diff options
| -rw-r--r-- | fs/crypto/fscrypt_private.h | 31 | ||||
| -rw-r--r-- | fs/crypto/keyring.c | 320 | ||||
| -rw-r--r-- | fs/crypto/keysetup.c | 18 | ||||
| -rw-r--r-- | include/uapi/linux/fscrypt.h | 6 |
4 files changed, 341 insertions, 34 deletions
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h index c89e37d38e42..d0e238234234 100644 --- a/fs/crypto/fscrypt_private.h +++ b/fs/crypto/fscrypt_private.h @@ -335,9 +335,16 @@ struct fscrypt_master_key { * FS_IOC_REMOVE_ENCRYPTION_KEY can be retried, or * FS_IOC_ADD_ENCRYPTION_KEY can add the secret again. * - * Locking: protected by key->sem. + * Locking: protected by key->sem (outer) and mk_secret_sem (inner). + * The reason for two locks is that key->sem also protects modifying + * mk_users, which ranks it above the semaphore for the keyring key + * type, which is in turn above page faults (via keyring_read). But + * sometimes filesystems call fscrypt_get_encryption_info() from within + * a transaction, which ranks it below page faults. So we need a + * separate lock which protects mk_secret but not also mk_users. */ struct fscrypt_master_key_secret mk_secret; + struct rw_semaphore mk_secret_sem; /* * For v1 policy keys: an arbitrary key descriptor which was assigned by @@ -348,6 +355,22 @@ struct fscrypt_master_key { struct fscrypt_key_specifier mk_spec; /* + * Keyring which contains a key of type 'key_type_fscrypt_user' for each + * user who has added this key. Normally each key will be added by just + * one user, but it's possible that multiple users share a key, and in + * that case we need to keep track of those users so that one user can't + * remove the key before the others want it removed too. + * + * This is NULL for v1 policy keys; those can only be added by root. + * + * Locking: in addition to this keyrings own semaphore, this is + * protected by the master key's key->sem, so we can do atomic + * search+insert. It can also be searched without taking any locks, but + * in that case the returned key may have already been removed. + */ + struct key *mk_users; + + /* * Length of ->mk_decrypted_inodes, plus one if mk_secret is present. * Once this goes to 0, the master key is removed from ->s_master_keys. * The 'struct fscrypt_master_key' will continue to live as long as the @@ -374,9 +397,9 @@ is_master_key_secret_present(const struct fscrypt_master_key_secret *secret) /* * The READ_ONCE() is only necessary for fscrypt_drop_inode() and * fscrypt_key_describe(). These run in atomic context, so they can't - * take key->sem and thus 'secret' can change concurrently which would - * be a data race. But they only need to know whether the secret *was* - * present at the time of check, so READ_ONCE() suffices. + * take ->mk_secret_sem and thus 'secret' can change concurrently which + * would be a data race. But they only need to know whether the secret + * *was* present at the time of check, so READ_ONCE() suffices. */ return READ_ONCE(secret->size) != 0; } diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c index fca3bdf01e7c..c654effb83f5 100644 --- a/fs/crypto/keyring.c +++ b/fs/crypto/keyring.c @@ -45,6 +45,7 @@ static void free_master_key(struct fscrypt_master_key *mk) for (i = 0; i < ARRAY_SIZE(mk->mk_mode_keys); i++) crypto_free_skcipher(mk->mk_mode_keys[i]); + key_put(mk->mk_users); kzfree(mk); } @@ -93,7 +94,39 @@ static struct key_type key_type_fscrypt = { .describe = fscrypt_key_describe, }; -/* Search ->s_master_keys */ +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) @@ -119,6 +152,13 @@ static struct key *search_fscrypt_keyring(struct key *keyring, #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) @@ -134,6 +174,23 @@ static void format_mk_description( 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) { @@ -181,6 +238,80 @@ struct key *fscrypt_find_master_key(struct super_block *sb, 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' @@ -202,11 +333,26 @@ static int add_new_master_key(struct fscrypt_master_key_secret *secret, mk->mk_spec = *mk_spec; move_master_key_secret(&mk->mk_secret, secret); + init_rwsem(&mk->mk_secret_sem); 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(), @@ -233,13 +379,45 @@ out_free_mk: static int add_existing_master_key(struct fscrypt_master_key *mk, struct fscrypt_master_key_secret *secret) { - if (is_master_key_secret_present(&mk->mk_secret)) - return 0; + struct key *mk_user; + bool rekey; + int err; - if (!refcount_inc_not_zero(&mk->mk_refcount)) + /* + * 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; - move_master_key_secret(&mk->mk_secret, secret); + /* 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) { + down_write(&mk->mk_secret_sem); + move_master_key_secret(&mk->mk_secret, secret); + up_write(&mk->mk_secret_sem); + } return 0; } @@ -266,7 +444,7 @@ retry: } else { /* * Found the key in ->s_master_keys. Re-add the secret if - * needed. + * needed, and add the user to ->mk_users if needed. */ down_write(&key->sem); err = add_existing_master_key(key->payload.data[0], secret); @@ -288,6 +466,23 @@ out_unlock: * 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. */ @@ -318,11 +513,18 @@ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg) if (copy_from_user(secret.raw, uarg->raw, secret.size)) goto out_wipe_secret; - err = -EACCES; - if (!capable(CAP_SYS_ADMIN)) - goto