Add unit test for man-in-the-middle attack on pull

Add a unit test that proves the digest of the received content being
checked. The check should ensure that the digest of the received content
is identical to the digest provided by the manifest in the layers[0]
descriptor. This check is currently implemented in containerd, so the
unit test ensures security in the case a breaking change is made in
containerd.

Signed-off-by: Peter Engelbert <pmengelbert@gmail.com>

internal/experimental/registry/client_test.go

@@ -24,11 +24,16 @@ import (
 	"io/ioutil"
 	"net"
 	"net/http"
+	"net/http/httptest"
+	"net/url"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 	"time"
 
+	"github.com/containerd/containerd/errdefs"
+
 	auth "github.com/deislabs/oras/pkg/auth/docker"
 	"github.com/docker/distribution/configuration"
 	"github.com/docker/distribution/registry"
@@ -49,10 +54,11 @@ var (
 
 type RegistryClientTestSuite struct {
 	suite.Suite
-	Out                io.Writer
-	DockerRegistryHost string
-	CacheRootDir       string
-	RegistryClient     *Client
+	Out                     io.Writer
+	DockerRegistryHost      string
+	CompromisedRegistryHost string
+	CacheRootDir            string
+	RegistryClient          *Client
 }
 
 func (suite *RegistryClientTestSuite) SetupSuite() {
@@ -116,6 +122,8 @@ func (suite *RegistryClientTestSuite) SetupSuite() {
 	dockerRegistry, err := registry.NewRegistry(context.Background(), config)
 	suite.Nil(err, "no error creating test registry")
 
+	suite.CompromisedRegistryHost = initCompromisedRegistryTestServer()
+
 	// Start Docker registry
 	go dockerRegistry.ListenAndServe()
 }
@@ -232,6 +240,16 @@ func (suite *RegistryClientTestSuite) Test_7_Logout() {
 	suite.Nil(err, "no error logging out of registry")
 }
 
+func (suite *RegistryClientTestSuite) Test_8_ManInTheMiddle() {
+	ref, err := ParseReference(fmt.Sprintf("%s/testrepo/supposedlysafechart:9.9.9", suite.CompromisedRegistryHost))
+	suite.Nil(err)
+
+	// returns content that does not match the expected digest
+	err = suite.RegistryClient.PullChart(ref)
+	suite.NotNil(err)
+	suite.True(errdefs.IsFailedPrecondition(err))
+}
+
 func TestRegistryClientTestSuite(t *testing.T) {
 	suite.Run(t, new(RegistryClientTestSuite))
 }
@@ -250,3 +268,43 @@ func getFreePort() (int, error) {
 	defer l.Close()
 	return l.Addr().(*net.TCPAddr).Port, nil
 }
+
+func initCompromisedRegistryTestServer() string {
+	s := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if strings.Contains(r.URL.Path, "manifests") {
+			w.Header().Set("Content-Type", "application/vnd.oci.image.manifest.v1+json")
+			w.WriteHeader(200)
+
+			// layers[0] is the blob []byte("a")
+			w.Write([]byte(
+				`{ "schemaVersion": 2, "config": {
+    "mediaType": "application/vnd.cncf.helm.config.v1+json",
+    "digest": "sha256:a705ee2789ab50a5ba20930f246dbd5cc01ff9712825bb98f57ee8414377f133",
+    "size": 181
+  },
+  "layers": [
+    {
+      "mediaType": "application/tar+gzip",
+      "digest": "sha256:ca978112ca1bbdcafac231b39a23dc4da786eff8147c4e72b9807785afee48bb",
+      "size": 1
+    }
+  ]
+}`))
+		} else if r.URL.Path == "/v2/testrepo/supposedlysafechart/blobs/sha256:a705ee2789ab50a5ba20930f246dbd5cc01ff9712825bb98f57ee8414377f133" {
+			w.Header().Set("Content-Type", "application/json")
+			w.WriteHeader(200)
+			w.Write([]byte("{\"name\":\"mychart\",\"version\":\"0.1.0\",\"description\":\"A Helm chart for Kubernetes\\n" +
+				"an 'application' or a 'library' chart.\",\"apiVersion\":\"v2\",\"appVersion\":\"1.16.0\",\"type\":" +
+				"\"application\"}"))
+		} else if r.URL.Path == "/v2/testrepo/supposedlysafechart/blobs/sha256:ca978112ca1bbdcafac231b39a23dc4da786eff8147c4e72b9807785afee48bb" {
+			w.Header().Set("Content-Type", "application/tar+gzip")
+			w.WriteHeader(200)
+			w.Write([]byte("b"))
+		} else {
+			w.WriteHeader(500)
+		}
+	}))
+
+	u, _ := url.Parse(s.URL)
+	return fmt.Sprintf("localhost:%s", u.Port())
+}