641 lines
17 KiB
C
641 lines
17 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Filesystem-level keyring for fscrypt
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*
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* Copyright 2019 Google LLC
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*/
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/*
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* This file implements management of fscrypt master keys in the
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* filesystem-level keyring, including the ioctls:
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*
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* - FS_IOC_ADD_ENCRYPTION_KEY
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* - FS_IOC_REMOVE_ENCRYPTION_KEY
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* - FS_IOC_GET_ENCRYPTION_KEY_STATUS
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*
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* See the "User API" section of Documentation/filesystems/fscrypt.rst for more
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* information about these ioctls.
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*/
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#include <crypto/skcipher.h>
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#include <linux/key-type.h>
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#include <linux/seq_file.h>
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#include "fscrypt_private.h"
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static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)
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{
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fscrypt_destroy_hkdf(&secret->hkdf);
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memzero_explicit(secret, sizeof(*secret));
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}
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static void move_master_key_secret(struct fscrypt_master_key_secret *dst,
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struct fscrypt_master_key_secret *src)
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{
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memcpy(dst, src, sizeof(*dst));
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memzero_explicit(src, sizeof(*src));
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}
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static void free_master_key(struct fscrypt_master_key *mk)
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{
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size_t i;
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wipe_master_key_secret(&mk->mk_secret);
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for (i = 0; i < ARRAY_SIZE(mk->mk_mode_keys); i++)
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crypto_free_skcipher(mk->mk_mode_keys[i]);
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kzfree(mk);
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}
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static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
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{
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if (spec->__reserved)
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return false;
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return master_key_spec_len(spec) != 0;
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}
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static int fscrypt_key_instantiate(struct key *key,
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struct key_preparsed_payload *prep)
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{
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key->payload.data[0] = (struct fscrypt_master_key *)prep->data;
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return 0;
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}
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static void fscrypt_key_destroy(struct key *key)
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{
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free_master_key(key->payload.data[0]);
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}
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static void fscrypt_key_describe(const struct key *key, struct seq_file *m)
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{
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seq_puts(m, key->description);
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if (key_is_positive(key)) {
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const struct fscrypt_master_key *mk = key->payload.data[0];
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if (!is_master_key_secret_present(&mk->mk_secret))
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seq_puts(m, ": secret removed");
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}
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}
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/*
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* Type of key in ->s_master_keys. Each key of this type represents a master
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* key which has been added to the filesystem. Its payload is a
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* 'struct fscrypt_master_key'. The "." prefix in the key type name prevents
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* users from adding keys of this type via the keyrings syscalls rather than via
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* the intended method of FS_IOC_ADD_ENCRYPTION_KEY.
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*/
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static struct key_type key_type_fscrypt = {
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.name = "._fscrypt",
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.instantiate = fscrypt_key_instantiate,
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.destroy = fscrypt_key_destroy,
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.describe = fscrypt_key_describe,
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};
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/* Search ->s_master_keys */
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static struct key *search_fscrypt_keyring(struct key *keyring,
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struct key_type *type,
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const char *description)
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{
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/*
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* We need to mark the keyring reference as "possessed" so that we
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* acquire permission to search it, via the KEY_POS_SEARCH permission.
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*/
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key_ref_t keyref = make_key_ref(keyring, true /* possessed */);
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keyref = keyring_search(keyref, type, description, false);
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if (IS_ERR(keyref)) {
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if (PTR_ERR(keyref) == -EAGAIN || /* not found */
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PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
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keyref = ERR_PTR(-ENOKEY);
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return ERR_CAST(keyref);
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}
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return key_ref_to_ptr(keyref);
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}
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#define FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE \
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(CONST_STRLEN("fscrypt-") + FIELD_SIZEOF(struct super_block, s_id))
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#define FSCRYPT_MK_DESCRIPTION_SIZE (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + 1)
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static void format_fs_keyring_description(
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char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE],
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const struct super_block *sb)
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{
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sprintf(description, "fscrypt-%s", sb->s_id);
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}
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static void format_mk_description(
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char description[FSCRYPT_MK_DESCRIPTION_SIZE],
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const struct fscrypt_key_specifier *mk_spec)
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{
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sprintf(description, "%*phN",
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master_key_spec_len(mk_spec), (u8 *)&mk_spec->u);
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}
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/* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */
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static int allocate_filesystem_keyring(struct super_block *sb)
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{
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char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE];
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struct key *keyring;
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if (sb->s_master_keys)
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return 0;
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format_fs_keyring_description(description, sb);
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keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
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current_cred(), KEY_POS_SEARCH |
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KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
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KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
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if (IS_ERR(keyring))
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return PTR_ERR(keyring);
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/* Pairs with READ_ONCE() in fscrypt_find_master_key() */
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smp_store_release(&sb->s_master_keys, keyring);
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return 0;
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}
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void fscrypt_sb_free(struct super_block *sb)
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{
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key_put(sb->s_master_keys);
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sb->s_master_keys = NULL;
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}
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/*
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* Find the specified master key in ->s_master_keys.
