Support sandbox images from private registries

**What this PR does / why we need it**:

The --pod-infra-container-image parameter allows the user to specify
an arbitrary image to be used as the pod infra container (AKA
sandbox), an internal piece of the dockershim implementation of the
Container Runtime Interface.

The dockershim does not have access to any of the pod-level image pull
credentials configuration, so if the user specifies an image from a
private registry, the image pull will fail.

This change allows the dockershim to read local docker configuration
(e.g. /root/.docker/config.json) and use it when pulling the pod infra
container image.

**Which issue this PR fixes**: fixes #45738

**Special notes for your reviewer**:
The changes to fake_client for writing local config files deserve some
attention.

**Release note**:

```release-note
NONE
```

pkg/kubelet/dockershim/BUILD

@@ -31,6 +31,7 @@ go_library(
     deps = [
         "//pkg/api/v1:go_default_library",
         "//pkg/apis/componentconfig:go_default_library",
+        "//pkg/credentialprovider:go_default_library",
         "//pkg/kubelet/apis/cri:go_default_library",
         "//pkg/kubelet/apis/cri/v1alpha1:go_default_library",
         "//pkg/kubelet/cm:go_default_library",

pkg/kubelet/dockershim/helpers.go

@@ -22,6 +22,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
+	"os"
 	"path/filepath"
 	"regexp"
 	"strconv"
@@ -34,6 +35,7 @@ import (
 	"github.com/golang/glog"
 
 	"k8s.io/kubernetes/pkg/api/v1"
+	"k8s.io/kubernetes/pkg/credentialprovider"
 	runtimeapi "k8s.io/kubernetes/pkg/kubelet/apis/cri/v1alpha1"
 	"k8s.io/kubernetes/pkg/kubelet/types"
 	"k8s.io/kubernetes/pkg/security/apparmor"
@@ -375,6 +377,11 @@ func getSecurityOptSeparator(v *semver.Version) rune {
 
 // ensureSandboxImageExists pulls the sandbox image when it's not present.
 func ensureSandboxImageExists(client libdocker.Interface, image string) error {
+	dockerCfgSearchPath := []string{"/.docker", filepath.Join(os.Getenv("HOME"), ".docker")}
+	return ensureSandboxImageExistsDockerCfg(client, image, dockerCfgSearchPath)
+}
+
+func ensureSandboxImageExistsDockerCfg(client libdocker.Interface, image string, dockerCfgSearchPath []string) error {
 	_, err := client.InspectImageByRef(image)
 	if err == nil {
 		return nil
@@ -382,8 +389,32 @@ func ensureSandboxImageExists(client libdocker.Interface, image string) error {
 	if !libdocker.IsImageNotFoundError(err) {
 		return fmt.Errorf("failed to inspect sandbox image %q: %v", image, err)
 	}
-	err = client.PullImage(image, dockertypes.AuthConfig{}, dockertypes.ImagePullOptions{})
+
+	// To support images in private registries, try to read docker config
+	authConfig := dockertypes.AuthConfig{}
+	keyring := &credentialprovider.BasicDockerKeyring{}
+	var cfgLoadErr error
+	if cfg, err := credentialprovider.ReadDockerConfigJSONFile(dockerCfgSearchPath); err == nil {
+		keyring.Add(cfg)
+	} else if cfg, err := credentialprovider.ReadDockercfgFile(dockerCfgSearchPath); err == nil {
+		keyring.Add(cfg)
+	} else {
+		cfgLoadErr = err
+	}
+	if creds, withCredentials := keyring.Lookup(image); withCredentials {
+		// Use the first one that matched our image
+		for _, cred := range creds {
+			authConfig.Username = cred.Username
+			authConfig.Password = cred.Password
+			break
+		}
+	}
+
+	err = client.PullImage(image, authConfig, dockertypes.ImagePullOptions{})
 	if err != nil {
+		if cfgLoadErr != nil {
+			glog.Warningf("Couldn't load Docker cofig. If sandbox image %q is in a private registry, this will cause further errors. Error: %v", image, cfgLoadErr)
+		}
 		return fmt.Errorf("unable to pull sandbox image %q: %v", image, err)
 	}
 	return nil

pkg/kubelet/dockershim/helpers_test.go

@@ -17,8 +17,12 @@ limitations under the License.
 package dockershim
 
 import (
+	"encoding/base64"
 	"fmt"
+	"io/ioutil"
+	"os"
 	"path"
+	"path/filepath"
 	"testing"
 
 	"github.com/blang/semver"
@@ -247,13 +251,33 @@ func TestGetSecurityOptSeparator(t *testing.T) {
 	}
 }
 
