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 // SPDX-License-Identifier: GPL-2.0
 /*
  * Filesystem-level keyring for fscrypt
  *
  * Copyright 2019 Google LLC
  */
 
 /*
  * This file implements management of fscrypt master keys in the
  * filesystem-level keyring, including the ioctls:
  *
  * - FS_IOC_ADD_ENCRYPTION_KEY
  * - FS_IOC_REMOVE_ENCRYPTION_KEY
  * - FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS
  * - FS_IOC_GET_ENCRYPTION_KEY_STATUS
  *
  * See the "User API" section of Documentation/filesystems/fscrypt.rst for more
  * information about these ioctls.
  */
 
 #include <crypto/skcipher.h>
 #include <linux/key-type.h>
 #include <linux/random.h>
 #include <linux/seq_file.h>
 
 #include "fscrypt_private.h"
 
 static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)
 {
     fscrypt_destroy_hkdf(&secret->hkdf);
     memzero_explicit(secret, sizeof(*secret));
 }
 
 static void move_master_key_secret(struct fscrypt_master_key_secret *dst,
                    struct fscrypt_master_key_secret *src)
 {
     memcpy(dst, src, sizeof(*dst));
     memzero_explicit(src, sizeof(*src));
 }
 
 static void free_master_key(struct fscrypt_master_key *mk)
 {
     size_t i;
 
     wipe_master_key_secret(&mk->mk_secret);
 
     for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {
         fscrypt_destroy_prepared_key(&mk->mk_direct_keys[i]);
         fscrypt_destroy_prepared_key(&mk->mk_iv_ino_lblk_64_keys[i]);
         fscrypt_destroy_prepared_key(&mk->mk_iv_ino_lblk_32_keys[i]);
     }
 
     key_put(mk->mk_users);
     kfree_sensitive(mk);
 }
 
 static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
 {
     if (spec->__reserved)
         return false;
     return master_key_spec_len(spec) != 0;
 }
 
 static int fscrypt_key_instantiate(struct key *key,
                    struct key_preparsed_payload *prep)
 {
     key->payload.data[0] = (struct fscrypt_master_key *)prep->data;
     return 0;
 }
 
 static void fscrypt_key_destroy(struct key *key)
 {
     free_master_key(key->payload.data[0]);
 }
 
 static void fscrypt_key_describe(const struct key *key, struct seq_file *m)
 {
     seq_puts(m, key->description);
 
     if (key_is_positive(key)) {
         const struct fscrypt_master_key *mk = key->payload.data[0];
 
         if (!is_master_key_secret_present(&mk->mk_secret))
             seq_puts(m, ": secret removed");
     }
 }
 
 /*
  * Type of key in ->s_master_keys.  Each key of this type represents a master
  * key which has been added to the filesystem.  Its payload is a
  * 'struct fscrypt_master_key'.  The "." prefix in the key type name prevents
  * users from adding keys of this type via the keyrings syscalls rather than via
  * the intended method of FS_IOC_ADD_ENCRYPTION_KEY.
  */
 static struct key_type key_type_fscrypt = {
     .name           = "._fscrypt",
     .instantiate        = fscrypt_key_instantiate,
     .destroy        = fscrypt_key_destroy,
     .describe       = fscrypt_key_describe,
 };
 
 static int fscrypt_user_key_instantiate(struct key *key,
                     struct key_preparsed_payload *prep)
 {
     /*
      * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
      * each key, regardless of the exact key size.  The amount of memory
      * actually used is greater than the size of the raw key anyway.
      */
     return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
 }
 
 static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
 {
     seq_puts(m, key->description);
 }
 
 /*
  * Type of key in ->mk_users.  Each key of this type represents a particular
  * user who has added a particular master key.
  *
  * Note that the name of this key type really should be something like
  * ".fscrypt-user" instead of simply ".fscrypt".  But the shorter name is chosen
  * mainly for simplicity of presentation in /proc/keys when read by a non-root
  * user.  And it is expected to be rare that a key is actually added by multiple
  * users, since users should keep their encryption keys confidential.
  */
 static struct key_type key_type_fscrypt_user = {
     .name           = ".fscrypt",
     .instantiate        = fscrypt_user_key_instantiate,
     .describe       = fscrypt_user_key_describe,
 };
 
