1 // SPDX-License-Identifier: GPL-2.0
3 * Filesystem-level keyring for fscrypt
5 * Copyright 2019 Google LLC
9 * This file implements management of fscrypt master keys in the
10 * filesystem-level keyring, including the ioctls:
12 * - FS_IOC_ADD_ENCRYPTION_KEY
13 * - FS_IOC_REMOVE_ENCRYPTION_KEY
14 * - FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS
15 * - FS_IOC_GET_ENCRYPTION_KEY_STATUS
17 * See the "User API" section of Documentation/filesystems/fscrypt.rst for more
18 * information about these ioctls.
21 #include <asm/unaligned.h>
22 #include <crypto/skcipher.h>
23 #include <linux/key-type.h>
24 #include <linux/random.h>
25 #include <linux/seq_file.h>
27 #include "fscrypt_private.h"
29 /* The master encryption keys for a filesystem (->s_master_keys) */
30 struct fscrypt_keyring {
32 * Lock that protects ->key_hashtable. It does *not* protect the
33 * fscrypt_master_key structs themselves.
37 /* Hash table that maps fscrypt_key_specifier to fscrypt_master_key */
38 struct hlist_head key_hashtable[128];
41 static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)
43 fscrypt_destroy_hkdf(&secret->hkdf);
44 memzero_explicit(secret, sizeof(*secret));
47 static void move_master_key_secret(struct fscrypt_master_key_secret *dst,
48 struct fscrypt_master_key_secret *src)
50 memcpy(dst, src, sizeof(*dst));
51 memzero_explicit(src, sizeof(*src));
54 static void fscrypt_free_master_key(struct rcu_head *head)
56 struct fscrypt_master_key *mk =
57 container_of(head, struct fscrypt_master_key, mk_rcu_head);
59 * The master key secret and any embedded subkeys should have already
60 * been wiped when the last active reference to the fscrypt_master_key
61 * struct was dropped; doing it here would be unnecessarily late.
62 * Nevertheless, use kfree_sensitive() in case anything was missed.
67 void fscrypt_put_master_key(struct fscrypt_master_key *mk)
69 if (!refcount_dec_and_test(&mk->mk_struct_refs))
72 * No structural references left, so free ->mk_users, and also free the
73 * fscrypt_master_key struct itself after an RCU grace period ensures
74 * that concurrent keyring lookups can no longer find it.
76 WARN_ON(refcount_read(&mk->mk_active_refs) != 0);
77 key_put(mk->mk_users);
79 call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key);
82 void fscrypt_put_master_key_activeref(struct fscrypt_master_key *mk)
84 struct super_block *sb = mk->mk_sb;
85 struct fscrypt_keyring *keyring = sb->s_master_keys;
88 if (!refcount_dec_and_test(&mk->mk_active_refs))
91 * No active references left, so complete the full removal of this
92 * fscrypt_master_key struct by removing it from the keyring and
93 * destroying any subkeys embedded in it.
96 spin_lock(&keyring->lock);
97 hlist_del_rcu(&mk->mk_node);
98 spin_unlock(&keyring->lock);
101 * ->mk_active_refs == 0 implies that ->mk_secret is not present and
102 * that ->mk_decrypted_inodes is empty.
104 WARN_ON(is_master_key_secret_present(&mk->mk_secret));
105 WARN_ON(!list_empty(&mk->mk_decrypted_inodes));
107 for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {
108 fscrypt_destroy_prepared_key(
109 sb, &mk->mk_direct_keys[i]);
110 fscrypt_destroy_prepared_key(
111 sb, &mk->mk_iv_ino_lblk_64_keys[i]);
112 fscrypt_destroy_prepared_key(
113 sb, &mk->mk_iv_ino_lblk_32_keys[i]);
115 memzero_explicit(&mk->mk_ino_hash_key,
116 sizeof(mk->mk_ino_hash_key));
117 mk->mk_ino_hash_key_initialized = false;
119 /* Drop the structural ref associated with the active refs. */
120 fscrypt_put_master_key(mk);
123 static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
125 if (spec->__reserved)
127 return master_key_spec_len(spec) != 0;
130 static int fscrypt_user_key_instantiate(struct key *key,
131 struct key_preparsed_payload *prep)
134 * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
135 * each key, regardless of the exact key size. The amount of memory
136 * actually used is greater than the size of the raw key anyway.
