| // 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/hashtable.h> |
| #include <linux/scatterlist.h> |
| #include <linux/ratelimit.h> |
| #include <crypto/aes.h> |
| #include <crypto/algapi.h> |
| #include <crypto/sha.h> |
| #include <crypto/skcipher.h> |
| #include "fscrypt_private.h" |
| |
| static struct crypto_shash *essiv_hash_tfm; |
| |
| /* Table of keys referenced by FS_POLICY_FLAG_DIRECT_KEY policies */ |
| static DEFINE_HASHTABLE(fscrypt_master_keys, 6); /* 6 bits = 64 buckets */ |
| static DEFINE_SPINLOCK(fscrypt_master_keys_lock); |
| |
| /* |
| * Key derivation function. This generates the derived key by encrypting the |
| * master key with AES-128-ECB using the inode's nonce as the AES key. |
| * |
| * The master key must be at least as long as the derived key. If the master |
| * key is longer, then only the first 'derived_keysize' bytes are used. |
| */ |
| static int derive_key_aes(const u8 *master_key, |
| const struct fscrypt_context *ctx, |
| u8 *derived_key, unsigned int derived_keysize) |
| { |
| int res = 0; |
| struct skcipher_request *req = NULL; |
| DECLARE_CRYPTO_WAIT(wait); |
| 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_FORBID_WEAK_KEYS); |
| 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, |
| crypto_req_done, &wait); |
| res = crypto_skcipher_setkey(tfm, ctx->nonce, sizeof(ctx->nonce)); |
| if (res < 0) |
| goto out; |
| |
| sg_init_one(&src_sg, master_key, derived_keysize); |
| sg_init_one(&dst_sg, derived_key, derived_keysize); |
| skcipher_request_set_crypt(req, &src_sg, &dst_sg, derived_keysize, |
| NULL); |
| res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait); |
| out: |
| skcipher_request_free(req); |
| crypto_free_skcipher(tfm); |
| return res; |
| } |
| |
| /* |
| * Search the current task's subscribed keyrings for a "logon" key with |
| * description prefix:descriptor, and if found acquire a read lock on it and |
| * return a pointer to its validated payload in *payload_ret. |
| */ |
| static struct key * |
| find_and_lock_process_key(const char *prefix, |
| const u8 descriptor[FS_KEY_DESCRIPTOR_SIZE], |
| unsigned int min_keysize, |
| const struct fscrypt_key **payload_ret) |
| { |
| char *description; |
| struct key *key; |
| const struct user_key_payload *ukp; |
| const struct fscrypt_key *payload; |
| |
| description = kasprintf(GFP_NOFS, "%s%*phN", prefix, |
| FS_KEY_DESCRIPTOR_SIZE, descriptor); |
| if (!description) |
| return ERR_PTR(-ENOMEM); |
| |
| key = request_key(&key_type_logon, description, NULL); |
| kfree(description); |
| if (IS_ERR(key)) |
| return key; |
| |
| down_read(&key->sem); |
| ukp = user_key_payload_locked(key); |
| |
| if (!ukp) /* was the key revoked before we acquired its semaphore? */ |
| goto invalid; |
| |
| payload = (const struct fscrypt_key *)ukp->data; |
| |
| if (ukp->datalen != sizeof(struct fscrypt_key) || |
| payload->size < 1 || payload->size > FS_MAX_KEY_SIZE) { |
| fscrypt_warn(NULL, |
| "key with description '%s' has invalid payload", |
| key->description); |
| goto invalid; |
| } |
| |
| if (payload->size < min_keysize) { |
| fscrypt_warn(NULL, |
| "key with description '%s' is too short (got %u bytes, need %u+ bytes)", |
| key->description, payload->size, min_keysize); |
| goto invalid; |
| } |
| |
| *payload_ret = payload; |
| return key; |
| |
| invalid: |
| up_read(&key->sem); |
| key_put(key); |
| return ERR_PTR(-ENOKEY); |
| } |
| |
| static struct fscrypt_mode available_modes[] = { |
| [FS_ENCRYPTION_MODE_AES_256_XTS] = { |
| .friendly_name = "AES-256-XTS", |
| .cipher_str = "xts(aes)", |