 /* Search ->s_master_keys or ->mk_users */
 static struct key *search_fscrypt_keyring(struct key *keyring,
                       struct key_type *type,
                       const char *description)
 {
     /*
      * We need to mark the keyring reference as "possessed" so that we
      * acquire permission to search it, via the KEY_POS_SEARCH permission.
      */
     key_ref_t keyref = make_key_ref(keyring, true /* possessed */);
 
     keyref = keyring_search(keyref, type, description, false);
     if (IS_ERR(keyref)) {
         if (PTR_ERR(keyref) == -EAGAIN || /* not found */
             PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
             keyref = ERR_PTR(-ENOKEY);
         return ERR_CAST(keyref);
     }
     return key_ref_to_ptr(keyref);
 }
 
 #define FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE \
     (CONST_STRLEN("fscrypt-") + sizeof_field(struct super_block, s_id))
 
 #define FSCRYPT_MK_DESCRIPTION_SIZE (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + 1)
 
 #define FSCRYPT_MK_USERS_DESCRIPTION_SIZE   \
     (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
      CONST_STRLEN("-users") + 1)
 
 #define FSCRYPT_MK_USER_DESCRIPTION_SIZE    \
     (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)
 
 static void format_fs_keyring_description(
             char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE],
             const struct super_block *sb)
 {
     sprintf(description, "fscrypt-%s", sb->s_id);
 }
 
 static void format_mk_description(
             char description[FSCRYPT_MK_DESCRIPTION_SIZE],
             const struct fscrypt_key_specifier *mk_spec)
 {
     sprintf(description, "%*phN",
         master_key_spec_len(mk_spec), (u8 *)&mk_spec->u);
 }
 
 static void format_mk_users_keyring_description(
             char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
             const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
 {
     sprintf(description, "fscrypt-%*phN-users",
         FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
 }
 
 static void format_mk_user_description(
             char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
             const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
 {
 
     sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
         mk_identifier, __kuid_val(current_fsuid()));
 }
 
 /* Create ->s_master_keys if needed.  Synchronized by fscrypt_add_key_mutex. */
 static int allocate_filesystem_keyring(struct super_block *sb)
 {
     char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE];
     struct key *keyring;
 
     if (sb->s_master_keys)
         return 0;
 
     format_fs_keyring_description(description, sb);
     keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
                 current_cred(), KEY_POS_SEARCH |
                   KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
                 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
     if (IS_ERR(keyring))
         return PTR_ERR(keyring);
 
     /*
      * Pairs with the smp_load_acquire() in fscrypt_find_master_key().
      * I.e., here we publish ->s_master_keys with a RELEASE barrier so that
      * concurrent tasks can ACQUIRE it.
      */
     smp_store_release(&sb->s_master_keys, keyring);
     return 0;
 }
 
 void fscrypt_sb_free(struct super_block *sb)
 {
     key_put(sb->s_master_keys);
     sb->s_master_keys = NULL;
 }
 
 /*
  * Find the specified master key in ->s_master_keys.
  * Returns ERR_PTR(-ENOKEY) if not found.
  */
 struct key *fscrypt_find_master_key(struct super_block *sb,
                     const struct fscrypt_key_specifier *mk_spec)
 {
     struct key *keyring;
     char description[FSCRYPT_MK_DESCRIPTION_SIZE];
 
     /*
      * Pairs with the smp_store_release() in allocate_filesystem_keyring().
      * I.e., another task can publish ->s_master_keys concurrently,
      * executing a RELEASE barrier.  We need to use smp_load_acquire() here
      * to safely ACQUIRE the memory the other task published.
      */
     keyring = smp_load_acquire(&sb->s_master_keys);
     if (keyring == NULL)
         return ERR_PTR(-ENOKEY); /* No keyring yet, so no keys yet. */
 
     format_mk_description(description, mk_spec);
     return search_fscrypt_keyring(keyring, &key_type_fscrypt, description);
 }
 
 static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
 {
     char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
     struct key *keyring;
 
     format_mk_users_keyring_description(description,
                         mk->mk_spec.u.identifier);
     keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
                 current_cred(), KEY_POS_SEARCH |
                   KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
                 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
     if (IS_ERR(keyring))
         return PTR_ERR(keyring);
 
     mk->mk_users = keyring;
     return 0;
 }
 
 /*
  * Find the current user's "key" in the master key's ->mk_users.
  * Returns ERR_PTR(-ENOKEY) if not found.
  */
 static struct key *find_master_key_user(struct fscrypt_master_key *mk)
 {
     char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
 
     format_mk_user_description(description, mk->mk_spec.u.identifier);
     return search_fscrypt_keyring(mk->mk_users, &key_type_fscrypt_user,
                       description);
 }
 