138 return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
141 static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
143 seq_puts(m, key->description);
147 * Type of key in ->mk_users. Each key of this type represents a particular
148 * user who has added a particular master key.
150 * Note that the name of this key type really should be something like
151 * ".fscrypt-user" instead of simply ".fscrypt". But the shorter name is chosen
152 * mainly for simplicity of presentation in /proc/keys when read by a non-root
153 * user. And it is expected to be rare that a key is actually added by multiple
154 * users, since users should keep their encryption keys confidential.
156 static struct key_type key_type_fscrypt_user = {
158 .instantiate = fscrypt_user_key_instantiate,
159 .describe = fscrypt_user_key_describe,
162 #define FSCRYPT_MK_USERS_DESCRIPTION_SIZE \
163 (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
164 CONST_STRLEN("-users") + 1)
166 #define FSCRYPT_MK_USER_DESCRIPTION_SIZE \
167 (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)
169 static void format_mk_users_keyring_description(
170 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
171 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
173 sprintf(description, "fscrypt-%*phN-users",
174 FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
177 static void format_mk_user_description(
178 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
179 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
182 sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
183 mk_identifier, __kuid_val(current_fsuid()));
186 /* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */
187 static int allocate_filesystem_keyring(struct super_block *sb)
189 struct fscrypt_keyring *keyring;
191 if (sb->s_master_keys)
194 keyring = kzalloc(sizeof(*keyring), GFP_KERNEL);
197 spin_lock_init(&keyring->lock);
199 * Pairs with the smp_load_acquire() in fscrypt_find_master_key().
200 * I.e., here we publish ->s_master_keys with a RELEASE barrier so that
201 * concurrent tasks can ACQUIRE it.
203 smp_store_release(&sb->s_master_keys, keyring);
208 * Release all encryption keys that have been added to the filesystem, along
209 * with the keyring that contains them.
211 * This is called at unmount time. The filesystem's underlying block device(s)
212 * are still available at this time; this is important because after user file
213 * accesses have been allowed, this function may need to evict keys from the
214 * keyslots of an inline crypto engine, which requires the block device(s).
216 * This is also called when the super_block is being freed. This is needed to
217 * avoid a memory leak if mounting fails after the "test_dummy_encryption"
218 * option was processed, as in that case the unmount-time call isn't made.
220 void fscrypt_destroy_keyring(struct super_block *sb)
222 struct fscrypt_keyring *keyring = sb->s_master_keys;
228 for (i = 0; i < ARRAY_SIZE(keyring->key_hashtable); i++) {
229 struct hlist_head *bucket = &keyring->key_hashtable[i];
230 struct fscrypt_master_key *mk;
231 struct hlist_node *tmp;
233 hlist_for_each_entry_safe(mk, tmp, bucket, mk_node) {
235 * Since all inodes were already evicted, every key
236 * remaining in the keyring should have an empty inode
237 * list, and should only still be in the keyring due to
238 * the single active ref associated with ->mk_secret.
239 * There should be no structural refs beyond the one
240 * associated with the active ref.
242 WARN_ON(refcount_read(&mk->mk_active_refs) != 1);
243 WARN_ON(refcount_read(&mk->mk_struct_refs) != 1);
244 WARN_ON(!is_master_key_secret_present(&mk->mk_secret));
245 wipe_master_key_secret(&mk->mk_secret);
246 fscrypt_put_master_key_activeref(mk);
249 kfree_sensitive(keyring);
250 sb->s_master_keys = NULL;
253 static struct hlist_head *
254 fscrypt_mk_hash_bucket(struct fscrypt_keyring *keyring,
255 const struct fscrypt_key_specifier *mk_spec)
258 * Since key specifiers should be "random" values, it is sufficient to
259 * use a trivial hash function that just takes the first several bits of
262 unsigned long i = get_unaligned((unsigned long *)&mk_spec->u);
264 return &keyring->key_hashtable[i % ARRAY_SIZE(keyring->key_hashtable)];
268 * Find the specified master key struct in ->s_master_keys and take a structural
269 * ref to it. The structural ref guarantees that the key struct continues to
270 * exist, but it does *not* guarantee that ->s_master_keys continues to contain
271 * the key struct. The structural ref needs to be dropped by
272 * fscrypt_put_master_key(). Returns NULL if the key struct is not found.
