[graph] Enforce manifest/layer digest verification

We noticed a regression since the 1.7.1 patch after some refactoring. This patch corrects the behavior and adds integration tests for modified manifest and rootfs layer blobs. Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)
2015-07-31 23:27:19 -07:00 · 2015-07-31 23:27:19 -07:00 · de52a3bcaa
--- a/graph/pull_v2.go
+++ b/graph/pull_v2.go
@ -102,13 +102,12 @@ func (p *v2Puller) pullV2Repository(tag string) (err error) {

 // downloadInfo is used to pass information from download to extractor
 type downloadInfo struct {
-	img      *image.Image
-	tmpFile  *os.File
-	digest   digest.Digest
-	layer    distribution.ReadSeekCloser
-	size     int64
-	err      chan error
-	verified bool
+	img     *image.Image
+	tmpFile *os.File
+	digest  digest.Digest
+	layer   distribution.ReadSeekCloser
+	size    int64
+	err     chan error
 }

 type errVerification struct{}
@ -176,9 +175,11 @@ func (p *v2Puller) download(di *downloadInfo) {

 	out.Write(p.sf.FormatProgress(stringid.TruncateID(di.img.ID), "Verifying Checksum", nil))

-	di.verified = verifier.Verified()
-	if !di.verified {
-		logrus.Infof("Image verification failed for layer %s", di.digest)
+	if !verifier.Verified() {
+		err = fmt.Errorf("filesystem layer verification failed for digest %s", di.digest)
+		logrus.Error(err)
+		di.err <- err
+		return
 	}

 	out.Write(p.sf.FormatProgress(stringid.TruncateID(di.img.ID), "Download complete", nil))
@ -252,7 +253,6 @@ func (p *v2Puller) pullV2Tag(tag, taggedName string) (bool, error) {
 				return false, err
 			}
 		}
-		verified = verified && d.verified
 		if d.layer != nil {
 			// if tmpFile is empty assume download and extracted elsewhere
 			defer os.Remove(d.tmpFile.Name())
@ -368,6 +368,28 @@ func (p *v2Puller) verifyTrustedKeys(namespace string, keys []libtrust.PublicKey
 }

 func (p *v2Puller) validateManifest(m *manifest.SignedManifest, tag string) (verified bool, err error) {
+	// If pull by digest, then verify the manifest digest. NOTE: It is
+	// important to do this first, before any other content validation. If the
+	// digest cannot be verified, don't even bother with those other things.
+	if manifestDigest, err := digest.ParseDigest(tag); err == nil {
+		verifier, err := digest.NewDigestVerifier(manifestDigest)
+		if err != nil {
+			return false, err
+		}
+		payload, err := m.Payload()
+		if err != nil {
+			return false, err
+		}
+		if _, err := verifier.Write(payload); err != nil {
+			return false, err
+		}
+		if !verifier.Verified() {
+			err := fmt.Errorf("image verification failed for digest %s", manifestDigest)
+			logrus.Error(err)
+			return false, err
+		}
+	}
+
 	// TODO(tiborvass): what's the usecase for having manifest == nil and err == nil ? Shouldn't be the error be "DoesNotExist" ?
 	if m == nil {
 		return false, fmt.Errorf("image manifest does not exist for tag %q", tag)
@ -389,21 +411,5 @@ func (p *v2Puller) validateManifest(m *manifest.SignedManifest, tag string) (ver
 	if err != nil {
 		return false, fmt.Errorf("error verifying manifest keys: %v", err)
 	}
-	localDigest, err := digest.ParseDigest(tag)
-	// if pull by digest, then verify
-	if err == nil {
-		verifier, err := digest.NewDigestVerifier(localDigest)
-		if err != nil {
-			return false, err
-		}
-		payload, err := m.Payload()
-		if err != nil {
-			return false, err
-		}
-		if _, err := verifier.Write(payload); err != nil {
-			return false, err
-		}
-		verified = verified && verifier.Verified()
-	}
 	return verified, nil
 }
--- a/integration-cli/docker_cli_by_digest_test.go
+++ b/integration-cli/docker_cli_by_digest_test.go
@ -1,25 +1,29 @@
 package main

 import (
+	"encoding/json"
 	"fmt"
 	"regexp"
 	"strings"

