diff options
Diffstat (limited to 'fs/crypto/keyring.c')
| -rw-r--r-- | fs/crypto/keyring.c | 1204 |
1 files changed, 1204 insertions, 0 deletions
diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c new file mode 100644 index 0000000000..7cbb1fd872 --- /dev/null +++ b/fs/crypto/keyring.c @@ -0,0 +1,1204 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Filesystem-level keyring for fscrypt + * + * Copyright 2019 Google LLC + */ + +/* + * This file implements management of fscrypt master keys in the + * filesystem-level keyring, including the ioctls: + * + * - FS_IOC_ADD_ENCRYPTION_KEY + * - FS_IOC_REMOVE_ENCRYPTION_KEY + * - FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS + * - FS_IOC_GET_ENCRYPTION_KEY_STATUS + * + * See the "User API" section of Documentation/filesystems/fscrypt.rst for more + * information about these ioctls. + */ + +#include <asm/unaligned.h> +#include <crypto/skcipher.h> +#include <linux/key-type.h> +#include <linux/random.h> +#include <linux/seq_file.h> + +#include "fscrypt_private.h" + +/* The master encryption keys for a filesystem (->s_master_keys) */ +struct fscrypt_keyring { + /* + * Lock that protects ->key_hashtable. It does *not* protect the + * fscrypt_master_key structs themselves. + */ + spinlock_t lock; + + /* Hash table that maps fscrypt_key_specifier to fscrypt_master_key */ + struct hlist_head key_hashtable[128]; +}; + +static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret) +{ + fscrypt_destroy_hkdf(&secret->hkdf); + memzero_explicit(secret, sizeof(*secret)); +} + +static void move_master_key_secret(struct fscrypt_master_key_secret *dst, + struct fscrypt_master_key_secret *src) +{ + memcpy(dst, src, sizeof(*dst)); + memzero_explicit(src, sizeof(*src)); +} + +static void fscrypt_free_master_key(struct rcu_head *head) +{ + struct fscrypt_master_key *mk = + container_of(head, struct fscrypt_master_key, mk_rcu_head); + /* + * The master key secret and any embedded subkeys should have already + * been wiped when the last active reference to the fscrypt_master_key + * struct was dropped; doing it here would be unnecessarily late. + * Nevertheless, use kfree_sensitive() in case anything was missed. + */ + kfree_sensitive(mk); +} + +void fscrypt_put_master_key(struct fscrypt_master_key *mk) +{ + if (!refcount_dec_and_test(&mk->mk_struct_refs)) + return; + /* + * No structural references left, so free ->mk_users, and also free the + * fscrypt_master_key struct itself after an RCU grace period ensures + * that concurrent keyring lookups can no longer find it. + */ + WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 0); + key_put(mk->mk_users); + mk->mk_users = NULL; + call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key); +} + +void fscrypt_put_master_key_activeref(struct super_block *sb, + struct fscrypt_master_key *mk) +{ + size_t i; + + if (!refcount_dec_and_test(&mk->mk_active_refs)) + return; + /* + * No active references left, so complete the full removal of this + * fscrypt_master_key struct by removing it from the keyring and + * destroying any subkeys embedded in it. + */ + + if (WARN_ON_ONCE(!sb->s_master_keys)) + return; + spin_lock(&sb->s_master_keys->lock); + hlist_del_rcu(&mk->mk_node); + spin_unlock(&sb->s_master_keys->lock); + + /* + * ->mk_active_refs == 0 implies that ->mk_secret is not present and + * that ->mk_decrypted_inodes is empty. + */ + WARN_ON_ONCE(is_master_key_secret_present(&mk->mk_secret)); + WARN_ON_ONCE(!list_empty(&mk->mk_decrypted_inodes)); + + for (i = 0; i <= FSCRYPT_MODE_MAX; i++) { + fscrypt_destroy_prepared_key( + sb, &mk->mk_direct_keys[i]); + fscrypt_destroy_prepared_key( + sb, &mk->mk_iv_ino_lblk_64_keys[i]); + fscrypt_destroy_prepared_key( + sb, &mk->mk_iv_ino_lblk_32_keys[i]); + } + memzero_explicit(&mk->mk_ino_hash_key, + sizeof(mk->mk_ino_hash_key)); + mk->mk_ino_hash_key_initialized = false; + + /* Drop the structural ref associated with the active refs. */ + fscrypt_put_master_key(mk); +} + +static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec) +{ + if (spec->__reserved) + return false; + return master_key_spec_len(spec) != 0; +} + +static int fscrypt_user_key_instantiate(struct key *key, + struct key_preparsed_payload *prep) +{ + /* + * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for + * each key, regardless of the exact key size. The amount of memory + * actually used is greater than the size of the raw key anyway. + */ + return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE); +} + +static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m) +{ + seq_puts(m, key->description); +} + +/* + * Type of key in ->mk_users. Each key of this type represents a particular + * user who