// SPDX-License-Identifier: GPL-2.0 /* * Filesystem-level keyring for fscrypt * * Copyright 2019 Google LLC */ /* * This file implements management of fscrypt master keys in the * filesystem-level keyring, including the ioctls: * * - FS_IOC_ADD_ENCRYPTION_KEY * - FS_IOC_REMOVE_ENCRYPTION_KEY * - FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS * - FS_IOC_GET_ENCRYPTION_KEY_STATUS * * See the "User API" section of Documentation/filesystems/fscrypt.rst for more * information about these ioctls. */ #include <linux/unaligned.h> #include <crypto/skcipher.h> #include <linux/key-type.h> #include <linux/random.h> #include <linux/once.h> #include <linux/seq_file.h> #include "fscrypt_private.h" /* The master encryption keys for a filesystem (->s_master_keys) */ struct fscrypt_keyring { /* * Lock that protects ->key_hashtable. It does *not* protect the * fscrypt_master_key structs themselves. */ spinlock_t lock; /* Hash table that maps fscrypt_key_specifier to fscrypt_master_key */ struct hlist_head key_hashtable[128]; }; static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret) { fscrypt_destroy_hkdf(&secret->hkdf); memzero_explicit(secret, sizeof(*secret)); } static void move_master_key_secret(struct fscrypt_master_key_secret *dst, struct fscrypt_master_key_secret *src) { memcpy(dst, src, sizeof(*dst)); memzero_explicit(src, sizeof(*src)); } static void fscrypt_free_master_key(struct rcu_head *head) { struct fscrypt_master_key *mk = container_of(head, struct fscrypt_master_key, mk_rcu_head); /* * The master key secret and any embedded subkeys should have already * been wiped when the last active reference to the fscrypt_master_key * struct was dropped; doing it here would be unnecessarily late. * Nevertheless, use kfree_sensitive() in case anything was missed. */ kfree_sensitive(mk); } void fscrypt_put_master_key(struct fscrypt_master_key *mk) { if (!refcount_dec_and_test(&mk->mk_struct_refs)) return; /* * No structural references left, so free ->mk_users, and also free the * fscrypt_master_key struct itself after an RCU grace period ensures * that concurrent keyring lookups can no longer find it. */ WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 0); if (mk->mk_users) { /* Clear the keyring so the quota gets released right away. */ keyring_clear(mk->mk_users); key_put(mk->mk_users); mk->mk_users = NULL; } call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key); } void fscrypt_put_master_key_activeref(struct super_block *sb, struct fscrypt_master_key *mk) { size_t i; if (!refcount_dec_and_test(&mk->mk_active_refs)) return; /* * No active references left, so complete the full removal of this * fscrypt_master_key struct by removing it from the keyring and * destroying any subkeys embedded in it. */ if (WARN_ON_ONCE(!sb->s_master_keys)) return; spin_lock(&sb->s_master_keys->lock); hlist_del_rcu(&mk->mk_node); spin_unlock(&sb->s_master_keys->lock); /* * ->mk_active_refs == 0 implies that ->mk_present is false and * ->mk_decrypted_inodes is empty. */ WARN_ON_ONCE(mk->mk_present); WARN_ON_ONCE(!list_empty(&mk->mk_decrypted_inodes)); for (i = 0; i <= FSCRYPT_MODE_MAX; i++) { fscrypt_destroy_prepared_key( sb, &mk->mk_direct_keys[i]); fscrypt_destroy_prepared_key( sb, &mk->mk_iv_ino_lblk_64_keys[i]); fscrypt_destroy_prepared_key( sb, &mk->mk_iv_ino_lblk_32_keys[i]); } memzero_explicit(&mk->mk_ino_hash_key, sizeof(mk->mk_ino_hash_key)); mk->mk_ino_hash_key_initialized = false; /* Drop the structural ref associated with the active refs. */ fscrypt_put_master_key(mk); } /* * This transitions the key state from present to incompletely removed, and then * potentially to absent (depending on whether inodes remain). */ static void fscrypt_initiate_key_removal(struct super_block *sb, struct fscrypt_master_key *mk) { WRITE_ONCE(mk->mk_present, false); wipe_master_key_secret(&mk->mk_secret); fscrypt_put_master_key_activeref(sb, mk); } static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec) { if (spec->__reserved) return false; return master_key_spec_len(spec) != 0; } static int fscrypt_user_key_instantiate(struct key *key, struct key_preparsed_payload *prep) { /* * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for * each key, regardless of the exact key size. The amount of memory * actually used is greater than the size of the raw key anyway. */ return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE); } static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m) { seq_puts(m, key->description); } /* * Type