// SPDX-License-Identifier: GPL-2.0 /* * Key setup for v1 encryption policies * * Copyright 2015, 2019 Google LLC */ /* * This file implements compatibility functions for the original encryption * policy version ("v1"), including: * * - Deriving per-file keys using the AES-128-ECB based KDF * (rather than the new method of using HKDF-SHA512) * * - Retrieving fscrypt master keys from process-subscribed keyrings * (rather than the new method of using a filesystem-level keyring) * * - Handling policies with the DIRECT_KEY flag set using a master key table * (rather than the new method of implementing DIRECT_KEY with per-mode keys * managed alongside the master keys in the filesystem-level keyring) */ #include <crypto/algapi.h> #include <crypto/skcipher.h> #include <keys/user-type.h> #include <linux/hashtable.h> #include <linux/scatterlist.h> #include "fscrypt_private.h" /* Table of keys referenced by DIRECT_KEY policies */ static DEFINE_HASHTABLE(fscrypt_direct_keys, 6); /* 6 bits = 64 buckets */ static DEFINE_SPINLOCK(fscrypt_direct_keys_lock); /* * v1 key derivation function. This generates the derived key by encrypting the * master key with AES-128-ECB using the nonce as the AES key. This provides a * unique derived key with sufficient entropy for each inode. However, it's * nonstandard, non-extensible, doesn't evenly distribute the entropy from the * master key, and is trivially reversible: an attacker who compromises a * derived key can "decrypt" it to get back to the master key, then derive any * other key. For all new code, use HKDF instead. * * 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 u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE], 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, nonce, FS_KEY_DERIVATION_NONCE_SIZE); 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[FSCRYPT_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, FSCRYPT_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 > FSCRYPT_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); } /* Master key referenced by DIRECT_KEY policy */ struct fscrypt_direct_key { struct hlist_node dk_node; refcount_t dk_refcount; const struct fscrypt_mode *dk_mode; struct crypto_skcipher *dk_ctfm; u8 dk_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE]; u8 dk_raw[FSCRYPT_MAX_KEY_SIZE]; }; static void free_direct_key(struct fscrypt_direct_key *dk) { if (dk) { crypto_free_skcipher(dk->dk_ctfm); kzfree(dk); } } void fscrypt_put_direct_key(struct fscrypt_direct_key *dk) { if (!refcount_dec_and_lock(&dk->dk_refcount, &fscrypt_direct_keys_lock)) return; hash_del(&dk->dk_node); spin_unlock(&fscrypt_direct_keys_lock); free_direct_key(dk); } /* * Find/insert the given key into the fscrypt_direct_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_direct_key * find_or_insert_direct_key(struct fscrypt_direct_key *to_insert, const u8 *raw_key, const struct fscrypt_info *ci) { unsigned long hash_key; struct fscrypt_direct_key *dk; /* * 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) > FSCRYPT_KEY_DESCRIPTOR_SIZE); memcpy(&hash_key, ci->ci_policy.v1.master_key_descriptor, sizeof(hash_key)); spin_lock(&fscrypt_direct_keys_lock); hash_for_each_possible(fscrypt_direct_keys, dk, dk_node, hash_key) { if (memcmp(ci->ci_policy.v1.master_key_descriptor, dk->dk_descriptor, FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0) continue; if (ci->ci_mode != dk->dk_mode) continue; if (crypto_memneq(raw_key, dk->dk_raw, ci->ci_mode->keysize)) continue; /* using existing tfm with same (descriptor, mode, raw_key) */ refcount_inc(&dk->dk_refcount); spin_unlock(&fscrypt_direct_keys_lock); free_direct_key(to_insert); return dk; } if (to_insert) hash_add(fscrypt_direct_keys, &to_insert->dk_node, hash_key); spin_unlock(&fscrypt_direct_keys_lock); return to_insert; } /* Prepare to encrypt directly using the master key in the given mode */ static struct fscrypt_direct_key * fscrypt_get_direct_key(const struct fscrypt_info *ci, const u8 *raw_key) { struct fscrypt_direct_key *dk; int err; /* Is there already a tfm for this key? */ dk = find_or_insert_direct_key(NULL, raw_key, ci); if (dk) return dk; /* Nope, allocate one. */ dk = kzalloc(sizeof(*dk), GFP_NOFS); if (!dk) return ERR_PTR(-ENOMEM); refcount_set(&dk->dk_refcount, 1); dk->dk_mode = ci->ci_mode; dk->dk_ctfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key, ci->ci_inode); if (IS_ERR(dk->dk_ctfm)) { err = PTR_ERR(dk->dk_ctfm); dk->dk_ctfm = NULL; goto err_free_dk; } memcpy(dk->dk_descriptor, ci->ci_policy.v1.master_key_descriptor, FSCRYPT_KEY_DESCRIPTOR_SIZE); memcpy(dk->dk_raw, raw_key, ci->ci_mode->keysize); return find_or_insert_direct_key(dk, raw_key, ci); err_free_dk: free_direct_key(dk); return ERR_PTR(err); } /* v1 policy, DIRECT_KEY: use the master key directly */ static int setup_v1_file_key_direct(struct fscrypt_info *ci, const u8 *raw_master_key) { const struct fscrypt_mode *mode = ci->ci_mode; struct fscrypt_direct_key *dk; if (!fscrypt_mode_supports_direct_key(mode)) { fscrypt_warn(ci->ci_inode, "Direct key mode not allowed with %s", mode->friendly_name); return -EINVAL; } if (ci->ci_policy.v1.contents_encryption_mode != ci->ci_policy.v1.filenames_encryption_mode) { fscrypt_warn(ci->ci_inode, "Direct key mode not allowed with different contents and filenames modes"); return -EINVAL; } /* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */ if (WARN_ON(mode->needs_essiv)) return -EINVAL; dk = fscrypt_get_direct_key(ci, raw_master_key); if (IS_ERR(dk)) return PTR_ERR(dk); ci->ci_direct_key = dk; ci->ci_ctfm = dk->dk_ctfm; return 0; } /* v1 policy, !DIRECT_KEY: derive the file's encryption key */ static int setup_v1_file_key_derived(struct fscrypt_info *ci, const u8 *raw_master_key) { u8 *derived_key; int err; /* * This cannot be a stack buffer because it will be passed to the * scatterlist crypto API during derive_key_aes(). */ derived_key = kmalloc(ci->ci_mode->keysize, GFP_NOFS); if (!derived_key) return -ENOMEM; err = derive_key_aes(raw_master_key, ci->ci_nonce, derived_key, ci->ci_mode->keysize); if (err) goto out; err = fscrypt_set_derived_key(ci, derived_key); out: kzfree(derived_key); return err; } int fscrypt_setup_v1_file_key(struct fscrypt_info *ci, const u8 *raw_master_key) { if (ci->ci_policy.v1.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) return setup_v1_file_key_direct(ci, raw_master_key); else return setup_v1_file_key_derived(ci, raw_master_key); } int fscrypt_setup_v1_file_key_via_subscribed_keyrings(struct fscrypt_info *ci) { struct key *key; const struct fscrypt_key *payload; int err; key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX, ci->ci_policy.v1.master_key_descriptor, ci->ci_mode->keysize, &payload); if (key == ERR_PTR(-ENOKEY) && ci->ci_inode->i_sb->s_cop->key_prefix) { key = find_and_lock_process_key(ci->ci_inode->i_sb->s_cop->key_prefix, ci->ci_policy.v1.master_key_descriptor, ci->ci_mode->keysize, &payload); } if (IS_ERR(key)) return PTR_ERR(key); err = fscrypt_setup_v1_file_key(ci, payload->raw); up_read(&key->sem); key_put(key); return err; }