 /*
  * Give the current user a "key" in ->mk_users.  This charges the user's quota
  * and marks the master key as added by the current user, so that it cannot be
  * removed by another user with the key.  Either the master key's key->sem must
  * be held for write, or the master key must be still undergoing initialization.
  */
 static int add_master_key_user(struct fscrypt_master_key *mk)
 {
     char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
     struct key *mk_user;
     int err;
 
     format_mk_user_description(description, mk->mk_spec.u.identifier);
     mk_user = key_alloc(&key_type_fscrypt_user, description,
                 current_fsuid(), current_gid(), current_cred(),
                 KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
     if (IS_ERR(mk_user))
         return PTR_ERR(mk_user);
 
     err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
     key_put(mk_user);
     return err;
 }
 
 /*
  * Remove the current user's "key" from ->mk_users.
  * The master key's key->sem must be held for write.
  *
  * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
  */
 static int remove_master_key_user(struct fscrypt_master_key *mk)
 {
     struct key *mk_user;
     int err;
 
     mk_user = find_master_key_user(mk);
     if (IS_ERR(mk_user))
         return PTR_ERR(mk_user);
     err = key_unlink(mk->mk_users, mk_user);
     key_put(mk_user);
     return err;
 }
 
 /*
  * Allocate a new fscrypt_master_key which contains the given secret, set it as
  * the payload of a new 'struct key' of type fscrypt, and link the 'struct key'
  * into the given keyring.  Synchronized by fscrypt_add_key_mutex.
  */
 static int add_new_master_key(struct fscrypt_master_key_secret *secret,
                   const struct fscrypt_key_specifier *mk_spec,
                   struct key *keyring)
 {
     struct fscrypt_master_key *mk;
     char description[FSCRYPT_MK_DESCRIPTION_SIZE];
     struct key *key;
     int err;
 
     mk = kzalloc(sizeof(*mk), GFP_KERNEL);
     if (!mk)
         return -ENOMEM;
 
     mk->mk_spec = *mk_spec;
 
     move_master_key_secret(&mk->mk_secret, secret);
 
     refcount_set(&mk->mk_refcount, 1); /* secret is present */
     INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
     spin_lock_init(&mk->mk_decrypted_inodes_lock);
 
     if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
         err = allocate_master_key_users_keyring(mk);
         if (err)
             goto out_free_mk;
         err = add_master_key_user(mk);
         if (err)
             goto out_free_mk;
     }
 
     /*
      * Note that we don't charge this key to anyone's quota, since when
      * ->mk_users is in use those keys are charged instead, and otherwise
      * (when ->mk_users isn't in use) only root can add these keys.
      */
     format_mk_description(description, mk_spec);
     key = key_alloc(&key_type_fscrypt, description,
             GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
             KEY_POS_SEARCH | KEY_USR_SEARCH | KEY_USR_VIEW,
             KEY_ALLOC_NOT_IN_QUOTA, NULL);
     if (IS_ERR(key)) {
         err = PTR_ERR(key);
         goto out_free_mk;
     }
     err = key_instantiate_and_link(key, mk, sizeof(*mk), keyring, NULL);
     key_put(key);
     if (err)
         goto out_free_mk;
 
     return 0;
 
 out_free_mk:
     free_master_key(mk);
     return err;
 }
 
 #define KEY_DEAD    1
 
 static int add_existing_master_key(struct fscrypt_master_key *mk,
                    struct fscrypt_master_key_secret *secret)
 {
     struct key *mk_user;
     bool rekey;
     int err;
 
     /*
      * If the current user is already in ->mk_users, then there's nothing to
      * do.  (Not applicable for v1 policy keys, which have NULL ->mk_users.)
      */
     if (mk->mk_users) {
         mk_user = find_master_key_user(mk);
         if (mk_user != ERR_PTR(-ENOKEY)) {
             if (IS_ERR(mk_user))
                 return PTR_ERR(mk_user);
             key_put(mk_user);
             return 0;
         }
     }
 
     /* If we'll be re-adding ->mk_secret, try to take the reference. */
     rekey = !is_master_key_secret_present(&mk->mk_secret);
     if (rekey && !refcount_inc_not_zero(&mk->mk_refcount))
         return KEY_DEAD;
 
     /* Add the current user to ->mk_users, if applicable. */
     if (mk->mk_users) {
         err = add_master_key_user(mk);
         if (err) {
             if (rekey && refcount_dec_and_test(&mk->mk_refcount))
                 return KEY_DEAD;
             return err;
         }
     }
 
