Metadata support for v2 encryption policies

Linux v5.4 and later supports v2 encryption policies.  These have
several advantages over v1 encryption policies:

- Their encryption keys can be added/removed to/from the filesystem by
  non-root users, thus gaining the benefits of the filesystem keyring
  while also retaining support for non-root use.

- They use a more standard, secure, and flexible key derivation
  function.  Because of this, some future kernel-level fscrypt features
  will be implemented for v2 policies only.

- They prevent a denial-of-service attack where a user could associate
  the wrong key with another user's encrypted files.

Prepare the fscrypt tool to support v2 encryption policies by:

- Adding a policy_version field to the EncryptionOptions, i.e. to the
  config file and to the policy metadata files.

- Using the kernel-specified algorithm to compute the key descriptor for
  v2 policies.

- Handling setting and getting v2 policies.

Actually adding/removing the keys for v2 policies to/from the kernel is
left for the next patch.

1 files changed, 27 insertions, 0 deletions

diff --git a/crypto/crypto_test.go b/crypto/crypto_test.go
index d0cef82..6eb0b02 100644
--- a/crypto/crypto_test.go
+++ b/crypto/crypto_test.go
@@ -464,6 +464,33 @@ func TestUnwrapWrongData(t *testing.T) {
 	}
 }
 
+func TestComputeKeyDescriptorV1(t *testing.T) {
+	descriptor, err := ComputeKeyDescriptor(fakeValidPolicyKey, 1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if descriptor != "8290608a029c5aae" {
+		t.Errorf("wrong v1 descriptor: %s", descriptor)
+	}
+}
+
+func TestComputeKeyDescriptorV2(t *testing.T) {
+	descriptor, err := ComputeKeyDescriptor(fakeValidPolicyKey, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if descriptor != "2139f52bf8386ee99845818ac7e91c4a" {
+		t.Errorf("wrong v2 descriptor: %s", descriptor)
+	}
+}
+
+func TestComputeKeyDescriptorBadVersion(t *testing.T) {
+	_, err := ComputeKeyDescriptor(fakeValidPolicyKey, 0)
+	if err == nil {
+		t.Error("computing key descriptor with bad version should fail")
+	}
+}
+
 // Run our test cases for passphrase hashing
 func TestPassphraseHashing(t *testing.T) {
 	for i, testCase := range hashTestCases {