274 struct fscrypt_master_key *
275 fscrypt_find_master_key(struct super_block *sb,
276 const struct fscrypt_key_specifier *mk_spec)
278 struct fscrypt_keyring *keyring;
279 struct hlist_head *bucket;
280 struct fscrypt_master_key *mk;
283 * Pairs with the smp_store_release() in allocate_filesystem_keyring().
284 * I.e., another task can publish ->s_master_keys concurrently,
285 * executing a RELEASE barrier. We need to use smp_load_acquire() here
286 * to safely ACQUIRE the memory the other task published.
288 keyring = smp_load_acquire(&sb->s_master_keys);
290 return NULL; /* No keyring yet, so no keys yet. */
292 bucket = fscrypt_mk_hash_bucket(keyring, mk_spec);
294 switch (mk_spec->type) {
295 case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
296 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
297 if (mk->mk_spec.type ==
298 FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
299 memcmp(mk->mk_spec.u.descriptor,
300 mk_spec->u.descriptor,
301 FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
302 refcount_inc_not_zero(&mk->mk_struct_refs))
306 case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
307 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
308 if (mk->mk_spec.type ==
309 FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
310 memcmp(mk->mk_spec.u.identifier,
311 mk_spec->u.identifier,
312 FSCRYPT_KEY_IDENTIFIER_SIZE) == 0 &&
313 refcount_inc_not_zero(&mk->mk_struct_refs))
324 static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
326 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
329 format_mk_users_keyring_description(description,
330 mk->mk_spec.u.identifier);
331 keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
332 current_cred(), KEY_POS_SEARCH |
333 KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
334 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
336 return PTR_ERR(keyring);
338 mk->mk_users = keyring;
343 * Find the current user's "key" in the master key's ->mk_users.
344 * Returns ERR_PTR(-ENOKEY) if not found.
346 static struct key *find_master_key_user(struct fscrypt_master_key *mk)
348 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
351 format_mk_user_description(description, mk->mk_spec.u.identifier);
354 * We need to mark the keyring reference as "possessed" so that we
355 * acquire permission to search it, via the KEY_POS_SEARCH permission.
357 keyref = keyring_search(make_key_ref(mk->mk_users, true /*possessed*/),
358 &key_type_fscrypt_user, description, false);
359 if (IS_ERR(keyref)) {
360 if (PTR_ERR(keyref) == -EAGAIN || /* not found */
361 PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
362 keyref = ERR_PTR(-ENOKEY);
363 return ERR_CAST(keyref);
365 return key_ref_to_ptr(keyref);
369 * Give the current user a "key" in ->mk_users. This charges the user's quota
370 * and marks the master key as added by the current user, so that it cannot be
371 * removed by another user with the key. Either ->mk_sem must be held for
372 * write, or the master key must be still undergoing initialization.
374 static int add_master_key_user(struct fscrypt_master_key *mk)
376 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
380 format_mk_user_description(description, mk->mk_spec.u.identifier);
381 mk_user = key_alloc(&key_type_fscrypt_user, description,
382 current_fsuid(), current_gid(), current_cred(),
383 KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
385 return PTR_ERR(mk_user);
387 err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
393 * Remove the current user's "key" from ->mk_users.
394 * ->mk_sem must be held for write.
396 * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
398 static int remove_master_key_user(struct fscrypt_master_key *mk)
403 mk_user = find_master_key_user(mk);
405 return PTR_ERR(mk_user);
406 err = key_unlink(mk->mk_users, mk_user);
412 * Allocate a new fscrypt_master_key, transfer the given secret over to it, and
413 * insert it into sb->s_master_keys.
