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_ONCE(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 super_block *sb,
83 struct fscrypt_master_key *mk)
87 if (!refcount_dec_and_test(&mk->mk_active_refs))
90 * No active references left, so complete the full removal of this
91 * fscrypt_master_key struct by removing it from the keyring and
92 * destroying any subkeys embedded in it.
95 if (WARN_ON_ONCE(!sb->s_master_keys))
97 spin_lock(&sb->s_master_keys->lock);
98 hlist_del_rcu(&mk->mk_node);
99 spin_unlock(&sb->s_master_keys->lock);
102 * ->mk_active_refs == 0 implies that ->mk_secret is not present and
103 * that ->mk_decrypted_inodes is empty.
105 WARN_ON_ONCE(is_master_key_secret_present(&mk->mk_secret));
106 WARN_ON_ONCE(!list_empty(&mk->mk_decrypted_inodes));
108 for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {
109 fscrypt_destroy_prepared_key(
110 sb, &mk->mk_direct_keys[i]);
111 fscrypt_destroy_prepared_key(
112 sb, &mk->mk_iv_ino_lblk_64_keys[i]);
113 fscrypt_destroy_prepared_key(
114 sb, &mk->mk_iv_ino_lblk_32_keys[i]);
116 memzero_explicit(&mk->mk_ino_hash_key,
117 sizeof(mk->mk_ino_hash_key));
118 mk->mk_ino_hash_key_initialized = false;
120 /* Drop the structural ref associated with the active refs. */
121 fscrypt_put_master_key(mk);
124 static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
126 if (spec->__reserved)
128 return master_key_spec_len(spec) != 0;
131 static int fscrypt_user_key_instantiate(struct key *key,
132 struct key_preparsed_payload *prep)
135 * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
136 * each key, regardless of the exact key size. The amount of memory
137 * actually used is greater than the size of the raw key anyway.
139 return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
142 static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
144 seq_puts(m, key->description);
148 * Type of key in ->mk_users. Each key of this type represents a particular
149 * user who has added a particular master key.
151 * Note that the name of this key type really should be something like
152 * ".fscrypt-user" instead of simply ".fscrypt". But the shorter name is chosen
153 * mainly for simplicity of presentation in /proc/keys when read by a non-root
154 * user. And it is expected to be rare that a key is actually added by multiple
155 * users, since users should keep their encryption keys confidential.
157 static struct key_type key_type_fscrypt_user = {
159 .instantiate = fscrypt_user_key_instantiate,
160 .describe = fscrypt_user_key_describe,
163 #define FSCRYPT_MK_USERS_DESCRIPTION_SIZE \
164 (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
165 CONST_STRLEN("-users") + 1)
167 #define FSCRYPT_MK_USER_DESCRIPTION_SIZE \
168 (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)
170 static void format_mk_users_keyring_description(
171 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
172 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
174 sprintf(description, "fscrypt-%*phN-users",
175 FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
178 static void format_mk_user_description(
179 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
180 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
183 sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
184 mk_identifier, __kuid_val(current_fsuid()));
187 /* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */
188 static int allocate_filesystem_keyring(struct super_block *sb)
190 struct fscrypt_keyring *keyring;
192 if (sb->s_master_keys)
195 keyring = kzalloc(sizeof(*keyring), GFP_KERNEL);
198 spin_lock_init(&keyring->lock);
200 * Pairs with the smp_load_acquire() in fscrypt_find_master_key().
201 * I.e., here we publish ->s_master_keys with a RELEASE barrier so that
202 * concurrent tasks can ACQUIRE it.
204 smp_store_release(&sb->s_master_keys, keyring);
209 * Release all encryption keys that have been added to the filesystem, along
210 * with the keyring that contains them.
212 * This is called at unmount time, after all potentially-encrypted inodes have
213 * been evicted. The filesystem's underlying block device(s) are still
214 * available at this time; this is important because after user file accesses
215 * have been allowed, this function may need to evict keys from the keyslots of
216 * an inline crypto engine, which requires the block device(s).
