| // SPDX-License-Identifier: GPL-2.0 |
| /* |
| * key management facility for FS encryption support. |
| * |
| * Copyright (C) 2015, Google, Inc. |
| * |
| * This contains encryption key functions. |
| * |
| * Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015. |
| */ |
| |
| #include <keys/user-type.h> |
| #include <linux/scatterlist.h> |
| #include <linux/ratelimit.h> |
| #include <crypto/aes.h> |
| #include <crypto/sha.h> |
| #include "fscrypt_private.h" |
| |
| static struct crypto_shash *essiv_hash_tfm; |
| |
| static void derive_crypt_complete(struct crypto_async_request *req, int rc) |
| { |
| struct fscrypt_completion_result *ecr = req->data; |
| |
| if (rc == -EINPROGRESS) |
| return; |
| |
| ecr->res = rc; |
| complete(&ecr->completion); |
| } |
| |
| /** |
| * 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_raw_key: Derived raw key. |
| * |
| * Return: Zero on success; non-zero otherwise. |
| */ |
| static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE], |
| const struct fscrypt_key *source_key, |
| u8 derived_raw_key[FS_MAX_KEY_SIZE]) |
| { |
| int res = 0; |
| struct skcipher_request *req = NULL; |
| DECLARE_FS_COMPLETION_RESULT(ecr); |
| struct scatterlist src_sg, dst_sg; |
| struct crypto_skcipher *tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0); |
| |
| if (IS_ERR(tfm)) { |
| res = PTR_ERR(tfm); |
| tfm = NULL; |
| goto out; |
| } |
| crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY); |
| req = skcipher_request_alloc(tfm, GFP_NOFS); |
| if (!req) { |
| res = -ENOMEM; |
| goto out; |
| } |
| skcipher_request_set_callback(req, |
| CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP, |
| derive_crypt_complete, &ecr); |
| res = crypto_skcipher_setkey(tfm, deriving_key, |
| FS_AES_128_ECB_KEY_SIZE); |
| if (res < 0) |
| goto out; |
| |
| 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); |
| res = ecr.res; |
| } |
| out: |
| skcipher_request_free(req); |
| crypto_free_skcipher(tfm); |
| return res; |
| } |
| |
| static int validate_user_key(struct fscrypt_info *crypt_info, |
| struct fscrypt_context *ctx, u8 *raw_key, |
| const char *prefix, int min_keysize) |
| { |
| char *description; |
| struct key *keyring_key; |
| struct fscrypt_key *master_key; |
| const struct user_key_payload *ukp; |
| int res; |
| |
| description = kasprintf(GFP_NOFS, "%s%*phN", prefix, |
| FS_KEY_DESCRIPTOR_SIZE, |
| ctx->master_key_descriptor); |
| if (!description) |
| return -ENOMEM; |
| |
| keyring_key = request_key(&key_type_logon, description, NULL); |
| kfree(description); |
| if (IS_ERR(keyring_key)) |
| return PTR_ERR(keyring_key); |
| down_read(&keyring_key->sem); |
| |
| if (keyring_key->type != &key_type_logon) { |
| printk_once(KERN_WARNING |
| "%s: key type must be logon\n", __func__); |
| res = -ENOKEY; |
| goto out; |
| } |
| ukp = user_key_payload_locked(keyring_key); |
| if (!ukp) { |
| /* key was revoked before we acquired its semaphore */ |
| res = -EKEYREVOKED; |
| goto out; |
| } |
| if (ukp->datalen != sizeof(struct fscrypt_key)) { |
| res = -EINVAL; |
| goto out; |
| } |
| 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 < 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_key); |
| out: |
| up_read(&keyring_key->sem); |
| key_put(keyring_key); |
| return res; |
| } |
| |
| static const struct { |
| const char *cipher_str; |
| int keysize; |
| } available_modes[] = { |
| [FS_ENCRYPTION_MODE_AES_256_XTS] = { "xts(aes)", |
| FS_AES_256_XTS_KEY_SIZE }, |
| [FS_ENCRYPTION_MODE_AES_256_CTS] = { "cts(cbc(aes))", |
| FS_AES_256_CTS_KEY_SIZE }, |
| [FS_ENCRYPTION_MODE_AES_128_CBC] = { "cbc(aes)", |
| FS_AES_128_CBC_KEY_SIZE }, |
| [FS_ENCRYPTION_MODE_AES_128_CTS] = { "cts(cbc(aes))", |
| FS_AES_128_CTS_KEY_SIZE }, |
| }; |
| |
| static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode, |
| const char **cipher_str_ret, int *keysize_ret) |
| { |
| u32 mode; |
| |
| if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) { |
| pr_warn_ratelimited("fscrypt: inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)\n", |
| inode->i_ino, |
| ci->ci_data_mode, ci->ci_filename_mode); |
| return -EINVAL; |
| } |
| |
| if (S_ISREG(inode->i_mode)) { |
| mode = ci->ci_data_mode; |
| } else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) { |
| mode = ci->ci_filename_mode; |
| } else { |
| WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n", |
| inode->i_ino, (inode->i_mode & S_IFMT)); |
| return -EINVAL; |
| } |
| |
| *cipher_str_ret = available_modes[mode].cipher_str; |
| *keysize_ret = available_modes[mode].keysize; |
| return 0; |
| } |
| |
| static void put_crypt_info(struct fscrypt_info *ci) |
| { |
