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1// SPDX-License-Identifier: GPL-2.02/*3 * Filesystem-level keyring for fscrypt4 *5 * Copyright 2019 Google LLC6 */7 8/*9 * This file implements management of fscrypt master keys in the10 * filesystem-level keyring, including the ioctls:11 *12 * - FS_IOC_ADD_ENCRYPTION_KEY13 * - FS_IOC_REMOVE_ENCRYPTION_KEY14 * - FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS15 * - FS_IOC_GET_ENCRYPTION_KEY_STATUS16 *17 * See the "User API" section of Documentation/filesystems/fscrypt.rst for more18 * information about these ioctls.19 */20 21#include <linux/unaligned.h>22#include <crypto/skcipher.h>23#include <linux/key-type.h>24#include <linux/random.h>25#include <linux/seq_file.h>26 27#include "fscrypt_private.h"28 29/* The master encryption keys for a filesystem (->s_master_keys) */30struct fscrypt_keyring {31 /*32 * Lock that protects ->key_hashtable. It does *not* protect the33 * fscrypt_master_key structs themselves.34 */35 spinlock_t lock;36 37 /* Hash table that maps fscrypt_key_specifier to fscrypt_master_key */38 struct hlist_head key_hashtable[128];39};40 41static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)42{43 fscrypt_destroy_hkdf(&secret->hkdf);44 memzero_explicit(secret, sizeof(*secret));45}46 47static void move_master_key_secret(struct fscrypt_master_key_secret *dst,48 struct fscrypt_master_key_secret *src)49{50 memcpy(dst, src, sizeof(*dst));51 memzero_explicit(src, sizeof(*src));52}53 54static void fscrypt_free_master_key(struct rcu_head *head)55{56 struct fscrypt_master_key *mk =57 container_of(head, struct fscrypt_master_key, mk_rcu_head);58 /*59 * The master key secret and any embedded subkeys should have already60 * been wiped when the last active reference to the fscrypt_master_key61 * struct was dropped; doing it here would be unnecessarily late.62 * Nevertheless, use kfree_sensitive() in case anything was missed.63 */64 kfree_sensitive(mk);65}66 67void fscrypt_put_master_key(struct fscrypt_master_key *mk)68{69 if (!refcount_dec_and_test(&mk->mk_struct_refs))70 return;71 /*72 * No structural references left, so free ->mk_users, and also free the73 * fscrypt_master_key struct itself after an RCU grace period ensures74 * that concurrent keyring lookups can no longer find it.75 */76 WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 0);77 if (mk->mk_users) {78 /* Clear the keyring so the quota gets released right away. */79 keyring_clear(mk->mk_users);80 key_put(mk->mk_users);81 mk->mk_users = NULL;82 }83 call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key);84}85 86void fscrypt_put_master_key_activeref(struct super_block *sb,87 struct fscrypt_master_key *mk)88{89 size_t i;90 91 if (!refcount_dec_and_test(&mk->mk_active_refs))92 return;93 /*94 * No active references left, so complete the full removal of this95 * fscrypt_master_key struct by removing it from the keyring and96 * destroying any subkeys embedded in it.97 */98 99 if (WARN_ON_ONCE(!sb->s_master_keys))100 return;101 spin_lock(&sb->s_master_keys->lock);102 hlist_del_rcu(&mk->mk_node);103 spin_unlock(&sb->s_master_keys->lock);104 105 /*106 * ->mk_active_refs == 0 implies that ->mk_present is false and107 * ->mk_decrypted_inodes is empty.108 */109 WARN_ON_ONCE(mk->mk_present);110 WARN_ON_ONCE(!list_empty(&mk->mk_decrypted_inodes));111 112 for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {113 fscrypt_destroy_prepared_key(114 sb, &mk->mk_direct_keys[i]);115 fscrypt_destroy_prepared_key(116 sb, &mk->mk_iv_ino_lblk_64_keys[i]);117 fscrypt_destroy_prepared_key(118 sb, &mk->mk_iv_ino_lblk_32_keys[i]);119 }120 memzero_explicit(&mk->mk_ino_hash_key,121 sizeof(mk->mk_ino_hash_key));122 mk->mk_ino_hash_key_initialized = false;123 124 /* Drop the structural ref associated with the active refs. */125 fscrypt_put_master_key(mk);126}127 128/*129 * This transitions the key state from present to incompletely removed, and then130 * potentially to absent (depending on whether inodes remain).131 */132static void fscrypt_initiate_key_removal(struct super_block *sb,133 struct fscrypt_master_key *mk)134{135 WRITE_ONCE(mk->mk_present, false);136 wipe_master_key_secret(&mk->mk_secret);137 fscrypt_put_master_key_activeref(sb, mk);138}139 140static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)141{142 if (spec->__reserved)143 return false;144 return master_key_spec_len(spec) != 0;145}146 147static int fscrypt_user_key_instantiate(struct key *key,148 struct key_preparsed_payload *prep)149{150 /*151 * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for152 * each key, regardless of the exact key size. The amount of memory153 * actually used is greater than the size of the raw key anyway.154 */155 return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);156}157 158static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)159{160 seq_puts(m, key->description);161}162 