218 void fscrypt_destroy_keyring(struct super_block *sb)
220 struct fscrypt_keyring *keyring = sb->s_master_keys;
226 for (i = 0; i < ARRAY_SIZE(keyring->key_hashtable); i++) {
227 struct hlist_head *bucket = &keyring->key_hashtable[i];
228 struct fscrypt_master_key *mk;
229 struct hlist_node *tmp;
231 hlist_for_each_entry_safe(mk, tmp, bucket, mk_node) {
233 * Since all potentially-encrypted inodes were already
234 * evicted, every key remaining in the keyring should
235 * have an empty inode list, and should only still be in
236 * the keyring due to the single active ref associated
237 * with ->mk_secret. There should be no structural refs
238 * beyond the one associated with the active ref.
240 WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 1);
241 WARN_ON_ONCE(refcount_read(&mk->mk_struct_refs) != 1);
242 WARN_ON_ONCE(!is_master_key_secret_present(&mk->mk_secret));
243 wipe_master_key_secret(&mk->mk_secret);
244 fscrypt_put_master_key_activeref(sb, mk);
247 kfree_sensitive(keyring);
248 sb->s_master_keys = NULL;
251 static struct hlist_head *
252 fscrypt_mk_hash_bucket(struct fscrypt_keyring *keyring,
253 const struct fscrypt_key_specifier *mk_spec)
256 * Since key specifiers should be "random" values, it is sufficient to
257 * use a trivial hash function that just takes the first several bits of
260 unsigned long i = get_unaligned((unsigned long *)&mk_spec->u);
262 return &keyring->key_hashtable[i % ARRAY_SIZE(keyring->key_hashtable)];
266 * Find the specified master key struct in ->s_master_keys and take a structural
267 * ref to it. The structural ref guarantees that the key struct continues to
268 * exist, but it does *not* guarantee that ->s_master_keys continues to contain
269 * the key struct. The structural ref needs to be dropped by
270 * fscrypt_put_master_key(). Returns NULL if the key struct is not found.
272 struct fscrypt_master_key *
273 fscrypt_find_master_key(struct super_block *sb,
274 const struct fscrypt_key_specifier *mk_spec)
276 struct fscrypt_keyring *keyring;
277 struct hlist_head *bucket;
278 struct fscrypt_master_key *mk;
281 * Pairs with the smp_store_release() in allocate_filesystem_keyring().
282 * I.e., another task can publish ->s_master_keys concurrently,
283 * executing a RELEASE barrier. We need to use smp_load_acquire() here
284 * to safely ACQUIRE the memory the other task published.
286 keyring = smp_load_acquire(&sb->s_master_keys);
288 return NULL; /* No keyring yet, so no keys yet. */
290 bucket = fscrypt_mk_hash_bucket(keyring, mk_spec);
292 switch (mk_spec->type) {
293 case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
294 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
295 if (mk->mk_spec.type ==
296 FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
297 memcmp(mk->mk_spec.u.descriptor,
298 mk_spec->u.descriptor,
299 FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
300 refcount_inc_not_zero(&mk->mk_struct_refs))
304 case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
305 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
306 if (mk->mk_spec.type ==
307 FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
308 memcmp(mk->mk_spec.u.identifier,
309 mk_spec->u.identifier,
310 FSCRYPT_KEY_IDENTIFIER_SIZE) == 0 &&
311 refcount_inc_not_zero(&mk->mk_struct_refs))
322 static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
324 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
327 format_mk_users_keyring_description(description,
328 mk->mk_spec.u.identifier);
329 keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
330 current_cred(), KEY_POS_SEARCH |
331 KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
332 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
334 return PTR_ERR(keyring);
336 mk->mk_users = keyring;
341 * Find the current user's "key" in the master key's ->mk_users.
342 * Returns ERR_PTR(-ENOKEY) if not found.
344 static struct key *find_master_key_user(struct fscrypt_master_key *mk)
346 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
349 format_mk_user_description(description, mk->mk_spec.u.identifier);
352 * We need to mark the keyring reference as "possessed" so that we
353 * acquire permission to search it, via the KEY_POS_SEARCH permission.
355 keyref = keyring_search(make_key_ref(mk->mk_users, true /*possessed*/),
356 &key_type_fscrypt_user, description, false);
357 if (IS_ERR(keyref)) {
358 if (PTR_ERR(keyref) == -EAGAIN || /* not found */
359 PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
360 keyref = ERR_PTR(-ENOKEY);
361 return ERR_CAST(keyref);
363 return key_ref_to_ptr(keyref);
367 * Give the current user a "key" in ->mk_users. This charges the user's quota
368 * and marks the master key as added by the current user, so that it cannot be
369 * removed by another user with the key. Either ->mk_sem must be held for
370 * write, or the master key must be still undergoing initialization.
