// IsRunningImageAllowed returns true iff the policy allows running the image.
// If it returns false, err must be non-nil, and should be an PolicyRequirementError if evaluation
// succeeded but the result was rejection.
// WARNING: This validates signatures and the manifest, but does not download or validate the
// layers. Users must validate that the layers match their expected digests.
func (pc *PolicyContext) IsRunningImageAllowed(image types.Image) (res bool, finalErr error) {
if err := pc.changeState(pcReady, pcInUse); err != nil {
return false, err
}
defer func() {
if err := pc.changeState(pcInUse, pcReady); err != nil {
res = false
finalErr = err
}
}()
logrus.Debugf("IsRunningImageAllowed for image %s", image.IntendedDockerReference())
reqs, err := pc.requirementsForImage(image)
if err != nil {
return false, err
}
if len(reqs) == 0 {
return false, PolicyRequirementError("List of verification policy requirements must not be empty")
}
for reqNumber, req := range reqs {
// FIXME: supply state
allowed, err := req.isRunningImageAllowed(image)
if !allowed {
logrus.Debugf("Requirement %d: denied, done", reqNumber)
return false, err
}
logrus.Debugf(" Requirement %d: allowed", reqNumber)
}
// We have tested that len(reqs) != 0, so at least one req must have explicitly allowed this image.
logrus.Debugf("Overall: allowed")
return true, nil
}
func (prm *prmMatchRepository) matchesDockerReference(image types.Image, signatureDockerReference string) bool {
intended, signature, err := parseDockerReferences(image.IntendedDockerReference(), signatureDockerReference)
if err != nil {
return false
}
return signature.Name() == intended.Name()
}
func (prm *prmMatchExact) matchesDockerReference(image types.Image, signatureDockerReference string) bool {
intended, signature, err := parseDockerReferences(image.IntendedDockerReference(), signatureDockerReference)
if err != nil {
return false
}
// Do not add default tags: image.IntendedDockerReference() has it added already per its construction, and signatureDockerReference should be exact; so, verify that now.
if reference.IsNameOnly(intended) || reference.IsNameOnly(signature) {
return false
}
return signature.String() == intended.String()
}
// requirementsForImage selects the appropriate requirements for image.
func (pc *PolicyContext) requirementsForImage(image types.Image) (PolicyRequirements, error) {
imageIdentity := image.IntendedDockerReference()
// We don't technically need to parse it first in order to match the full name:tag,
// but do so anyway to ensure that the intended identity really does follow that
// format, or at least that it is not demonstrably wrong.
ref, err := reference.ParseNamed(imageIdentity)
if err != nil {
return nil, err
}
ref = reference.WithDefaultTag(ref)
// Look for a full match.
fullyExpanded, err := fullyExpandedDockerReference(ref)
if err != nil { // Coverage: This cannot currently happen.
return nil, err
}
if req, ok := pc.Policy.Specific[fullyExpanded]; ok {
logrus.Debugf(" Using specific policy section %s", fullyExpanded)
return req, nil
}
// Look for a match of the repository, and then of the possible parent
// namespaces. Note that this only happens on the expanded host names
// and repository names, i.e. "busybox" is looked up as "docker.io/library/busybox",
// then in its parent "docker.io/library"; in none of "busybox",
// un-namespaced "library" nor in "" implicitly representing "library/".
//
// ref.FullName() == ref.Hostname() + "/" + ref.RemoteName(), so the last
// iteration matches the host name (for any namespace).
name := ref.FullName()
for {
if req, ok := pc.Policy.Specific[name]; ok {
logrus.Debugf(" Using specific policy section %s", name)
return req, nil
}
lastSlash := strings.LastIndex(name, "/")
if lastSlash == -1 {
break
}
name = name[:lastSlash]
}
logrus.Debugf(" Using default policy section")
return pc.Policy.Default, nil
}
func (pr *prSignedBy) isRunningImageAllowed(image types.Image) (bool, error) {
sigs, err := image.Signatures()
if err != nil {
return false, err
}
var rejections []error
for _, s := range sigs {
var reason error
switch res, _, err := pr.isSignatureAuthorAccepted(image, s); res {
case sarAccepted:
// One accepted signature is enough.
return true, nil
case sarRejected:
reason = err
case sarUnknown:
// Huh?! This should not happen at all; treat it as any other invalid value.
fallthrough
default:
reason = fmt.Errorf(`Internal error: Unexpected signature verification result "%s"`, string(res))
}
rejections = append(rejections, reason)
}
var summary error
switch len(rejections) {
case 0:
summary = PolicyRequirementError("A signature was required, but no signature exists")
case 1:
summary = rejections[0]
default:
var msgs []string
for _, e := range rejections {
msgs = append(msgs, e.Error())
}
summary = PolicyRequirementError(fmt.Sprintf("None of the signatures were accepted, reasons: %s",
strings.Join(msgs, "; ")))
}
return false, summary
}
func (pr *prSignedBy) isSignatureAuthorAccepted(image types.Image, sig []byte) (signatureAcceptanceResult, *Signature, error) {
switch pr.KeyType {
case SBKeyTypeGPGKeys:
case SBKeyTypeSignedByGPGKeys, SBKeyTypeX509Certificates, SBKeyTypeSignedByX509CAs:
// FIXME? Reject this at policy parsing time already?
