path: root/fs/crypto/keyring.c

// 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 <asm/unaligned.h>
#include <crypto/skcipher.h>
#include <linux/key-type.h>
#include <linux/random.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(refcount_read(&mk->mk_active_refs) != 0);
	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 fscrypt_master_key *mk)
{
	struct super_block *sb = mk->mk_sb;
	struct fscrypt_keyring *keyring = sb->s_master_keys;
	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.
	 */

	spin_lock(&keyring->lock);
	hlist_del_rcu(&mk->mk_node);
	spin_unlock(&keyring->lock);

	/*
	 * ->mk_active_refs == 0 implies that ->mk_secret is not present and
	 * that ->mk_decrypted_inodes is empty.
	 */
	WARN_ON(is_master_key_secret_present(&mk->mk_secret));
	WARN_ON(!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);
}

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 somethi