372 static int add_master_key_user(struct fscrypt_master_key *mk)
374 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
378 format_mk_user_description(description, mk->mk_spec.u.identifier);
379 mk_user = key_alloc(&key_type_fscrypt_user, description,
380 current_fsuid(), current_gid(), current_cred(),
381 KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
383 return PTR_ERR(mk_user);
385 err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
391 * Remove the current user's "key" from ->mk_users.
392 * ->mk_sem must be held for write.
394 * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
396 static int remove_master_key_user(struct fscrypt_master_key *mk)
401 mk_user = find_master_key_user(mk);
403 return PTR_ERR(mk_user);
404 err = key_unlink(mk->mk_users, mk_user);
410 * Allocate a new fscrypt_master_key, transfer the given secret over to it, and
411 * insert it into sb->s_master_keys.
413 static int add_new_master_key(struct super_block *sb,
414 struct fscrypt_master_key_secret *secret,
415 const struct fscrypt_key_specifier *mk_spec)
417 struct fscrypt_keyring *keyring = sb->s_master_keys;
418 struct fscrypt_master_key *mk;
421 mk = kzalloc(sizeof(*mk), GFP_KERNEL);
425 init_rwsem(&mk->mk_sem);
426 refcount_set(&mk->mk_struct_refs, 1);
427 mk->mk_spec = *mk_spec;
429 INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
430 spin_lock_init(&mk->mk_decrypted_inodes_lock);
432 if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
433 err = allocate_master_key_users_keyring(mk);
436 err = add_master_key_user(mk);
441 move_master_key_secret(&mk->mk_secret, secret);
442 refcount_set(&mk->mk_active_refs, 1); /* ->mk_secret is present */
444 spin_lock(&keyring->lock);
445 hlist_add_head_rcu(&mk->mk_node,
446 fscrypt_mk_hash_bucket(keyring, mk_spec));
447 spin_unlock(&keyring->lock);
451 fscrypt_put_master_key(mk);
457 static int add_existing_master_key(struct fscrypt_master_key *mk,
458 struct fscrypt_master_key_secret *secret)
463 * If the current user is already in ->mk_users, then there's nothing to
464 * do. Otherwise, we need to add the user to ->mk_users. (Neither is
465 * applicable for v1 policy keys, which have NULL ->mk_users.)
468 struct key *mk_user = find_master_key_user(mk);
470 if (mk_user != ERR_PTR(-ENOKEY)) {
472 return PTR_ERR(mk_user);
476 err = add_master_key_user(mk);
481 /* Re-add the secret if needed. */
482 if (!is_master_key_secret_present(&mk->mk_secret)) {
483 if (!refcount_inc_not_zero(&mk->mk_active_refs))
485 move_master_key_secret(&mk->mk_secret, secret);
491 static int do_add_master_key(struct super_block *sb,
492 struct fscrypt_master_key_secret *secret,
493 const struct fscrypt_key_specifier *mk_spec)
495 static DEFINE_MUTEX(fscrypt_add_key_mutex);
496 struct fscrypt_master_key *mk;
499 mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
501 mk = fscrypt_find_master_key(sb, mk_spec);
503 /* Didn't find the key in ->s_master_keys. Add it. */
504 err = allocate_filesystem_keyring(sb);
506 err = add_new_master_key(sb, secret, mk_spec);
509 * Found the key in ->s_master_keys. Re-add the secret if
510 * needed, and add the user to ->mk_users if needed.
512 down_write(&mk->mk_sem);
513 err = add_existing_master_key(mk, secret);
514 up_write(&mk->mk_sem);
515 if (err == KEY_DEAD) {
517 * We found a key struct, but it's already been fully
518 * removed. Ignore the old struct and add a new one.
519 * fscrypt_add_key_mutex means we don't need to worry
520 * about concurrent adds.
