// 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 <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; 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 (fscrypt_has_encryption_key(inode)) 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_release(&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); /** * fscrypt_put_encryption_info - free most of an inode's fscrypt data * * Free the inode's fscrypt_info. Filesystems must call this when the inode is * being evicted. An RCU grace period need not have elapsed yet. */ 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); /** * fscrypt_free_inode - free an inode's fscrypt data requiring RCU delay * * Free the inode's cached decrypted symlink target, if any. Filesystems must * call this after an RCU grace period, just before they free the inode. */ void fscrypt_free_inode(struct inode *inode) { if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) { kfree(inode->i_link); inode->i_link = NULL; } } EXPORT_SYMBOL(fscrypt_free_inode);