From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 25 Apr 2017 13:10:01 -0700 From: Eric Biggers Subject: Re: [PATCH v2] fscrypt: Add support for AES-128-CBC Message-ID: <20170425201001.GA133970@gmail.com> References: <20170330173840.72909-1-david@sigma-star.at> <20170425144100.11484-1-david@sigma-star.at> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170425144100.11484-1-david@sigma-star.at> To: David Gstir Cc: tytso@mit.edu, jaegeuk@kernel.org, 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 List-ID: Hi Daniel and David, On Tue, Apr 25, 2017 at 04:41:00PM +0200, David Gstir wrote: > @@ -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 There are two critical bugs here. First the IV is being zeroed before being encrypted with the ESSIV tfm, so the resulting IV will always be the same for a given file. It should be encrypting the block number instead. Second what's actually being passed into the crypto API is '&iv' where IV is a pointer to something on the stack... I really doubt that does what's intended :) Probably the cleanest way to do this correctly is to just have the struct be the 'iv', so there's no extra pointer to deal with: struct { __le64 index; u8 padding[FS_IV_SIZE - sizeof(__le64)]; } iv; [...] BUILD_BUG_ON(sizeof(iv) != FS_IV_SIZE); BUILD_BUG_ON(AES_BLOCK_SIZE != FS_IV_SIZE); iv.index = cpu_to_le64(lblk_num); memset(iv.padding, 0, sizeof(iv.padding)); if (ci->ci_essiv_tfm != NULL) { crypto_cipher_encrypt_one(ci->ci_essiv_tfm, (u8 *)&iv, (u8 *)&iv); } [...] skcipher_request_set_crypt(req, &src, &dst, len, &iv); > +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; > +} There are a few issues with how the ESSIV generator is initialized: 1.) It's allocating a possibly asynchronous SHA-256 implementation but then not handling it actually being asynchronous. I suggest using the 'shash' API which is easier to use. 2.) No one is going to change the digest size of SHA-256; it's fixed at 32 bytes. So just #include and allocate a 'u8 salt[SHA256_DIGEST_SIZE];' on the stack. Make sure to do memzero_explicit(salt, sizeof(salt)) in all cases. 3.) It's always keying the ESSIV transform using a 256-bit AES key. It's still secure of course, but I'm not sure it's what you intended, given that it's used in combination with AES-128. I really think that someone who's more of an expert on ESSIV really should weigh in, but my intuition is that you really only need to be using AES-128, using the first 'keysize' bytes of the hash. You also don't really need to handle freeing the essiv_tfm on errors, as long as you assign it to the fscrypt_info first. Also crypto_alloc_cipher() returns an ERR_PTR(), never NULL. Also, fs/crypto/Kconfig needs a 'select CRYPTO_SHA256' now. Here's a revised version to consider, not actually tested though: static int derive_essiv_salt(const u8 *raw_key, int keysize, u8 salt[SHA256_DIGEST_SIZE]) { struct crypto_shash *hash_tfm; hash_tfm = crypto_alloc_shash("sha256", 0, 0); if (IS_ERR(hash_tfm)) { pr_warn_ratelimited("fscrypt: error allocating SHA-256 transform: %ld", PTR_ERR(hash_tfm)); return PTR_ERR(hash_tfm); } else { SHASH_DESC_ON_STACK(desc, hash_tfm); int err; desc->tfm = hash_tfm; desc->flags = 0; BUG_ON(crypto_shash_digestsize(hash_tfm) != SHA256_DIGEST_SIZE); err = crypto_shash_digest(desc, raw_key, keysize, salt); crypto_free_shash(hash_tfm); return err; } } static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key, int keysize) { struct crypto_cipher *essiv_tfm; u8 salt[SHA256_DIGEST_SIZE]; int err; if (WARN_ON_ONCE(keysize > sizeof(salt))) return -EINVAL; essiv_tfm = crypto_alloc_cipher("aes", 0, 0); if (IS_ERR(essiv_tfm)) return PTR_ERR(essiv_tfm); ci->ci_essiv_tfm = essiv_tfm; err = derive_essiv_salt(raw_key, keysize, salt); if (err) goto out; err = crypto_cipher_setkey(essiv_tfm, salt, keysize); out: memzero_explicit(salt, sizeof(salt)); return err; } > + > 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; > + Indent this properly > 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; If you're changing this line just make it print i_ino as an 'unsigned long', no need to cast it. Same below. > } > 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; Indent properly: if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode, policy->filenames_encryption_mode)) - Eric