| .keysize = 64, |
| .ivsize = 16, |
| }, |
| [FS_ENCRYPTION_MODE_AES_256_CTS] = { |
| .friendly_name = "AES-256-CTS-CBC", |
| .cipher_str = "cts(cbc(aes))", |
| .keysize = 32, |
| .ivsize = 16, |
| }, |
| [FS_ENCRYPTION_MODE_AES_128_CBC] = { |
| .friendly_name = "AES-128-CBC", |
| .cipher_str = "cbc(aes)", |
| .keysize = 16, |
| .ivsize = 16, |
| .needs_essiv = true, |
| }, |
| [FS_ENCRYPTION_MODE_AES_128_CTS] = { |
| .friendly_name = "AES-128-CTS-CBC", |
| .cipher_str = "cts(cbc(aes))", |
| .keysize = 16, |
| .ivsize = 16, |
| }, |
| [FS_ENCRYPTION_MODE_ADIANTUM] = { |
| .friendly_name = "Adiantum", |
| .cipher_str = "adiantum(xchacha12,aes)", |
| .keysize = 32, |
| .ivsize = 32, |
| }, |
| }; |
| |
| static struct fscrypt_mode * |
| select_encryption_mode(const struct fscrypt_info *ci, const struct inode *inode) |
| { |
| if (!fscrypt_valid_enc_modes(ci->ci_data_mode, ci->ci_filename_mode)) { |
| fscrypt_warn(inode->i_sb, |
| "inode %lu uses unsupported encryption modes (contents mode %d, filenames mode %d)", |
| inode->i_ino, ci->ci_data_mode, |
| ci->ci_filename_mode); |
| return ERR_PTR(-EINVAL); |
| } |
| |
| if (S_ISREG(inode->i_mode)) |
| return &available_modes[ci->ci_data_mode]; |
| |
| if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) |
| return &available_modes[ci->ci_filename_mode]; |
| |
| 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 ERR_PTR(-EINVAL); |
| } |
| |
| /* Find the master key, then derive the inode's actual encryption key */ |
| static int find_and_derive_key(const struct inode *inode, |
| const struct fscrypt_context *ctx, |
| u8 *derived_key, const struct fscrypt_mode *mode) |
| { |
| struct key *key; |
| const struct fscrypt_key *payload; |
| int err; |
| |
| key = find_and_lock_process_key(FS_KEY_DESC_PREFIX, |
| ctx->master_key_descriptor, |
| mode->keysize, &payload); |
| if (key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) { |
| key = find_and_lock_process_key(inode->i_sb->s_cop->key_prefix, |
| ctx->master_key_descriptor, |
| mode->keysize, &payload); |
| } |
| if (IS_ERR(key)) |
| return PTR_ERR(key); |
| |
| if (ctx->flags & FS_POLICY_FLAG_DIRECT_KEY) { |
| if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) { |
| fscrypt_warn(inode->i_sb, |
| "direct key mode not allowed with %s", |
| mode->friendly_name); |
| err = -EINVAL; |
| } else if (ctx->contents_encryption_mode != |
| ctx->filenames_encryption_mode) { |
| fscrypt_warn(inode->i_sb, |
| "direct key mode not allowed with different contents and filenames modes"); |
| err = -EINVAL; |
| } else { |
| memcpy(derived_key, payload->raw, mode->keysize); |
| err = 0; |
| } |
| } else { |
| err = derive_key_aes(payload->raw, ctx, derived_key, |
| mode->keysize); |
| } |
| up_read(&key->sem); |
| key_put(key); |
| return err; |
| } |
| |
| /* Allocate and key a symmetric cipher object for the given encryption mode */ |
| static struct crypto_skcipher * |
| allocate_skcipher_for_mode(struct fscrypt_mode *mode, const u8 *raw_key, |
| const struct inode *inode) |
| { |
| struct crypto_skcipher *tfm; |
| int err; |
| |
| tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0); |
| if (IS_ERR(tfm)) { |
| fscrypt_warn(inode->i_sb, |
| "error allocating '%s' transform for inode %lu: %ld", |
| mode->cipher_str, inode->i_ino, PTR_ERR(tfm)); |
| return tfm; |
| } |
| if (unlikely(!mode->logged_impl_name)) { |
| /* |
| * fscrypt performance can vary greatly depending on which |
| * crypto algorithm implementation is used. Help people debug |
| * performance problems by logging the ->cra_driver_name the |