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* Returns ERR_PTR(-ENOKEY) if not found.
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*/
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struct key *fscrypt_find_master_key(struct super_block *sb,
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const struct fscrypt_key_specifier *mk_spec)
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{
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struct key *keyring;
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char description[FSCRYPT_MK_DESCRIPTION_SIZE];
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/* pairs with smp_store_release() in allocate_filesystem_keyring() */
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keyring = READ_ONCE(sb->s_master_keys);
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if (keyring == NULL)
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return ERR_PTR(-ENOKEY); /* No keyring yet, so no keys yet. */
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format_mk_description(description, mk_spec);
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return search_fscrypt_keyring(keyring, &key_type_fscrypt, description);
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}
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/*
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* Allocate a new fscrypt_master_key which contains the given secret, set it as
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* the payload of a new 'struct key' of type fscrypt, and link the 'struct key'
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* into the given keyring. Synchronized by fscrypt_add_key_mutex.
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*/
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static int add_new_master_key(struct fscrypt_master_key_secret *secret,
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const struct fscrypt_key_specifier *mk_spec,
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struct key *keyring)
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{
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struct fscrypt_master_key *mk;
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char description[FSCRYPT_MK_DESCRIPTION_SIZE];
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struct key *key;
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int err;
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mk = kzalloc(sizeof(*mk), GFP_KERNEL);
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if (!mk)
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return -ENOMEM;
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mk->mk_spec = *mk_spec;
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move_master_key_secret(&mk->mk_secret, secret);
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refcount_set(&mk->mk_refcount, 1); /* secret is present */
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INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
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spin_lock_init(&mk->mk_decrypted_inodes_lock);
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format_mk_description(description, mk_spec);
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key = key_alloc(&key_type_fscrypt, description,
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GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
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KEY_POS_SEARCH | KEY_USR_SEARCH | KEY_USR_VIEW,
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KEY_ALLOC_NOT_IN_QUOTA, NULL);
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if (IS_ERR(key)) {
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err = PTR_ERR(key);
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goto out_free_mk;
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}
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err = key_instantiate_and_link(key, mk, sizeof(*mk), keyring, NULL);
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key_put(key);
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if (err)
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goto out_free_mk;
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return 0;
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out_free_mk:
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free_master_key(mk);
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return err;
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}
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#define KEY_DEAD 1
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static int add_existing_master_key(struct fscrypt_master_key *mk,
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struct fscrypt_master_key_secret *secret)
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{
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if (is_master_key_secret_present(&mk->mk_secret))
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return 0;
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if (!refcount_inc_not_zero(&mk->mk_refcount))
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return KEY_DEAD;
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move_master_key_secret(&mk->mk_secret, secret);
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return 0;
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}
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static int add_master_key(struct super_block *sb,
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struct fscrypt_master_key_secret *secret,
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const struct fscrypt_key_specifier *mk_spec)
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{
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static DEFINE_MUTEX(fscrypt_add_key_mutex);
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struct key *key;
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int err;
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mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
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retry:
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key = fscrypt_find_master_key(sb, mk_spec);
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if (IS_ERR(key)) {
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err = PTR_ERR(key);
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if (err != -ENOKEY)
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goto out_unlock;
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/* Didn't find the key in ->s_master_keys. Add it. */
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err = allocate_filesystem_keyring(sb);
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if (err)
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goto out_unlock;
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err = add_new_master_key(secret, mk_spec, sb->s_master_keys);
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} else {
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/*
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* Found the key in ->s_master_keys. Re-add the secret if
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* needed.
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*/
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down_write(&key->sem);
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err = add_existing_master_key(key->payload.data[0], secret);
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up_write(&key->sem);
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if (err == KEY_DEAD) {
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/* Key being removed or needs to be removed */
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key_invalidate(key);
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key_put(key);
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goto retry;
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}
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key_put(key);
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}
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out_unlock:
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mutex_unlock(&fscrypt_add_key_mutex);
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return err;
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}
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/*
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* Add a master encryption key to the filesystem, causing all files which were
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* encrypted with it to appear "unlocked" (decrypted) when accessed.
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*
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* For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
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* Documentation/filesystems/fscrypt.rst.