+	"github.com/docker/distribution/digest"
+	"github.com/docker/distribution/manifest"
 	"github.com/docker/docker/utils"
 	"github.com/go-check/check"
 )

 var (
-	repoName        = fmt.Sprintf("%v/dockercli/busybox-by-dgst", privateRegistryURL)
+	remoteRepoName  = "dockercli/busybox-by-dgst"
+	repoName        = fmt.Sprintf("%v/%s", privateRegistryURL, remoteRepoName)
 	pushDigestRegex = regexp.MustCompile("[\\S]+: digest: ([\\S]+) size: [0-9]+")
 	digestRegex     = regexp.MustCompile("Digest: ([\\S]+)")
 )

-func setupImage(c *check.C) (string, error) {
+func setupImage(c *check.C) (digest.Digest, error) {
 	return setupImageWithTag(c, "latest")
 }

-func setupImageWithTag(c *check.C, tag string) (string, error) {
+func setupImageWithTag(c *check.C, tag string) (digest.Digest, error) {
 	containerName := "busyboxbydigest"

 	dockerCmd(c, "run", "-d", "-e", "digest=1", "--name", containerName, "busybox")
@ -52,7 +56,7 @@ func setupImageWithTag(c *check.C, tag string) (string, error) {
 	}
 	pushDigest := matches[1]

-	return pushDigest, nil
+	return digest.Digest(pushDigest), nil
 }

 func (s *DockerRegistrySuite) TestPullByTagDisplaysDigest(c *check.C) {
@ -72,7 +76,7 @@ func (s *DockerRegistrySuite) TestPullByTagDisplaysDigest(c *check.C) {
 	pullDigest := matches[1]

 	// make sure the pushed and pull digests match
-	if pushDigest != pullDigest {
+	if pushDigest.String() != pullDigest {
 		c.Fatalf("push digest %q didn't match pull digest %q", pushDigest, pullDigest)
 	}
 }
@ -95,7 +99,7 @@ func (s *DockerRegistrySuite) TestPullByDigest(c *check.C) {
 	pullDigest := matches[1]

 	// make sure the pushed and pull digests match
-	if pushDigest != pullDigest {
+	if pushDigest.String() != pullDigest {
 		c.Fatalf("push digest %q didn't match pull digest %q", pushDigest, pullDigest)
 	}
 }
@ -291,7 +295,7 @@ func (s *DockerRegistrySuite) TestListImagesWithDigests(c *check.C) {
 	out, _ := dockerCmd(c, "images", "--digests")

 	// make sure repo shown, tag=<none>, digest = $digest1
-	re1 := regexp.MustCompile(`\s*` + repoName + `\s*<none>\s*` + digest1 + `\s`)
+	re1 := regexp.MustCompile(`\s*` + repoName + `\s*<none>\s*` + digest1.String() + `\s`)
 	if !re1.MatchString(out) {
 		c.Fatalf("expected %q: %s", re1.String(), out)
 	}
@ -319,7 +323,7 @@ func (s *DockerRegistrySuite) TestListImagesWithDigests(c *check.C) {
 	}

 	// make sure repo shown, tag=<none>, digest = $digest2
-	re2 := regexp.MustCompile(`\s*` + repoName + `\s*<none>\s*` + digest2 + `\s`)
+	re2 := regexp.MustCompile(`\s*` + repoName + `\s*<none>\s*` + digest2.String() + `\s`)
 	if !re2.MatchString(out) {
 		c.Fatalf("expected %q: %s", re2.String(), out)
 	}
@ -332,7 +336,7 @@ func (s *DockerRegistrySuite) TestListImagesWithDigests(c *check.C) {

