From b7e7cf7a66a27e62c5f873a0068cee34094bf5d7 Mon Sep 17 00:00:00 2001 From: Daniel Walter Date: Mon, 19 Jun 2017 09:27:58 +0200 Subject: fscrypt: add support for AES-128-CBC fscrypt provides facilities to use different encryption algorithms which are selectable by userspace when setting the encryption policy. Currently, only AES-256-XTS for file contents and AES-256-CBC-CTS for file names are implemented. This is a clear case of kernel offers the mechanism and userspace selects a policy. Similar to what dm-crypt and ecryptfs have. This patch adds support for using AES-128-CBC for file contents and AES-128-CBC-CTS for file name encryption. To mitigate watermarking attacks, IVs are generated using the ESSIV algorithm. While AES-CBC is actually slightly less secure than AES-XTS from a security point of view, there is more widespread hardware support. Using AES-CBC gives us the acceptable performance while still providing a moderate level of security for persistent storage. Especially low-powered embedded devices with crypto accelerators such as CAAM or CESA often only support AES-CBC. Since using AES-CBC over AES-XTS is basically thought of a last resort, we use AES-128-CBC over AES-256-CBC since it has less encryption rounds and yields noticeable better performance starting from a file size of just a few kB. Signed-off-by: Daniel Walter [david@sigma-star.at: addressed review comments] Signed-off-by: David Gstir Reviewed-by: Eric Biggers Signed-off-by: Theodore Ts'o --- include/linux/fscrypt_common.h | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) (limited to 'include/linux') diff --git a/include/linux/fscrypt_common.h b/include/linux/fscrypt_common.h index 0a30c106c1e5..4022c61f7e9b 100644 --- a/include/linux/fscrypt_common.h +++ b/include/linux/fscrypt_common.h @@ -91,14 +91,18 @@ static inline bool fscrypt_dummy_context_enabled(struct inode *inode) return false; } -static inline bool fscrypt_valid_contents_enc_mode(u32 mode) +static inline bool fscrypt_valid_enc_modes(u32 contents_mode, + u32 filenames_mode) { - return (mode == FS_ENCRYPTION_MODE_AES_256_XTS); -} + if (contents_mode == FS_ENCRYPTION_MODE_AES_128_CBC && + filenames_mode == FS_ENCRYPTION_MODE_AES_128_CTS) + return true; -static inline bool fscrypt_valid_filenames_enc_mode(u32 mode) -{ - return (mode == FS_ENCRYPTION_MODE_AES_256_CTS); + if (contents_mode == FS_ENCRYPTION_MODE_AES_256_XTS && + filenames_mode == FS_ENCRYPTION_MODE_AES_256_CTS) + return true; + + return false; } static inline bool fscrypt_is_dot_dotdot(const struct qstr *str) -- cgit v1.2.3