has added a particular master key. + * + * Note that the name of this key type really should be something like + * ".fscrypt-user" instead of simply ".fscrypt". But the shorter name is chosen + * mainly for simplicity of presentation in /proc/keys when read by a non-root + * user. And it is expected to be rare that a key is actually added by multiple + * users, since users should keep their encryption keys confidential. + */ +static struct key_type key_type_fscrypt_user = { + .name = ".fscrypt", + .instantiate = fscrypt_user_key_instantiate, + .describe = fscrypt_user_key_describe, +}; + +#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE \ + (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \ + CONST_STRLEN("-users") + 1) + +#define FSCRYPT_MK_USER_DESCRIPTION_SIZE \ + (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1) + +static void format_mk_users_keyring_description( + char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE], + const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]) +{ + sprintf(description, "fscrypt-%*phN-users", + FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier); +} + +static void format_mk_user_description( + char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE], + const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]) +{ + + sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE, + mk_identifier, __kuid_val(current_fsuid())); +} + +/* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */ +static int allocate_filesystem_keyring(struct super_block *sb) +{ + struct fscrypt_keyring *keyring; + + if (sb->s_master_keys) + return 0; + + keyring = kzalloc(sizeof(*keyring), GFP_KERNEL); + if (!keyring) + return -ENOMEM; + spin_lock_init(&keyring->lock); + /* + * Pairs with the smp_load_acquire() in fscrypt_find_master_key(). + * I.e., here we publish ->s_master_keys with a RELEASE barrier so that + * concurrent tasks can ACQUIRE it. + */ + smp_store_release(&sb->s_master_keys, keyring); + return 0; +} + +/* + * Release all encryption keys that have been added to the filesystem, along + * with the keyring that contains them. + * + * This is called at unmount time, after all potentially-encrypted inodes have + * been evicted. The filesystem's underlying block device(s) are still + * available at this time; this is important because after user file accesses + * have been allowed, this function may need to evict keys from the keyslots of + * an inline crypto engine, which requires the block device(s). + */ +void fscrypt_destroy_keyring(struct super_block *sb) +{ + struct fscrypt_keyring *keyring = sb->s_master_keys; + size_t i; + + if (!keyring) + return; + + for (i = 0; i < ARRAY_SIZE(keyring->key_hashtable); i++) { + struct hlist_head *bucket = &keyring->key_hashtable[i]; + struct fscrypt_master_key *mk; + struct hlist_node *tmp; + + hlist_for_each_entry_safe(mk, tmp, bucket, mk_node) { + /* + * Since all potentially-encrypted inodes were already + * evicted, every key remaining in the keyring should + * have an empty inode list, and should only still be in + * the keyring due to the single active ref associated + * with ->mk_secret. There should be no structural refs + * beyond the one associated with the active ref. + */ + WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 1); + WARN_ON_ONCE(refcount_read(&mk->mk_struct_refs) != 1); + WARN_ON_ONCE(!is_master_key_secret_present(&mk->mk_secret)); + wipe_master_key_secret(&mk->mk_secret); + fscrypt_put_master_key_activeref(sb, mk); + } + } + kfree_sensitive(keyring); + sb->s_master_keys = NULL; +} + +static struct hlist_head * +fscrypt_mk_hash_bucket(struct fscrypt_keyring *keyring, + const struct fscrypt_key_specifier *mk_spec) +{ + /* + * Since key specifiers should be "random" values, it is sufficient to + * use a trivial hash function that just takes the first several bits of + * the key specifier. + */ + unsigned long i = get_unaligned((unsigned long *)&mk_spec->u); + + return &keyring->key_hashtable[i % ARRAY_SIZE(keyring->key_hashtable)]; +} + +/* + * Find the specified master key struct in ->s_master_keys and take a structural + * ref to it. The structural ref guarantees that the key struct continues to + * exist, but it does *not* guarantee that ->s_master_keys continues to contain + * the key struct. The structural ref needs to be dropped by + * fscrypt_put_master_key(). Returns NULL if the key struct is not found. + */ +struct fscrypt_master_key * +fscrypt_find_master_key(struct super_block *sb, + const struct fscrypt_key_specifier *mk_spec) +{ + struct fscrypt_keyring *keyring; + struct hlist_head *bucket; + struct fscrypt_master_key *mk; + + /* + * Pairs with the smp_store_release() in