522 err = add_new_master_key(sb, secret, mk_spec);
524 fscrypt_put_master_key(mk);
526 mutex_unlock(&fscrypt_add_key_mutex);
530 static int add_master_key(struct super_block *sb,
531 struct fscrypt_master_key_secret *secret,
532 struct fscrypt_key_specifier *key_spec)
536 if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
537 err = fscrypt_init_hkdf(&secret->hkdf, secret->raw,
543 * Now that the HKDF context is initialized, the raw key is no
546 memzero_explicit(secret->raw, secret->size);
548 /* Calculate the key identifier */
549 err = fscrypt_hkdf_expand(&secret->hkdf,
550 HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0,
551 key_spec->u.identifier,
552 FSCRYPT_KEY_IDENTIFIER_SIZE);
556 return do_add_master_key(sb, secret, key_spec);
559 static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
561 const struct fscrypt_provisioning_key_payload *payload = prep->data;
563 if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||
564 prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)
567 if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
568 payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)
571 if (payload->__reserved)
574 prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);
575 if (!prep->payload.data[0])
578 prep->quotalen = prep->datalen;
582 static void fscrypt_provisioning_key_free_preparse(
583 struct key_preparsed_payload *prep)
585 kfree_sensitive(prep->payload.data[0]);
588 static void fscrypt_provisioning_key_describe(const struct key *key,
591 seq_puts(m, key->description);
592 if (key_is_positive(key)) {
593 const struct fscrypt_provisioning_key_payload *payload =
594 key->payload.data[0];
596 seq_printf(m, ": %u [%u]", key->datalen, payload->type);
600 static void fscrypt_provisioning_key_destroy(struct key *key)
602 kfree_sensitive(key->payload.data[0]);
605 static struct key_type key_type_fscrypt_provisioning = {
606 .name = "fscrypt-provisioning",
607 .preparse = fscrypt_provisioning_key_preparse,
608 .free_preparse = fscrypt_provisioning_key_free_preparse,
609 .instantiate = generic_key_instantiate,
610 .describe = fscrypt_provisioning_key_describe,
611 .destroy = fscrypt_provisioning_key_destroy,
615 * Retrieve the raw key from the Linux keyring key specified by 'key_id', and
616 * store it into 'secret'.
618 * The key must be of type "fscrypt-provisioning" and must have the field
619 * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's
620 * only usable with fscrypt with the particular KDF version identified by
621 * 'type'. We don't use the "logon" key type because there's no way to
622 * completely restrict the use of such keys; they can be used by any kernel API
623 * that accepts "logon" keys and doesn't require a specific service prefix.
625 * The ability to specify the key via Linux keyring key is intended for cases
626 * where userspace needs to re-add keys after the filesystem is unmounted and
627 * re-mounted. Most users should just provide the raw key directly instead.
629 static int get_keyring_key(u32 key_id, u32 type,
630 struct fscrypt_master_key_secret *secret)
634 const struct fscrypt_provisioning_key_payload *payload;
637 ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);
640 key = key_ref_to_ptr(ref);
642 if (key->type != &key_type_fscrypt_provisioning)
644 payload = key->payload.data[0];
646 /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */
647 if (payload->type != type)
650 secret->size = key->datalen - sizeof(*payload);
651 memcpy(secret->raw, payload->raw, secret->size);
663 * Add a master encryption key to the filesystem, causing all files which were
664 * encrypted with it to appear "unlocked" (decrypted) when accessed.
666 * When adding a key for use by v1 encryption policies, this ioctl is
667 * privileged, and userspace must provide the 'key_descriptor'.
669 * When adding a key for use by v2+ encryption policies, this ioctl is
670 * unprivileged. This is needed, in general, to allow non-root users to use
671 * encryption without encountering the visibility problems of process-subscribed
672 * keyrings and the inability to properly remove keys. This works by having
673 * each key identified by its cryptographically secure hash --- the
674 * 'key_identifier'. The cryptographic hash ensures that a malicious user
675 * cannot add the wrong key for a given identifier. Furthermore, each added key
676 * is charged to the appropriate user's quota for the keyrings service, which
677 * prevents a malicious user from adding too many keys. Finally, we forbid a
678 * user from removing a key while other users have added it too, which prevents
679 * a user who knows another user's key from causing a denial-of-service by
680 * removing it at an inopportune time. (We tolerate that a user who knows a key
681 * can prevent other users from removing it.)
683 * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
684 * Documentation/filesystems/fscrypt.rst.