163/*164 * Type of key in ->mk_users. Each key of this type represents a particular165 * user who has added a particular master key.166 *167 * Note that the name of this key type really should be something like168 * ".fscrypt-user" instead of simply ".fscrypt". But the shorter name is chosen169 * mainly for simplicity of presentation in /proc/keys when read by a non-root170 * user. And it is expected to be rare that a key is actually added by multiple171 * users, since users should keep their encryption keys confidential.172 */173static struct key_type key_type_fscrypt_user = {174 .name = ".fscrypt",175 .instantiate = fscrypt_user_key_instantiate,176 .describe = fscrypt_user_key_describe,177};178 179#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE \180 (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \181 CONST_STRLEN("-users") + 1)182 183#define FSCRYPT_MK_USER_DESCRIPTION_SIZE \184 (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)185 186static void format_mk_users_keyring_description(187 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],188 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])189{190 sprintf(description, "fscrypt-%*phN-users",191 FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);192}193 194static void format_mk_user_description(195 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],196 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])197{198 199 sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,200 mk_identifier, __kuid_val(current_fsuid()));201}202 203/* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */204static int allocate_filesystem_keyring(struct super_block *sb)205{206 struct fscrypt_keyring *keyring;207 208 if (sb->s_master_keys)209 return 0;210 211 keyring = kzalloc(sizeof(*keyring), GFP_KERNEL);212 if (!keyring)213 return -ENOMEM;214 spin_lock_init(&keyring->lock);215 /*216 * Pairs with the smp_load_acquire() in fscrypt_find_master_key().217 * I.e., here we publish ->s_master_keys with a RELEASE barrier so that218 * concurrent tasks can ACQUIRE it.219 */220 smp_store_release(&sb->s_master_keys, keyring);221 return 0;222}223 224/*225 * Release all encryption keys that have been added to the filesystem, along226 * with the keyring that contains them.227 *228 * This is called at unmount time, after all potentially-encrypted inodes have229 * been evicted. The filesystem's underlying block device(s) are still230 * available at this time; this is important because after user file accesses231 * have been allowed, this function may need to evict keys from the keyslots of232 * an inline crypto engine, which requires the block device(s).233 */234void fscrypt_destroy_keyring(struct super_block *sb)235{236 struct fscrypt_keyring *keyring = sb->s_master_keys;237 size_t i;238 239 if (!keyring)240 return;241 242 for (i = 0; i < ARRAY_SIZE(keyring->key_hashtable); i++) {243 struct hlist_head *bucket = &keyring->key_hashtable[i];244 struct fscrypt_master_key *mk;245 struct hlist_node *tmp;246 247 hlist_for_each_entry_safe(mk, tmp, bucket, mk_node) {248 /*249 * Since all potentially-encrypted inodes were already250 * evicted, every key remaining in the keyring should251 * have an empty inode list, and should only still be in252 * the keyring due to the single active ref associated253 * with ->mk_present. There should be no structural254 * refs beyond the one associated with the active ref.255 */256 WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 1);257 WARN_ON_ONCE(refcount_read(&mk->mk_struct_refs) != 1);258 WARN_ON_ONCE(!mk->mk_present);259 fscrypt_initiate_key_removal(sb, mk);260 }261 }262 kfree_sensitive(keyring);263 sb->s_master_keys = NULL;264}265 266static struct hlist_head *267fscrypt_mk_hash_bucket(struct fscrypt_keyring *keyring,268 const struct fscrypt_key_specifier *mk_spec)269{270 /*271 * Since key specifiers should be "random" values, it is sufficient to272 * use a trivial hash function that just takes the first several bits of273 * the key specifier.274 */275 unsigned long i = get_unaligned((unsigned long *)&mk_spec->u);276 277 return &keyring->key_hashtable[i % ARRAY_SIZE(keyring->key_hashtable)];278}279 280/*281 * Find the specified master key struct in ->s_master_keys and take a structural282 * ref to it. The structural ref guarantees that the key struct continues to283 * exist, but it does *not* guarantee that ->s_master_keys continues to contain284 * the key struct. The structural ref needs to be dropped by285 * fscrypt_put_master_key(). Returns NULL if the key struct is not found.286 */287struct fscrypt_master_key *288fscrypt_find_master_key(struct super_block *sb,289 const struct fscrypt_key_specifier *mk_spec)290{291 struct fscrypt_keyring *keyring;292 struct hlist_head *bucket;293 struct fscrypt_master_key *mk;294 295 /*296 * Pairs with the smp_store_release() in allocate_filesystem_keyring().297 * I.e., another task