terraform/internal/getproviders/package_authentication.go

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package getproviders
import (
"bytes"
"crypto/sha256"
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"encoding/hex"
"fmt"
"io"
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"log"
"os"
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"strings"
"golang.org/x/crypto/openpgp"
openpgpArmor "golang.org/x/crypto/openpgp/armor"
openpgpErrors "golang.org/x/crypto/openpgp/errors"
)
type packageAuthenticationResult int
const (
verifiedChecksum packageAuthenticationResult = iota
officialProvider
partnerProvider
communityProvider
)
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// PackageAuthenticationResult is returned from a PackageAuthentication
// implementation. It is a mostly-opaque type intended for use in UI, which
// implements Stringer and includes an optional Warning field.
//
// A failed PackageAuthentication attempt will return an "unauthenticated"
// result, which is represented by nil.
type PackageAuthenticationResult struct {
result packageAuthenticationResult
Warning string
}
func (t *PackageAuthenticationResult) String() string {
if t == nil {
return "unauthenticated"
}
return []string{
"verified checksum",
"official provider",
"partner provider",
"community provider",
}[t.result]
}
// SigningKey represents a key used to sign packages from a registry, along
// with an optional trust signature from the registry operator. These are
// both in ASCII armored OpenPGP format.
//
// The JSON struct tags represent the field names used by the Registry API.
type SigningKey struct {
ASCIIArmor string `json:"ascii_armor"`
TrustSignature string `json:"trust_signature"`
}
// PackageAuthentication is an interface implemented by the optional package
// authentication implementations a source may include on its PackageMeta
// objects.
//
// A PackageAuthentication implementation is responsible for authenticating
// that a package is what its distributor intended to distribute and that it
// has not been tampered with.
type PackageAuthentication interface {
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// AuthenticatePackage takes the local location of a package (which may or
// may not be the same as the original source location), and returns a
// PackageAuthenticationResult, or an error if the authentication checks
// fail.
//
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// The local location is guaranteed not to be a PackageHTTPURL: a remote
// package will always be staged locally for inspection first.
AuthenticatePackage(localLocation PackageLocation) (*PackageAuthenticationResult, error)
}
type packageAuthenticationAll []PackageAuthentication
// PackageAuthenticationAll combines several authentications together into a
// single check value, which passes only if all of the given ones pass.
//
// The checks are processed in the order given, so a failure of an earlier
// check will prevent execution of a later one.
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//
// The returned result is from the last authentication, so callers should
// take care to order the authentications such that the strongest is last.
func PackageAuthenticationAll(checks ...PackageAuthentication) PackageAuthentication {
return packageAuthenticationAll(checks)
}
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func (checks packageAuthenticationAll) AuthenticatePackage(localLocation PackageLocation) (*PackageAuthenticationResult, error) {
var authResult *PackageAuthenticationResult
for _, check := range checks {
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var err error
authResult, err = check.AuthenticatePackage(localLocation)
if err != nil {
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return authResult, err
}
}
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return authResult, nil
}
type archiveHashAuthentication struct {
WantSHA256Sum [sha256.Size]byte
}
// NewArchiveChecksumAuthentication returns a PackageAuthentication
// implementation that checks that the original distribution archive matches
// the given hash.
//
// This authentication is suitable only for PackageHTTPURL and
// PackageLocalArchive source locations, because the unpacked layout
// (represented by PackageLocalDir) does not retain access to the original
// source archive. Therefore this authenticator will return an error if its
// given localLocation is not PackageLocalArchive.
func NewArchiveChecksumAuthentication(wantSHA256Sum [sha256.Size]byte) PackageAuthentication {
return archiveHashAuthentication{wantSHA256Sum}
}
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func (a archiveHashAuthentication) AuthenticatePackage(localLocation PackageLocation) (*PackageAuthenticationResult, error) {
archiveLocation, ok := localLocation.(PackageLocalArchive)
if !ok {
// A source should not use this authentication type for non-archive
// locations.
