Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1948232AbdDYOlR (ORCPT ); Tue, 25 Apr 2017 10:41:17 -0400 Received: from mail.sigma-star.at ([95.130.255.111]:45996 "EHLO mail.sigma-star.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1948189AbdDYOlI (ORCPT ); Tue, 25 Apr 2017 10:41:08 -0400 From: David Gstir To: tytso@mit.edu, jaegeuk@kernel.org Cc: ebiggers3@gmail.com, dwalter@sigma-star.at, richard@sigma-star.at, herbert@gondor.apana.org.au, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fscrypt@vger.kernel.org Subject: [PATCH v2] fscrypt: Add support for AES-128-CBC Date: Tue, 25 Apr 2017 16:41:00 +0200 Message-Id: <20170425144100.11484-1-david@sigma-star.at> X-Mailer: git-send-email 2.12.2 In-Reply-To: <20170330173840.72909-1-david@sigma-star.at> References: <20170330173840.72909-1-david@sigma-star.at> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 15303 Lines: 461 From: Daniel Walter 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. Especially low-powered embedded devices with crypto accelerators such as CAAM or CESA support only AES-CBC-128 with an acceptable speed. Using AES-CBC gives us the acceptable performance while still providing a moderate level of security for persistent storage. Signed-off-by: Daniel Walter [david@sigma-star.at: massaged commit message] Signed-off-by: David Gstir --- v2: Compute ESSIV salt using SHA256 instead of SHA1 and improve style as pointed out by Eric Biggers [1]. [1] https://lkml.kernel.org/r/20170331062149.GA32409%20()%20zzz fs/crypto/crypto.c | 22 ++++-- fs/crypto/fscrypt_private.h | 5 +- fs/crypto/keyinfo.c | 165 ++++++++++++++++++++++++++++++++++------- fs/crypto/policy.c | 7 +- include/linux/fscrypt_common.h | 13 ++-- include/uapi/linux/fs.h | 2 + 6 files changed, 169 insertions(+), 45 deletions(-) diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c index 6d6eca394d4d..9dd5f23a55a5 100644 --- a/fs/crypto/crypto.c +++ b/fs/crypto/crypto.c @@ -26,6 +26,7 @@ #include #include #include +#include #include "fscrypt_private.h" static unsigned int num_prealloc_crypto_pages = 32; @@ -147,17 +148,28 @@ int fscrypt_do_page_crypto(const struct inode *inode, fscrypt_direction_t rw, { struct { __le64 index; - u8 padding[FS_XTS_TWEAK_SIZE - sizeof(__le64)]; - } xts_tweak; + u8 padding[FS_IV_SIZE - sizeof(__le64)]; + } blk_desc; struct skcipher_request *req = NULL; DECLARE_FS_COMPLETION_RESULT(ecr); struct scatterlist dst, src; struct fscrypt_info *ci = inode->i_crypt_info; struct crypto_skcipher *tfm = ci->ci_ctfm; int res = 0; + u8 *iv = (u8 *)&blk_desc; BUG_ON(len == 0); + BUILD_BUG_ON(sizeof(blk_desc) != FS_IV_SIZE); + BUILD_BUG_ON(AES_BLOCK_SIZE != FS_IV_SIZE); + blk_desc.index = cpu_to_le64(lblk_num); + memset(blk_desc.padding, 0, sizeof(blk_desc.padding)); + + if (ci->ci_essiv_tfm != NULL) { + memset(iv, 0, sizeof(blk_desc)); + crypto_cipher_encrypt_one(ci->ci_essiv_tfm, iv, iv); + } + req = skcipher_request_alloc(tfm, gfp_flags); if (!req) { printk_ratelimited(KERN_ERR @@ -170,15 +182,11 @@ int fscrypt_do_page_crypto(const struct inode *inode, fscrypt_direction_t rw, req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP, page_crypt_complete, &ecr); - BUILD_BUG_ON(sizeof(xts_tweak) != FS_XTS_TWEAK_SIZE); - xts_tweak.index = cpu_to_le64(lblk_num); - memset(xts_tweak.padding, 0, sizeof(xts_tweak.padding)); - sg_init_table(&dst, 1); sg_set_page(&dst, dest_page, len, offs); sg_init_table(&src, 1); sg_set_page(&src, src_page, len, offs); - skcipher_request_set_crypt(req, &src, &dst, len, &xts_tweak); + skcipher_request_set_crypt(req, &src, &dst, len, &iv); if (rw == FS_DECRYPT) res = crypto_skcipher_decrypt(req); else diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h index e39696e64494..81ce9af449cb 100644 --- a/fs/crypto/fscrypt_private.h +++ b/fs/crypto/fscrypt_private.h @@ -16,8 +16,10 @@ #define FS_FNAME_CRYPTO_DIGEST_SIZE 32 /* Encryption parameters */ -#define FS_XTS_TWEAK_SIZE 16 +#define FS_IV_SIZE 16 #define FS_AES_128_ECB_KEY_SIZE 16 +#define FS_AES_128_CBC_KEY_SIZE 16 +#define FS_AES_128_CTS_KEY_SIZE 16 #define FS_AES_256_GCM_KEY_SIZE 32 #define FS_AES_256_CBC_KEY_SIZE 32 #define FS_AES_256_CTS_KEY_SIZE 32 @@ -67,6 +69,7 @@ struct fscrypt_info { u8 ci_filename_mode; u8 ci_flags; struct crypto_skcipher *ci_ctfm; + struct crypto_cipher *ci_essiv_tfm; u8 ci_master_key[FS_KEY_DESCRIPTOR_SIZE]; }; diff --git a/fs/crypto/keyinfo.c b/fs/crypto/keyinfo.c index 8cdfddce2b34..590efb0a891d 100644 --- a/fs/crypto/keyinfo.c +++ b/fs/crypto/keyinfo.c @@ -10,6 +10,8 @@ #include #include +#include +#include #include "fscrypt_private.h" static void derive_crypt_complete(struct crypto_async_request *req, int rc) @@ -27,13 +29,13 @@ static void derive_crypt_complete(struct crypto_async_request *req, int rc) * derive_key_aes() - Derive a key using AES-128-ECB * @deriving_key: Encryption key used for derivation. * @source_key: Source key to which to apply derivation. - * @derived_key: Derived key. + * @derived_key_raw: Derived raw key. * * Return: Zero on success; non-zero otherwise. */ static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE], - u8 source_key[FS_AES_256_XTS_KEY_SIZE], - u8 derived_key[FS_AES_256_XTS_KEY_SIZE]) + const struct fscrypt_key *source_key, + u8 derived_raw_key[FS_MAX_KEY_SIZE]) { int res = 0; struct skcipher_request *req = NULL; @@ -60,10 +62,10 @@ static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE], if (res < 0) goto out; - sg_init_one(&src_sg, source_key, FS_AES_256_XTS_KEY_SIZE); - sg_init_one(&dst_sg, derived_key, FS_AES_256_XTS_KEY_SIZE); - skcipher_request_set_crypt(req, &src_sg, &dst_sg, - FS_AES_256_XTS_KEY_SIZE, NULL); + sg_init_one(&src_sg, source_key->raw, source_key->size); + sg_init_one(&dst_sg, derived_raw_key, source_key->size); + skcipher_request_set_crypt(req, &src_sg, &dst_sg, source_key->size, + NULL); res = crypto_skcipher_encrypt(req); if (res == -EINPROGRESS || res == -EBUSY) { wait_for_completion(&ecr.completion); @@ -77,7 +79,7 @@ static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE], static int validate_user_key(struct fscrypt_info *crypt_info, struct fscrypt_context *ctx, u8 *raw_key, - const char *prefix) + const char *prefix, int min_keysize) { char *description; struct key *keyring_key; @@ -111,14 +113,15 @@ static int validate_user_key(struct fscrypt_info *crypt_info, master_key = (struct fscrypt_key *)ukp->data; BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE); - if (master_key->size != FS_AES_256_XTS_KEY_SIZE) { + if (master_key->size < min_keysize || master_key->size > FS_MAX_KEY_SIZE + || master_key->size % AES_BLOCK_SIZE != 0) { printk_once(KERN_WARNING "%s: key size incorrect: %d\n", __func__, master_key->size); res = -ENOKEY; goto out; } - res = derive_key_aes(ctx->nonce, master_key->raw, raw_key); + res = derive_key_aes(ctx->nonce, master_key, raw_key); out: up_read(&keyring_key->sem); key_put(keyring_key); @@ -129,27 +132,37 @@ static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode, const char **cipher_str_ret, int *keysize_ret) { if (S_ISREG(inode->i_mode)) { - if (ci->ci_data_mode == FS_ENCRYPTION_MODE_AES_256_XTS) { + switch (ci->ci_data_mode) { + case FS_ENCRYPTION_MODE_AES_256_XTS: *cipher_str_ret = "xts(aes)"; *keysize_ret = FS_AES_256_XTS_KEY_SIZE; return 0; + case FS_ENCRYPTION_MODE_AES_128_CBC: + *cipher_str_ret = "cbc(aes)"; + *keysize_ret = FS_AES_128_CBC_KEY_SIZE; + return 0; + default: + pr_warn_once("fscrypto: unsupported contents encryption mode %d for inode %lu\n", + ci->ci_data_mode, inode->i_ino); + return -ENOKEY; } - pr_warn_once("fscrypto: unsupported contents encryption mode " - "%d for inode %lu\n", - ci->ci_data_mode, inode->i_ino); - return -ENOKEY; } if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) { - if (ci->ci_filename_mode == FS_ENCRYPTION_MODE_AES_256_CTS) { + switch (ci->ci_filename_mode) { + case FS_ENCRYPTION_MODE_AES_256_CTS: *cipher_str_ret = "cts(cbc(aes))"; *keysize_ret = FS_AES_256_CTS_KEY_SIZE; return 0; + case FS_ENCRYPTION_MODE_AES_128_CTS: + *cipher_str_ret = "cts(cbc(aes))"; + *keysize_ret = FS_AES_128_CTS_KEY_SIZE; + return 0; + default: + pr_warn_once("fscrypto: unsupported filenames encryption mode %d for inode %lu\n", + ci->ci_filename_mode, inode->i_ino); + return -ENOKEY; } - pr_warn_once("fscrypto: unsupported filenames encryption mode " - "%d for inode %lu\n", - ci->ci_filename_mode, inode->i_ino); - return -ENOKEY; } pr_warn_once("fscrypto: unsupported file type %d for inode %lu\n", @@ -163,14 +176,100 @@ static void put_crypt_info(struct fscrypt_info *ci) return; crypto_free_skcipher(ci->ci_ctfm); + crypto_free_cipher(ci->ci_essiv_tfm); kmem_cache_free(fscrypt_info_cachep, ci); } +static int derive_essiv_salt(u8 *raw_key, int keysize, u8 **salt_out, + unsigned int *saltsize) +{ + int res; + struct crypto_ahash *hash_tfm; + unsigned int digestsize; + u8 *salt = NULL; + struct scatterlist sg; + struct ahash_request *req = NULL; + + hash_tfm = crypto_alloc_ahash("sha256", 0, 0); + if (IS_ERR(hash_tfm)) + return PTR_ERR(hash_tfm); + + digestsize = crypto_ahash_digestsize(hash_tfm); + salt = kzalloc(digestsize, GFP_NOFS); + if (!salt) { + res = -ENOMEM; + goto out; + } + + req = ahash_request_alloc(hash_tfm, GFP_NOFS); + if (!req) { + kfree(salt); + res = -ENOMEM; + goto out; + } + + sg_init_one(&sg, raw_key, keysize); + ahash_request_set_callback(req, + CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP, + NULL, NULL); + ahash_request_set_crypt(req, &sg, salt, keysize); + + res = crypto_ahash_digest(req); + if (res) { + kfree(salt); + goto out; + } + + *salt_out = salt; + *saltsize = digestsize; + +out: + crypto_free_ahash(hash_tfm); + ahash_request_free(req); + return res; +} + +static int init_essiv_generator(struct fscrypt_info *ci, u8 *raw_key, + int keysize) +{ + int res; + struct crypto_cipher *essiv_tfm; + u8 *salt = NULL; + unsigned int saltsize; + + /* init ESSIV generator */ + essiv_tfm = crypto_alloc_cipher("aes", 0, 0); + if (!essiv_tfm || IS_ERR(essiv_tfm)) { + res = essiv_tfm ? PTR_ERR(essiv_tfm) : -ENOMEM; + goto err; + } + + res = derive_essiv_salt(raw_key, keysize, &salt, &saltsize); + if (res) + goto err; + + res = crypto_cipher_setkey(essiv_tfm, salt, saltsize); + if (res) + goto err; + + ci->ci_essiv_tfm = essiv_tfm; + + return 0; + +err: + if (essiv_tfm && !IS_ERR(essiv_tfm)) + crypto_free_cipher(essiv_tfm); + + kzfree(salt); + return res; +} + int fscrypt_get_encryption_info(struct inode *inode) { struct fscrypt_info *crypt_info; struct fscrypt_context ctx; struct crypto_skcipher *ctfm; + const char *cipher_str; int keysize; u8 *raw_key = NULL; @@ -207,6 +306,10 @@ int fscrypt_get_encryption_info(struct inode *inode) if (ctx.flags & ~FS_POLICY_FLAGS_VALID) return -EINVAL; + if (!fscrypt_valid_enc_modes(ctx.contents_encryption_mode, + ctx.filenames_encryption_mode)) + return -EINVAL; + crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS); if (!crypt_info) return -ENOMEM; @@ -215,6 +318,7 @@ int fscrypt_get_encryption_info(struct inode *inode) crypt_info->ci_data_mode = ctx.contents_encryption_mode; crypt_info->ci_filename_mode = ctx.filenames_encryption_mode; crypt_info->ci_ctfm = NULL; + crypt_info->ci_essiv_tfm = NULL; memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor, sizeof(crypt_info->ci_master_key)); @@ -231,10 +335,12 @@ int fscrypt_get_encryption_info(struct inode *inode) if (!raw_key) goto out; - res = validate_user_key(crypt_info, &ctx, raw_key, FS_KEY_DESC_PREFIX); + res = validate_user_key(crypt_info, &ctx, raw_key, FS_KEY_DESC_PREFIX, + keysize); if (res && inode->i_sb->s_cop->key_prefix) { int res2 = validate_user_key(crypt_info, &ctx, raw_key, - inode->i_sb->s_cop->key_prefix); + inode->i_sb->s_cop->key_prefix, + keysize); if (res2) { if (res2 == -ENOKEY) res = -ENOKEY; @@ -246,9 +352,9 @@ int fscrypt_get_encryption_info(struct inode *inode) ctfm = crypto_alloc_skcipher(cipher_str, 0, 0); if (!ctfm || IS_ERR(ctfm)) { res = ctfm ? PTR_ERR(ctfm) : -ENOMEM; - printk(KERN_DEBUG - "%s: error %d (inode %u) allocating crypto tfm\n", - __func__, res, (unsigned) inode->i_ino); + pr_debug( + "%s: error %d (inode %u) allocating crypto tfm\n", + __func__, res, (unsigned int) inode->i_ino); goto out; } crypt_info->ci_ctfm = ctfm; @@ -258,6 +364,15 @@ int fscrypt_get_encryption_info(struct inode *inode) if (res) goto out; + if (crypt_info->ci_data_mode == FS_ENCRYPTION_MODE_AES_128_CBC) { + res = init_essiv_generator(crypt_info, raw_key, keysize); + if (res) { + pr_debug( + "%s: error %d (inode %u) allocating essiv tfm\n", + __func__, res, (unsigned int) inode->i_ino); + goto out; + } + } if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL) crypt_info = NULL; out: diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c index 4908906d54d5..bac8009245f2 100644 --- a/fs/crypto/policy.c +++ b/fs/crypto/policy.c @@ -41,11 +41,8 @@ static int create_encryption_context_from_policy(struct inode *inode, memcpy(ctx.master_key_descriptor, policy->master_key_descriptor, FS_KEY_DESCRIPTOR_SIZE); - if (!fscrypt_valid_contents_enc_mode( - policy->contents_encryption_mode)) - return -EINVAL; - - if (!fscrypt_valid_filenames_enc_mode( + if (!fscrypt_valid_enc_modes( + policy->contents_encryption_mode, policy->filenames_encryption_mode)) return -EINVAL; diff --git a/include/linux/fscrypt_common.h b/include/linux/fscrypt_common.h index 10c1abfbac6c..a91ce99f6e19 100644 --- a/include/linux/fscrypt_common.h +++ b/include/linux/fscrypt_common.h @@ -102,14 +102,13 @@ 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); -} - -static inline bool fscrypt_valid_filenames_enc_mode(u32 mode) -{ - return (mode == FS_ENCRYPTION_MODE_AES_256_CTS); + return ((contents_mode == FS_ENCRYPTION_MODE_AES_128_CBC && + filenames_mode == FS_ENCRYPTION_MODE_AES_128_CTS) || + (contents_mode == FS_ENCRYPTION_MODE_AES_256_XTS && + filenames_mode == FS_ENCRYPTION_MODE_AES_256_CTS)); } static inline bool fscrypt_is_dot_dotdot(const struct qstr *str) diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 048a85e9f017..231b15d4a90e 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -272,6 +272,8 @@ struct fsxattr { #define FS_ENCRYPTION_MODE_AES_256_GCM 2 #define FS_ENCRYPTION_MODE_AES_256_CBC 3 #define FS_ENCRYPTION_MODE_AES_256_CTS 4 +#define FS_ENCRYPTION_MODE_AES_128_CBC 5 +#define FS_ENCRYPTION_MODE_AES_128_CTS 6 struct fscrypt_policy { __u8 version; -- 2.12.0