimeService.RemovePodSandbox(sb))
+			}()
+
+			const (
+				testImage     = "gcr.io/k8s-cri-containerd/private-workdir:1.0"
+				containerName = "test-container"
+			)
+			t.Logf("Pull test image %q", testImage)
+			img, err := imageService.PullImage(&runtime.ImageSpec{Image: testImage}, nil, sbConfig)
+			require.NoError(t, err)
+			defer func() {
+				assert.NoError(t, imageService.RemoveImage(&runtime.ImageSpec{Image: img}))
+			}()
+
+			t.Log("Create a container to print capabilities")
+			cnConfig := ContainerConfig(
+				containerName,
+				testImage,
+				WithCommand("ls", "/"),
+				WithLogPath(containerName),
+				WithRunAsUser(test.uid),
+			)
+			cn, err := runtimeService.CreateContainer(sb, cnConfig, sbConfig)
+			require.NoError(t, err)
+
+			t.Log("Start the container")
+			if test.startOK {
+				require.NoError(t, runtimeService.StartContainer(cn))
+			} else {
+				require.Error(t, runtimeService.StartContainer(cn))
+			}
+		})
+	}
+}

pkg/containerd/opts/spec_unix.go

@@ -328,7 +328,7 @@ func WithDevices(osi osinterface.OS, config *runtime.ContainerConfig) oci.SpecOp
 	}
 }
 
-// WithCapabilities sets the provided capabilties from the security context
+// WithCapabilities sets the provided capabilities from the security context
 func WithCapabilities(sc *runtime.LinuxContainerSecurityContext) oci.SpecOpts {
 	capabilities := sc.GetCapabilities()
 	if capabilities == nil {
@@ -637,3 +637,16 @@ func GetUTSNamespace(pid uint32) string {
 func GetPIDNamespace(pid uint32) string {
 	return fmt.Sprintf(pidNSFormat, pid)
 }
+
+// WithCapDropForNonRootUser drops effective and permitted capabilities
+// if the user is non-root.
+// See https://github.com/moby/moby/pull/36587.
+//
+// This option should be behind options for setting users and capabilities.
+func WithCapDropForNonRootUser(_ context.Context, _ oci.Client, _ *containers.Container, s *runtimespec.Spec) error {
+	if s.Process != nil && s.Process.User.UID != 0 && s.Process.Capabilities != nil {
+		s.Process.Capabilities.Effective = []string{}
+		s.Process.Capabilities.Permitted = []string{}
+	}
+	return nil
+}

pkg/server/container_create_unix.go

@@ -288,6 +288,9 @@ func (c *criService) containerSpecOpts(config *runtime.ContainerConfig, imageCon
 	if seccompSpecOpts != nil {
 		specOpts = append(specOpts, seccompSpecOpts)
 	}
+
+	// Add this at the end to make sure that capabilities and users have both been set.
+	specOpts = append(specOpts, customopts.WithCapDropForNonRootUser)
 	return specOpts, nil
 }