Implement file hole passtrough

Fixes xfstests generic/010

Note that file holes are not authenticated,

1 files changed, 9 insertions, 0 deletions

diff --git a/cryptfs/cryptfs_content.go b/cryptfs/cryptfs_content.go
index 0494b69..e42011a 100644
--- a/cryptfs/cryptfs_content.go
+++ b/cryptfs/cryptfs_content.go
@@ -32,6 +32,9 @@ func (be *CryptFS) DecryptBlocks(ciphertext []byte) ([]byte, error) {
 }
 
 // DecryptBlock - Verify and decrypt GCM block
+//
+// Corner case: A full-sized block of all-zero ciphertext bytes is translated
+// to an all-zero plaintext block, i.e. file hole passtrough.
 func (be *CryptFS) DecryptBlock(ciphertext []byte) ([]byte, error) {
 
 	// Empty block?
@@ -39,6 +42,12 @@ func (be *CryptFS) DecryptBlock(ciphertext []byte) ([]byte, error) {
 		return ciphertext, nil
 	}
 
+	// All-zero block?
+	if bytes.Equal(ciphertext, be.allZeroBlock) {
+		Debug.Printf("DecryptBlock: file hole encountered\n")
+		return make([]byte, be.plainBS), nil
+	}
+
 	if len(ciphertext) < NONCE_LEN {
 		Warn.Printf("decryptBlock: Block is too short: %d bytes\n", len(ciphertext))
 		return nil, errors.New("Block is too short")