     /* Re-add the secret if needed. */
     if (rekey)
         move_master_key_secret(&mk->mk_secret, secret);
     return 0;
 }
 
 static int do_add_master_key(struct super_block *sb,
                  struct fscrypt_master_key_secret *secret,
                  const struct fscrypt_key_specifier *mk_spec)
 {
     static DEFINE_MUTEX(fscrypt_add_key_mutex);
     struct key *key;
     int err;
 
     mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
 retry:
     key = fscrypt_find_master_key(sb, mk_spec);
     if (IS_ERR(key)) {
         err = PTR_ERR(key);
         if (err != -ENOKEY)
             goto out_unlock;
         /* Didn't find the key in ->s_master_keys.  Add it. */
         err = allocate_filesystem_keyring(sb);
         if (err)
             goto out_unlock;
         err = add_new_master_key(secret, mk_spec, sb->s_master_keys);
     } else {
         /*
          * Found the key in ->s_master_keys.  Re-add the secret if
          * needed, and add the user to ->mk_users if needed.
          */
         down_write(&key->sem);
         err = add_existing_master_key(key->payload.data[0], secret);
         up_write(&key->sem);
         if (err == KEY_DEAD) {
             /* Key being removed or needs to be removed */
             key_invalidate(key);
             key_put(key);
             goto retry;
         }
         key_put(key);
     }
 out_unlock:
     mutex_unlock(&fscrypt_add_key_mutex);
     return err;
 }
 
 static int add_master_key(struct super_block *sb,
               struct fscrypt_master_key_secret *secret,
               struct fscrypt_key_specifier *key_spec)
 {
     int err;
 
     if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
         err = fscrypt_init_hkdf(&secret->hkdf, secret->raw,
                     secret->size);
         if (err)
             return err;
 
         /*
          * Now that the HKDF context is initialized, the raw key is no
          * longer needed.
          */
         memzero_explicit(secret->raw, secret->size);
 
         /* Calculate the key identifier */
         err = fscrypt_hkdf_expand(&secret->hkdf,
                       HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0,
                       key_spec->u.identifier,
                       FSCRYPT_KEY_IDENTIFIER_SIZE);
         if (err)
             return err;
     }
     return do_add_master_key(sb, secret, key_spec);
 }
 
 static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
 {
     const struct fscrypt_provisioning_key_payload *payload = prep->data;
 
     if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||
         prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)
         return -EINVAL;
 
     if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
         payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)
         return -EINVAL;
 
     if (payload->__reserved)
         return -EINVAL;
 
     prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);
     if (!prep->payload.data[0])
         return -ENOMEM;
 
     prep->quotalen = prep->datalen;
     return 0;
 }
 
 static void fscrypt_provisioning_key_free_preparse(
                     struct key_preparsed_payload *prep)
 {
     kfree_sensitive(prep->payload.data[0]);
 }
 
 static void fscrypt_provisioning_key_describe(const struct key *key,
                           struct seq_file *m)
 {
     seq_puts(m, key->description);
     if (key_is_positive(key)) {
         const struct fscrypt_provisioning_key_payload *payload =
             key->payload.data[0];
 
         seq_printf(m, ": %u [%u]", key->datalen, payload->type);
     }
 }
 
 static void fscrypt_provisioning_key_destroy(struct key *key)
 {
     kfree_sensitive(key->payload.data[0]);
 }
 
 static struct key_type key_type_fscrypt_provisioning = {
     .name           = "fscrypt-provisioning",
     .preparse       = fscrypt_provisioning_key_preparse,
     .free_preparse      = fscrypt_provisioning_key_free_preparse,
     .instantiate        = generic_key_instantiate,
     .describe       = fscrypt_provisioning_key_describe,
     .destroy        = fscrypt_provisioning_key_destroy,
 };
 
 /*
  * Retrieve the raw key from the Linux keyring key specified by 'key_id', and
  * store it into 'secret'.
  *
  * The key must be of type "fscrypt-provisioning" and must have the field
  * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's
  * only usable with fscrypt with the particular KDF version identified by
  * 'type'.  We don't use the "logon" key type because there's no way to
  * completely restrict the use of such keys; they can be used by any kernel API
  * that accepts "logon" keys and doesn't require a specific service prefix.
  *
  * The ability to specify the key via Linux keyring key is intended for cases
  * where userspace needs to re-add keys after the filesystem is unmounted and
  * re-mounted.  Most users should just provide the raw key directly instead.
  */
 static int get_keyring_key(u32 key_id, u32 type,
                struct fscrypt_master_key_secret *secret)
 {
     key_ref_t ref;
     struct key *key;
     const struct fscrypt_provisioning_key_payload *payload;
     int err;
 
     ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);
     if (IS_ERR(ref))
         return PTR_ERR(ref);
     key = key_ref_to_ptr(ref);
 
     if (key->type != &key_type_fscrypt_provisioning)
         goto bad_key;
     payload = key->payload.data[0];
 
     /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */
     if (payload->type != type)
         goto bad_key;
 
     secret->size = key->datalen - sizeof(*payload);
     memcpy(secret->raw, payload->raw, secret->size);
     err = 0;
     goto out_put;
 
 bad_key:
     err = -EKEYREJECTED;
 out_put:
     key_ref_put(ref);
     return err;
 }
 
 /*
  * Add a master encryption key to the filesystem, causing all files which were
  * encrypted with it to appear "unlocked" (decrypted) when accessed.
  *
  * When adding a key for use by v1 encryption policies, this ioctl is
  * privileged, and userspace must provide the 'key_descriptor'.
  *
  * When adding a key for use by v2+ encryption policies, this ioctl is
  * unprivileged.  This is needed, in general, to allow non-root users to use
  * encryption without encountering the visibility problems of process-subscribed
  * keyrings and the inability to properly remove keys.  This works by having
  * each key identified by its cryptographically secure hash --- the
  * 'key_identifier'.  The cryptographic hash ensures that a malicious user
  * cannot add the wrong key for a given identifier.  Furthermore, each added key
  * is charged to the appropriate user's quota for the keyrings service, which
  * prevents a malicious user from adding too many keys.  Finally, we forbid a
  * user from removing a key while other users have added it too, which prevents
  * a user who knows another user's key from causing a denial-of-service by
  * removing it at an inopportune time.  (We tolerate that a user who knows a key
  * can prevent other users from removing it.)
  *
  * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
  * Documentation/filesystems/fscrypt.rst.
  */
 int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
 {
     struct super_block *sb = file_inode(filp)->i_sb;
     struct fscrypt_add_key_arg __user *uarg = _uarg;
     struct fscrypt_add_key_arg arg;
     struct fscrypt_master_key_secret secret;
     int err;
 
     if (copy_from_user(&arg, uarg, sizeof(arg)))
         return -EFAULT;
 
     if (!valid_key_spec(&arg.key_spec))
         return -EINVAL;
 
     if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
         return -EINVAL;
 
     /*
      * Only root can add keys that are identified by an arbitrary descriptor
      * rather than by a cryptographic hash --- since otherwise a malicious
      * user could add the wrong key.
      */
     if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
         !capable(CAP_SYS_ADMIN))
         return -EACCES;
 
     memset(&secret, 0, sizeof(secret));
     if (arg.key_id) {
         if (arg.raw_size != 0)
             return -EINVAL;
         err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);
         if (err)
             goto out_wipe_secret;
     } else {
         if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
             arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
             return -EINVAL;
         secret.size = arg.raw_size;
         err = -EFAULT;
         if (copy_from_user(secret.raw, uarg->raw, secret.size))
             goto out_wipe_secret;
     }
 
     err = add_master_key(sb, &secret, &arg.key_spec);
     if (err)
         goto out_wipe_secret;
 
     /* Return the key identifier to userspace, if applicable */
     err = -EFAULT;
     if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
         copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier,
              FSCRYPT_KEY_IDENTIFIER_SIZE))
         goto out_wipe_secret;
     err = 0;
 out_wipe_secret:
     wipe_master_key_secret(&secret);
     return err;
 }
 EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
 
 static void
 fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret)
 {
     static u8 test_key[FSCRYPT_MAX_KEY_SIZE];
 
     get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
 
     memset(secret, 0, sizeof(*secret));
     secret->size = FSCRYPT_MAX_KEY_SIZE;
     memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE);
 }
 
 int fscrypt_get_test_dummy_key_identifier(
                 u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
 {
     struct fscrypt_master_key_secret secret;
     int err;
 
     fscrypt_get_test_dummy_secret(&secret);
 
     err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
     if (err)
         goto out;
     err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER,
                   NULL, 0, key_identifier,
                   FSCRYPT_KEY_IDENTIFIER_SIZE);
 out:
     wipe_master_key_secret(&secret);
     return err;
 }
 