415 static int add_new_master_key(struct super_block *sb,
416 struct fscrypt_master_key_secret *secret,
417 const struct fscrypt_key_specifier *mk_spec)
419 struct fscrypt_keyring *keyring = sb->s_master_keys;
420 struct fscrypt_master_key *mk;
423 mk = kzalloc(sizeof(*mk), GFP_KERNEL);
428 init_rwsem(&mk->mk_sem);
429 refcount_set(&mk->mk_struct_refs, 1);
430 mk->mk_spec = *mk_spec;
432 INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
433 spin_lock_init(&mk->mk_decrypted_inodes_lock);
435 if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
436 err = allocate_master_key_users_keyring(mk);
439 err = add_master_key_user(mk);
444 move_master_key_secret(&mk->mk_secret, secret);
445 refcount_set(&mk->mk_active_refs, 1); /* ->mk_secret is present */
447 spin_lock(&keyring->lock);
448 hlist_add_head_rcu(&mk->mk_node,
449 fscrypt_mk_hash_bucket(keyring, mk_spec));
450 spin_unlock(&keyring->lock);
454 fscrypt_put_master_key(mk);
460 static int add_existing_master_key(struct fscrypt_master_key *mk,
461 struct fscrypt_master_key_secret *secret)
466 * If the current user is already in ->mk_users, then there's nothing to
467 * do. Otherwise, we need to add the user to ->mk_users. (Neither is
468 * applicable for v1 policy keys, which have NULL ->mk_users.)
471 struct key *mk_user = find_master_key_user(mk);
473 if (mk_user != ERR_PTR(-ENOKEY)) {
475 return PTR_ERR(mk_user);
479 err = add_master_key_user(mk);
484 /* Re-add the secret if needed. */
485 if (!is_master_key_secret_present(&mk->mk_secret)) {
486 if (!refcount_inc_not_zero(&mk->mk_active_refs))
488 move_master_key_secret(&mk->mk_secret, secret);
494 static int do_add_master_key(struct super_block *sb,
495 struct fscrypt_master_key_secret *secret,
496 const struct fscrypt_key_specifier *mk_spec)
498 static DEFINE_MUTEX(fscrypt_add_key_mutex);
499 struct fscrypt_master_key *mk;
502 mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
504 mk = fscrypt_find_master_key(sb, mk_spec);
506 /* Didn't find the key in ->s_master_keys. Add it. */
507 err = allocate_filesystem_keyring(sb);
509 err = add_new_master_key(sb, secret, mk_spec);
512 * Found the key in ->s_master_keys. Re-add the secret if
513 * needed, and add the user to ->mk_users if needed.
515 down_write(&mk->mk_sem);
516 err = add_existing_master_key(mk, secret);
517 up_write(&mk->mk_sem);
518 if (err == KEY_DEAD) {
520 * We found a key struct, but it's already been fully
521 * removed. Ignore the old struct and add a new one.
522 * fscrypt_add_key_mutex means we don't need to worry
523 * about concurrent adds.
525 err = add_new_master_key(sb, secret, mk_spec);
527 fscrypt_put_master_key(mk);
529 mutex_unlock(&fscrypt_add_key_mutex);
533 static int add_master_key(struct super_block *sb,
534 struct fscrypt_master_key_secret *secret,
535 struct fscrypt_key_specifier *key_spec)
539 if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
540 err = fscrypt_init_hkdf(&secret->hkdf, secret->raw,
546 * Now that the HKDF context is initialized, the raw key is no
549 memzero_explicit(secret->raw, secret->size);
551 /* Calculate the key identifier */
552 err = fscrypt_hkdf_expand(&secret->hkdf,
553 HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0,
554 key_spec->u.identifier,
555 FSCRYPT_KEY_IDENTIFIER_SIZE);
559 return do_add_master_key(sb, secret, key_spec);
562 static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
564 const struct fscrypt_provisioning_key_payload *payload = prep->data;
566 if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||
567 prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)
570 if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
571 payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)
574 if (payload->__reserved)
577 prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);
578 if (!prep->payload.data[0])
581 prep->quotalen = prep->datalen;
585 static void fscrypt_provisioning_key_free_preparse(
586 struct key_preparsed_payload *prep)
588 kfree_sensitive(prep->payload.data[0]);
591 static void fscrypt_provisioning_key_describe(const struct key *key,
594 seq_puts(m, key->description);
595 if (key_is_positive(key)) {
596 const struct fscrypt_provisioning_key_payload *payload =
597 key->payload.data[0];
599 seq_printf(m, ": %u [%u]", key->datalen, payload->type);
603 static void fscrypt_provisioning_key_destroy(struct key *key)
605 kfree_sensitive(key->payload.data[0]);
608 static struct key_type key_type_fscrypt_provisioning = {
609 .name = "fscrypt-provisioning",
610 .preparse = fscrypt_provisioning_key_preparse,
611 .free_preparse = fscrypt_provisioning_key_free_preparse,
612 .instantiate = generic_key_instantiate,
613 .describe = fscrypt_provisioning_key_describe,
614 .destroy = fscrypt_provisioning_key_destroy,
618 * Retrieve the raw key from the Linux keyring key specified by 'key_id', and
619 * store it into 'secret'.