allocate_filesystem_keyring(). + * I.e., another task can publish ->s_master_keys concurrently, + * executing a RELEASE barrier. We need to use smp_load_acquire() here + * to safely ACQUIRE the memory the other task published. + */ + keyring = smp_load_acquire(&sb->s_master_keys); + if (keyring == NULL) + return NULL; /* No keyring yet, so no keys yet. */ + + bucket = fscrypt_mk_hash_bucket(keyring, mk_spec); + rcu_read_lock(); + switch (mk_spec->type) { + case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR: + hlist_for_each_entry_rcu(mk, bucket, mk_node) { + if (mk->mk_spec.type == + FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR && + memcmp(mk->mk_spec.u.descriptor, + mk_spec->u.descriptor, + FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 && + refcount_inc_not_zero(&mk->mk_struct_refs)) + goto out; + } + break; + case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER: + hlist_for_each_entry_rcu(mk, bucket, mk_node) { + if (mk->mk_spec.type == + FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER && + memcmp(mk->mk_spec.u.identifier, + mk_spec->u.identifier, + FSCRYPT_KEY_IDENTIFIER_SIZE) == 0 && + refcount_inc_not_zero(&mk->mk_struct_refs)) + goto out; + } + break; + } + mk = NULL; +out: + rcu_read_unlock(); + return mk; +} + +static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk) +{ + char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE]; + struct key *keyring; + + format_mk_users_keyring_description(description, + mk->mk_spec.u.identifier); + keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, + current_cred(), KEY_POS_SEARCH | + KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW, + KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL); + if (IS_ERR(keyring)) + return PTR_ERR(keyring); + + mk->mk_users = keyring; + return 0; +} + +/* + * Find the current user's "key" in the master key's ->mk_users. + * Returns ERR_PTR(-ENOKEY) if not found. + */ +static struct key *find_master_key_user(struct fscrypt_master_key *mk) +{ + char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE]; + key_ref_t keyref; + + format_mk_user_description(description, mk->mk_spec.u.identifier); + + /* + * We need to mark the keyring reference as "possessed" so that we + * acquire permission to search it, via the KEY_POS_SEARCH permission. + */ + keyref = keyring_search(make_key_ref(mk->mk_users, true /*possessed*/), + &key_type_fscrypt_user, description, false); + if (IS_ERR(keyref)) { + if (PTR_ERR(keyref) == -EAGAIN || /* not found */ + PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */ + keyref = ERR_PTR(-ENOKEY); + return ERR_CAST(keyref); + } + return key_ref_to_ptr(keyref); +} + +/* + * Give the current user a "key" in ->mk_users. This charges the user's quota + * and marks the master key as added by the current user, so that it cannot be + * removed by another user with the key. Either ->mk_sem must be held for + * write, or the master key must be still undergoing initialization. + */ +static int add_master_key_user(struct fscrypt_master_key *mk) +{ + char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE]; + struct key *mk_user; + int err; + + format_mk_user_description(description, mk->mk_spec.u.identifier); + mk_user = key_alloc(&key_type_fscrypt_user, description, + current_fsuid(), current_gid(), current_cred(), + KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL); + if (IS_ERR(mk_user)) + return PTR_ERR(mk_user); + + err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL); + key_put(mk_user); + return err; +} + +/* + * Remove the current user's "key" from ->mk_users. + * ->mk_sem must be held for write. + * + * Returns 0 if removed, -ENOKEY if not found, or another -errno code. + */ +static int remove_master_key_user(struct fscrypt_master_key *mk) +{ + struct key *mk_user; + int err; + + mk_user = find_master_key_user(mk); + if (IS_ERR(mk_user)) + return PTR_ERR(mk_user); + err = key_unlink(mk->mk_users, mk_user); + key_put(mk_user); + return err; +} + +/* + * Allocate a new fscrypt_master_key, transfer the given secret over to it, and + * insert it into sb->s_master_keys. + */ +static int add_new_master_key(struct super_block *sb, + struct fscrypt_master_key_secret *secret, + const struct fscrypt_key_specifier *mk_spec) +{ + struct fscrypt_keyring *keyring = sb->s_master_keys; + struct fscrypt_master_key *mk; + int err; + + mk = kzalloc(sizeof(*mk), GFP_KERNEL); + if (!mk) + return -ENOMEM; + + init_rwsem(&mk->mk_sem); + refcount_set(&mk->mk_struct_refs, 1); + mk->mk_spec = *mk_spec; + + INIT_LIST_HEAD(&mk->mk_decrypted_inodes); + spin_lock_init(&mk->mk_decrypted_inodes_lock); + + if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) { + err = allocate_master_key_users_keyring(mk); + if (err) + goto out_put; + err = add_master_key_user(mk); + if (err) + goto out_put; + } + + move_master_key_secret(&mk->mk_secret, secret); + refcount_set(&mk->mk_active_refs, 1); /* ->mk_secret is present */ + + spin_lock(&keyring->lock); + hlist_add_head_rcu(&mk->mk_node, + fscrypt_mk_hash_bucket(keyring, mk_spec)); + spin_unlock(&keyring->lock); + return 0; + +out_put: + fscrypt_put_master_key(mk); + return err; +} + +#define KEY_DEAD 1 + +static int add_existing_master_key(struct fscrypt_master_key *mk, + struct fscrypt_master_key_secret *secret) +{ + int err; + + /* + * If the current user is already in ->mk_users, then there's nothing to + * do. Otherwise, we need to add the user to ->mk_users. (Neither is + * applicable for v1 policy keys, which have NULL ->mk_users.) + */ + if (mk->mk_users) { + struct key *mk_user = find_master_key_user(mk); + + if (mk_user != ERR_PTR(-ENOKEY)) { + if (IS_ERR(mk_user)) + return PTR_ERR(mk_user); + key_put(mk_user); + return 0; + } + err = add_master_key_user(mk); + if (err) + return err; + } + + /* Re-add the secret if needed. */ + if (!is_master_key_secret_present(&mk->mk_secret)) { + if (!refcount_inc_not_zero(&mk->mk_active_refs)) + return KEY_DEAD; + move_master_key_secret(&mk->mk_secret, secret); + } + + return 0; +} + +static int do_add_master_key(struct super_block *sb, + struct fscrypt_master_key_secret *secret, + const struct fscrypt_key_specifier *mk_spec) +{ + static DEFINE_MUTEX(fscrypt_add_key_mutex); + struct fscrypt_master_key *mk; + int err; + + mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */ + + mk = fscrypt_find_master_key(sb, mk_spec); + if (!mk) { + /* Didn't find the key in ->s_master_keys. Add it. */ + err = allocate_filesystem_keyring(sb); + if (!err) + err = add_new_master_key(sb, secret, mk_spec); + } else { + /* + * Found the key in ->s_master_keys. Re-add the secret if + * needed, and add the user to ->mk_users if needed. + */ + down_write(&mk->mk_sem); + err = add_existing_master_key(mk, secret); + up_write(&mk->mk_sem); + if (err == KEY_DEAD) { + /* + * We found a key struct, but it's already been fully + * removed. Ignore the old struct and add a new one. + * fscrypt_add_key_mutex means we don't need to worry + * about concurrent adds. + */ + err = add_new_master_key(sb, secret, mk_spec); + } + fscrypt_put_master_key(mk); + } + mutex_unlock(&fscrypt_add_key_mutex); + return err; +} + +static int add_master_key(struct super_block *sb, + struct fscrypt_master_key_secret *secret, + struct fscrypt_key_specifier *key_spec) +{ + int err; + + if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) { + err = fscrypt_init_hkdf(&secret->hkdf, secret->raw, + secret->size); + if (err) + return err; + + /* + * Now that the HKDF context is initialized, the raw key is no + * longer needed. + */ + memzero_explicit(secret->raw, secret->size); + + /* Calculate the key identifier */ + err = fscrypt_hkdf_expand(&secret->hkdf, + HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0, + key_spec->u.identifier, + FSCRYPT_KEY_IDENTIFIER_SIZE); + if (err) + return err; + } + return do_add_master_key(sb, secret, key_spec); +} + +static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep) +{ + const struct fscrypt_provisioning_key_payload *payload = prep->data; + + if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE || + prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE) + return -EINVAL; + + if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR && + payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) + return -EINVAL; + + if (payload->__reserved) + return -EINVAL; + + prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL); + if (!prep->payload.data[0]) + return -ENOMEM; + + prep->quotalen = prep->datalen; + return 0; +} + +static void fscrypt_provisioning_key_free_preparse( + struct key_preparsed_payload *prep) +{ + kfree_sensitive(prep->payload.data[0]); +} + +static void fscrypt_provisioning_key_describe(const struct key *key, + struct seq_file *m) +{ + seq_puts(m, key->description); + if (key_is_positive(key)) { + const struct fscrypt_provisioning_key_payload *payload = + key->payload.data[0]; + + seq_printf(m, ": %u [%u]", key->datalen, payload->type); + } +} + +static void fscrypt_provisioning_key_destroy(struct key *key) +{ + kfree_sensitive(key->payload.data[0]); +} + +static struct key_type key_type_fscrypt_provisioning = { + .name = "fscrypt-provisioning", + .preparse = fscrypt_provisioning_key_preparse, + .free_preparse = fscrypt_provisioning_key_free_preparse, + .instantiate = generic_key_instantiate, + .describe = fscrypt_provisioning_key_describe, + .destroy = fscrypt_provisioning_key_destroy, +}; + +/* + * Retrieve the raw key from the Linux keyring key specified by 'key_id', and + * store it into 'secret'. + * + * The key must be of type "fscrypt-provisioning" and must have the field + * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's + * only usable with fscrypt with the particular KDF version identified by + * 'type'. We don't use the "logon" key type because there's no way to + * completely restrict the use of such keys; they can be used by any kernel API + * that accepts "logon" keys and doesn't require a specific service prefix. + * + * The ability to specify the key via Linux keyring key is intended for cases + * where userspace needs to re-add keys after the filesystem is unmounted and + * re-mounted. Most users should just provide the raw key directly instead. + */ +static int get_keyring_key(u32 key_id, u32 type, + struct fscrypt_master_key_secret *secret) +{ + key_ref_t ref; + struct key *key; + const struct fscrypt_provisioning_key_payload *payload; + int err; + + ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH); + if (IS_ERR(ref)) + return PTR_ERR(ref); + key = key_ref_to_ptr(ref); + + if (key->type != &key_type_fscrypt_provisioning) + goto bad_key; + payload = key->payload.data[0]; + + /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */ + if (payload->type != type) + goto bad_key; + + secret->size = key->datalen - sizeof(*payload); + memcpy(secret->raw, payload->raw, secret->size); + err = 0; + goto out_put; + +bad_key: + err = -EKEYREJECTED; +out_put: + key_ref_put(ref); + return err; +} + +/* + * Add a master encryption key to the filesystem, causing all files which were + * encrypted with it to appear "unlocked" (decrypted) when accessed. + * + * When adding a key for use by v1 encryption policies, this ioctl is + * privileged, and userspace must provide the 'key_descriptor'. + * + * When adding a key for use by v2+ encryption policies, this ioctl is + * unprivileged. This is needed, in general, to allow non-root users to use + * encryption without encountering the visibility problems of process-subscribed + * keyrings and the inability to properly remove keys. This works by having + * each key identified by its cryptographically secure hash --- the + * 'key_identifier'. The cryptographic hash ensures that a malicious user + * cannot add the wrong key for a given identifier. Furthermore, each added key + * is charged to the appropriate user's quota for the keyrings service, which + * prevents a malicious user from adding too many keys. Finally, we forbid a + * user from removing a key while other users have added it too, which prevents + * a user who knows another user's key from causing a denial-of-service by + * removing it at an inopportune time. (We tolerate that a user who knows a key + * can prevent other users from removing it.) + * + * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of + * Documentation/filesystems/fscrypt.rst. + */ +int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg) +{ + struct super_block *sb = file_inode(filp)->i_sb; + struct fscrypt_add_key_arg __user *uarg = _uarg; + struct fscrypt_add_key_arg arg; + struct fscrypt_master_key_secret secret; + int err; + + if (copy_from_user(&arg, uarg, sizeof(arg))) + return -EFAULT; + + if (!valid_key_spec(&arg.key_spec)) + return -EINVAL; + + if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved))) + return -EINVAL; + + /* + * Only root can add keys that are identified by an arbitrary descriptor + * rather than by a cryptographic hash --- since otherwise a malicious + * user could add the wrong key. + */ + if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR && + !capable(CAP_SYS_ADMIN)) + return -EACCES; + + memset(&secret, 0, sizeof(secret)); + if (arg.key_id) { + if (arg.raw_size != 0) + return -EINVAL; + err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret); + if (err) + goto out_wipe_secret; + } else { + if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE || + arg.raw_size > FSCRYPT_MAX_KEY_SIZE) + return -EINVAL; + secret.size = arg.raw_size; + err = -EFAULT; + if (copy_from_user(secret.raw, uarg->raw, secret.size)) + goto out_wipe_secret; + } + + err = add_master_key(sb, &secret, &arg.key_spec); + if (err) + goto out_wipe_secret; + + /* Return the key identifier to userspace, if applicable */ + err = -EFAULT; + if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER && + copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier, + FSCRYPT_KEY_IDENTIFIER_SIZE)) + goto out_wipe_secret; + err = 0; +out_wipe_secret: + wipe_master_key_secret(&secret); + return err; +} +EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key); + +static