| * first time a mode is used. Note that multiple threads can |
| * race here, but it doesn't really matter. |
| */ |
| mode->logged_impl_name = true; |
| pr_info("fscrypt: %s using implementation \"%s\"\n", |
| mode->friendly_name, |
| crypto_skcipher_alg(tfm)->base.cra_driver_name); |
| } |
| crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS); |
| err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize); |
| if (err) |
| goto err_free_tfm; |
| |
| return tfm; |
| |
| err_free_tfm: |
| crypto_free_skcipher(tfm); |
| return ERR_PTR(err); |
| } |
| |
| /* Master key referenced by FS_POLICY_FLAG_DIRECT_KEY policy */ |
| struct fscrypt_master_key { |
| struct hlist_node mk_node; |
| refcount_t mk_refcount; |
| const struct fscrypt_mode *mk_mode; |
| struct crypto_skcipher *mk_ctfm; |
| u8 mk_descriptor[FS_KEY_DESCRIPTOR_SIZE]; |
| u8 mk_raw[FS_MAX_KEY_SIZE]; |
| }; |
| |
| static void free_master_key(struct fscrypt_master_key *mk) |
| { |
| if (mk) { |
| crypto_free_skcipher(mk->mk_ctfm); |
| kzfree(mk); |
| } |
| } |
| |
| static void put_master_key(struct fscrypt_master_key *mk) |
| { |
| if (!refcount_dec_and_lock(&mk->mk_refcount, &fscrypt_master_keys_lock)) |
| return; |
| hash_del(&mk->mk_node); |
| spin_unlock(&fscrypt_master_keys_lock); |
| |
| free_master_key(mk); |
| } |
| |
| /* |
| * Find/insert the given master key into the fscrypt_master_keys table. If |
| * found, it is returned with elevated refcount, and 'to_insert' is freed if |
| * non-NULL. If not found, 'to_insert' is inserted and returned if it's |
| * non-NULL; otherwise NULL is returned. |
| */ |
| static struct fscrypt_master_key * |
| find_or_insert_master_key(struct fscrypt_master_key *to_insert, |
| const u8 *raw_key, const struct fscrypt_mode *mode, |
| const struct fscrypt_info *ci) |
| { |
| unsigned long hash_key; |
| struct fscrypt_master_key *mk; |
| |
| /* |
| * Careful: to avoid potentially leaking secret key bytes via timing |
| * information, we must key the hash table by descriptor rather than by |
| * raw key, and use crypto_memneq() when comparing raw keys. |
| */ |
| |
| BUILD_BUG_ON(sizeof(hash_key) > FS_KEY_DESCRIPTOR_SIZE); |
| memcpy(&hash_key, ci->ci_master_key_descriptor, sizeof(hash_key)); |
| |
| spin_lock(&fscrypt_master_keys_lock); |
| hash_for_each_possible(fscrypt_master_keys, mk, mk_node, hash_key) { |
| if (memcmp(ci->ci_master_key_descriptor, mk->mk_descriptor, |
| FS_KEY_DESCRIPTOR_SIZE) != 0) |
| continue; |
| if (mode != mk->mk_mode) |
| continue; |
| if (crypto_memneq(raw_key, mk->mk_raw, mode->keysize)) |
| continue; |
| /* using existing tfm with same (descriptor, mode, raw_key) */ |
| refcount_inc(&mk->mk_refcount); |
| spin_unlock(&fscrypt_master_keys_lock); |
| free_master_key(to_insert); |
| return mk; |
| } |
| if (to_insert) |
| hash_add(fscrypt_master_keys, &to_insert->mk_node, hash_key); |
| spin_unlock(&fscrypt_master_keys_lock); |
| return to_insert; |
| } |
| |
| /* Prepare to encrypt directly using the master key in the given mode */ |
| static struct fscrypt_master_key * |
| fscrypt_get_master_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode, |
| const u8 *raw_key, const struct inode *inode) |
| { |
| struct fscrypt_master_key *mk; |
| int err; |
| |
| /* Is there already a tfm for this key? */ |
| mk = find_or_insert_master_key(NULL, raw_key, mode, ci); |
| if (mk) |
| return mk; |
| |
| /* Nope, allocate one. */ |
| mk = kzalloc(sizeof(*mk), GFP_NOFS); |
| if (!mk) |
| return ERR_PTR(-ENOMEM); |
| refcount_set(&mk->mk_refcount, 1); |
| mk->mk_mode = mode; |
| mk->mk_ctfm = allocate_skcipher_for_mode(mode, raw_key, inode); |