can publish ->s_master_keys concurrently,298 * executing a RELEASE barrier. We need to use smp_load_acquire() here299 * to safely ACQUIRE the memory the other task published.300 */301 keyring = smp_load_acquire(&sb->s_master_keys);302 if (keyring == NULL)303 return NULL; /* No keyring yet, so no keys yet. */304 305 bucket = fscrypt_mk_hash_bucket(keyring, mk_spec);306 rcu_read_lock();307 switch (mk_spec->type) {308 case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:309 hlist_for_each_entry_rcu(mk, bucket, mk_node) {310 if (mk->mk_spec.type ==311 FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&312 memcmp(mk->mk_spec.u.descriptor,313 mk_spec->u.descriptor,314 FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&315 refcount_inc_not_zero(&mk->mk_struct_refs))316 goto out;317 }318 break;319 case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:320 hlist_for_each_entry_rcu(mk, bucket, mk_node) {321 if (mk->mk_spec.type ==322 FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&323 memcmp(mk->mk_spec.u.identifier,324 mk_spec->u.identifier,325 FSCRYPT_KEY_IDENTIFIER_SIZE) == 0 &&326 refcount_inc_not_zero(&mk->mk_struct_refs))327 goto out;328 }329 break;330 }331 mk = NULL;332out:333 rcu_read_unlock();334 return mk;335}336 337static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)338{339 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];340 struct key *keyring;341 342 format_mk_users_keyring_description(description,343 mk->mk_spec.u.identifier);344 keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,345 current_cred(), KEY_POS_SEARCH |346 KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,347 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);348 if (IS_ERR(keyring))349 return PTR_ERR(keyring);350 351 mk->mk_users = keyring;352 return 0;353}354 355/*356 * Find the current user's "key" in the master key's ->mk_users.357 * Returns ERR_PTR(-ENOKEY) if not found.358 */359static struct key *find_master_key_user(struct fscrypt_master_key *mk)360{361 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];362 key_ref_t keyref;363 364 format_mk_user_description(description, mk->mk_spec.u.identifier);365 366 /*367 * We need to mark the keyring reference as "possessed" so that we368 * acquire permission to search it, via the KEY_POS_SEARCH permission.369 */370 keyref = keyring_search(make_key_ref(mk->mk_users, true /*possessed*/),371 &key_type_fscrypt_user, description, false);372 if (IS_ERR(keyref)) {373 if (PTR_ERR(keyref) == -EAGAIN || /* not found */374 PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */375 keyref = ERR_PTR(-ENOKEY);376 return ERR_CAST(keyref);377 }378 return key_ref_to_ptr(keyref);379}380 381/*382 * Give the current user a "key" in ->mk_users. This charges the user's quota383 * and marks the master key as added by the current user, so that it cannot be384 * removed by another user with the key. Either ->mk_sem must be held for385 * write, or the master key must be still undergoing initialization.386 */387static int add_master_key_user(struct fscrypt_master_key *mk)388{389 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];390 struct key *mk_user;391 int err;392 393 format_mk_user_description(description, mk->mk_spec.u.identifier);394 mk_user = key_alloc(&key_type_fscrypt_user, description,395 current_fsuid(), current_gid(), current_cred(),396 KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);397 if (IS_ERR(mk_user))398 return PTR_ERR(mk_user);399 400 err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);401 key_put(mk_user);402 return err;403}404 405/*406 * Remove the current user's "key" from ->mk_users.407 * ->mk_sem must be held for write.408 *409 * Returns 0 if removed, -ENOKEY if not found, or another -errno code.410 */411static int remove_master_key_user(struct fscrypt_master_key *mk)412{413 struct key *mk_user;414 int err;415 416 mk_user = find_master_key_user(mk);417 if (IS_ERR(mk_user))418 return PTR_ERR(mk_user);419 err = key_unlink(mk->mk_users, mk_user);420 key_put(mk_user);421 return err;422}423 424/*425 * Allocate a new fscrypt_master_key, transfer the given secret over to it, and426 * insert it into sb->s_master_keys.427 */428static int add_new_master_key(struct super_block *sb,429 struct fscrypt_master_key_secret *secret,430 const struct fscrypt_key_specifier *mk_spec)431{432 struct fscrypt_keyring *keyring = sb->s_master_keys;433 struct fscrypt_master_key *mk;434 int err;435 436 mk = kzalloc(sizeof(*mk), GFP_KERNEL);437 if (!mk)438 return -ENOMEM;439 440 init_rwsem(&mk->mk_sem);441 refcount_set(&mk->mk_struct_refs, 1);442 mk->mk_spec = *mk_spec;443 444 INIT_LIST_HEAD(&mk->mk_decrypted_inodes);445 spin_lock_init(&mk->mk_decrypted_inodes_lock);446 447 if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {448 err = allocate_master_key_users_keyring(mk);449 if (err)450 goto out_put;451 err = add_master_key_user(mk);452 if (err)453 