 	// make sure image 1 has repo, tag, <none> AND repo, <none>, digest
 	reWithTag1 := regexp.MustCompile(`\s*` + repoName + `\s*tag1\s*<none>\s`)
-	reWithDigest1 := regexp.MustCompile(`\s*` + repoName + `\s*<none>\s*` + digest1 + `\s`)
+	reWithDigest1 := regexp.MustCompile(`\s*` + repoName + `\s*<none>\s*` + digest1.String() + `\s`)
 	if !reWithTag1.MatchString(out) {
 		c.Fatalf("expected %q: %s", reWithTag1.String(), out)
 	}
@ -357,7 +361,7 @@ func (s *DockerRegistrySuite) TestListImagesWithDigests(c *check.C) {

 	// make sure image 2 has repo, tag, digest
 	reWithTag2 := regexp.MustCompile(`\s*` + repoName + `\s*tag2\s*<none>\s`)
-	reWithDigest2 := regexp.MustCompile(`\s*` + repoName + `\s*<none>\s*` + digest2 + `\s`)
+	reWithDigest2 := regexp.MustCompile(`\s*` + repoName + `\s*<none>\s*` + digest2.String() + `\s`)
 	if !reWithTag2.MatchString(out) {
 		c.Fatalf("expected %q: %s", reWithTag2.String(), out)
 	}
@ -401,3 +405,95 @@ func (s *DockerRegistrySuite) TestDeleteImageByIDOnlyPulledByDigest(c *check.C)

 	dockerCmd(c, "rmi", imageID)
 }
+
+// TestPullFailsWithAlteredManifest tests that a `docker pull` fails when
+// we have modified a manifest blob and its digest cannot be verified.
+func (s *DockerRegistrySuite) TestPullFailsWithAlteredManifest(c *check.C) {
+	manifestDigest, err := setupImage(c)
+	if err != nil {
+		c.Fatalf("error setting up image: %v", err)
+	}
+
+	// Load the target manifest blob.
+	manifestBlob := s.reg.readBlobContents(c, manifestDigest)
+
+	var imgManifest manifest.Manifest
+	if err := json.Unmarshal(manifestBlob, &imgManifest); err != nil {
+		c.Fatalf("unable to decode image manifest from blob: %s", err)
+	}
+
+	// Add a malicious layer digest to the list of layers in the manifest.
+	imgManifest.FSLayers = append(imgManifest.FSLayers, manifest.FSLayer{
+		BlobSum: digest.Digest("sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"),
+	})
+
+	// Move the existing data file aside, so that we can replace it with a
+	// malicious blob of data. NOTE: we defer the returned undo func.
+	undo := s.reg.tempMoveBlobData(c, manifestDigest)
+	defer undo()
+
+	alteredManifestBlob, err := json.Marshal(imgManifest)
+	if err != nil {
+		c.Fatalf("unable to encode altered image manifest to JSON: %s", err)
+	}
+
+	s.reg.writeBlobContents(c, manifestDigest, alteredManifestBlob)
+
+	// Now try pulling that image by digest. We should get an error about
+	// digest verification for the manifest digest.
+
+	// Pull from the registry using the <name>@<digest> reference.
+	imageReference := fmt.Sprintf("%s@%s", repoName, manifestDigest)
+	out, exitStatus, _ := dockerCmdWithError("pull", imageReference)
+	if exitStatus == 0 {
+		c.Fatalf("expected a zero exit status but got %d: %s", exitStatus, out)
+	}
+
+	expectedErrorMsg := fmt.Sprintf("image verification failed for digest %s", manifestDigest)
+	if !strings.Contains(out, expectedErrorMsg) {
+		c.Fatalf("expected error message %q in output: %s", expectedErrorMsg, out)
+	}
+}
+
+// TestPullFailsWithAlteredLayer tests that a `docker pull` fails when
+// we have modified a layer blob and its digest cannot be verified.
+func (s *DockerRegistrySuite) TestPullFailsWithAlteredLayer(c *check.C) {
+	manifestDigest, err := setupImage(c)
+	if err != nil {
+		c.Fatalf("error setting up image: %v", err)
+	}
+
+	// Load the target manifest blob.
+	manifestBlob := s.reg.readBlobContents(c, manifestDigest)
+
+	var imgManifest manifest.Manifest
+	if err := json.Unmarshal(manifestBlob, &imgManifest); err != nil {
+		c.Fatalf("unable to decode image manifest from blob: %s", err)
+	}
+
+	// Next, get the digest of one of the layers from the manifest.
+	targetLayerDigest := imgManifest.FSLayers[0].BlobSum
+
+	// Move the existing data file aside, so that we can replace it with a
+	// malicious blob of data. NOTE: we defer the returned undo func.
+	undo := s.reg.tempMoveBlobData(c, targetLayerDigest)
+	defer undo()
+
+	// Now make a fake data blob in this directory.
+	s.reg.writeBlobContents(c, targetLayerDigest, []byte("This is not the data you are looking for."))
+
+	// Now try pulling that image by digest. We should get an error about
+	// digest verification for the target layer digest.
+
+	// Pull from the registry using the <name>@<digest> reference.
+	imageReference := fmt.Sprintf("%s@%s", repoName, manifestDigest)
+	out, exitStatus, _ := dockerCmdWithError("pull", imageReference)
+	if exitStatus == 0 {
+		c.Fatalf("expected a zero exit status but got: %d", exitStatus)
+	}
+
+	expectedErrorMsg := fmt.Sprintf("filesystem layer verification failed for digest %s", targetLayerDigest)
+	if !strings.Contains(out, expectedErrorMsg) {
+		c.Fatalf("expected error message %q in output: %s", expectedErrorMsg, out)
+	}
+}
--- a/integration-cli/registry.go
+++ b/integration-cli/registry.go
@ -8,6 +8,7 @@ import (
 	"os/exec"
 	"path/filepath"