+// writeDockerConfig will write a config file into a temporary dir, and return that dir.
+// Caller is responsible for deleting the dir and its contents.
+func writeDockerConfig(cfg string) (string, error) {
+	tmpdir, err := ioutil.TempDir("", "dockershim=helpers_test.go=")
+	if err != nil {
+		return "", err
+	}
+	dir := filepath.Join(tmpdir, ".docker")
+	if err := os.Mkdir(dir, 0755); err != nil {
+		return "", err
+	}
+	return tmpdir, ioutil.WriteFile(filepath.Join(dir, "config.json"), []byte(cfg), 0644)
+}
+
 func TestEnsureSandboxImageExists(t *testing.T) {
 	sandboxImage := "gcr.io/test/image"
+	registryHost := "https://gcr.io/"
+	authConfig := dockertypes.AuthConfig{Username: "user", Password: "pass"}
+	authB64 := base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%s:%s", authConfig.Username, authConfig.Password)))
+	authJSON := fmt.Sprintf("{\"auths\": {\"%s\": {\"auth\": \"%s\"} } }", registryHost, authB64)
 	for desc, test := range map[string]struct {
-		injectImage bool
-		injectErr   error
-		calls       []string
-		err         bool
+		injectImage  bool
+		imgNeedsAuth bool
+		injectErr    error
+		calls        []string
+		err          bool
+		configJSON   string
 	}{
 		"should not pull image when it already exists": {
 			injectImage: true,
@@ -271,14 +295,42 @@ func TestEnsureSandboxImageExists(t *testing.T) {
 			calls:       []string{"inspect_image"},
 			err:         true,
 		},
+		"should return error when image pull needs private auth, but none provided": {
+			injectImage:  true,
+			imgNeedsAuth: true,
+			injectErr:    libdocker.ImageNotFoundError{ID: "image_id"},
+			calls:        []string{"inspect_image", "pull"},
+			err:          true,
+		},
+		"should pull private image using dockerauth if image doesn't exist": {
+			injectImage:  true,
+			imgNeedsAuth: true,
+			injectErr:    libdocker.ImageNotFoundError{ID: "image_id"},
+			calls:        []string{"inspect_image", "pull"},
+			configJSON:   authJSON,
+			err:          false,
+		},
 	} {
 		t.Logf("TestCase: %q", desc)
 		_, fakeDocker, _ := newTestDockerService()
 		if test.injectImage {
-			fakeDocker.InjectImages([]dockertypes.Image{{ID: sandboxImage}})
+			images := []dockertypes.Image{{ID: sandboxImage}}
+			fakeDocker.InjectImages(images)
+			if test.imgNeedsAuth {
+				fakeDocker.MakeImagesPrivate(images, authConfig)
+			}
 		}
 		fakeDocker.InjectError("inspect_image", test.injectErr)
-		err := ensureSandboxImageExists(fakeDocker, sandboxImage)
+
+		var dockerCfgSearchPath []string
+		if test.configJSON != "" {
+			tmpdir, err := writeDockerConfig(test.configJSON)
+			require.NoError(t, err, "could not create a temp docker config file")
+			dockerCfgSearchPath = append(dockerCfgSearchPath, filepath.Join(tmpdir, ".docker"))
+			defer os.RemoveAll(tmpdir)
+		}
+
+		err := ensureSandboxImageExistsDockerCfg(fakeDocker, sandboxImage, dockerCfgSearchPath)
 		assert.NoError(t, fakeDocker.AssertCalls(test.calls))
 		assert.Equal(t, test.err, err != nil)
 	}

pkg/kubelet/dockershim/libdocker/fake_client.go

@@ -55,6 +55,7 @@ type FakeDockerClient struct {
 	ContainerMap         map[string]*dockertypes.ContainerJSON
 	ImageInspects        map[string]*dockertypes.ImageInspect
 	Images               []dockertypes.Image
+	ImageIDsNeedingAuth  map[string]dockertypes.AuthConfig
 	Errors               map[string]error
 	called               []calledDetail
 	pulled               []string
@@ -91,8 +92,9 @@ func NewFakeDockerClient() *FakeDockerClient {
 		ContainerMap: make(map[string]*dockertypes.ContainerJSON),
 		Clock:        clock.RealClock{},
 		// default this to true, so that we trace calls, image pulls and container lifecycle
-		EnableTrace:   true,
-		ImageInspects: make(map[string]*dockertypes.ImageInspect),
+		EnableTrace:         true,
+		ImageInspects:       make(map[string]*dockertypes.ImageInspect),
+		ImageIDsNeedingAuth: make(map[string]dockertypes.AuthConfig),
 	}
 }
 
@@ -632,6 +634,14 @@ func (f *FakeDockerClient) Logs(id string, opts dockertypes.ContainerLogsOptions
 	return f.popError("logs")
 }
 
+func (f *FakeDockerClient) isAuthorizedForImage(image string, auth dockertypes.AuthConfig) bool {
+	if reqd, exists := f.ImageIDsNeedingAuth[image]; !exists {
+		return true // no auth needed
+	} else {
+		return auth.Username == reqd.Username && auth.Password == reqd.Password
+	}
+}
+
 // PullImage is a test-spy implementation of Interface.PullImage.
 // It adds an entry "pull" to the internal method call record.
 func (f *FakeDockerClient) PullImage(image string, auth dockertypes.AuthConfig, opts dockertypes.ImagePullOptions) error {
@@ -640,6 +650,10 @@ func (f *FakeDockerClient) PullImage(image string, auth dockertypes.AuthConfig,
 	f.appendCalled(calledDetail{name: "pull"})
 	err := f.popError("pull")
 	if err == nil {
+		if !f.isAuthorizedForImage(image, auth) {
+			return ImageNotFoundError{ID: image}
+		}
+
 		authJson, _ := json.Marshal(auth)
 		inspect := createImageInspectFromRef(image)
 		f.ImageInspects[image] = inspect
@@ -720,11 +734,20 @@ func (f *FakeDockerClient) InjectImages(images []dockertypes.Image) {
 	}
 }
 
+func (f *FakeDockerClient) MakeImagesPrivate(images []dockertypes.Image, auth dockertypes.AuthConfig) {
+	f.Lock()
+	defer f.Unlock()
+	for _, i := range images {
+		f.ImageIDsNeedingAuth[i.ID] = auth
+	}
+}
+
 func (f *FakeDockerClient) ResetImages() {
 	f.Lock()
 	defer f.Unlock()
 	f.Images = []dockertypes.Image{}
 	f.ImageInspects = make(map[string]*dockertypes.ImageInspect)
+	f.ImageIDsNeedingAuth = make(map[string]dockertypes.AuthConfig)
 }
 
 func (f *FakeDockerClient) InjectImageInspects(inspects []dockertypes.ImageInspect) {