goto out_put;454 }455 456 move_master_key_secret(&mk->mk_secret, secret);457 mk->mk_present = true;458 refcount_set(&mk->mk_active_refs, 1); /* ->mk_present is true */459 460 spin_lock(&keyring->lock);461 hlist_add_head_rcu(&mk->mk_node,462 fscrypt_mk_hash_bucket(keyring, mk_spec));463 spin_unlock(&keyring->lock);464 return 0;465 466out_put:467 fscrypt_put_master_key(mk);468 return err;469}470 471#define KEY_DEAD 1472 473static int add_existing_master_key(struct fscrypt_master_key *mk,474 struct fscrypt_master_key_secret *secret)475{476 int err;477 478 /*479 * If the current user is already in ->mk_users, then there's nothing to480 * do. Otherwise, we need to add the user to ->mk_users. (Neither is481 * applicable for v1 policy keys, which have NULL ->mk_users.)482 */483 if (mk->mk_users) {484 struct key *mk_user = find_master_key_user(mk);485 486 if (mk_user != ERR_PTR(-ENOKEY)) {487 if (IS_ERR(mk_user))488 return PTR_ERR(mk_user);489 key_put(mk_user);490 return 0;491 }492 err = add_master_key_user(mk);493 if (err)494 return err;495 }496 497 /* If the key is incompletely removed, make it present again. */498 if (!mk->mk_present) {499 if (!refcount_inc_not_zero(&mk->mk_active_refs)) {500 /*501 * Raced with the last active ref being dropped, so the502 * key has become, or is about to become, "absent".503 * Therefore, we need to allocate a new key struct.504 */505 return KEY_DEAD;506 }507 move_master_key_secret(&mk->mk_secret, secret);508 WRITE_ONCE(mk->mk_present, true);509 }510 511 return 0;512}513 514static int do_add_master_key(struct super_block *sb,515 struct fscrypt_master_key_secret *secret,516 const struct fscrypt_key_specifier *mk_spec)517{518 static DEFINE_MUTEX(fscrypt_add_key_mutex);519 struct fscrypt_master_key *mk;520 int err;521 522 mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */523 524 mk = fscrypt_find_master_key(sb, mk_spec);525 if (!mk) {526 /* Didn't find the key in ->s_master_keys. Add it. */527 err = allocate_filesystem_keyring(sb);528 if (!err)529 err = add_new_master_key(sb, secret, mk_spec);530 } else {531 /*532 * Found the key in ->s_master_keys. Add the user to ->mk_users533 * if needed, and make the key "present" again if possible.534 */535 down_write(&mk->mk_sem);536 err = add_existing_master_key(mk, secret);537 up_write(&mk->mk_sem);538 if (err == KEY_DEAD) {539 /*540 * We found a key struct, but it's already been fully541 * removed. Ignore the old struct and add a new one.542 * fscrypt_add_key_mutex means we don't need to worry543 * about concurrent adds.544 */545 err = add_new_master_key(sb, secret, mk_spec);546 }547 fscrypt_put_master_key(mk);548 }549 mutex_unlock(&fscrypt_add_key_mutex);550 return err;551}552 553static int add_master_key(struct super_block *sb,554 struct fscrypt_master_key_secret *secret,555 struct fscrypt_key_specifier *key_spec)556{557 int err;558 559 if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {560 err = fscrypt_init_hkdf(&secret->hkdf, secret->raw,561 secret->size);562 if (err)563 return err;564 565 /*566 * Now that the HKDF context is initialized, the raw key is no567 * longer needed.568 */569 memzero_explicit(secret->raw, secret->size);570 571 /* Calculate the key identifier */572 err = fscrypt_hkdf_expand(&secret->hkdf,573 HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0,574 key_spec->u.identifier,575 FSCRYPT_KEY_IDENTIFIER_SIZE);576 if (err)577 return err;578 }579 return do_add_master_key(sb, secret, key_spec);580}581 582static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)583{584 const struct fscrypt_provisioning_key_payload *payload = prep->data;585 586 if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||587 prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)588 return -EINVAL;589 590 if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&591 payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)592 return -EINVAL;593 594 if (payload->__reserved)595 return -EINVAL;596 597 prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);598 if (!prep->payload.data[0])599 return -ENOMEM;600 601 prep->quotalen = prep->datalen;602 return 0;603}604 605static void fscrypt_provisioning_key_free_preparse(606 struct key_preparsed_payload *prep)607{608 kfree_sensitive(prep->payload.data[0]);609}610 611static void fscrypt_provisioning_key_describe(const struct key *key,612 struct seq_file *m)613{614 seq_puts(m, key->description);615 if (key_is_positive(key)) {616 const struct fscrypt_provisioning_key_payload *payload =617 key->payload.data[0];618 619 seq_printf(m, ": %u [%u]", key->datalen, payload->type);620 }621}622 623static void fscrypt_provisioning_key_destroy(struct key *key)624{625 kfree_sensitive(key->payload.data[0]);626}627 628static struct key_type key_type_fscrypt_provisioning = {629 .name = "fscrypt-provisioning",630 .preparse = fscrypt_provisioning_key_preparse,631 .free_preparse = fscrypt_provisioning_key_free_preparse,632 .instantiate = generic_key_instantiate,633 .describe = fscrypt_provisioning_key_describe,634 .destroy = fscrypt_provisioning_key_destroy,635};636 637/*638 * Retrieve the raw key from the Linux keyring key specified by 'key_id', and639 * store it into 'secret'.640 *641 * The key must be of type "fscrypt-provisioning" and must have the field642 * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's643 * only usable with fscrypt with the particular KDF version identified by644 * 'type'. We don't use the "logon" key type because there's no way to645 * completely restrict the use of such keys; they can be used by any kernel API646 * that accepts "logon" keys and doesn't require a specific service prefix.647 *648 * The ability to specify the key via Linux keyring key is intended for cases649 * where userspace needs to re-add keys after the filesystem is unmounted and650 * re-mounted. Most users should just provide the raw key directly instead.651 */652static int get_keyring_key(u32 key_id, u32 type,653 struct fscrypt_master_key_secret *secret)654{655 key_ref_t ref;656 struct key *key;657 const struct fscrypt_provisioning_key_payload *payload;658 int err;659 660 ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);661 if (IS_ERR(ref))662 return PTR_ERR(ref);663 key = key_ref_to_ptr(ref);664 665 if (key->type != &key_type_fscrypt_provisioning)666 goto bad_key;667 payload = key->payload.data[0];668 669 /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */670 if (payload->type != type)671 goto bad_key;672 673 secret->size = key->datalen - sizeof(*payload);674 memcpy(secret->raw, payload->raw, secret->size);675 err = 0;676 goto out_put;677 678bad_key:679 err = -EKEYREJECTED;680out_put:681 key_ref_put(ref);682 return err;683}684 685/*686 * Add a master encryption key to the filesystem, causing all files which were687 * encrypted with it to appear "unlocked" (decrypted) when accessed.688 *689 * When adding a key for use by v1 encryption policies, this ioctl is690 * privileged, and userspace must provide the 'key_descriptor'.691 *692 * When adding a key for use by v2+ encryption policies, this ioctl is693 * unprivileged. This is needed, in general, to allow non-root users to use694 * encryption without encountering the visibility problems of process-subscribed695 * keyrings and the inability to properly remove keys. This works by having696 * each key identified by its cryptographically secure hash --- the697 * 'key_identifier'. The cryptographic hash ensures that a malicious user698 * cannot add the wrong key for a given identifier. Furthermore, each added key699 * is charged to the appropriate user's quota for the keyrings service, which700 * prevents a malicious user from adding too many keys. Finally, we forbid a701 * user from removing a key while other users have added it too, which prevents702 * a user who knows another user's key from causing a denial-of-service by703 * removing it at an inopportune time. (We tolerate that a user who knows a key704 * can prevent other users from removing it.)705 *706 * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of707 * Documentation/filesystems/fscrypt.rst.708 */709int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)710{711 struct super_block *sb = file_inode(filp)->i_sb;712 struct fscrypt_add_key_arg __user *uarg = _uarg;713 struct fscrypt_add_key_arg arg;714 struct fscrypt_master_key_secret secret;715 int err;716 717 if (copy_from_user(&arg, uarg, sizeof(arg)))718 return -EFAULT;719 720 if (!valid_key_spec(&arg.key_spec))721 return -EINVAL;722 723 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))724 return -EINVAL;725 726 /*727 * Only root can add keys that are identified by an arbitrary descriptor728 * rather than by a cryptographic hash --- since otherwise a malicious729 * user could add the wrong key.730 */731 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&732 !capable(CAP_SYS_ADMIN))733 return -EACCES;734 735 memset(&secret, 0, sizeof(secret));736 if (arg.key_id) {737 if (arg.raw_size != 0)738 return -EINVAL;739 err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);740 if (err)741 goto out_wipe_secret;742 } else {743 if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||744 arg.raw_size > FSCRYPT_MAX_KEY_SIZE)745 return -EINVAL;746 secret.size = arg.raw_size;747 err = -EFAULT;748 if (copy_from_user(secret.raw, uarg->raw, secret.size))749 goto out_wipe_secret;750 }751 752 err = add_master_key(sb, &secret, &arg.key_spec);753 if (err)754 goto out_wipe_secret;755 756 /* Return the key identifier to userspace, if applicable */757 err = -EFAULT;758 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&759 copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier,760 FSCRYPT_KEY_IDENTIFIER_SIZE))761 goto out_wipe_secret;762 err = 0;763out_wipe_secret:764 wipe_master_key_secret(&secret);765 return