| if (IS_ERR(mk->mk_ctfm)) { |
| err = PTR_ERR(mk->mk_ctfm); |
| mk->mk_ctfm = NULL; |
| goto err_free_mk; |
| } |
| memcpy(mk->mk_descriptor, ci->ci_master_key_descriptor, |
| FS_KEY_DESCRIPTOR_SIZE); |
| memcpy(mk->mk_raw, raw_key, mode->keysize); |
| |
| return find_or_insert_master_key(mk, raw_key, mode, ci); |
| |
| err_free_mk: |
| free_master_key(mk); |
| return ERR_PTR(err); |
| } |
| |
| 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)) { |
| fscrypt_warn(NULL, |
| "error allocating SHA-256 transform: %ld", |
| 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); |
| } |
| |
| /* |
| * Given the encryption mode and key (normally the derived key, but for |
| * FS_POLICY_FLAG_DIRECT_KEY mode it's the master key), set up the inode's |
| * symmetric cipher transform object(s). |
| */ |
| static int setup_crypto_transform(struct fscrypt_info *ci, |
| struct fscrypt_mode *mode, |
| const u8 *raw_key, const struct inode *inode) |
| { |
| struct fscrypt_master_key *mk; |
| struct crypto_skcipher *ctfm; |
| int err; |
| |
| if (ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY) { |
| mk = fscrypt_get_master_key(ci, mode, raw_key, inode); |
| if (IS_ERR(mk)) |
| return PTR_ERR(mk); |
| ctfm = mk->mk_ctfm; |
| } else { |
| mk = NULL; |
| ctfm = allocate_skcipher_for_mode(mode, raw_key, inode); |
| if (IS_ERR(ctfm)) |
| return PTR_ERR(ctfm); |
| } |
| ci->ci_master_key = mk; |
| ci->ci_ctfm = ctfm; |
| |
| if (mode->needs_essiv) { |
| /* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */ |
| WARN_ON(mode->ivsize != AES_BLOCK_SIZE); |
| WARN_ON(ci->ci_flags & FS_POLICY_FLAG_DIRECT_KEY); |
| |
| err = init_essiv_generator(ci, raw_key, mode->keysize); |
| if (err) { |
| fscrypt_warn(inode->i_sb, |
| "error initializing ESSIV generator for inode %lu: %d", |
| inode->i_ino, err); |
| return err; |
| } |
| } |
| return 0; |
| } |
| |
| static void put_crypt_info(struct fscrypt_info *ci) |
| { |
| if (!ci) |
| return; |
| |
| if (ci->ci_master_key) { |
| put_master_key(ci->ci_master_key); |
| } else { |
| crypto_free_skcipher(ci->ci_ctfm); |
| crypto_free_cipher(ci->ci_essiv_tfm); |
| } |
| kmem_cache_free(fscrypt_info_cachep, ci); |
| } |
| |
| int fscrypt_get_encryption_info(struct inode *inode) |
| { |
| struct fscrypt_info *crypt_info; |
| struct fscrypt_context ctx; |
| struct fscrypt_mode *mode; |
| 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) || |
| 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_zalloc(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; |
| memcpy(crypt_info->ci_master_key_descriptor, ctx.master_key_descriptor, |
| FS_KEY_DESCRIPTOR_SIZE); |
| memcpy(crypt_info->ci_nonce, ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE); |
| |
| mode = select_encryption_mode(crypt_info, inode); |
| if (IS_ERR(mode)) { |
| res = PTR_ERR(mode); |
| goto out; |
| } |
| WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE); |
| crypt_info->ci_mode = mode; |
| |
| /* |
| * This cannot be a stack buffer because it may be passed to the |
| * scatterlist crypto API as part of key derivation. |
| */ |
| res = -ENOMEM; |
| raw_key = kmalloc(mode->keysize, GFP_NOFS); |
| if (!raw_key) |
| goto out; |
| |
| res = find_and_derive_key(inode, &ctx, raw_key, mode); |
| if (res) |
| goto out; |
| |
| res = setup_crypto_transform(crypt_info, mode, raw_key, inode); |
| if (res) |
| 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) |
| { |
| put_crypt_info(inode->i_crypt_info); |
| inode->i_crypt_info = NULL; |
| } |
| EXPORT_SYMBOL(fscrypt_put_encryption_info); |