of key in ->mk_users. Each key of this type represents a particular * user who has added a particular master key. * * Note that the name of this key type really should be something like * ".fscrypt-user" instead of simply ".fscrypt". But the shorter name is chosen * mainly for simplicity of presentation in /proc/keys when read by a non-root * user. And it is expected to be rare that a key is actually added by multiple * users, since users should keep their encryption keys confidential. */ static struct key_type key_type_fscrypt_user = { .name = ".fscrypt", .instantiate = fscrypt_user_key_instantiate, .describe = fscrypt_user_key_describe, }; #define FSCRYPT_MK_USERS_DESCRIPTION_SIZE \ (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \ CONST_STRLEN("-users") + 1) #define FSCRYPT_MK_USER_DESCRIPTION_SIZE \ (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1) static void format_mk_users_keyring_description( char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE], const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]) { sprintf(description, "fscrypt-%*phN-users", FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier); } static void format_mk_user_description( char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE], const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]) { sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier, __kuid_val(current_fsuid())); } /* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */ static int allocate_filesystem_keyring(struct super_block *sb) { struct fscrypt_keyring *keyring; if (sb->s_master_keys) return 0; keyring = kzalloc(sizeof(*keyring), GFP_KERNEL); if (!keyring) return -ENOMEM; spin_lock_init(&keyring->lock); /* * Pairs with the smp_load_acquire() in fscrypt_find_master_key(). * I.e., here we publish ->s_master_keys with a RELEASE barrier so that * concurrent tasks can ACQUIRE it. */ smp_store_release(&sb->s_master_keys, keyring); return 0; } /* * Release all encryption keys that have been added to the filesystem, along * with the keyring that contains them. * * This is called at unmount time, after all potentially-encrypted inodes have * been evicted. The filesystem's underlying block device(s) are still * available at this time; this is important because after user file accesses * have been allowed, this function may need to evict keys from the keyslots of * an inline crypto engine, which requires the block device(s). */ void fscrypt_destroy_keyring(struct super_block *sb) { struct fscrypt_keyring *keyring = sb->s_master_keys; size_t i; if (!keyring) return; for (i = 0; i < ARRAY_SIZE(keyring->key_hashtable); i++) { struct hlist_head *bucket = &keyring->key_hashtable[i]; struct fscrypt_master_key *mk; struct hlist_node *tmp; hlist_for_each_entry_safe(mk, tmp, bucket, mk_node) { /* * Since all potentially-encrypted inodes were already * evicted, every key remaining in the keyring should * have an empty inode list, and should only still be in * the keyring due to the single active ref associated * with ->mk_present. There should be no structural * refs beyond the one associated with the active ref. */ WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 1); WARN_ON_ONCE(refcount_read(&mk->mk_struct_refs) != 1); WARN_ON_ONCE(!mk->mk_present); fscrypt_initiate_key_removal(sb, mk); } } kfree_sensitive(keyring); sb->s_master_keys = NULL; } static struct hlist_head * fscrypt_mk_hash_bucket(struct fscrypt_keyring *keyring, const struct fscrypt_key_specifier *mk_spec) { /* * Since key specifiers should be "random" values, it is sufficient to * use a trivial hash function that just takes the first several bits of * the key specifier. */ unsigned long i = get_unaligned((unsigned long *)&mk_spec->u); return &keyring->key_hashtable[i % ARRAY_SIZE(keyring->key_hashtable)]; } /* * Find the specified master key struct in ->s_master_keys and take a structural * ref to it. The structural ref guarantees that the key struct continues to * exist, but it does *not* guarantee that ->s_master_keys continues to contain * the key struct. The structural ref needs to be dropped by * fscrypt_put_master_key(). Returns NULL if the key struct is not found. */ struct fscrypt_master_key * fscrypt_find_master_key(struct super_block *sb, const struct fscrypt_key_specifier *mk_spec) { struct fscrypt_keyring *keyring; struct hlist_head *bucket; struct fscrypt_master_key *mk; /* * Pairs with the smp_store_release() in allocate_filesystem_keyring(). * I.e., another task can publish ->s_master_keys concurrently, * executing a RELEASE barrier. We need to use smp_load_acquire() here * to safely ACQUIRE the memory the other task published. */ keyring = smp_load_acquire(&sb->s_master_keys); if (keyring == NULL) return NULL; /* No keyring yet, so no keys yet. */ bucket = fscrypt_mk_hash_bucket(keyring, mk_spec); rcu_read_lock(); switch (mk_spec->type) { case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR: hlist_for_each_entry_rcu(mk, bucket, mk_node) { if (mk->mk_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR && memcmp(mk->mk_spec.u.descriptor, mk_spec->u.descriptor, FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 && refcount_inc_not_zero(&mk->mk_struct_refs)) goto out; } break; case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER: hlist_for_each_entry_rcu(mk, bucket, mk_node) { if (mk->mk_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER && memcmp(mk->mk_spec.u.identifier, mk_spec->u.identifier, FSCRYPT_KEY_IDENTIFIER_SIZE) == 0 && refcount_inc_not_zero(&mk->mk_struct_refs)) goto out; } break; } mk = NULL; out: rcu_read_unlock(); return mk; } static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk) { char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE]; struct key *keyring; format_mk_users_keyring_description(description, mk->mk_spec.u.identifier); keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(), KEY_POS_SEARCH | KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW, KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL); if (IS_ERR(keyring)) return PTR_ERR(keyring); mk->mk_users = keyring; return 0; } /* * Find the current user's "key" in the master key's ->mk_users. * Returns ERR_PTR(-ENOKEY) if not found. */ static struct key *find_master_key_user(struct fscrypt_master_key *mk) { char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE]; key_ref_t keyref; format_mk_user_description(description, mk->mk_spec.u.identifier); /* * We need to mark the keyring reference as "possessed" so that we * acquire permission to search it, via the KEY_POS_SEARCH permission. */ keyref = keyring_search(make_key_ref(mk->mk_users, true /*possessed*/), &key_type_fscrypt_user, description, false); if (IS_ERR(keyref)) { if (PTR_ERR(keyref) == -EAGAIN || /* not found */ PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */ keyref = ERR_PTR(-ENOKEY); return ERR_CAST(keyref); } return key_ref_to_ptr(keyref); } /* * Give the current user a "key" in ->mk_users. This charges the user's quota * and marks the master key as added by the current user, so that it cannot be * removed by another user with the key. Either ->mk_sem must be held for * write, or the master key must be still undergoing initialization. */ static int add_master_key_user(struct fscrypt_master_key *mk) { char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE]; struct key *mk_user; int err; format_mk_user_description(description, mk->mk_spec.u.identifier); mk_user = key_alloc(&key_type_fscrypt_user, description, current_fsuid(), current_gid(), current_cred(), KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL); if (IS_ERR(mk_user)) return PTR_ERR(mk_user); err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL); key_put(mk_user); return err; } /* * Remove the current user's "key" from ->mk_users. * ->mk_sem must be held for write. * * Returns 0 if removed, -ENOKEY if not found, or another -errno code. */ static int remove_master_key_user(struct fscrypt_master_key *mk) { struct key *mk_user; int err; mk_user = find_master_key_user(mk); if (IS_ERR(mk_user)) return PTR_ERR(mk_user); err = key_unlink(mk->mk_users, mk_user); key_put(mk_user); return err; } /* * Allocate a new fscrypt_master_key, transfer the given secret over to it, and * insert it into sb->s_master_keys. */ static int add_new_master_key(struct super_block *sb, struct fscrypt_master_key_secret *secret, const struct fscrypt_key_specifier *mk_spec) { struct fscrypt_keyring *keyring = sb->s_master_keys; struct fscrypt_master_key *mk; int err; mk = kzalloc(sizeof(*mk), GFP_KERNEL); if (!mk) return -ENOMEM; init_rwsem(&mk->mk_sem); refcount_set(&mk->mk_struct_refs, 1); mk->mk_spec = *mk_spec; INIT_LIST_HEAD(&mk->mk_decrypted_inodes); spin_lock_init(&mk->mk_decrypted_inodes_lock); if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) { err = allocate_master_key_users_keyring(mk); if (err) goto out_put; err = add_master_key_user(mk); if (err) goto out_put; } move_master_key_secret(&mk->mk_secret, secret); mk->mk_present = true; refcount_set(&mk->mk_active_refs, 1); /* ->mk_present is true */ spin_lock(&keyring->lock); hlist_add_head_rcu(&mk->mk_node, fscrypt_mk_hash_bucket(keyring, mk_spec)); spin_unlock(&keyring->lock); return 0; out_put: fscrypt_put_master_key(mk); return err; } #define KEY_DEAD 1 static int add_existing_master_key(struct fscrypt_master_key *mk, struct fscrypt_master_key_secret *secret) { int err; /* * If the current user is already in ->mk_users, then there's nothing to * do. Otherwise, we need to add the user to ->mk_users. (Neither is * applicable for v1 policy keys, which have NULL ->mk_users.) */ if (mk->mk_users) { struct key *mk_user = find_master_key_user(mk); if (mk_user != ERR_PTR(-ENOKEY)) { if (IS_ERR(mk_user)) return PTR_ERR(mk_user); key_put(mk_user); return 0; } err = add_master_key_user(mk); if (err) return err; } /* If the key is incompletely removed, make it present again. */ if (!mk->mk_present) { if (!refcount_inc_not_zero(&mk->mk_active_refs)) { /* * Raced with the last active ref being dropped, so the * key has become, or is about to become, "absent". * Therefore, we need to allocate a new key struct. */ return KEY_DEAD; } move_master_key_secret(&mk->mk_secret, secret); WRITE_ONCE(mk->mk_present, true); } return 0; } static int do_add_master_key(struct super_block *sb, struct fscrypt_master_key_secret *secret, const struct fscrypt_key_specifier *mk_spec) { static DEFINE_MUTEX(fscrypt_add_key_mutex); struct fscrypt_master_key *mk; int err; mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */ mk = fscrypt_find_master_key(sb, mk_spec); if (!mk) { /* Didn't find the key in ->s_master_keys. Add it. */ err = allocate_filesystem_keyring(sb); if (!err) err = add_new_master_key(sb, secret, mk_spec); } else { /* * Found the key in ->s_master_keys. Add the user to ->mk_users * if needed, and make the key "present" again if possible. */ down_write(&mk->mk_sem); err = add_existing_master_key(mk, secret); up_write(&mk->mk_sem); if (err == KEY_DEAD) { /* * We found a key struct, but it's already been fully * removed. Ignore the old struct and add a new one. * fscrypt_add_key_mutex means we don't need to worry * about concurrent adds. */ err = add_new_master_key(sb, secret, mk_spec); } fscrypt_put_master_key(mk); } mutex_unlock(&fscrypt_add_key_mutex); return err; } static int add_master_key(struct super_block *sb, struct fscrypt_master_key_secret *secret, struct fscrypt_key_specifier *key_spec) { int err; if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) { err = fscrypt_init_hkdf(&secret->hkdf, secret->raw, secret->size); if (err) return err; /* * Now that the HKDF context is initialized, the raw key is no * longer needed. */ memzero_explicit(secret->raw, secret->size); /* Calculate the key identifier */ err = fscrypt_hkdf_expand(&secret->hkdf, HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0, key_spec->u.identifier, FSCRYPT_KEY_IDENTIFIER_SIZE); if (err) return err; } return do_add_master_key(sb, secret, key_spec); } static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep) { const struct fscrypt_provisioning_key_payload *payload = prep->data; if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE || prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE) return -EINVAL; if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR && payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) return -EINVAL; if (payload->__reserved) return -EINVAL; prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL); if (!prep->payload.data[0]) return -ENOMEM; prep->quotalen = prep->datalen; return 0; } static void fscrypt_provisioning_key_free_preparse( struct key_preparsed_payload *prep) { kfree_sensitive(prep->payload.data[0]); } static void fscrypt_provisioning_key_describe(const struct key *key, struct seq_file *m) { seq_puts(m, key->description); if (key_is_positive(key)) { const struct fscrypt_provisioning_key_payload *payload = key->payload.data[0]; seq_printf(m, ": %u [%u]", key->datalen, payload->type); } } static void fscrypt_provisioning_key_destroy(struct key *key) { kfree_sensitive(key->payload.data[0]); } static struct key_type key_type_fscrypt_provisioning = { .name = "fscrypt-provisioning", .preparse = fscrypt_provisioning_key_preparse, .free_preparse = fscrypt_provisioning_key_free_preparse, .instantiate = generic_key_instantiate, .describe = fscrypt_provisioning_key_describe, .destroy = fscrypt_provisioning_key_destroy, }; /* * Retrieve the raw key from the Linux keyring key specified by 'key_id', and * store it into 'secret'. * * The key must be of type "fscrypt-provisioning" and must have the field * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's * only usable with fscrypt with the particular KDF version identified by * 'type'. We don't use the "logon" key type because there's no way to * completely restrict the use of such keys; they can be used by any kernel API * that accepts "logon" keys and doesn't require a specific service prefix. * * The ability to specify the key via Linux keyring key is intended for cases * where userspace needs to re-add keys after the filesystem is unmounted and * re-mounted. Most users should just provide the raw key directly instead. */ static int get_keyring_key(u32 key_id, u32 type, struct fscrypt_master_key_secret *secret) { key_ref_t ref; struct key *key; const struct fscrypt_provisioning_key_payload *payload; int err; ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH); if (IS_ERR(ref)) return PTR_ERR(ref); key = key_ref_to_ptr(ref); if (key->type != &key_type_fscrypt_provisioning) goto bad_key; payload = key->payload.data[0]; /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */ if (payload->type != type) goto bad_key; secret->size = key->datalen - sizeof(*payload); memcpy(secret->raw, payload->raw, secret->size); err = 0; goto out_put; bad_key: err = -EKEYREJECTED; out_put: key_ref_put(ref); return err; } /* * Add a master encryption key to the filesystem, causing all files which were * encrypted with it to appear "unlocked" (decrypted) when accessed. * * When adding a key for use by v1 encryption policies, this ioctl is * privileged, and userspace must provide the 'key_descriptor'. * * When adding a key for use by v2+ encryption policies, this ioctl is * unprivileged. This is needed, in general, to allow non-root users to use * encryption without encountering the visibility problems of process-subscribed * keyrings and the inability to properly remove keys. This works by having * each key identified by its cryptographically secure hash --- the * 'key_identifier'. The cryptographic hash ensures that a malicious user * cannot add the wrong key for a given identifier. Furthermore, each added key * is charged to the appropriate user's quota for the keyrings service, which * prevents a malicious user from adding too many keys. Finally, we forbid a * user from removing a key while other users have added it too, which prevents * a user who knows another user's key from causing a denial-of-service by * removing it at an inopportune time. (We tolerate that a user who knows a key * can prevent other users from removing it.) * * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of * Documentation/filesystems/fscrypt.rst. */ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg) { struct super_block *sb = file_inode(filp)->i_sb; struct fscrypt_add_key_arg __user *uarg = _uarg; struct fscrypt_add_key_arg arg; struct fscrypt_master_key_secret secret; int err; if (copy_from_user(&arg, uarg, sizeof(arg))) return -EFAULT; if (!valid_key_spec(&arg.key_spec)) return -EINVAL; if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved))) return -EINVAL; /* * Only root can add keys that are identified by an arbitrary descriptor * rather than by a cryptographic hash --- since otherwise a malicious * user could add the wrong key. */ if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR && !capable(CAP_SYS_ADMIN)) return -EACCES; memset(&secret, 0, sizeof(secret)); if (arg.key_id) { if (arg.raw_size != 0) return -EINVAL; err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret); if (err) goto out_wipe_secret; } else { if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE || arg.raw_size > FSCRYPT_MAX_KEY_SIZE) return -EINVAL; secret.size = arg.raw_size; err = -EFAULT; if (copy_from_user(secret.raw, uarg->raw, secret.size)) goto out_wipe_secret; } err = add_master_key(sb, &secret, &arg.key_spec); if (err) goto out_wipe_secret; /* Return the key identifier to userspace, if applicable */ err = -EFAULT; if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER && copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier, FSCRYPT_KEY_IDENTIFIER_SIZE)) goto