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return nil, fmt.Errorf("cannot check archive hash for non-archive location %s", localLocation)
}
f, err := os.Open(string(archiveLocation))
if err != nil {
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return nil, err
}
defer f.Close()
h := sha256.New()
_, err = io.Copy(h, f)
if err != nil {
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return nil, err
}
gotHash := h.Sum(nil)
if !bytes.Equal(gotHash, a.WantSHA256Sum[:]) {
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return nil, fmt.Errorf("archive has incorrect SHA-256 checksum %x (expected %x)", gotHash, a.WantSHA256Sum[:])
}
return &PackageAuthenticationResult{result: verifiedChecksum}, nil
}
type matchingChecksumAuthentication struct {
Document []byte
Filename string
WantSHA256Sum [sha256.Size]byte
}
// NewMatchingChecksumAuthentication returns a PackageAuthentication
// implementation that scans a registry-provided SHA256SUMS document for a
// specified filename, and compares the SHA256 hash against the expected hash.
// This is necessary to ensure that the signed SHA256SUMS document matches the
// declared SHA256 hash for the package, and therefore that a valid signature
// of this document authenticates the package.
//
// This authentication always returns a nil result, since it alone cannot offer
// any assertions about package integrity. It should be combined with other
// authentications to be useful.
func NewMatchingChecksumAuthentication(document []byte, filename string, wantSHA256Sum [sha256.Size]byte) PackageAuthentication {
return matchingChecksumAuthentication{
Document: document,
Filename: filename,
WantSHA256Sum: wantSHA256Sum,
}
}
func (m matchingChecksumAuthentication) AuthenticatePackage(location PackageLocation) (*PackageAuthenticationResult, error) {
// Find the checksum in the list with matching filename. The document is
// in the form "0123456789abcdef filename.zip".
filename := []byte(m.Filename)
var checksum []byte
for _, line := range bytes.Split(m.Document, []byte("\n")) {
parts := bytes.Fields(line)
if len(parts) > 1 && bytes.Equal(parts[1], filename) {
checksum = parts[0]
break
}
}
if checksum == nil {
return nil, fmt.Errorf("checksum list has no SHA-256 hash for %q", m.Filename)
}
// Decode the ASCII checksum into a byte array for comparison.
var gotSHA256Sum [sha256.Size]byte
if _, err := hex.Decode(gotSHA256Sum[:], checksum); err != nil {
return nil, fmt.Errorf("checksum list has invalid SHA256 hash %q: %s", string(checksum), err)
}
// If the checksums don't match, authentication fails.
if !bytes.Equal(gotSHA256Sum[:], m.WantSHA256Sum[:]) {
return nil, fmt.Errorf("checksum list has unexpected SHA-256 hash %x (expected %x)", gotSHA256Sum, m.WantSHA256Sum[:])
}
// Success! But this doesn't result in any real authentication, only a
// lack of authentication errors, so we return a nil result.
return nil, nil
}
type signatureAuthentication struct {
Document []byte
Signature []byte
Keys []SigningKey
}
// NewSignatureAuthentication returns a PackageAuthentication implementation
// that verifies the cryptographic signature for a package against any of the
// provided keys.
//
// The signing key for a package will be auto detected by attempting each key
// in turn until one is successful. If such a key is found, there are three
// possible successful authentication results:
//
// 1. If the signing key is the HashiCorp official key, it is an official
// provider;
// 2. Otherwise, if the signing key has a trust signature from the HashiCorp
// Partners key, it is a partner provider;
// 3. If neither of the above is true, it is a community provider.