 /**
  * fscrypt_add_test_dummy_key() - add the test dummy encryption key
  * @sb: the filesystem instance to add the key to
  * @dummy_policy: the encryption policy for test_dummy_encryption
  *
  * If needed, add the key for the test_dummy_encryption mount option to the
  * filesystem.  To prevent misuse of this mount option, a per-boot random key is
  * used instead of a hardcoded one.  This makes it so that any encrypted files
  * created using this option won't be accessible after a reboot.
  *
  * Return: 0 on success, -errno on failure
  */
 int fscrypt_add_test_dummy_key(struct super_block *sb,
                    const struct fscrypt_dummy_policy *dummy_policy)
 {
     const union fscrypt_policy *policy = dummy_policy->policy;
     struct fscrypt_key_specifier key_spec;
     struct fscrypt_master_key_secret secret;
     int err;
 
     if (!policy)
         return 0;
     err = fscrypt_policy_to_key_spec(policy, &key_spec);
     if (err)
         return err;
     fscrypt_get_test_dummy_secret(&secret);
     err = add_master_key(sb, &secret, &key_spec);
     wipe_master_key_secret(&secret);
     return err;
 }
 EXPORT_SYMBOL_GPL(fscrypt_add_test_dummy_key);
 
 /*
  * Verify that the current user has added a master key with the given identifier
  * (returns -ENOKEY if not).  This is needed to prevent a user from encrypting
  * their files using some other user's key which they don't actually know.
  * Cryptographically this isn't much of a problem, but the semantics of this
  * would be a bit weird, so it's best to just forbid it.
  *
  * The system administrator (CAP_FOWNER) can override this, which should be
  * enough for any use cases where encryption policies are being set using keys
  * that were chosen ahead of time but aren't available at the moment.
  *
  * Note that the key may have already removed by the time this returns, but
  * that's okay; we just care whether the key was there at some point.
  *
  * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
  */
 int fscrypt_verify_key_added(struct super_block *sb,
                  const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
 {
     struct fscrypt_key_specifier mk_spec;
     struct key *key, *mk_user;
     struct fscrypt_master_key *mk;
     int err;
 
     mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
     memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
 
     key = fscrypt_find_master_key(sb, &mk_spec);
     if (IS_ERR(key)) {
         err = PTR_ERR(key);
         goto out;
     }
     mk = key->payload.data[0];
     mk_user = find_master_key_user(mk);
     if (IS_ERR(mk_user)) {
         err = PTR_ERR(mk_user);
     } else {
         key_put(mk_user);
         err = 0;
     }
     key_put(key);
 out:
     if (err == -ENOKEY && capable(CAP_FOWNER))
         err = 0;
     return err;
 }
 
 /*
  * Try to evict the inode's dentries from the dentry cache.  If the inode is a
  * directory, then it can have at most one dentry; however, that dentry may be
  * pinned by child dentries, so first try to evict the children too.
  */
 static void shrink_dcache_inode(struct inode *inode)
 {
     struct dentry *dentry;
 
     if (S_ISDIR(inode->i_mode)) {
         dentry = d_find_any_alias(inode);
         if (dentry) {
             shrink_dcache_parent(dentry);
             dput(dentry);
         }
     }
     d_prune_aliases(inode);
 }
 
 static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
 {
     struct fscrypt_info *ci;
     struct inode *inode;
     struct inode *toput_inode = NULL;
 
     spin_lock(&mk->mk_decrypted_inodes_lock);
 
     list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
         inode = ci->ci_inode;
         spin_lock(&inode->i_lock);
         if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
             spin_unlock(&inode->i_lock);
             continue;
         }
         __iget(inode);
         spin_unlock(&inode->i_lock);
         spin_unlock(&mk->mk_decrypted_inodes_lock);
 
         shrink_dcache_inode(inode);
         iput(toput_inode);
         toput_inode = inode;
 
         spin_lock(&mk->mk_decrypted_inodes_lock);
     }
 
     spin_unlock(&mk->mk_decrypted_inodes_lock);
     iput(toput_inode);
 }
 
 static int check_for_busy_inodes(struct super_block *sb,
                  struct fscrypt_master_key *mk)
 {
     struct list_head *pos;
     size_t busy_count = 0;
     unsigned long ino;
     char ino_str[50] = "";
 
     spin_lock(&mk->mk_decrypted_inodes_lock);
 
     list_for_each(pos, &mk->mk_decrypted_inodes)
         busy_count++;
 
     if (busy_count == 0) {
         spin_unlock(&mk->mk_decrypted_inodes_lock);
         return 0;
     }
 