out_wipe_secret; err = 0; out_wipe_secret: wipe_master_key_secret(&secret); return err; } EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key); static void fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret) { static u8 test_key[FSCRYPT_MAX_KEY_SIZE]; get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE); memset(secret, 0, sizeof(*secret)); secret->size = FSCRYPT_MAX_KEY_SIZE; memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE); } int fscrypt_get_test_dummy_key_identifier( u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]) { struct fscrypt_master_key_secret secret; int err; fscrypt_get_test_dummy_secret(&secret); err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size); if (err) goto out; err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0, key_identifier, FSCRYPT_KEY_IDENTIFIER_SIZE); out: wipe_master_key_secret(&secret); return err; } /** * fscrypt_add_test_dummy_key() - add the test dummy encryption key * @sb: the filesystem instance to add the key to * @key_spec: the key specifier of the test dummy encryption key * * Add the key for the test_dummy_encryption mount option to the filesystem. To * prevent misuse of this mount option, a per-boot random key is used instead of * a hardcoded one. This makes it so that any encrypted files created using * this option won't be accessible after a reboot. * * Return: 0 on success, -errno on failure */ int fscrypt_add_test_dummy_key(struct super_block *sb, struct fscrypt_key_specifier *key_spec) { struct fscrypt_master_key_secret secret; int err; fscrypt_get_test_dummy_secret(&secret); err = add_master_key(sb, &secret, key_spec); wipe_master_key_secret(&secret); return err; } /* * Verify that the current user has added a master key with the given identifier * (returns -ENOKEY if not). This is needed to prevent a user from encrypting * their files using some other user's key which they don't actually know. * Cryptographically this isn't much of a problem, but the semantics of this * would be a bit weird, so it's best to just forbid it. * * The system administrator (CAP_FOWNER) can override this, which should be * enough for any use cases where encryption policies are being set using keys * that were chosen ahead of time but aren't available at the moment. * * Note that the key may have already removed by the time this returns, but * that's okay; we just care whether the key was there at some point. * * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code */ int fscrypt_verify_key_added(struct super_block *sb, const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]) { struct fscrypt_key_specifier mk_spec; struct fscrypt_master_key *mk; struct key *mk_user; int err; mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER; memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE); mk = fscrypt_find_master_key(sb, &mk_spec); if (!mk) { err = -ENOKEY; goto out; } down_read(&mk->mk_sem); mk_user = find_master_key_user(mk); if (IS_ERR(mk_user)) { err = PTR_ERR(mk_user); } else { key_put(mk_user); err = 0; } up_read(&mk->mk_sem); fscrypt_put_master_key(mk); out: if (err == -ENOKEY && capable(CAP_FOWNER)) err = 0; return err; } /* * Try to evict the inode's dentries from the dentry cache. If the inode is a * directory, then it can have at most one dentry; however, that dentry may be * pinned by child dentries, so first try to evict the children too. */ static void shrink_dcache_inode(struct inode *inode) { struct dentry *dentry; if (S_ISDIR(inode->i_mode)) { dentry = d_find_any_alias(inode); if (dentry) { shrink_dcache_parent(dentry); dput(dentry); } } d_prune_aliases(inode); } static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk) { struct fscrypt_inode_info *ci; struct inode *inode; struct inode *toput_inode = NULL; spin_lock(&mk->mk_decrypted_inodes_lock); list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) { inode = ci->ci_inode; spin_lock(&inode->i_lock); if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) { spin_unlock(&inode->i_lock); continue; } __iget(inode); spin_unlock(&inode->i_lock); spin_unlock(&mk->mk_decrypted_inodes_lock); shrink_dcache_inode(inode); iput(toput_inode); toput_inode = inode; spin_lock(&mk->mk_decrypted_inodes_lock); } spin_unlock(&mk->mk_decrypted_inodes_lock); iput(toput_inode); } static int check_for_busy_inodes(struct super_block *sb, struct fscrypt_master_key *mk) { struct