686 int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
688 struct super_block *sb = file_inode(filp)->i_sb;
689 struct fscrypt_add_key_arg __user *uarg = _uarg;
690 struct fscrypt_add_key_arg arg;
691 struct fscrypt_master_key_secret secret;
694 if (copy_from_user(&arg, uarg, sizeof(arg)))
697 if (!valid_key_spec(&arg.key_spec))
700 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
704 * Only root can add keys that are identified by an arbitrary descriptor
705 * rather than by a cryptographic hash --- since otherwise a malicious
706 * user could add the wrong key.
708 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
709 !capable(CAP_SYS_ADMIN))
712 memset(&secret, 0, sizeof(secret));
714 if (arg.raw_size != 0)
716 err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);
718 goto out_wipe_secret;
720 if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
721 arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
723 secret.size = arg.raw_size;
725 if (copy_from_user(secret.raw, uarg->raw, secret.size))
726 goto out_wipe_secret;
729 err = add_master_key(sb, &secret, &arg.key_spec);
731 goto out_wipe_secret;
733 /* Return the key identifier to userspace, if applicable */
735 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
736 copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier,
737 FSCRYPT_KEY_IDENTIFIER_SIZE))
738 goto out_wipe_secret;
741 wipe_master_key_secret(&secret);
744 EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
747 fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret)
749 static u8 test_key[FSCRYPT_MAX_KEY_SIZE];
751 get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
753 memset(secret, 0, sizeof(*secret));
754 secret->size = FSCRYPT_MAX_KEY_SIZE;
755 memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE);
758 int fscrypt_get_test_dummy_key_identifier(
759 u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
761 struct fscrypt_master_key_secret secret;
764 fscrypt_get_test_dummy_secret(&secret);
766 err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
769 err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER,
770 NULL, 0, key_identifier,
771 FSCRYPT_KEY_IDENTIFIER_SIZE);
773 wipe_master_key_secret(&secret);
778 * fscrypt_add_test_dummy_key() - add the test dummy encryption key
779 * @sb: the filesystem instance to add the key to
780 * @key_spec: the key specifier of the test dummy encryption key
782 * Add the key for the test_dummy_encryption mount option to the filesystem. To
783 * prevent misuse of this mount option, a per-boot random key is used instead of
784 * a hardcoded one. This makes it so that any encrypted files created using
785 * this option won't be accessible after a reboot.
787 * Return: 0 on success, -errno on failure
789 int fscrypt_add_test_dummy_key(struct super_block *sb,
790 struct fscrypt_key_specifier *key_spec)
792 struct fscrypt_master_key_secret secret;
795 fscrypt_get_test_dummy_secret(&secret);
796 err = add_master_key(sb, &secret, key_spec);
797 wipe_master_key_secret(&secret);
802 * Verify that the current user has added a master key with the given identifier
803 * (returns -ENOKEY if not). This is needed to prevent a user from encrypting
804 * their files using some other user's key which they don't actually know.
805 * Cryptographically this isn't much of a problem, but the semantics of this
806 * would be a bit weird, so it's best to just forbid it.
808 * The system administrator (CAP_FOWNER) can override this, which should be
809 * enough for any use cases where encryption policies are being set using keys
810 * that were chosen ahead of time but aren't available at the moment.
812 * Note that the key may have already removed by the time this returns, but
813 * that's okay; we just care whether the key was there at some point.
815 * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
817 int fscrypt_verify_key_added(struct super_block *sb,
818 const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
820 struct fscrypt_key_specifier mk_spec;
821 struct fscrypt_master_key *mk;
825 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
826 memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
828 mk = fscrypt_find_master_key(sb, &mk_spec);
833 down_read(&mk->mk_sem);
834 mk_user = find_master_key_user(mk);
835 if (IS_ERR(mk_user)) {
836 err = PTR_ERR(mk_user);
841 up_read(&mk->mk_sem);
842 fscrypt_put_master_key(mk);
844 if (err == -ENOKEY && capable(CAP_FOWNER))
850 * Try to evict the inode's dentries from the dentry cache. If the inode is a
851 * directory, then it can have at most one dentry; however, that dentry may be
852 * pinned by child dentries, so first try to evict the children too.
