linux/fs/crypto/keyring.c
Eric Biggers 41b2ad80fd fscrypt: use WARN_ON_ONCE instead of WARN_ON
As per Linus's suggestion
(https://lore.kernel.org/r/CAHk-=whefxRGyNGzCzG6BVeM=5vnvgb-XhSeFJVxJyAxAF8XRA@mail.gmail.com),
use WARN_ON_ONCE instead of WARN_ON.  This barely adds any extra
overhead, and it makes it so that if any of these ever becomes reachable
(they shouldn't, but that's the point), the logs can't be flooded.

Link: https://lore.kernel.org/r/20230320233943.73600-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
2023-03-27 21:15:50 -07:00

1205 lines
36 KiB
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_ONCE(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 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_secret is not present and
* that ->mk_decrypted_inodes is empty.
*/
WARN_ON_ONCE(is_master_key_secret_present(&mk->mk_secret));
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);
}
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_secret. 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(!is_master_key_secret_present(&mk->mk_secret));
wipe_master_key_secret(&mk->mk_secret);
fscrypt_put_master_key_activeref(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);
refcount_set(&mk->mk_active_refs, 1); /* ->mk_secret is present */
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;
}
/* Re-add the secret if needed. */
if (!is_master_key_secret_present(&mk->mk_secret)) {
if (!refcount_inc_not_zero(&mk->mk_active_refs))
return KEY_DEAD;
move_master_key_secret(&mk->mk_secret, secret);
}
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. Re-add the secret if
* needed, and add the user to ->mk_users if needed.
*/
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_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_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 wipe the actual master key secret, 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 (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.
*/
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. Go ahead and wipe the secret. */
err = -ENOKEY;
if (is_master_key_secret_present(&mk->mk_secret)) {
wipe_master_key_secret(&mk->mk_secret);
fscrypt_put_master_key_activeref(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, 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.
*/
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. "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).
*
* 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 (!is_master_key_secret_present(&mk->mk_secret)) {
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;
}