621 * The key must be of type "fscrypt-provisioning" and must have the field
622 * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's
623 * only usable with fscrypt with the particular KDF version identified by
624 * 'type'. We don't use the "logon" key type because there's no way to
625 * completely restrict the use of such keys; they can be used by any kernel API
626 * that accepts "logon" keys and doesn't require a specific service prefix.
628 * The ability to specify the key via Linux keyring key is intended for cases
629 * where userspace needs to re-add keys after the filesystem is unmounted and
630 * re-mounted. Most users should just provide the raw key directly instead.
632 static int get_keyring_key(u32 key_id, u32 type,
633 struct fscrypt_master_key_secret *secret)
637 const struct fscrypt_provisioning_key_payload *payload;
640 ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);
643 key = key_ref_to_ptr(ref);
645 if (key->type != &key_type_fscrypt_provisioning)
647 payload = key->payload.data[0];
649 /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */
650 if (payload->type != type)
653 secret->size = key->datalen - sizeof(*payload);
654 memcpy(secret->raw, payload->raw, secret->size);
666 * Add a master encryption key to the filesystem, causing all files which were
667 * encrypted with it to appear "unlocked" (decrypted) when accessed.
669 * When adding a key for use by v1 encryption policies, this ioctl is
670 * privileged, and userspace must provide the 'key_descriptor'.
672 * When adding a key for use by v2+ encryption policies, this ioctl is
673 * unprivileged. This is needed, in general, to allow non-root users to use
674 * encryption without encountering the visibility problems of process-subscribed
675 * keyrings and the inability to properly remove keys. This works by having
676 * each key identified by its cryptographically secure hash --- the
677 * 'key_identifier'. The cryptographic hash ensures that a malicious user
678 * cannot add the wrong key for a given identifier. Furthermore, each added key
679 * is charged to the appropriate user's quota for the keyrings service, which
680 * prevents a malicious user from adding too many keys. Finally, we forbid a
681 * user from removing a key while other users have added it too, which prevents
682 * a user who knows another user's key from causing a denial-of-service by
683 * removing it at an inopportune time. (We tolerate that a user who knows a key
684 * can prevent other users from removing it.)
686 * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
687 * Documentation/filesystems/fscrypt.rst.
689 int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
691 struct super_block *sb = file_inode(filp)->i_sb;
692 struct fscrypt_add_key_arg __user *uarg = _uarg;
693 struct fscrypt_add_key_arg arg;
694 struct fscrypt_master_key_secret secret;
697 if (copy_from_user(&arg, uarg, sizeof(arg)))
700 if (!valid_key_spec(&arg.key_spec))
703 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
707 * Only root can add keys that are identified by an arbitrary descriptor
708 * rather than by a cryptographic hash --- since otherwise a malicious
709 * user could add the wrong key.