list_head *pos; size_t busy_count = 0; unsigned long ino; char ino_str[50] = ""; spin_lock(&mk->mk_decrypted_inodes_lock); list_for_each(pos, &mk->mk_decrypted_inodes) busy_count++; if (busy_count == 0) { spin_unlock(&mk->mk_decrypted_inodes_lock); return 0; } { /* select an example file to show for debugging purposes */ struct inode *inode = list_first_entry(&mk->mk_decrypted_inodes, struct fscrypt_inode_info, ci_master_key_link)->ci_inode; ino = inode->i_ino; } spin_unlock(&mk->mk_decrypted_inodes_lock); /* If the inode is currently being created, ino may still be 0. */ if (ino) snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino); fscrypt_warn(NULL, "%s: %zu inode(s) still busy after removing key with %s %*phN%s", sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec), master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u, ino_str); return -EBUSY; } static int try_to_lock_encrypted_files(struct super_block *sb, struct fscrypt_master_key *mk) { int err1; int err2; /* * An inode can't be evicted while it is dirty or has dirty pages. * Thus, we first have to clean the inodes in ->mk_decrypted_inodes. * * Just do it the easy way: call sync_filesystem(). It's overkill, but * it works, and it's more important to minimize the amount of caches we * drop than the amount of data we sync. Also, unprivileged users can * already call sync_filesystem() via sys_syncfs() or sys_sync(). */ down_read(&sb->s_umount); err1 = sync_filesystem(sb); up_read(&sb->s_umount); /* If a sync error occurs, still try to evict as much as possible. */ /* * Inodes are pinned by their dentries, so we have to evict their * dentries. shrink_dcache_sb() would suffice, but would be overkill * and inappropriate for use by unprivileged users. So instead go * through the inodes' alias lists and try to evict each dentry. */ evict_dentries_for_decrypted_inodes(mk); /* * evict_dentries_for_decrypted_inodes() already iput() each inode in * the list; any inodes for which that dropped the last reference will * have been evicted due to fscrypt_drop_inode() detecting the key * removal and telling the VFS to evict the inode. So to finish, we * just need to check whether any inodes couldn't be evicted. */ err2 = check_for_busy_inodes(sb, mk); return err1 ?: err2; } /* * Try to remove an fscrypt master encryption key. * * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's * claim to the key, then removes the key itself if no other users have claims. * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the * key itself. * * To "remove the key itself", first we transition the key to the "incompletely * removed" state, so that no more inodes can be unlocked with it. Then we try * to evict all cached inodes that had been unlocked with the key. * * If all inodes were evicted, then we unlink the fscrypt_master_key from the * keyring. Otherwise it remains in the keyring in the "incompletely removed" * state where it tracks the list of remaining inodes. Userspace can execute * the ioctl again later to retry eviction, or alternatively can re-add the key. * * For more details, see the "Removing keys" section of * Documentation/filesystems/fscrypt.rst. */ static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users) { struct super_block *sb = file_inode(filp)->i_sb; struct fscrypt_remove_key_arg __user *uarg = _uarg; struct fscrypt_remove_key_arg arg; struct fscrypt_master_key *mk; u32 status_flags = 0; int err; bool inodes_remain; if (copy_from_user(&arg, uarg, sizeof(arg))) return -EFAULT; if (!valid_key_spec(&arg.key_spec)) return -EINVAL; if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved))) return -EINVAL; /* * Only root can add and remove keys that are identified by an arbitrary * descriptor rather than by a cryptographic hash. */ if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR && !capable(CAP_SYS_ADMIN)) return -EACCES; /* Find the key being removed. */ mk = fscrypt_find_master_key(sb, &arg.key_spec); if (!mk) return -ENOKEY; down_write(&mk->mk_sem); /* If relevant, remove current user's (or all users) claim to the key */ if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) { if (all_users) err = keyring_clear(mk->mk_users); else err = remove_master_key_user(mk); if (err) { up_write(&mk->mk_sem); goto out_put_key; } if (mk->mk_users->keys.nr_leaves_on_tree != 0) { /* * Other users have still added the key too. We removed * the current user's claim to the key, but