854 static void shrink_dcache_inode(struct inode *inode)
856 struct dentry *dentry;
858 if (S_ISDIR(inode->i_mode)) {
859 dentry = d_find_any_alias(inode);
861 shrink_dcache_parent(dentry);
865 d_prune_aliases(inode);
868 static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
870 struct fscrypt_info *ci;
872 struct inode *toput_inode = NULL;
874 spin_lock(&mk->mk_decrypted_inodes_lock);
876 list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
877 inode = ci->ci_inode;
878 spin_lock(&inode->i_lock);
879 if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
880 spin_unlock(&inode->i_lock);
884 spin_unlock(&inode->i_lock);
885 spin_unlock(&mk->mk_decrypted_inodes_lock);
887 shrink_dcache_inode(inode);
891 spin_lock(&mk->mk_decrypted_inodes_lock);
894 spin_unlock(&mk->mk_decrypted_inodes_lock);
898 static int check_for_busy_inodes(struct super_block *sb,
899 struct fscrypt_master_key *mk)
901 struct list_head *pos;
902 size_t busy_count = 0;
904 char ino_str[50] = "";
906 spin_lock(&mk->mk_decrypted_inodes_lock);
908 list_for_each(pos, &mk->mk_decrypted_inodes)
911 if (busy_count == 0) {
912 spin_unlock(&mk->mk_decrypted_inodes_lock);
917 /* select an example file to show for debugging purposes */
918 struct inode *inode =
919 list_first_entry(&mk->mk_decrypted_inodes,
921 ci_master_key_link)->ci_inode;
924 spin_unlock(&mk->mk_decrypted_inodes_lock);
926 /* If the inode is currently being created, ino may still be 0. */
928 snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino);
931 "%s: %zu inode(s) still busy after removing key with %s %*phN%s",
932 sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
933 master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
938 static int try_to_lock_encrypted_files(struct super_block *sb,
939 struct fscrypt_master_key *mk)
945 * An inode can't be evicted while it is dirty or has dirty pages.
946 * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
948 * Just do it the easy way: call sync_filesystem(). It's overkill, but
949 * it works, and it's more important to minimize the amount of caches we
950 * drop than the amount of data we sync. Also, unprivileged users can
951 * already call sync_filesystem() via sys_syncfs() or sys_sync().
953 down_read(&sb->s_umount);
954 err1 = sync_filesystem(sb);
955 up_read(&sb->s_umount);
956 /* If a sync error occurs, still try to evict as much as possible. */
959 * Inodes are pinned by their dentries, so we have to evict their
960 * dentries. shrink_dcache_sb() would suffice, but would be overkill
961 * and inappropriate for use by unprivileged users. So instead go
962 * through the inodes' alias lists and try to evict each dentry.
964 evict_dentries_for_decrypted_inodes(mk);
967 * evict_dentries_for_decrypted_inodes() already iput() each inode in
968 * the list; any inodes for which that dropped the last reference will
969 * have been evicted due to fscrypt_drop_inode() detecting the key
970 * removal and telling the VFS to evict the inode. So to finish, we
971 * just need to check whether any inodes couldn't be evicted.
973 err2 = check_for_busy_inodes(sb, mk);
979 * Try to remove an fscrypt master encryption key.
981 * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's
982 * claim to the key, then removes the key itself if no other users have claims.
983 * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the
986 * To "remove the key itself", first we wipe the actual master key secret, so
987 * that no more inodes can be unlocked with it. Then we try to evict all cached
988 * inodes that had been unlocked with the key.
990 * If all inodes were evicted, then we unlink the fscrypt_master_key from the
991 * keyring. Otherwise it remains in the keyring in the "incompletely removed"
992 * state (without the actual secret key) where it tracks the list of remaining
993 * inodes. Userspace can execute the ioctl again later to retry eviction, or
994 * alternatively can re-add the secret key again.
996 * For more details, see the "Removing keys" section of
997 * Documentation/filesystems/fscrypt.rst.
999 static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
1001 struct super_block *sb = file_inode(filp)->i_sb;
1002 struct fscrypt_remove_key_arg __user *uarg = _uarg;
1003 struct fscrypt_remove_key_arg arg;
1004 struct fscrypt_master_key *mk;
1005 u32 status_flags = 0;
1009 if (copy_from_user(&arg, uarg, sizeof(arg)))
1012 if (!valid_key_spec(&arg.key_spec))
1015 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1019 * Only root can add and remove keys that are identified by an arbitrary
1020 * descriptor rather than by a cryptographic hash.