return sarRejected, nil, fmt.Errorf(`"Unimplemented "keyType" value "%s"`, string(pr.KeyType))
default:
// This should never happen, newPRSignedBy ensures KeyType.IsValid()
return sarRejected, nil, fmt.Errorf(`"Unknown "keyType" value "%s"`, string(pr.KeyType))
}
if pr.KeyPath != "" && pr.KeyData != nil {
return sarRejected, nil, errors.New(`Internal inconsistency: both "keyPath" and "keyData" specified`)
}
// FIXME: move this to per-context initialization
var data []byte
if pr.KeyData != nil {
data = pr.KeyData
} else {
d, err := ioutil.ReadFile(pr.KeyPath)
if err != nil {
return sarRejected, nil, err
}
data = d
}
// FIXME: move this to per-context initialization
dir, err := ioutil.TempDir("", "skopeo-signedBy-")
if err != nil {
return sarRejected, nil, err
}
defer os.RemoveAll(dir)
mech, err := newGPGSigningMechanismInDirectory(dir)
if err != nil {
return sarRejected, nil, err
}
trustedIdentities, err := mech.ImportKeysFromBytes(data)
if err != nil {
return sarRejected, nil, err
}
if len(trustedIdentities) == 0 {
return sarRejected, nil, PolicyRequirementError("No public keys imported")
}
signature, err := verifyAndExtractSignature(mech, sig, signatureAcceptanceRules{
validateKeyIdentity: func(keyIdentity string) error {
for _, trustedIdentity := range trustedIdentities {
if keyIdentity == trustedIdentity {
return nil
}
}
// Coverage: We use a private GPG home directory and only import trusted keys, so this should
// not be reachable.
return PolicyRequirementError(fmt.Sprintf("Signature by key %s is not accepted", keyIdentity))
},
validateSignedDockerReference: func(ref string) error {
if !pr.SignedIdentity.matchesDockerReference(image, ref) {
return PolicyRequirementError(fmt.Sprintf("Signature for identity %s is not accepted", ref))
}
return nil
},
validateSignedDockerManifestDigest: func(digest string) error {
m, _, err := image.Manifest()
if err != nil {
return err
}
digestMatches, err := manifest.MatchesDigest(m, digest)
if err != nil {
return err
}
if !digestMatches {
return PolicyRequirementError(fmt.Sprintf("Signature for digest %s does not match", digest))
}
return nil
},
})
if err != nil {
return sarRejected, nil, err
}
return sarAccepted, signature, nil
}
// GetSignaturesWithAcceptedAuthor returns those signatures from an image
// for which the policy accepts the author (and which have been successfully
// verified).
// NOTE: This may legitimately return an empty list and no error, if the image
// has no signatures or only invalid signatures.
// WARNING: This makes the signature contents acceptable for futher processing,
// but it does not necessarily mean that the contents of the signature are
// consistent with local policy.
// For example:
// - Do not use a an existence of an accepted signature to determine whether to run
// a container based on this image; use IsRunningImageAllowed instead.
// - Just because a signature is accepted does not automatically mean the contents of the
// signature are authorized to run code as root, or to affect system or cluster configuration.
func (pc *PolicyContext) GetSignaturesWithAcceptedAuthor(image types.Image) (sigs []*Signature, finalErr error) {
if err := pc.changeState(pcReady, pcInUse); err != nil {
return nil, err
}
defer func() {
if err := pc.changeState(pcInUse, pcReady); err != nil {
sigs = nil
finalErr = err
}
}()
logrus.Debugf("GetSignaturesWithAcceptedAuthor for image %s", image.IntendedDockerReference())
reqs, err := pc.requirementsForImage(image)
if err != nil {
return nil, err
}
// FIXME: rename Signatures to UnverifiedSignatures
unverifiedSignatures, err := image.Signatures()
if err != nil {
return nil, err
}
res := make([]*Signature, 0, len(unverifiedSignatures))
for sigNumber, sig := range unverifiedSignatures {
var acceptedSig *Signature // non-nil if accepted
rejected := false
// FIXME? Say more about the contents of the signature, i.e. parse it even before verification?!
logrus.Debugf("Evaluating signature %d:", sigNumber)
interpretingReqs:
for reqNumber, req := range reqs {
// FIXME: Log the requirement itself? For now, we use just the number.
// FIXME: supply state
switch res, as, err := req.isSignatureAuthorAccepted(image, sig); res {
case sarAccepted:
if as == nil { // Coverage: this should never happen
logrus.Debugf(" Requirement %d: internal inconsistency: sarAccepted but no parsed contents", reqNumber)
rejected = true
break interpretingReqs
}
logrus.Debugf(" Requirement %d: signature accepted", reqNumber)
if acceptedSig == nil {
acceptedSig = as
} else if *as != *acceptedSig { // Coverage: this should never happen
// Huh?! Two ways of verifying the same signature blob resulted in two different parses of its already accepted contents?
logrus.Debugf(" Requirement %d: internal inconsistency: sarAccepted but different parsed contents", reqNumber)
rejected = true
acceptedSig = nil
break interpretingReqs
}
case sarRejected:
logrus.Debugf(" Requirement %d: signature rejected: %s", reqNumber, err.Error())
rejected = true
break interpretingReqs
case sarUnknown:
if err != nil { // Coverage: this should never happen
logrus.Debugf(" Requirement %d: internal inconsistency: sarUnknown but an error message %s", reqNumber, err.Error())
rejected = true
break interpretingReqs
}
logrus.Debugf(" Requirement %d: signature state unknown, continuing", reqNumber)
default: // Coverage: this should never happen
logrus.Debugf(" Requirement %d: internal inconsistency: unknown result %#v", reqNumber, string(res))
rejected = true
break interpretingReqs
}
}
// This also handles the (invalid) case of empty reqs, by rejecting the signature.
if acceptedSig != nil && !rejected {
logrus.Debugf(" Overall: OK, signature accepted")
res = append(res, acceptedSig)
} else {
logrus.Debugf(" Overall: Signature not accepted")
}
}
return res, nil
}