void +fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret) +{ + static u8 test_key[FSCRYPT_MAX_KEY_SIZE]; + + get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE); + + memset(secret, 0, sizeof(*secret)); + secret->size = FSCRYPT_MAX_KEY_SIZE; + memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE); +} + +int fscrypt_get_test_dummy_key_identifier( + u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]) +{ + struct fscrypt_master_key_secret secret; + int err; + + fscrypt_get_test_dummy_secret(&secret); + + err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size); + if (err) + goto out; + err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER, + NULL, 0, key_identifier, + FSCRYPT_KEY_IDENTIFIER_SIZE); +out: + wipe_master_key_secret(&secret); + return err; +} + +/** + * fscrypt_add_test_dummy_key() - add the test dummy encryption key + * @sb: the filesystem instance to add the key to + * @key_spec: the key specifier of the test dummy encryption key + * + * Add the key for the test_dummy_encryption mount option to the filesystem. To + * prevent misuse of this mount option, a per-boot random key is used instead of + * a hardcoded one. This makes it so that any encrypted files created using + * this option won't be accessible after a reboot. + * + * Return: 0 on success, -errno on failure + */ +int fscrypt_add_test_dummy_key(struct super_block *sb, + struct fscrypt_key_specifier *key_spec) +{ + struct fscrypt_master_key_secret secret; + int err; + + fscrypt_get_test_dummy_secret(&secret); + err = add_master_key(sb, &secret, key_spec); + wipe_master_key_secret(&secret); + return err; +} + +/* + * Verify that the current user has added a master key with the given identifier + * (returns -ENOKEY if not). This is needed to prevent a user from encrypting + * their files using some other user's key which they don't actually know. + * Cryptographically this isn't much of a problem, but the semantics of this + * would be a bit weird, so it's best to just forbid it. + * + * The system administrator (CAP_FOWNER) can override this, which should be + * enough for any use cases where encryption policies are being set using keys + * that were chosen ahead of time but aren't available at the moment. + * + * Note that the key may have already removed by the time this returns, but + * that's okay; we just care whether the key was there at some point. + * + * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code + */ +int fscrypt_verify_key_added(struct super_block *sb, + const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]) +{ + struct fscrypt_key_specifier mk_spec; + struct fscrypt_master_key *mk; + struct key *mk_user; + int err; + + mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER; + memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE); + + mk = fscrypt_find_master_key(sb, &mk_spec); + if (!mk) { + err = -ENOKEY; + goto out; + } + down_read(&mk->mk_sem); + mk_user = find_master_key_user(mk); + if (IS_ERR(mk_user)) { + err = PTR_ERR(mk_user); + } else { + key_put(mk_user); + err = 0; + } + up_read(&mk->mk_sem); + fscrypt_put_master_key(mk); +out: + if (err == -ENOKEY && capable(CAP_FOWNER)) + err = 0; + return err; +} + +/* + * Try to evict the inode's dentries from the dentry cache. If the inode is a + * directory, then it can have at most one dentry; however, that dentry may be + * pinned by child dentries, so first try to evict the children too. + */ +static void shrink_dcache_inode(struct inode *inode) +{ + struct dentry *dentry; + + if (S_ISDIR(inode->i_mode)) { + dentry = d_find_any_alias(inode); + if (dentry) { + shrink_dcache_parent(dentry); + dput(dentry); + } + } + d_prune_aliases(inode); +} + +static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk) +{ + struct fscrypt_info *ci; + struct inode *inode; + struct inode *toput_inode = NULL; + + spin_lock(&mk->mk_decrypted_inodes_lock); + + list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) { + inode = ci->ci_inode; + spin_lock(&inode->i_lock); + if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) { + spin_unlock(&inode->i_lock); + continue; + } + __iget(inode); + spin_unlock(&inode->i_lock); + spin_unlock(&mk->mk_decrypted_inodes_lock); + + shrink_dcache_inode(inode); + iput(toput_inode); + toput_inode = inode; + + spin_lock(&mk->mk_decrypted_inodes_lock); + } + + spin_unlock(&mk->mk_decrypted_inodes_lock); + iput(toput_inode); +} + +static int check_for_busy_inodes(struct super_block *sb, + struct fscrypt_master_key *mk) +{ + struct list_head *pos; + size_t busy_count = 0; + unsigned long ino; + char ino_str[50] = ""; + + spin_lock(&mk->mk_decrypted_inodes_lock); + + list_for_each(pos, &mk->mk_decrypted_inodes) + busy_count++; + + if (busy_count == 0) { + spin_unlock(&mk->mk_decrypted_inodes_lock); + return 0; + } + + { + /* select an example file to show for debugging purposes */ + struct inode *inode = + list_first_entry(&mk->mk_decrypted_inodes, + struct fscrypt_info, + ci_master_key_link)->ci_inode; + ino = inode->i_ino; + } + spin_unlock(&mk->mk_decrypted_inodes_lock); + + /* If the inode is currently being created, ino may still be 0. */ + if (ino) + snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino); + + fscrypt_warn(NULL, + "%s: %zu inode(s) still busy after removing key with %s %*phN%s", + sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec), + master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u, + ino_str); + return -EBUSY; +} + +static int try_to_lock_encrypted_files(struct super_block *sb, + struct fscrypt_master_key *mk) +{ + int err1; + int err2; + + /* + * An inode can't be evicted while it is dirty or has dirty pages. + * Thus, we first have to clean the inodes in ->mk_decrypted_inodes. + * + * Just do it the easy way: call sync_filesystem(). It's overkill, but + * it works, and it's more important to minimize the amount of caches we + * drop than the amount of data we sync. Also, unprivileged users can + * already call sync_filesystem() via sys_syncfs() or sys_sync(). + */ + down_read(&sb->s_umount); + err1 = sync_filesystem(sb); + up_read(&sb->s_umount); + /* If a sync error occurs, still try to evict as much as possible. */ + + /* + * Inodes are pinned by their dentries, so we have to evict their + * dentries. shrink_dcache_sb() would suffice, but would be overkill + * and inappropriate for use by unprivileged users. So instead go + * through the inodes' alias lists and try to evict each dentry. + */ + evict_dentries_for_decrypted_inodes(mk); + + /* + * evict_dentries_for_decrypted_inodes() already iput() each inode in + * the list; any inodes for which that dropped the last reference will + * have been evicted due to fscrypt_drop_inode() detecting the key + * removal and telling the VFS to evict the inode. So to finish, we + * just need to check whether any inodes couldn't be evicted. + */ + err2 = check_for_busy_inodes(sb, mk); + + return err1 ?: err2; +} + +/* + * Try to remove an fscrypt master encryption key. + * + * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's + * claim to the key, then removes the key itself if no other users have claims. + * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the + * key itself. + * + * To "remove the key itself", first we wipe the actual master key secret, so + * that no more inodes can be unlocked with it. Then we try to evict all cached + * inodes that had been unlocked with the key. + * + * If all inodes were evicted, then we unlink the fscrypt_master_key from the + * keyring. Otherwise it remains in the keyring in the "incompletely removed" + * state (without the actual secret key) where it tracks the list of remaining + * inodes. Userspace can execute the ioctl again later to retry eviction, or + * alternatively can re-add the secret key again. + * + * For more details, see the "Removing keys" section of + * Documentation/filesystems/fscrypt.rst. + */ +static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users) +{ + struct super_block *sb = file_inode(filp)->i_sb; + struct fscrypt_remove_key_arg __user *uarg = _uarg; + struct fscrypt_remove_key_arg arg; + struct fscrypt_master_key *mk; + u32 status_flags = 0; + int err; + bool inodes_remain; + + if (copy_from_user(&arg, uarg, sizeof(arg))) + return -EFAULT; + + if (!valid_key_spec(&arg.key_spec)) + return -EINVAL; + + if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved))) + return -EINVAL; + + /* + * Only root can add and remove keys that are identified by an arbitrary + * descriptor rather than by a cryptographic hash. + */ + if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR && + !capable(CAP_SYS_ADMIN)) + return -EACCES; + + /* Find the key being removed. */ + mk = fscrypt_find_master_key(sb, &arg.key_spec); + if (!mk) + return -ENOKEY; + down_write(&mk->mk_sem); + + /* If relevant, remove current user's (or all users) claim to the key */ + if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) { + if (all_users) + err = keyring_clear(mk->mk_users); + else + err = remove_master_key_user(mk); + if (err) { + up_write(&mk->mk_sem); + goto out_put_key; + } + if (mk->mk_users->keys.nr_leaves_on_tree != 0) { + /* + * Other users have still added the key too. We removed + * the current user's claim to the key, but we still + * can't remove the key itself. + */ + status_flags |= + FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS; + err = 