1022 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
1023 !capable(CAP_SYS_ADMIN))
1026 /* Find the key being removed. */
1027 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1030 down_write(&mk->mk_sem);
1032 /* If relevant, remove current user's (or all users) claim to the key */
1033 if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
1035 err = keyring_clear(mk->mk_users);
1037 err = remove_master_key_user(mk);
1039 up_write(&mk->mk_sem);
1042 if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
1044 * Other users have still added the key too. We removed
1045 * the current user's claim to the key, but we still
1046 * can't remove the key itself.
1049 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;
1051 up_write(&mk->mk_sem);
1056 /* No user claims remaining. Go ahead and wipe the secret. */
1058 if (is_master_key_secret_present(&mk->mk_secret)) {
1059 wipe_master_key_secret(&mk->mk_secret);
1060 fscrypt_put_master_key_activeref(sb, mk);
1063 inodes_remain = refcount_read(&mk->mk_active_refs) > 0;
1064 up_write(&mk->mk_sem);
1066 if (inodes_remain) {
1067 /* Some inodes still reference this key; try to evict them. */
1068 err = try_to_lock_encrypted_files(sb, mk);
1069 if (err == -EBUSY) {
1071 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;
1076 * We return 0 if we successfully did something: removed a claim to the
1077 * key, wiped the secret, or tried locking the files again. Users need
1078 * to check the informational status flags if they care whether the key
1079 * has been fully removed including all files locked.
1082 fscrypt_put_master_key(mk);
1084 err = put_user(status_flags, &uarg->removal_status_flags);
1088 int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)
1090 return do_remove_key(filp, uarg, false);
1092 EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
1094 int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)
1096 if (!capable(CAP_SYS_ADMIN))
1098 return do_remove_key(filp, uarg, true);
1100 EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);
1103 * Retrieve the status of an fscrypt master encryption key.
1105 * We set ->status to indicate whether the key is absent, present, or
1106 * incompletely removed. "Incompletely removed" means that the master key
1107 * secret has been removed, but some files which had been unlocked with it are
1108 * still in use. This field allows applications to easily determine the state
1109 * of an encrypted directory without using a hack such as trying to open a
1110 * regular file in it (which can confuse the "incompletely removed" state with
1111 * absent or present).
1113 * In addition, for v2 policy keys we allow applications to determine, via
1114 * ->status_flags and ->user_count, whether the key has been added by the
1115 * current user, by other users, or by both. Most applications should not need
1116 * this, since ordinarily only one user should know a given key. However, if a
1117 * secret key is shared by multiple users, applications may wish to add an
1118 * already-present key to prevent other users from removing it. This ioctl can
1119 * be used to check whether that really is the case before the work is done to
1120 * add the key --- which might e.g. require prompting the user for a passphrase.
1122 * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of
1123 * Documentation/filesystems/fscrypt.rst.
1125 int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
1127 struct super_block *sb = file_inode(filp)->i_sb;
1128 struct fscrypt_get_key_status_arg arg;
1129 struct fscrypt_master_key *mk;
1132 if (copy_from_user(&arg, uarg, sizeof(arg)))
1135 if (!valid_key_spec(&arg.key_spec))
1138 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1141 arg.status_flags = 0;
1143 memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
1145 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1147 arg.status = FSCRYPT_KEY_STATUS_ABSENT;
1151 down_read(&mk->mk_sem);
1153 if (!is_master_key_secret_present(&mk->mk_secret)) {
1154 arg.status = refcount_read(&mk->mk_active_refs) > 0 ?
1155 FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED :
1156 FSCRYPT_KEY_STATUS_ABSENT /* raced with full removal */;
1158 goto out_release_key;
1161 arg.status = FSCRYPT_KEY_STATUS_PRESENT;
1163 struct key *mk_user;
1165 arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
1166 mk_user = find_master_key_user(mk);
1167 if (!IS_ERR(mk_user)) {
1169 FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
1171 } else if (mk_user != ERR_PTR(-ENOKEY)) {
1172 err = PTR_ERR(mk_user);
1173 goto out_release_key;
1178 up_read(&mk->mk_sem);
1179 fscrypt_put_master_key(mk);
1181 if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
1185 EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
1187 int __init fscrypt_init_keyring(void)
1191 err = register_key_type(&key_type_fscrypt_user);
1195 err = register_key_type(&key_type_fscrypt_provisioning);
1197 goto err_unregister_fscrypt_user;
1201 err_unregister_fscrypt_user:
1202 unregister_key_type(&key_type_fscrypt_user);