+	"github.com/docker/distribution/digest"
 	"github.com/go-check/check"
 )

@ -70,3 +71,50 @@ func (t *testRegistryV2) Close() {
 	t.cmd.Process.Kill()
 	os.RemoveAll(t.dir)
 }
+
+func (t *testRegistryV2) getBlobFilename(blobDigest digest.Digest) string {
+	// Split the digest into it's algorithm and hex components.
+	dgstAlg, dgstHex := blobDigest.Algorithm(), blobDigest.Hex()
+
+	// The path to the target blob data looks something like:
+	//   baseDir + "docker/registry/v2/blobs/sha256/a3/a3ed...46d4/data"
+	return fmt.Sprintf("%s/docker/registry/v2/blobs/%s/%s/%s/data", t.dir, dgstAlg, dgstHex[:2], dgstHex)
+}
+
+func (t *testRegistryV2) readBlobContents(c *check.C, blobDigest digest.Digest) []byte {
+	// Load the target manifest blob.
+	manifestBlob, err := ioutil.ReadFile(t.getBlobFilename(blobDigest))
+	if err != nil {
+		c.Fatalf("unable to read blob: %s", err)
+	}
+
+	return manifestBlob
+}
+
+func (t *testRegistryV2) writeBlobContents(c *check.C, blobDigest digest.Digest, data []byte) {
+	if err := ioutil.WriteFile(t.getBlobFilename(blobDigest), data, os.FileMode(0644)); err != nil {
+		c.Fatalf("unable to write malicious data blob: %s", err)
+	}
+}
+
+func (t *testRegistryV2) tempMoveBlobData(c *check.C, blobDigest digest.Digest) (undo func()) {
+	tempFile, err := ioutil.TempFile("", "registry-temp-blob-")
+	if err != nil {
+		c.Fatalf("unable to get temporary blob file: %s", err)
+	}
+	tempFile.Close()
+
+	blobFilename := t.getBlobFilename(blobDigest)
+
+	// Move the existing data file aside, so that we can replace it with a
+	// another blob of data.
+	if err := os.Rename(blobFilename, tempFile.Name()); err != nil {
+		os.Remove(tempFile.Name())
+		c.Fatalf("unable to move data blob: %s", err)
+	}
+
+	return func() {
+		os.Rename(tempFile.Name(), blobFilename)
+		os.Remove(tempFile.Name())
+	}
+}