| if (!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(const u8 *key, int keysize, u8 *salt) |
| { |
| struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm); |
| |
| /* init hash transform on demand */ |
| if (unlikely(!tfm)) { |
| struct crypto_shash *prev_tfm; |
| |
| tfm = crypto_alloc_shash("sha256", 0, 0); |
| if (IS_ERR(tfm)) { |
| pr_warn_ratelimited("fscrypt: error allocating SHA-256 transform: %ld\n", |
| PTR_ERR(tfm)); |
| return PTR_ERR(tfm); |
| } |
| prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm); |
| if (prev_tfm) { |
| crypto_free_shash(tfm); |
| tfm = prev_tfm; |
| } |
| } |
| |
| { |
| SHASH_DESC_ON_STACK(desc, tfm); |
| desc->tfm = tfm; |
| desc->flags = 0; |
| |
| return crypto_shash_digest(desc, key, keysize, salt); |
| } |
| } |
| |
| static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key, |
| int keysize) |
| { |
| int err; |
| struct crypto_cipher *essiv_tfm; |
| u8 salt[SHA256_DIGEST_SIZE]; |
| |
| 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; |
| |
| /* |
| * Using SHA256 to derive the salt/key will result in AES-256 being |
| * used for IV generation. File contents encryption will still use the |
| * configured keysize (AES-128) nevertheless. |
| */ |
| err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt)); |
| if (err) |
| goto out; |
| |
| out: |
| memzero_explicit(salt, sizeof(salt)); |
| return err; |
| } |
| |
| void __exit fscrypt_essiv_cleanup(void) |
| { |
| crypto_free_shash(essiv_hash_tfm); |
| } |
| |
| 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; |
| int res; |
| |
| if (inode->i_crypt_info) |
| return 0; |
| |
| res = fscrypt_initialize(inode->i_sb->s_cop->flags); |
| if (res) |
| return res; |
| |
| res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx)); |
| if (res < 0) { |
| if (!fscrypt_dummy_context_enabled(inode) || |
| inode->i_sb->s_cop->is_encrypted(inode)) |
| return res; |
| /* Fake up a context for an unencrypted directory */ |
| memset(&ctx, 0, sizeof(ctx)); |
| ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1; |
| ctx.contents_encryption_mode = FS_ENCRYPTION_MODE_AES_256_XTS; |
| ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS; |
| memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE); |
| } else if (res != sizeof(ctx)) { |
| return -EINVAL; |
| } |
| |
| if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1) |
| return -EINVAL; |
| |
| if (ctx.flags & ~FS_POLICY_FLAGS_VALID) |
| return -EINVAL; |
| |
| crypt_info = kmem_cache_alloc(fscrypt_info_cachep, GFP_NOFS); |
| if (!crypt_info) |
| return -ENOMEM; |
| |
| crypt_info->ci_flags = ctx.flags; |
| 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)); |
| |
| res = determine_cipher_type(crypt_info, inode, &cipher_str, &keysize); |
| if (res) |
| goto out; |
| |
| /* |
| * This cannot be a stack buffer because it is passed to the scatterlist |
| * crypto API as part of key derivation. |
| */ |
| res = -ENOMEM; |
| raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS); |
| if (!raw_key) |
| goto out; |
| |
| 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, |
| keysize); |
| if (res2) { |
| if (res2 == -ENOKEY) |
| res = -ENOKEY; |
| goto out; |
| } |
| } else if (res) { |
| goto out; |
| } |
| ctfm = crypto_alloc_skcipher(cipher_str, 0, 0); |
| if (!ctfm || IS_ERR(ctfm)) { |
| res = ctfm ? PTR_ERR(ctfm) : -ENOMEM; |
| pr_debug("%s: error %d (inode %lu) allocating crypto tfm\n", |
| __func__, res, inode->i_ino); |
| goto out; |
| } |
| crypt_info->ci_ctfm = ctfm; |
| crypto_skcipher_clear_flags(ctfm, ~0); |
| crypto_skcipher_set_flags(ctfm, CRYPTO_TFM_REQ_WEAK_KEY); |
| /* |
| * if the provided key is longer than keysize, we use the first |
| * keysize bytes of the derived key only |
| */ |
| res = crypto_skcipher_setkey(ctfm, raw_key, keysize); |
| if (res) |
| goto out; |
| |
| if (S_ISREG(inode->i_mode) && |
| 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 %lu) allocating essiv tfm\n", |
| __func__, res, inode->i_ino); |
| goto out; |
| } |
| } |
| if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) == NULL) |
| crypt_info = NULL; |
| out: |
| if (res == -ENOKEY) |
| res = 0; |
| put_crypt_info(crypt_info); |
| kzfree(raw_key); |
| return res; |
| } |
| EXPORT_SYMBOL(fscrypt_get_encryption_info); |
| |
| void fscrypt_put_encryption_info(struct inode *inode, struct fscrypt_info *ci) |
| { |
| struct fscrypt_info *prev; |
| |
| if (ci == NULL) |
| ci = READ_ONCE(inode->i_crypt_info); |
| if (ci == NULL) |
| return; |
| |
| prev = cmpxchg(&inode->i_crypt_info, ci, NULL); |
| if (prev != ci) |
| return; |
| |
| put_crypt_info(ci); |
| } |
| EXPORT_SYMBOL(fscrypt_put_encryption_info); |