[WIP]Support podman image sign

Generate a signature claim for an image using user keyring (--sign-by). The signature file will be stored in simple json format under the default or the given directory (--directory or yaml file in /etc/containers/registries.d/).

Signed-off-by: Qi Wang <qiwan@redhat.com>

cmd/podman/image.go

@@ -20,6 +20,7 @@ var (
 		saveCommand,
 		tagCommand,
 		trustCommand,
+		signCommand,
 	}
 
 	imageDescription = "Manage images"

cmd/podman/sign.go

@@ -0,0 +1,194 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net/url"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/containers/image/signature"
+	"github.com/containers/image/transports"
+	"github.com/containers/image/transports/alltransports"
+	"github.com/containers/libpod/cmd/podman/libpodruntime"
+	"github.com/containers/libpod/libpod/image"
+	"github.com/containers/libpod/pkg/trust"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+	"github.com/urfave/cli"
+)
+
+var (
+	signFlags = []cli.Flag{
+		cli.StringFlag{
+			Name:  "sign-by",
+			Usage: "Name of the signing key",
+		},
+		cli.StringFlag{
+			Name:  "directory, d",
+			Usage: "Define an alternate directory to store signatures",
+		},
+	}
+
+	signDescription = "Create a signature file that can be used later to verify the image"
+	signCommand     = cli.Command{
+		Name:         "sign",
+		Usage:        "Sign an image",
+		Description:  signDescription,
+		Flags:        sortFlags(signFlags),
+		Action:       signCmd,
+		ArgsUsage:    "IMAGE-NAME [IMAGE-NAME ...]",
+		OnUsageError: usageErrorHandler,
+	}
+)
+
+// SignatureStoreDir defines default directory to store signatures
+const SignatureStoreDir = "/var/lib/containers/sigstore"
+
+func signCmd(c *cli.Context) error {
+	args := c.Args()
+	if len(args) < 1 {
+		return errors.Errorf("at least one image name must be specified")
+	}
+	runtime, err := libpodruntime.GetRuntime(c)
+	if err != nil {
+		return errors.Wrapf(err, "could not create runtime")
+	}
+	defer runtime.Shutdown(false)
+
+	signby := c.String("sign-by")
+	if signby == "" {
+		return errors.Errorf("You must provide an identity")
+	}
+
+	var sigStoreDir string
+	if c.IsSet("directory") {
+		sigStoreDir = c.String("directory")
+		if _, err := os.Stat(sigStoreDir); err != nil {
+			return errors.Wrapf(err, "invalid directory %s", sigStoreDir)
+		}
+	}
+
+	mech, err := signature.NewGPGSigningMechanism()
+	if err != nil {
+		return errors.Wrap(err, "Error initializing GPG")
+	}
+	defer mech.Close()
+	if err := mech.SupportsSigning(); err != nil {
+		return errors.Wrap(err, "Signing is not supported")
+	}
+
+	systemRegistriesDirPath := trust.RegistriesDirPath(runtime.SystemContext())
+	registryConfigs, err := trust.LoadAndMergeConfig(systemRegistriesDirPath)
+	if err != nil {
+		return errors.Wrapf(err, "error reading registry configuration")
+	}
+
+	for _, signimage := range args {
+		srcRef, err := alltransports.ParseImageName(signimage)
+		if err != nil {
+			return errors.Wrapf(err, "error parsing image name")
+		}
+		rawSource, err := srcRef.NewImageSource(getContext(), runtime.SystemContext())
+		if err != nil {
+			return errors.Wrapf(err, "error getting image source")
+		}
+		manifest, _, err := rawSource.GetManifest(getContext(), nil)
+		if err != nil {
+			return errors.Wrapf(err, "error getting manifest")
+		}
+		dockerReference := rawSource.Reference().DockerReference()
+		if dockerReference == nil {
+			return errors.Errorf("Cannot determine canonical Docker reference for destination %s", transports.ImageName(rawSource.Reference()))
+		}
+
+		// create the signstore file
+		newImage, err := runtime.ImageRuntime().New(getContext(), signimage, runtime.GetConfig().SignaturePolicyPath, "", os.Stderr, nil, image.SigningOptions{SignBy: signby}, false)
+		if err != nil {
+			return errors.Wrapf(err, "error pulling image %s", signimage)
+		}
+
+		registryInfo := trust.HaveMatchRegistry(rawSource.Reference().DockerReference().String(), registryConfigs)
+		if registryInfo != nil {
+			if sigStoreDir == "" {
+				sigStoreDir = registryInfo.SigStoreStaging
+				if sigStoreDir == "" {
+					sigStoreDir = registryInfo.SigStore
+				}
+			}
+			sigStoreDir, err = isValidSigStoreDir(sigStoreDir)
+			if err != nil {
+				return errors.Wrapf(err, "invalid signature storage %s", sigStoreDir)
+			}
+		}
+		if sigStoreDir == "" {
+			sigStoreDir = SignatureStoreDir
+		}
+
+		repos := newImage.RepoDigests()
+		if len(repos) == 0 {
+			logrus.Errorf("no repodigests associated with the image %s", signimage)
+			continue
+		}
+
+		// create signature
+		newSig, err := signature.SignDockerManifest(manifest, dockerReference.String(), mech, signby)
+		if err != nil {
+			return errors.Wrapf(err, "error creating new signature")
+		}
+
+		sigStoreDir = fmt.Sprintf("%s/%s", sigStoreDir, strings.Replace(repos[0][strings.Index(repos[0], "/")+1:len(repos[0])], ":", "=", 1))
+		if err := os.MkdirAll(sigStoreDir, 0751); err != nil {
+			// The directory is allowed to exist
+			if !os.IsExist(err) {
+				logrus.Errorf("error creating directory %s: %s", sigStoreDir, err)
+				continue
+			}
+		}
+		sigFilename, err := getSigFilename(sigStoreDir)
+		if err != nil {
+			logrus.Errorf("error creating sigstore file: %v", err)
+			continue
+		}
+		err = ioutil.WriteFile(sigStoreDir+"/"+sigFilename, newSig, 0644)
+		if err != nil {
+			logrus.Errorf("error storing signature for %s", rawSource.Reference().DockerReference().String())
+			continue
+		}
+	}
+	return nil
+}
+
+func getSigFilename(sigStoreDirPath string) (string, error) {
+	sigFileSuffix := 1
+	sigFiles, err := ioutil.ReadDir(sigStoreDirPath)
+	if err != nil {
+		return "", err
+	}
+	sigFilenames := make(map[string]bool)
+	for _, file := range sigFiles {
+		sigFilenames[file.Name()] = true
+	}
+	for {
+		sigFilename := "signature-" + strconv.Itoa(sigFileSuffix)
+		if _, exists := sigFilenames[sigFilename]; !exists {
+			return sigFilename, nil
+		}
+		sigFileSuffix++
+	}
+}
+
+func isValidSigStoreDir(sigStoreDir string) (string, error) {
+	writeURIs := map[string]bool{"file": true}
+	url, err := url.Parse(sigStoreDir)
+	if err != nil {
+		return sigStoreDir, errors.Wrapf(err, "invalid directory %s", sigStoreDir)
+	}
+	_, exists := writeURIs[url.Scheme]
+	if !exists {
+		return sigStoreDir, errors.Errorf("Writing to %s is not supported. Use a supported scheme", sigStoreDir)
+	}
+	sigStoreDir = url.Path
+	return sigStoreDir, nil
+}