711 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
712 !capable(CAP_SYS_ADMIN))
715 memset(&secret, 0, sizeof(secret));
717 if (arg.raw_size != 0)
719 err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);
721 goto out_wipe_secret;
723 if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
724 arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
726 secret.size = arg.raw_size;
728 if (copy_from_user(secret.raw, uarg->raw, secret.size))
729 goto out_wipe_secret;
732 err = add_master_key(sb, &secret, &arg.key_spec);
734 goto out_wipe_secret;
736 /* Return the key identifier to userspace, if applicable */
738 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
739 copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier,
740 FSCRYPT_KEY_IDENTIFIER_SIZE))
741 goto out_wipe_secret;
744 wipe_master_key_secret(&secret);
747 EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
750 fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret)
752 static u8 test_key[FSCRYPT_MAX_KEY_SIZE];
754 get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
756 memset(secret, 0, sizeof(*secret));
757 secret->size = FSCRYPT_MAX_KEY_SIZE;
758 memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE);
761 int fscrypt_get_test_dummy_key_identifier(
762 u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
764 struct fscrypt_master_key_secret secret;
767 fscrypt_get_test_dummy_secret(&secret);
769 err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
772 err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER,
773 NULL, 0, key_identifier,
774 FSCRYPT_KEY_IDENTIFIER_SIZE);
776 wipe_master_key_secret(&secret);
781 * fscrypt_add_test_dummy_key() - add the test dummy encryption key
782 * @sb: the filesystem instance to add the key to
783 * @dummy_policy: the encryption policy for test_dummy_encryption
785 * If needed, add the key for the test_dummy_encryption mount option to the
786 * filesystem. To prevent misuse of this mount option, a per-boot random key is
787 * used instead of a hardcoded one. This makes it so that any encrypted files
788 * created using this option won't be accessible after a reboot.
790 * Return: 0 on success, -errno on failure
792 int fscrypt_add_test_dummy_key(struct super_block *sb,
793 const struct fscrypt_dummy_policy *dummy_policy)
795 const union fscrypt_policy *policy = dummy_policy->policy;
796 struct fscrypt_key_specifier key_spec;
797 struct fscrypt_master_key_secret secret;
802 err = fscrypt_policy_to_key_spec(policy, &key_spec);
805 fscrypt_get_test_dummy_secret(&secret);
806 err = add_master_key(sb, &secret, &key_spec);
807 wipe_master_key_secret(&secret);
810 EXPORT_SYMBOL_GPL(fscrypt_add_test_dummy_key);
813 * Verify that the current user has added a master key with the given identifier
814 * (returns -ENOKEY if not). This is needed to prevent a user from encrypting
815 * their files using some other user's key which they don't actually know.
816 * Cryptographically this isn't much of a problem, but the semantics of this
817 * would be a bit weird, so it's best to just forbid it.
819 * The system administrator (CAP_FOWNER) can override this, which should be
820 * enough for any use cases where encryption policies are being set using keys
821 * that were chosen ahead of time but aren't available at the moment.
823 * Note that the key may have already removed by the time this returns, but
824 * that's okay; we just care whether the key was there at some point.
826 * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
828 int fscrypt_verify_key_added(struct super_block *sb,
829 const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
831 struct fscrypt_key_specifier mk_spec;
832 struct fscrypt_master_key *mk;
836 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
837 memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
839 mk = fscrypt_find_master_key(sb, &mk_spec);
844 down_read(&mk->mk_sem);
845 mk_user = find_master_key_user(mk);
846 if (IS_ERR(mk_user)) {
847 err = PTR_ERR(mk_user);
852 up_read(&mk->mk_sem);
853 fscrypt_put_master_key(mk);
855 if (err == -ENOKEY && capable(CAP_FOWNER))
861 * Try to evict the inode's dentries from the dentry cache. If the inode is a
862 * directory, then it can have at most one dentry; however, that dentry may be
863 * pinned by child dentries, so first try to evict the children too.