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*/
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int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
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{
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struct super_block *sb = file_inode(filp)->i_sb;
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struct fscrypt_add_key_arg __user *uarg = _uarg;
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struct fscrypt_add_key_arg arg;
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struct fscrypt_master_key_secret secret;
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int err;
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if (copy_from_user(&arg, uarg, sizeof(arg)))
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return -EFAULT;
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if (!valid_key_spec(&arg.key_spec))
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return -EINVAL;
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if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
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arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
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return -EINVAL;
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if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
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return -EINVAL;
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memset(&secret, 0, sizeof(secret));
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secret.size = arg.raw_size;
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err = -EFAULT;
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if (copy_from_user(secret.raw, uarg->raw, secret.size))
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goto out_wipe_secret;
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err = -EACCES;
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if (!capable(CAP_SYS_ADMIN))
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goto out_wipe_secret;
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if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
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err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
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if (err)
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goto out_wipe_secret;
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/*
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* Now that the HKDF context is initialized, the raw key is no
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* longer needed.
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*/
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memzero_explicit(secret.raw, secret.size);
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/* Calculate the key identifier and return it to userspace. */
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err = fscrypt_hkdf_expand(&secret.hkdf,
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HKDF_CONTEXT_KEY_IDENTIFIER,
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NULL, 0, arg.key_spec.u.identifier,
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FSCRYPT_KEY_IDENTIFIER_SIZE);
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if (err)
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goto out_wipe_secret;
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err = -EFAULT;
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if (copy_to_user(uarg->key_spec.u.identifier,
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arg.key_spec.u.identifier,
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FSCRYPT_KEY_IDENTIFIER_SIZE))
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goto out_wipe_secret;
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}
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err = add_master_key(sb, &secret, &arg.key_spec);
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out_wipe_secret:
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wipe_master_key_secret(&secret);
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return err;
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}
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EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
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/*
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* Try to evict the inode's dentries from the dentry cache. If the inode is a
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* directory, then it can have at most one dentry; however, that dentry may be
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* pinned by child dentries, so first try to evict the children too.
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*/
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static void shrink_dcache_inode(struct inode *inode)
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{
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struct dentry *dentry;
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if (S_ISDIR(inode->i_mode)) {
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dentry = d_find_any_alias(inode);
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if (dentry) {
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shrink_dcache_parent(dentry);
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dput(dentry);
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}
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}
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d_prune_aliases(inode);
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}
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static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
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{
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struct fscrypt_info *ci;
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struct inode *inode;
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struct inode *toput_inode = NULL;
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spin_lock(&mk->mk_decrypted_inodes_lock);
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list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
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inode = ci->ci_inode;
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spin_lock(&inode->i_lock);
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if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
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spin_unlock(&inode->i_lock);
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continue;
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}
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__iget(inode);
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spin_unlock(&inode->i_lock);
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spin_unlock(&mk->mk_decrypted_inodes_lock);
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shrink_dcache_inode(inode);
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iput(toput_inode);
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toput_inode = inode;
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spin_lock(&mk->mk_decrypted_inodes_lock);
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}
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spin_unlock(&mk->mk_decrypted_inodes_lock);
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iput(toput_inode);
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}
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static int check_for_busy_inodes(struct super_block *sb,
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struct fscrypt_master_key *mk)
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{
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struct list_head *pos;
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size_t busy_count = 0;
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unsigned long ino;
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struct dentry *dentry;
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char _path[256];
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char *path = NULL;
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spin_lock(&mk->mk_decrypted_inodes_lock);
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list_for_each(pos, &mk->mk_decrypted_inodes)
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busy_count++;
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if (busy_count == 0) {
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spin_unlock(&mk->mk_decrypted_inodes_lock);
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return 0;
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}
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{
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/* select an example file to show for debugging purposes */
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struct inode *inode =
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list_first_entry(&mk->mk_decrypted_inodes,
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struct fscrypt_info,
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ci_master_key_link)->ci_inode;
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ino = inode->i_ino;
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dentry = d_find_alias(inode);
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}
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spin_unlock(&mk->mk_decrypted_inodes_lock);
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if (dentry) {
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path = dentry_path(dentry, _path, sizeof(_path));
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dput(dentry);
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}
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if (IS_ERR_OR_NULL(path))
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path = "(unknown)";
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fscrypt_warn(NULL,
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"%s: %zu inode(s) still busy after removing key with %s %*phN, including ino %lu (%s)",
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sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
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master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
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ino, path);
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return -EBUSY;
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}
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static int try_to_lock_encrypted_files(struct super_block *sb,
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struct fscrypt_master_key *mk)
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{
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int err1;
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int err2;
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/*
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* An inode can't be evicted while it is dirty or has dirty pages.
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* Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
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*
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* Just do it the easy way: call sync_filesystem(). It's overkill, but
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* it works, and it's more important to minimize the amount of caches we
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* drop than the amount of data we sync. Also, unprivileged users can
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* already call sync_filesystem() via sys_syncfs() or sys_sync().