     {
         /* select an example file to show for debugging purposes */
         struct inode *inode =
             list_first_entry(&mk->mk_decrypted_inodes,
                      struct fscrypt_info,
                      ci_master_key_link)->ci_inode;
         ino = inode->i_ino;
     }
     spin_unlock(&mk->mk_decrypted_inodes_lock);
 
     /* If the inode is currently being created, ino may still be 0. */
     if (ino)
         snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino);
 
     fscrypt_warn(NULL,
              "%s: %zu inode(s) still busy after removing key with %s %*phN%s",
              sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
              master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
              ino_str);
     return -EBUSY;
 }
 
 static int try_to_lock_encrypted_files(struct super_block *sb,
                        struct fscrypt_master_key *mk)
 {
     int err1;
     int err2;
 
     /*
      * An inode can't be evicted while it is dirty or has dirty pages.
      * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
      *
      * Just do it the easy way: call sync_filesystem().  It's overkill, but
      * it works, and it's more important to minimize the amount of caches we
      * drop than the amount of data we sync.  Also, unprivileged users can
      * already call sync_filesystem() via sys_syncfs() or sys_sync().
      */
     down_read(&sb->s_umount);
     err1 = sync_filesystem(sb);
     up_read(&sb->s_umount);
     /* If a sync error occurs, still try to evict as much as possible. */
 
     /*
      * Inodes are pinned by their dentries, so we have to evict their
      * dentries.  shrink_dcache_sb() would suffice, but would be overkill
      * and inappropriate for use by unprivileged users.  So instead go
      * through the inodes' alias lists and try to evict each dentry.
      */
     evict_dentries_for_decrypted_inodes(mk);
 
     /*
      * evict_dentries_for_decrypted_inodes() already iput() each inode in
      * the list; any inodes for which that dropped the last reference will
      * have been evicted due to fscrypt_drop_inode() detecting the key
      * removal and telling the VFS to evict the inode.  So to finish, we
      * just need to check whether any inodes couldn't be evicted.
      */
     err2 = check_for_busy_inodes(sb, mk);
 
     return err1 ?: err2;
 }
 
 /*
  * Try to remove an fscrypt master encryption key.
  *
  * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's
  * claim to the key, then removes the key itself if no other users have claims.
  * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the
  * key itself.
  *
  * To "remove the key itself", first we wipe the actual master key secret, so
  * that no more inodes can be unlocked with it.  Then we try to evict all cached
  * inodes that had been unlocked with the key.
  *
  * If all inodes were evicted, then we unlink the fscrypt_master_key from the
  * keyring.  Otherwise it remains in the keyring in the "incompletely removed"
  * state (without the actual secret key) where it tracks the list of remaining
  * inodes.  Userspace can execute the ioctl again later to retry eviction, or
  * alternatively can re-add the secret key again.
  *
  * For more details, see the "Removing keys" section of
  * Documentation/filesystems/fscrypt.rst.
  */
 static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
 {
     struct super_block *sb = file_inode(filp)->i_sb;
     struct fscrypt_remove_key_arg __user *uarg = _uarg;
     struct fscrypt_remove_key_arg arg;
     struct key *key;
     struct fscrypt_master_key *mk;
     u32 status_flags = 0;
     int err;
     bool dead;
 
     if (copy_from_user(&arg, uarg, sizeof(arg)))
         return -EFAULT;
 
     if (!valid_key_spec(&arg.key_spec))
         return -EINVAL;
 
     if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
         return -EINVAL;
 
     /*
      * Only root can add and remove keys that are identified by an arbitrary
      * descriptor rather than by a cryptographic hash.
      */
     if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
         !capable(CAP_SYS_ADMIN))
         return -EACCES;
 
     /* Find the key being removed. */
     key = fscrypt_find_master_key(sb, &arg.key_spec);
     if (IS_ERR(key))
         return PTR_ERR(key);
     mk = key->payload.data[0];
 
     down_write(&key->sem);
 
     /* If relevant, remove current user's (or all users) claim to the key */
     if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
         if (all_users)
             err = keyring_clear(mk->mk_users);
         else
             err = remove_master_key_user(mk);
         if (err) {
             up_write(&key->sem);
             goto out_put_key;
         }
         if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
             /*
              * Other users have still added the key too.  We removed
              * the current user's claim to the key, but we still
              * can't remove the key itself.
              */
             status_flags |=
                 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;
             err = 0;
             up_write(&key->sem);
             goto out_put_key;
         }
     }
 