//
// Any failure in the process of validating the signature will result in an
// unauthenticated result.
func NewSignatureAuthentication(document, signature []byte, keys []SigningKey) PackageAuthentication {
return signatureAuthentication{
Document: document,
Signature: signature,
Keys: keys,
}
}
func (s signatureAuthentication) AuthenticatePackage(location PackageLocation) (*PackageAuthenticationResult, error) {
// Find the key that signed the checksum file. This can fail if there is no
// valid signature for any of the provided keys.
signingKey, err := s.findSigningKey()
if err != nil {
return nil, err
}
// Verify the signature using the HashiCorp public key. If this succeeds,
// this is an official provider.
hashicorpKeyring, err := openpgp.ReadArmoredKeyRing(strings.NewReader(HashicorpPublicKey))
if err != nil {
return nil, fmt.Errorf("error creating HashiCorp keyring: %s", err)
}
_, err = openpgp.CheckDetachedSignature(hashicorpKeyring, bytes.NewReader(s.Document), bytes.NewReader(s.Signature))
if err == nil {
return &PackageAuthenticationResult{result: officialProvider}, nil
}
// If the signing key has a trust signature, attempt to verify it with the
// HashiCorp partners public key.
if signingKey.TrustSignature != "" {
hashicorpPartnersKeyring, err := openpgp.ReadArmoredKeyRing(strings.NewReader(HashicorpPartnersKey))
if err != nil {
return nil, fmt.Errorf("error creating HashiCorp Partners keyring: %s", err)
}
authorKey, err := openpgpArmor.Decode(strings.NewReader(signingKey.ASCIIArmor))
if err != nil {
return nil, fmt.Errorf("error decoding signing key: %s", err)
}
trustSignature, err := openpgpArmor.Decode(strings.NewReader(signingKey.TrustSignature))
if err != nil {
return nil, fmt.Errorf("error decoding trust signature: %s", err)
}
_, err = openpgp.CheckDetachedSignature(hashicorpPartnersKeyring, authorKey.Body, trustSignature.Body)
if err != nil {
return nil, fmt.Errorf("error verifying trust signature: %s", err)
}
return &PackageAuthenticationResult{result: partnerProvider}, nil
}
// We have a valid signature, but it's not from the HashiCorp key, and it
// also isn't a trusted partner. This is a community provider.
// FIXME: we may want to add a more detailed warning here explaining the
// difference between partner and community providers.
return &PackageAuthenticationResult{result: communityProvider}, nil
}
// findSigningKey attempts to verify the signature using each of the keys
// returned by the registry. If a valid signature is found, it returns the
// signing key.
//
// Note: currently the registry only returns one key, but this may change in
// the future.
func (s signatureAuthentication) findSigningKey() (*SigningKey, error) {
for _, key := range s.Keys {
keyring, err := openpgp.ReadArmoredKeyRing(strings.NewReader(key.ASCIIArmor))
if err != nil {
return nil, fmt.Errorf("error decoding signing key: %s", err)
}
entity, err := openpgp.CheckDetachedSignature(keyring, bytes.NewReader(s.Document), bytes.NewReader(s.Signature))
// If the signature issuer does not match the the key, keep trying the
// rest of the provided keys.
if err == openpgpErrors.ErrUnknownIssuer {
continue
}
// Any other signature error is terminal.
if err != nil {
return nil, fmt.Errorf("error checking signature: %s", err)
}
log.Printf("[DEBUG] Provider signed by %s", entityString(entity))
return &key, nil
}
// If none of the provided keys issued the signature, this package is
// unsigned. This is currently a terminal authentication error.
return nil, fmt.Errorf("authentication signature from unknown issuer")
}
// entityString extracts the key ID and identity name(s) from an openpgp.Entity
// for logging.
func entityString(entity *openpgp.Entity) string {
if entity == nil {
return ""
}
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keyID := "n/a"
if entity.PrimaryKey != nil {
keyID = entity.PrimaryKey.KeyIdString()
}
var names []string
for _, identity := range entity.Identities {
names = append(names, identity.Name)
}
return fmt.Sprintf("%s %s", keyID, strings.Join(names, ", "))
}