865 static void shrink_dcache_inode(struct inode *inode)
867 struct dentry *dentry;
869 if (S_ISDIR(inode->i_mode)) {
870 dentry = d_find_any_alias(inode);
872 shrink_dcache_parent(dentry);
876 d_prune_aliases(inode);
879 static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
881 struct fscrypt_info *ci;
883 struct inode *toput_inode = NULL;
885 spin_lock(&mk->mk_decrypted_inodes_lock);
887 list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
888 inode = ci->ci_inode;
889 spin_lock(&inode->i_lock);
890 if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
891 spin_unlock(&inode->i_lock);
895 spin_unlock(&inode->i_lock);
896 spin_unlock(&mk->mk_decrypted_inodes_lock);
898 shrink_dcache_inode(inode);
902 spin_lock(&mk->mk_decrypted_inodes_lock);
905 spin_unlock(&mk->mk_decrypted_inodes_lock);
909 static int check_for_busy_inodes(struct super_block *sb,
910 struct fscrypt_master_key *mk)
912 struct list_head *pos;
913 size_t busy_count = 0;
915 char ino_str[50] = "";
917 spin_lock(&mk->mk_decrypted_inodes_lock);
919 list_for_each(pos, &mk->mk_decrypted_inodes)
922 if (busy_count == 0) {
923 spin_unlock(&mk->mk_decrypted_inodes_lock);
928 /* select an example file to show for debugging purposes */
929 struct inode *inode =
930 list_first_entry(&mk->mk_decrypted_inodes,
932 ci_master_key_link)->ci_inode;
935 spin_unlock(&mk->mk_decrypted_inodes_lock);
937 /* If the inode is currently being created, ino may still be 0. */
939 snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino);
942 "%s: %zu inode(s) still busy after removing key with %s %*phN%s",
943 sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
944 master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
949 static int try_to_lock_encrypted_files(struct super_block *sb,
950 struct fscrypt_master_key *mk)
956 * An inode can't be evicted while it is dirty or has dirty pages.
957 * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
959 * Just do it the easy way: call sync_filesystem(). It's overkill, but
960 * it works, and it's more important to minimize the amount of caches we
961 * drop than the amount of data we sync. Also, unprivileged users can
962 * already call sync_filesystem() via sys_syncfs() or sys_sync().
964 down_read(&sb->s_umount);
965 err1 = sync_filesystem(sb);
966 up_read(&sb->s_umount);
967 /* If a sync error occurs, still try to evict as much as possible. */
970 * Inodes are pinned by their dentries, so we have to evict their
971 * dentries. shrink_dcache_sb() would suffice, but would be overkill
972 * and inappropriate for use by unprivileged users. So instead go
973 * through the inodes' alias lists and try to evict each dentry.
975 evict_dentries_for_decrypted_inodes(mk);
978 * evict_dentries_for_decrypted_inodes() already iput() each inode in
979 * the list; any inodes for which that dropped the last reference will
980 * have been evicted due to fscrypt_drop_inode() detecting the key
981 * removal and telling the VFS to evict the inode. So to finish, we
982 * just need to check whether any inodes couldn't be evicted.
984 err2 = check_for_busy_inodes(sb, mk);
990 * Try to remove an fscrypt master encryption key.
992 * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's
993 * claim to the key, then removes the key itself if no other users have claims.
994 * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the
997 * To "remove the key itself", first we wipe the actual master key secret, so
998 * that no more inodes can be unlocked with it. Then we try to evict all cached
999 * inodes that had been unlocked with the key.
1001 * If all inodes were evicted, then we unlink the fscrypt_master_key from the
1002 * keyring. Otherwise it remains in the keyring in the "incompletely removed"
1003 * state (without the actual secret key) where it tracks the list of remaining
1004 * inodes. Userspace can execute the ioctl again later to retry eviction, or
1005 * alternatively can re-add the secret key again.
1007 * For more details, see the "Removing keys" section of
1008 * Documentation/filesystems/fscrypt.rst.
1010 static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
1012 struct super_block *sb = file_inode(filp)->i_sb;
1013 struct fscrypt_remove_key_arg __user *uarg = _uarg;
1014 struct fscrypt_remove_key_arg arg;
1015 struct fscrypt_master_key *mk;
1016 u32 status_flags = 0;
1020 if (copy_from_user(&arg, uarg, sizeof(arg)))
1023 if (!valid_key_spec(&arg.key_spec))
1026 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1030 * Only root can add and remove keys that are identified by an arbitrary
1031 * descriptor rather than by a cryptographic hash.
1033 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
1034 !capable(CAP_SYS_ADMIN))
1037 /* Find the key being removed. */
1038 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1041 down_write(&mk->mk_sem);
1043 /* If relevant, remove current user's (or all users) claim to the key */
1044 if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
1046 err = keyring_clear(mk->mk_users);
1048 err = remove_master_key_user(mk);
1050 up_write(&mk->mk_sem);
1053 if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
1055 * Other users have still added the key too. We removed
1056 * the current user's claim to the key, but we still
1057 * can't remove the key itself.