we still * can't remove the key itself. */ status_flags |= FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS; err = 0; up_write(&mk->mk_sem); goto out_put_key; } } /* No user claims remaining. Initiate removal of the key. */ err = -ENOKEY; if (mk->mk_present) { fscrypt_initiate_key_removal(sb, mk); err = 0; } inodes_remain = refcount_read(&mk->mk_active_refs) > 0; up_write(&mk->mk_sem); if (inodes_remain) { /* Some inodes still reference this key; try to evict them. */ err = try_to_lock_encrypted_files(sb, mk); if (err == -EBUSY) { status_flags |= FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY; err = 0; } } /* * We return 0 if we successfully did something: removed a claim to the * key, initiated removal of the key, or tried locking the files again. * Users need to check the informational status flags if they care * whether the key has been fully removed including all files locked. */ out_put_key: fscrypt_put_master_key(mk); if (err == 0) err = put_user(status_flags, &uarg->removal_status_flags); return err; } int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg) { return do_remove_key(filp, uarg, false); } EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key); int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg) { if (!capable(CAP_SYS_ADMIN)) return -EACCES; return do_remove_key(filp, uarg, true); } EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users); /* * Retrieve the status of an fscrypt master encryption key. * * We set ->status to indicate whether the key is absent, present, or * incompletely removed. (For an explanation of what these statuses mean and * how they are represented internally, see struct fscrypt_master_key.) This * field allows applications to easily determine the status of an encrypted * directory without using a hack such as trying to open a regular file in it * (which can confuse the "incompletely removed" status with absent or present). * * In addition, for v2 policy keys we allow applications to determine, via * ->status_flags and ->user_count, whether the key has been added by the * current user, by other users, or by both. Most applications should not need * this, since ordinarily only one user should know a given key. However, if a * secret key is shared by multiple users, applications may wish to add an * already-present key to prevent other users from removing it. This ioctl can * be used to check whether that really is the case before the work is done to * add the key --- which might e.g. require prompting the user for a passphrase. * * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of * Documentation/filesystems/fscrypt.rst. */ int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg) { struct super_block *sb = file_inode(filp)->i_sb; struct fscrypt_get_key_status_arg arg; struct fscrypt_master_key *mk; int err; if (copy_from_user(&arg, uarg, sizeof(arg))) return -EFAULT; if (!valid_key_spec(&arg.key_spec)) return -EINVAL; if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved))) return -EINVAL; arg.status_flags = 0; arg.user_count = 0; memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved)); mk = fscrypt_find_master_key(sb, &arg.key_spec); if (!mk) { arg.status = FSCRYPT_KEY_STATUS_ABSENT; err = 0; goto out; } down_read(&mk->mk_sem); if (!mk->mk_present) { arg.status = refcount_read(&mk->mk_active_refs) > 0 ? FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED : FSCRYPT_KEY_STATUS_ABSENT /* raced with full removal */; err = 0; goto out_release_key; } arg.status = FSCRYPT_KEY_STATUS_PRESENT; if (mk->mk_users) { struct key *mk_user; arg.user_count = mk->mk_users->keys.nr_leaves_on_tree; mk_user = find_master_key_user(mk); if (!IS_ERR(mk_user)) { arg.status_flags |= FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF; key_put(mk_user); } else if (mk_user != ERR_PTR(-ENOKEY)) { err = PTR_ERR(mk_user); goto out_release_key; } } err = 0; out_release_key: up_read(&mk->mk_sem); fscrypt_put_master_key(mk); out: if (!err && copy_to_user(uarg, &arg, sizeof(arg))) err = -EFAULT; return err; } EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status); int __init fscrypt_init_keyring(void) { int err; err = register_key_type(&key_type_fscrypt_user); if (err) return err; err = register_key_type(&key_type_fscrypt_provisioning); if (err) goto err_unregister_fscrypt_user; return 0; err_unregister_fscrypt_user: unregister_key_type(&key_type_fscrypt_user); return err; }