err;766}767EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);768 769static void770fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret)771{772 static u8 test_key[FSCRYPT_MAX_KEY_SIZE];773 774 get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);775 776 memset(secret, 0, sizeof(*secret));777 secret->size = FSCRYPT_MAX_KEY_SIZE;778 memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE);779}780 781int fscrypt_get_test_dummy_key_identifier(782 u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])783{784 struct fscrypt_master_key_secret secret;785 int err;786 787 fscrypt_get_test_dummy_secret(&secret);788 789 err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);790 if (err)791 goto out;792 err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER,793 NULL, 0, key_identifier,794 FSCRYPT_KEY_IDENTIFIER_SIZE);795out:796 wipe_master_key_secret(&secret);797 return err;798}799 800/**801 * fscrypt_add_test_dummy_key() - add the test dummy encryption key802 * @sb: the filesystem instance to add the key to803 * @key_spec: the key specifier of the test dummy encryption key804 *805 * Add the key for the test_dummy_encryption mount option to the filesystem. To806 * prevent misuse of this mount option, a per-boot random key is used instead of807 * a hardcoded one. This makes it so that any encrypted files created using808 * this option won't be accessible after a reboot.809 *810 * Return: 0 on success, -errno on failure811 */812int fscrypt_add_test_dummy_key(struct super_block *sb,813 struct fscrypt_key_specifier *key_spec)814{815 struct fscrypt_master_key_secret secret;816 int err;817 818 fscrypt_get_test_dummy_secret(&secret);819 err = add_master_key(sb, &secret, key_spec);820 wipe_master_key_secret(&secret);821 return err;822}823 824/*825 * Verify that the current user has added a master key with the given identifier826 * (returns -ENOKEY if not). This is needed to prevent a user from encrypting827 * their files using some other user's key which they don't actually know.828 * Cryptographically this isn't much of a problem, but the semantics of this829 * would be a bit weird, so it's best to just forbid it.830 *831 * The system administrator (CAP_FOWNER) can override this, which should be832 * enough for any use cases where encryption policies are being set using keys833 * that were chosen ahead of time but aren't available at the moment.834 *835 * Note that the key may have already removed by the time this returns, but836 * that's okay; we just care whether the key was there at some point.837 *838 * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code839 */840int fscrypt_verify_key_added(struct super_block *sb,841 const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])842{843 struct fscrypt_key_specifier mk_spec;844 struct fscrypt_master_key *mk;845 struct key *mk_user;846 int err;847 848 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;849 memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);850 851 mk = fscrypt_find_master_key(sb, &mk_spec);852 if (!mk) {853 err = -ENOKEY;854 goto out;855 }856 down_read(&mk->mk_sem);857 mk_user = find_master_key_user(mk);858 if (IS_ERR(mk_user)) {859 err = PTR_ERR(mk_user);860 } else {861 key_put(mk_user);862 err = 0;863 }864 up_read(&mk->mk_sem);865 fscrypt_put_master_key(mk);866out:867 if (err == -ENOKEY && capable(CAP_FOWNER))868 err = 0;869 return err;870}871 872/*873 * Try to evict the inode's dentries from the dentry cache. If the inode is a874 * directory, then it can have at most one dentry; however, that dentry may be875 * pinned by child dentries, so first try to evict the children too.876 */877static void shrink_dcache_inode(struct inode *inode)878{879 struct dentry *dentry;880 881 if (S_ISDIR(inode->i_mode)) {882 dentry = d_find_any_alias(inode);883 if (dentry) {884 shrink_dcache_parent(dentry);885 dput(dentry);886 }887 }888 d_prune_aliases(inode);889}890 891static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)892{893 struct fscrypt_inode_info *ci;894 struct inode *inode;895 struct inode *toput_inode = NULL;896 897 spin_lock(&mk->mk_decrypted_inodes_lock);898 899 list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {900 inode = ci->ci_inode;901 spin_lock(&inode->i_lock);902 if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {903 spin_unlock(&inode->i_lock);904 continue;905 }906 __iget(inode);907 spin_unlock(&inode->i_lock);908 spin_unlock(&mk->mk_decrypted_inodes_lock);909 910 shrink_dcache_inode(inode);911 iput(toput_inode);912 toput_inode = inode;913 914 spin_lock(&mk->mk_decrypted_inodes_lock);915 }916 917 spin_unlock(&mk->mk_decrypted_inodes_lock);918 iput(toput_inode);919}920 921static int check_for_busy_inodes(struct super_block *sb,922 struct fscrypt_master_key *mk)923{924 struct list_head *pos;925 size_t busy_count = 0;926 unsigned long ino;927 char ino_str[50] = "";928 929 spin_lock(&mk->mk_decrypted_inodes_lock);930 931 