From a44cd7a05496d60fd2ba8cca080e3db8f481549b Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Fri, 1 May 2015 16:56:50 -0400 Subject: ext4 crypto: add padding to filenames before encrypting This obscures the length of the filenames, to decrease the amount of information leakage. By default, we pad the filenames to the next 4 byte boundaries. This costs nothing, since the directory entries are aligned to 4 byte boundaries anyway. Filenames can also be padded to 8, 16, or 32 bytes, which will consume more directory space. Change-Id: Ibb7a0fb76d2c48e2061240a709358ff40b14f322 Signed-off-by: Theodore Ts'o --- fs/ext4/ext4_crypto.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'fs/ext4/ext4_crypto.h') diff --git a/fs/ext4/ext4_crypto.h b/fs/ext4/ext4_crypto.h index c2ba35a914b6..d75159c101ce 100644 --- a/fs/ext4/ext4_crypto.h +++ b/fs/ext4/ext4_crypto.h @@ -20,12 +20,20 @@ struct ext4_encryption_policy { char version; char contents_encryption_mode; char filenames_encryption_mode; + char flags; char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE]; } __attribute__((__packed__)); #define EXT4_ENCRYPTION_CONTEXT_FORMAT_V1 1 #define EXT4_KEY_DERIVATION_NONCE_SIZE 16 +#define EXT4_POLICY_FLAGS_PAD_4 0x00 +#define EXT4_POLICY_FLAGS_PAD_8 0x01 +#define EXT4_POLICY_FLAGS_PAD_16 0x02 +#define EXT4_POLICY_FLAGS_PAD_32 0x03 +#define EXT4_POLICY_FLAGS_PAD_MASK 0x03 +#define EXT4_POLICY_FLAGS_VALID 0x03 + /** * Encryption context for inode * @@ -41,7 +49,7 @@ struct ext4_encryption_context { char format; char contents_encryption_mode; char filenames_encryption_mode; - char reserved; + char flags; char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE]; char nonce[EXT4_KEY_DERIVATION_NONCE_SIZE]; } __attribute__((__packed__)); @@ -120,6 +128,7 @@ struct ext4_fname_crypto_ctx { struct crypto_hash *htfm; struct page *workpage; struct ext4_encryption_key key; + unsigned flags : 8; unsigned has_valid_key : 1; unsigned ctfm_key_is_ready : 1; }; -- cgit v1.2.2