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*/
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down_read(&sb->s_umount);
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err1 = sync_filesystem(sb);
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up_read(&sb->s_umount);
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/* If a sync error occurs, still try to evict as much as possible. */
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/*
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* Inodes are pinned by their dentries, so we have to evict their
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* dentries. shrink_dcache_sb() would suffice, but would be overkill
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* and inappropriate for use by unprivileged users. So instead go
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* through the inodes' alias lists and try to evict each dentry.
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*/
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evict_dentries_for_decrypted_inodes(mk);
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/*
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* evict_dentries_for_decrypted_inodes() already iput() each inode in
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* the list; any inodes for which that dropped the last reference will
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* have been evicted due to fscrypt_drop_inode() detecting the key
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* removal and telling the VFS to evict the inode. So to finish, we
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* just need to check whether any inodes couldn't be evicted.
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*/
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err2 = check_for_busy_inodes(sb, mk);
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return err1 ?: err2;
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}
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/*
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* Try to remove an fscrypt master encryption key.
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*
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* First we wipe the actual master key secret, so that no more inodes can be
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* unlocked with it. Then we try to evict all cached inodes that had been
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* unlocked with the key.
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|
*
|
|
* 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 (without the actual secret key) where it tracks the list of remaining
|
|
* inodes. Userspace can execute the ioctl again later to retry eviction, or
|
|
* alternatively can re-add the secret key again.
|
|
*
|
|
* For more details, see the "Removing keys" section of
|
|
* Documentation/filesystems/fscrypt.rst.
|
|
*/
|
|
int fscrypt_ioctl_remove_key(struct file *filp, void __user *_uarg)
|
|
{
|
|
struct super_block *sb = file_inode(filp)->i_sb;
|
|
struct fscrypt_remove_key_arg __user *uarg = _uarg;
|
|
struct fscrypt_remove_key_arg arg;
|
|
struct key *key;
|
|
struct fscrypt_master_key *mk;
|
|
u32 status_flags = 0;
|
|
int err;
|
|
bool dead;
|
|
|
|
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;
|
|
|
|
if (!capable(CAP_SYS_ADMIN))
|
|
return -EACCES;
|
|
|
|
/* Find the key being removed. */
|
|
key = fscrypt_find_master_key(sb, &arg.key_spec);
|
|
if (IS_ERR(key))
|
|
return PTR_ERR(key);
|
|
mk = key->payload.data[0];
|
|
|
|
down_write(&key->sem);
|
|
|
|
/* Wipe the secret. */
|
|
dead = false;
|
|
if (is_master_key_secret_present(&mk->mk_secret)) {
|
|
wipe_master_key_secret(&mk->mk_secret);
|
|
dead = refcount_dec_and_test(&mk->mk_refcount);
|
|
}
|
|
up_write(&key->sem);
|
|
if (dead) {
|
|
/*
|
|
* No inodes reference the key, and we wiped the secret, so the
|
|
* key object is free to be removed from the keyring.
|
|
*/
|
|
key_invalidate(key);
|
|
err = 0;
|
|
} else {
|
|
/* 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: wiped the secret, 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.
|
|
*/
|
|
key_put(key);
|
|
if (err == 0)
|
|
err = put_user(status_flags, &uarg->removal_status_flags);
|
|
return err;
|
|
}
|
|
EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
|
|
|
|
/*
|
|
* Retrieve the status of an fscrypt master encryption key.
|
|
*
|
|
* We set ->status to indicate whether the key is absent, present, or
|
|
* incompletely removed. "Incompletely removed" means that the master key
|
|
* secret has been removed, but some files which had been unlocked with it are
|
|
* still in use. This field allows applications to easily determine the state
|
|
* of an encrypted directory without using a hack such as trying to open a
|
|
* regular file in it (which can confuse the "incompletely removed" state with
|
|
* absent or present).
|
|
*
|
|
* 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 key *key;
|
|
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;
|
|
|
|
memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
|
|
|
|
key = fscrypt_find_master_key(sb, &arg.key_spec);
|
|
if (IS_ERR(key)) {
|
|
if (key != ERR_PTR(-ENOKEY))
|
|
return PTR_ERR(key);
|
|
arg.status = FSCRYPT_KEY_STATUS_ABSENT;
|
|
err = 0;
|
|
goto out;
|
|
}
|
|
mk = key->payload.data[0];
|
|
down_read(&key->sem);
|
|
|
|
if (!is_master_key_secret_present(&mk->mk_secret)) {
|
|
arg.status = FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED;
|
|
err = 0;
|
|
goto out_release_key;
|
|
}
|
|
|
|
arg.status = FSCRYPT_KEY_STATUS_PRESENT;
|
|
err = 0;
|
|
out_release_key:
|
|
up_read(&key->sem);
|
|
key_put(key);
|
|
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)
|
|
{
|
|
return register_key_type(&key_type_fscrypt);
|
|
}
|