list_for_each(pos, &mk->mk_decrypted_inodes)932 busy_count++;933 934 if (busy_count == 0) {935 spin_unlock(&mk->mk_decrypted_inodes_lock);936 return 0;937 }938 939 {940 /* select an example file to show for debugging purposes */941 struct inode *inode =942 list_first_entry(&mk->mk_decrypted_inodes,943 struct fscrypt_inode_info,944 ci_master_key_link)->ci_inode;945 ino = inode->i_ino;946 }947 spin_unlock(&mk->mk_decrypted_inodes_lock);948 949 /* If the inode is currently being created, ino may still be 0. */950 if (ino)951 snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino);952 953 fscrypt_warn(NULL,954 "%s: %zu inode(s) still busy after removing key with %s %*phN%s",955 sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),956 master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,957 ino_str);958 return -EBUSY;959}960 961static int try_to_lock_encrypted_files(struct super_block *sb,962 struct fscrypt_master_key *mk)963{964 int err1;965 int err2;966 967 /*968 * An inode can't be evicted while it is dirty or has dirty pages.969 * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.970 *971 * Just do it the easy way: call sync_filesystem(). It's overkill, but972 * it works, and it's more important to minimize the amount of caches we973 * drop than the amount of data we sync. Also, unprivileged users can974 * already call sync_filesystem() via sys_syncfs() or sys_sync().975 */976 down_read(&sb->s_umount);977 err1 = sync_filesystem(sb);978 up_read(&sb->s_umount);979 /* If a sync error occurs, still try to evict as much as possible. */980 981 /*982 * Inodes are pinned by their dentries, so we have to evict their983 * dentries. shrink_dcache_sb() would suffice, but would be overkill984 * and inappropriate for use by unprivileged users. So instead go985 * through the inodes' alias lists and try to evict each dentry.986 */987 evict_dentries_for_decrypted_inodes(mk);988 989 /*990 * evict_dentries_for_decrypted_inodes() already iput() each inode in991 * the list; any inodes for which that dropped the last reference will992 * have been evicted due to fscrypt_drop_inode() detecting the key993 * removal and telling the VFS to evict the inode. So to finish, we994 * just need to check whether any inodes couldn't be evicted.995 */996 err2 = check_for_busy_inodes(sb, mk);997 998 return err1 ?: err2;999}1000 1001/*1002 * Try to remove an fscrypt master encryption key.1003 *1004 * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's1005 * claim to the key, then removes the key itself if no other users have claims.1006 * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the1007 * key itself.1008 *1009 * To "remove the key itself", first we transition the key to the "incompletely1010 * removed" state, so that no more inodes can be unlocked with it. Then we try1011 * to evict all cached inodes that had been unlocked with the key.1012 *1013 * If all inodes were evicted, then we unlink the fscrypt_master_key from the1014 * keyring. Otherwise it remains in the keyring in the "incompletely removed"1015 * state where it tracks the list of remaining inodes. Userspace can execute1016 * the ioctl again later to retry eviction, or alternatively can re-add the key.1017 *1018 * For more details, see the "Removing keys" section of1019 * Documentation/filesystems/fscrypt.rst.1020 */1021static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)1022{1023 struct super_block *sb = file_inode(filp)->i_sb;1024 struct fscrypt_remove_key_arg __user *uarg = _uarg;1025 struct fscrypt_remove_key_arg arg;1026 struct fscrypt_master_key *mk;1027 u32 status_flags = 0;1028 int err;1029 bool inodes_remain;1030 1031 if (copy_from_user(&arg, uarg, sizeof(arg)))1032 return -EFAULT;1033 1034 if (!valid_key_spec(&arg.key_spec))1035 return -EINVAL;1036 1037 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))1038 return -EINVAL;1039 1040 /*1041 * Only root can add and remove keys that are identified by an arbitrary1042 * descriptor rather than by a cryptographic hash.1043 */1044 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&1045 !capable(CAP_SYS_ADMIN))1046 return -EACCES;1047 1048 /* Find the key being removed. */1049 mk = fscrypt_find_master_key(sb, &arg.key_spec);1050 if (!mk)1051 return -ENOKEY;1052 down_write(&mk->mk_sem);1053 1054 /* If relevant, remove current user's (or all users) claim to the key */1055 if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {1056 if (all_users)1057 err = keyring_clear(mk->mk_users);1058 else1059 err = remove_master_key_user(mk);1060 if (err) {1061 up_write(&mk->mk_sem);1062 goto out_put_key;1063 }1064 if (mk->mk_users->keys.nr_leaves_on_tree != 0) {1065 /*1066 * Other users have still added the key too. We removed1067 * the current user's claim to the key, but we still1068 * can't remove the key itself.1069 */1070 status_flags |=1071 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;1072 