docs/podman-image-sign.1.md

@@ -0,0 +1,52 @@
+% podman-image-sign(1)
+
+# NAME
+podman-image-sign- Create a signature for an image
+
+# SYNOPSIS
+**podman image sign**
+[**-h**|**--help**]
+[**-d**, **--directory**]
+[**--sign-by**]
+[ IMAGE... ]
+
+# DESCRIPTION
+**podmain image sign** will create a local signature for one or more local images that have
+been pulled from a registry. The signature will be written to a directory
+derived from the registry configuration files in /etc/containers/registries.d. By default, the signature will be written into /var/lib/containers/sigstore directory.
+
+# OPTIONS
+**-h** **--help**
+  Print usage statement.
+
+**-d** **--directory**
+  Store the signatures in the specified directory.  Default: /var/lib/containers/sigstore
+
+**--sign-by**
+  Override the default identity of the signature.
+
+# EXAMPLES
+Sign the busybox image with the identify of foo@bar.com with a user's keyring and save the signature in /tmp/signatures/.
+
+   sudo podman image sign --sign-by foo@bar.com -d /tmp/signatures transport://privateregistry.example.com/foobar
+
+# RELATED CONFIGURATION
+
+The write (and read) location for signatures is defined in YAML-based
+configuration files in /etc/containers/registries.d/.  When you sign
+an image, podman will use those configuration files to determine
+where to write the signature based on the the name of the originating
+registry or a default storage value unless overriden with the -d
+option. For example, consider the following configuration file.
+
+docker:
+  privateregistry.example.com:
+    sigstore: file:///var/lib/containers/sigstore
+
+When signing an image preceeded with the registry name 'privateregistry.example.com',
+the signature will be written into subdirectories of
+/var/lib/containers/sigstore/privateregistry.example.com. The use of 'sigstore' also means
+the signature will be 'read' from that same location on a pull-related function.
+
+# HISTORY
+November 2018, Originally compiled by Qi Wang (qiwan at redhat dot com)

docs/podman-image.1.md

@@ -27,7 +27,8 @@ The image command allows you to manage images
 | rm       | [podman-rm(1)](podman-rmi.1.md)           | Removes one or more locally stored images.                                     |
 | save     | [podman-save(1)](podman-save.1.md)        | Save an image to docker-archive or oci.                                        |
 | tag      | [podman-tag(1)](podman-tag.1.md)          | Add an additional name to a local image.                                       |
-| trust    | [podman-image-trust(1)](podman-image-trust.1.md)  | Manage container image trust policy.
+| trust    | [podman-image-trust(1)](podman-image-trust.1.md)  | Manage container image trust policy.                                   |
+| sign    | [podman-image-sign(1)](podman-image-sign.1.md)  | Sign an image.                                                            |
 
 ## SEE ALSO
 podman