1060 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;
1062 up_write(&mk->mk_sem);
1067 /* No user claims remaining. Go ahead and wipe the secret. */
1069 if (is_master_key_secret_present(&mk->mk_secret)) {
1070 wipe_master_key_secret(&mk->mk_secret);
1071 fscrypt_put_master_key_activeref(mk);
1074 inodes_remain = refcount_read(&mk->mk_active_refs) > 0;
1075 up_write(&mk->mk_sem);
1077 if (inodes_remain) {
1078 /* Some inodes still reference this key; try to evict them. */
1079 err = try_to_lock_encrypted_files(sb, mk);
1080 if (err == -EBUSY) {
1082 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;
1087 * We return 0 if we successfully did something: removed a claim to the
1088 * key, wiped the secret, or tried locking the files again. Users need
1089 * to check the informational status flags if they care whether the key
1090 * has been fully removed including all files locked.
1093 fscrypt_put_master_key(mk);
1095 err = put_user(status_flags, &uarg->removal_status_flags);
1099 int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)
1101 return do_remove_key(filp, uarg, false);
1103 EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
1105 int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)
1107 if (!capable(CAP_SYS_ADMIN))
1109 return do_remove_key(filp, uarg, true);
1111 EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);
1114 * Retrieve the status of an fscrypt master encryption key.
1116 * We set ->status to indicate whether the key is absent, present, or
1117 * incompletely removed. "Incompletely removed" means that the master key
1118 * secret has been removed, but some files which had been unlocked with it are
1119 * still in use. This field allows applications to easily determine the state
1120 * of an encrypted directory without using a hack such as trying to open a
1121 * regular file in it (which can confuse the "incompletely removed" state with
1122 * absent or present).
1124 * In addition, for v2 policy keys we allow applications to determine, via
1125 * ->status_flags and ->user_count, whether the key has been added by the
1126 * current user, by other users, or by both. Most applications should not need
1127 * this, since ordinarily only one user should know a given key. However, if a
1128 * secret key is shared by multiple users, applications may wish to add an
1129 * already-present key to prevent other users from removing it. This ioctl can
1130 * be used to check whether that really is the case before the work is done to
1131 * add the key --- which might e.g. require prompting the user for a passphrase.
1133 * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of
1134 * Documentation/filesystems/fscrypt.rst.
1136 int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
1138 struct super_block *sb = file_inode(filp)->i_sb;
1139 struct fscrypt_get_key_status_arg arg;
1140 struct fscrypt_master_key *mk;
1143 if (copy_from_user(&arg, uarg, sizeof(arg)))
1146 if (!valid_key_spec(&arg.key_spec))
1149 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1152 arg.status_flags = 0;
1154 memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
1156 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1158 arg.status = FSCRYPT_KEY_STATUS_ABSENT;
1162 down_read(&mk->mk_sem);
1164 if (!is_master_key_secret_present(&mk->mk_secret)) {
1165 arg.status = refcount_read(&mk->mk_active_refs) > 0 ?
1166 FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED :
1167 FSCRYPT_KEY_STATUS_ABSENT /* raced with full removal */;
1169 goto out_release_key;
1172 arg.status = FSCRYPT_KEY_STATUS_PRESENT;
1174 struct key *mk_user;
1176 arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
1177 mk_user = find_master_key_user(mk);
1178 if (!IS_ERR(mk_user)) {
1180 FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
1182 } else if (mk_user != ERR_PTR(-ENOKEY)) {
1183 err = PTR_ERR(mk_user);
1184 goto out_release_key;
1189 up_read(&mk->mk_sem);
1190 fscrypt_put_master_key(mk);
1192 if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
1196 EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
1198 int __init fscrypt_init_keyring(void)
1202 err = register_key_type(&key_type_fscrypt_user);
1206 err = register_key_type(&key_type_fscrypt_provisioning);
1208 goto err_unregister_fscrypt_user;
1212 err_unregister_fscrypt_user:
1213 unregister_key_type(&key_type_fscrypt_user);