err = 0;1073 up_write(&mk->mk_sem);1074 goto out_put_key;1075 }1076 }1077 1078 /* No user claims remaining. Initiate removal of the key. */1079 err = -ENOKEY;1080 if (mk->mk_present) {1081 fscrypt_initiate_key_removal(sb, mk);1082 err = 0;1083 }1084 inodes_remain = refcount_read(&mk->mk_active_refs) > 0;1085 up_write(&mk->mk_sem);1086 1087 if (inodes_remain) {1088 /* Some inodes still reference this key; try to evict them. */1089 err = try_to_lock_encrypted_files(sb, mk);1090 if (err == -EBUSY) {1091 status_flags |=1092 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;1093 err = 0;1094 }1095 }1096 /*1097 * We return 0 if we successfully did something: removed a claim to the1098 * key, initiated removal of the key, or tried locking the files again.1099 * Users need to check the informational status flags if they care1100 * whether the key has been fully removed including all files locked.1101 */1102out_put_key:1103 fscrypt_put_master_key(mk);1104 if (err == 0)1105 err = put_user(status_flags, &uarg->removal_status_flags);1106 return err;1107}1108 1109int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)1110{1111 return do_remove_key(filp, uarg, false);1112}1113EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);1114 1115int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)1116{1117 if (!capable(CAP_SYS_ADMIN))1118 return -EACCES;1119 return do_remove_key(filp, uarg, true);1120}1121EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);1122 1123/*1124 * Retrieve the status of an fscrypt master encryption key.1125 *1126 * We set ->status to indicate whether the key is absent, present, or1127 * incompletely removed. (For an explanation of what these statuses mean and1128 * how they are represented internally, see struct fscrypt_master_key.) This1129 * field allows applications to easily determine the status of an encrypted1130 * directory without using a hack such as trying to open a regular file in it1131 * (which can confuse the "incompletely removed" status with absent or present).1132 *1133 * In addition, for v2 policy keys we allow applications to determine, via1134 * ->status_flags and ->user_count, whether the key has been added by the1135 * current user, by other users, or by both. Most applications should not need1136 * this, since ordinarily only one user should know a given key. However, if a1137 * secret key is shared by multiple users, applications may wish to add an1138 * already-present key to prevent other users from removing it. This ioctl can1139 * be used to check whether that really is the case before the work is done to1140 * add the key --- which might e.g. require prompting the user for a passphrase.1141 *1142 * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of1143 * Documentation/filesystems/fscrypt.rst.1144 */1145int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)1146{1147 struct super_block *sb = file_inode(filp)->i_sb;1148 struct fscrypt_get_key_status_arg arg;1149 struct fscrypt_master_key *mk;1150 int err;1151 1152 if (copy_from_user(&arg, uarg, sizeof(arg)))1153 return -EFAULT;1154 1155 if (!valid_key_spec(&arg.key_spec))1156 return -EINVAL;1157 1158 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))1159 return -EINVAL;1160 1161 arg.status_flags = 0;1162 arg.user_count = 0;1163 memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));1164 1165 mk = fscrypt_find_master_key(sb, &arg.key_spec);1166 if (!mk) {1167 arg.status = FSCRYPT_KEY_STATUS_ABSENT;1168 err = 0;1169 goto out;1170 }1171 down_read(&mk->mk_sem);1172 1173 if (!mk->mk_present) {1174 arg.status = refcount_read(&mk->mk_active_refs) > 0 ?1175 FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED :1176 FSCRYPT_KEY_STATUS_ABSENT /* raced with full removal */;1177 err = 0;1178 goto out_release_key;1179 }1180 1181 arg.status = FSCRYPT_KEY_STATUS_PRESENT;1182 if (mk->mk_users) {1183 struct key *mk_user;1184 1185 arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;1186 mk_user = find_master_key_user(mk);1187 if (!IS_ERR(mk_user)) {1188 arg.status_flags |=1189 FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;1190 key_put(mk_user);1191 } else if (mk_user != ERR_PTR(-ENOKEY)) {1192 err = PTR_ERR(mk_user);1193 goto out_release_key;1194 }1195 }1196 err = 0;1197out_release_key:1198 up_read(&mk->mk_sem);1199 fscrypt_put_master_key(mk);1200out:1201 if (!err && copy_to_user(uarg, &arg, sizeof(arg)))1202 err = -EFAULT;1203 return err;1204}1205EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);1206 1207int __init fscrypt_init_keyring(void)1208{1209 int err;1210 1211 err = register_key_type(&key_type_fscrypt_user);1212 if (err)1213 return err;1214 1215 err = register_key_type(&key_type_fscrypt_provisioning);1216 if (err)1217 goto err_unregister_fscrypt_user;1218 1219 return 0;1220 1221err_unregister_fscrypt_user:1222 unregister_key_type(&key_type_fscrypt_user);1223 return err;1224}1225