     /* No user claims remaining.  Go ahead and wipe the secret. */
     dead = false;
     if (is_master_key_secret_present(&mk->mk_secret)) {
         wipe_master_key_secret(&mk->mk_secret);
         dead = refcount_dec_and_test(&mk->mk_refcount);
     }
     up_write(&key->sem);
     if (dead) {
         /*
          * No inodes reference the key, and we wiped the secret, so the
          * key object is free to be removed from the keyring.
          */
         key_invalidate(key);
         err = 0;
     } else {
         /* Some inodes still reference this key; try to evict them. */
         err = try_to_lock_encrypted_files(sb, mk);
         if (err == -EBUSY) {
             status_flags |=
                 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;
             err = 0;
         }
     }
     /*
      * We return 0 if we successfully did something: removed a claim to the
      * key, wiped the secret, or tried locking the files again.  Users need
      * to check the informational status flags if they care whether the key
      * has been fully removed including all files locked.
      */
 out_put_key:
     key_put(key);
     if (err == 0)
         err = put_user(status_flags, &uarg->removal_status_flags);
     return err;
 }
 
 int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)
 {
     return do_remove_key(filp, uarg, false);
 }
 EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
 
 int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)
 {
     if (!capable(CAP_SYS_ADMIN))
         return -EACCES;
     return do_remove_key(filp, uarg, true);
 }
 EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);
 
 /*
  * Retrieve the status of an fscrypt master encryption key.
  *
  * We set ->status to indicate whether the key is absent, present, or
  * incompletely removed.  "Incompletely removed" means that the master key
  * secret has been removed, but some files which had been unlocked with it are
  * still in use.  This field allows applications to easily determine the state
  * of an encrypted directory without using a hack such as trying to open a
  * regular file in it (which can confuse the "incompletely removed" state with
  * absent or present).
  *
  * In addition, for v2 policy keys we allow applications to determine, via
  * ->status_flags and ->user_count, whether the key has been added by the
  * current user, by other users, or by both.  Most applications should not need
  * this, since ordinarily only one user should know a given key.  However, if a
  * secret key is shared by multiple users, applications may wish to add an
  * already-present key to prevent other users from removing it.  This ioctl can
  * be used to check whether that really is the case before the work is done to
  * add the key --- which might e.g. require prompting the user for a passphrase.
  *
  * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of
  * Documentation/filesystems/fscrypt.rst.
  */
 int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
 {
     struct super_block *sb = file_inode(filp)->i_sb;
     struct fscrypt_get_key_status_arg arg;
     struct key *key;
     struct fscrypt_master_key *mk;
     int err;
 
     if (copy_from_user(&arg, uarg, sizeof(arg)))
         return -EFAULT;
 
     if (!valid_key_spec(&arg.key_spec))
         return -EINVAL;
 
     if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
         return -EINVAL;
 
     arg.status_flags = 0;
     arg.user_count = 0;
     memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
 
     key = fscrypt_find_master_key(sb, &arg.key_spec);
     if (IS_ERR(key)) {
         if (key != ERR_PTR(-ENOKEY))
             return PTR_ERR(key);
         arg.status = FSCRYPT_KEY_STATUS_ABSENT;
         err = 0;
         goto out;
     }
     mk = key->payload.data[0];
     down_read(&key->sem);
 
     if (!is_master_key_secret_present(&mk->mk_secret)) {
         arg.status = FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED;
         err = 0;
         goto out_release_key;
     }
 
     arg.status = FSCRYPT_KEY_STATUS_PRESENT;
     if (mk->mk_users) {
         struct key *mk_user;
 
         arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
         mk_user = find_master_key_user(mk);
         if (!IS_ERR(mk_user)) {
             arg.status_flags |=
                 FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
             key_put(mk_user);
         } else if (mk_user != ERR_PTR(-ENOKEY)) {
             err = PTR_ERR(mk_user);
             goto out_release_key;
         }
     }
     err = 0;
 out_release_key:
     up_read(&key->sem);
     key_put(key);
 out:
     if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
         err = -EFAULT;
     return err;
 }
 EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
 
 int __init fscrypt_init_keyring(void)
 {
     int err;
 
     err = register_key_type(&key_type_fscrypt);
     if (err)
         return err;
 
     err = register_key_type(&key_type_fscrypt_user);
     if (err)
         goto err_unregister_fscrypt;
 
     err = register_key_type(&key_type_fscrypt_provisioning);
     if (err)
         goto err_unregister_fscrypt_user;
 
     return 0;
 
 err_unregister_fscrypt_user:
     unregister_key_type(&key_type_fscrypt_user);
 err_unregister_fscrypt:
     unregister_key_type(&key_type_fscrypt);
     return err;
 }

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