0; + up_write(&mk->mk_sem); + goto out_put_key; + } + } + + /* No user claims remaining. Go ahead and wipe the secret. */ + err = -ENOKEY; + if (is_master_key_secret_present(&mk->mk_secret)) { + wipe_master_key_secret(&mk->mk_secret); + fscrypt_put_master_key_activeref(sb, mk); + err = 0; + } + inodes_remain = refcount_read(&mk->mk_active_refs) > 0; + up_write(&mk->mk_sem); + + if (inodes_remain) { + /* Some inodes still reference this key; try to evict them. */ + err = try_to_lock_encrypted_files(sb, mk); + if (err == -EBUSY) { + status_flags |= + FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY; + err = 0; + } + } + /* + * We return 0 if we successfully did something: removed a claim to the + * key, wiped the secret, or tried locking the files again. Users need + * to check the informational status flags if they care whether the key + * has been fully removed including all files locked. + */ +out_put_key: + fscrypt_put_master_key(mk); + if (err == 0) + err = put_user(status_flags, &uarg->removal_status_flags); + return err; +} + +int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg) +{ + return do_remove_key(filp, uarg, false); +} +EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key); + +int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg) +{ + if (!capable(CAP_SYS_ADMIN)) + return -EACCES; + return do_remove_key(filp, uarg, true); +} +EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users); + +/* + * Retrieve the status of an fscrypt master encryption key. + * + * We set ->status to indicate whether the key is absent, present, or + * incompletely removed. "Incompletely removed" means that the master key + * secret has been removed, but some files which had been unlocked with it are + * still in use. This field allows applications to easily determine the state + * of an encrypted directory without using a hack such as trying to open a + * regular file in it (which can confuse the "incompletely removed" state with + * absent or present). + * + * In addition, for v2 policy keys we allow applications to determine, via + * ->status_flags and ->user_count, whether the key has been added by the + * current user, by other users, or by both. Most applications should not need + * this, since ordinarily only one user should know a given key. However, if a + * secret key is shared by multiple users, applications may wish to add an + * already-present key to prevent other users from removing it. This ioctl can + * be used to check whether that really is the case before the work is done to + * add the key --- which might e.g. require prompting the user for a passphrase. + * + * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of + * Documentation/filesystems/fscrypt.rst. + */ +int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg) +{ + struct super_block *sb = file_inode(filp)->i_sb; + struct fscrypt_get_key_status_arg arg; + struct fscrypt_master_key *mk; + int err; + + if (copy_from_user(&arg, uarg, sizeof(arg))) + return -EFAULT; + + if (!valid_key_spec(&arg.key_spec)) + return -EINVAL; + + if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved))) + return -EINVAL; + + arg.status_flags = 0; + arg.user_count = 0; + memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved)); + + mk = fscrypt_find_master_key(sb, &arg.key_spec); + if (!mk) { + arg.status = FSCRYPT_KEY_STATUS_ABSENT; + err = 0; + goto out; + } + down_read(&mk->mk_sem); + + if (!is_master_key_secret_present(&mk->mk_secret)) { + arg.status = refcount_read(&mk->mk_active_refs) > 0 ? + FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED : + FSCRYPT_KEY_STATUS_ABSENT /* raced with full removal */; + err = 0; + goto out_release_key; + } + + arg.status = FSCRYPT_KEY_STATUS_PRESENT; + if (mk->mk_users) { + struct key *mk_user; + + arg.user_count = mk->mk_users->keys.nr_leaves_on_tree; + mk_user = find_master_key_user(mk); + if (!IS_ERR(mk_user)) { + arg.status_flags |= + FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF; + key_put(mk_user); + } else if (mk_user != ERR_PTR(-ENOKEY)) { + err = PTR_ERR(mk_user); + goto out_release_key; + } + } + err = 0; +out_release_key: + up_read(&mk->mk_sem); + fscrypt_put_master_key(mk); +out: + if (!err && copy_to_user(uarg, &arg, sizeof(arg))) + err = -EFAULT; + return err; +} +EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status); + +int __init fscrypt_init_keyring(void) +{ + int err; + + err = register_key_type(&key_type_fscrypt_user); + if (err) + return err; + + err = register_key_type(&key_type_fscrypt_provisioning); + if (err) + goto err_unregister_fscrypt_user; + + return 0; + +err_unregister_fscrypt_user: + unregister_key_type(&key_type_fscrypt_user); + return err; +} |