out_wipe_secret; - - if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) { + switch (arg.key_spec.type) { + case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR: + /* + * 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. + */ + err = -EACCES; + if (!capable(CAP_SYS_ADMIN)) + goto out_wipe_secret; + break; + case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER: err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size); if (err) goto out_wipe_secret; @@ -345,6 +547,11 @@ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg) arg.key_spec.u.identifier, FSCRYPT_KEY_IDENTIFIER_SIZE)) goto out_wipe_secret; + break; + default: + WARN_ON(1); + err = -EINVAL; + goto out_wipe_secret; } err = add_master_key(sb, &secret, &arg.key_spec); @@ -492,9 +699,12 @@ static int try_to_lock_encrypted_files(struct super_block *sb, /* * Try to remove an fscrypt master encryption key. * - * 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. + * This removes the current user's claim to the key, then removes the key itself + * if no other users have claims. + * + * 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" @@ -525,7 +735,12 @@ int fscrypt_ioctl_remove_key(struct file *filp, void __user *_uarg) if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved))) return -EINVAL; - if (!capable(CAP_SYS_ADMIN)) + /* + * 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. */ @@ -536,11 +751,34 @@ int fscrypt_ioctl_remove_key(struct file *filp, void __user *_uarg) down_write(&key->sem); - /* Wipe the secret. */ + /* If relevant, remove current user's claim to the key */ + if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) { + 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)) { + down_write(&mk->mk_secret_sem); wipe_master_key_secret(&mk->mk_secret); dead = refcount_dec_and_test(&mk->mk_refcount); + up_write(&mk->mk_secret_sem); } up_write(&key->sem); if (dead) { @@ -560,11 +798,12 @@ int fscrypt_ioctl_remove_key(struct file *filp, void __user *_uarg) } } /* - * We return 0 if we successfully did something: 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. + * 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); @@ -583,6 +822,15 @@ EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key); * 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. */ @@ -603,6 +851,8 @@ int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg) 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); @@ -623,6 +873,20 @@ int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg) } 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); @@ -636,5 +900,19 @@ EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status); int __init fscrypt_init_keyring(void) { - return register_key_type(&key_type_fscrypt); + 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; + + return 0; + +err_unregister_fscrypt: + unregister_key_type(&key_type_fscrypt); + return err; } diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c index f423d48264db..d71c2d6dd162 100644 --- a/fs/crypto/keysetup.c +++ b/fs/crypto/keysetup.c @@ -286,10 +286,10 @@ static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci, * * If the master key is found in the filesystem-level keyring, then the * corresponding 'struct key' is returned in *master_key_ret with - * ->sem read-locked. This is needed to ensure that only one task links the - * fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race to create - * an fscrypt_info for the same inode), and to synchronize the master key being - * removed with a new inode starting to use it. + * ->mk_secret_sem read-locked. This is needed to ensure that only one task + * links the fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race + * to create an fscrypt_info for the same inode), and to synchronize the master + * key being removed with a new inode starting to use it. */ static int setup_file_encryption_key(struct fscrypt_info *ci, struct key **master_key_ret) @@ -333,7 +333,7 @@ static int setup_file_encryption_key(struct fscrypt_info *ci, } mk = key->payload.data[0]; - down_read(&key->sem); + down_read(&mk->mk_secret_sem); /* Has the secret been removed (via FS_IOC_REMOVE_ENCRYPTION_KEY)? */ if (!is_master_key_secret_present(&mk->mk_secret)) { @@ -376,7 +376,7 @@ static int setup_file_encryption_key(struct fscrypt_info *ci, return 0; out_release_key: - up_read(&key->sem); + up_read(&mk->mk_secret_sem); key_put(key); return err; } @@ -514,7 +514,9 @@ int fscrypt_get_encryption_info(struct inode *inode) res = 0; out: if (master_key) { - up_read(&master_key->sem); + struct fscrypt_master_key *mk = master_key->payload.data[0]; + + up_read(&mk->mk_secret_sem); key_put(master_key); } if (res == -ENOKEY) @@ -577,7 +579,7 @@ int fscrypt_drop_inode(struct inode *inode) mk = ci->ci_master_key->payload.data[0]; /* - * Note: since we aren't holding key->sem, the result here can + * Note: since we aren't holding ->mk_secret_sem, the result here can * immediately become outdated. But there's no correctness problem with * unnecessarily evicting. Nor is there a correctness problem with not * evicting while iput() is racing with the key being removed, since diff --git a/include/uapi/linux/fscrypt.h b/include/uapi/linux/fscrypt.h index f961ebf83e98..b9fb775e3db8 100644 --- a/include/uapi/linux/fscrypt.h +++ b/include/uapi/linux/fscrypt.h @@ -120,6 +120,7 @@ struct fscrypt_add_key_arg { struct fscrypt_remove_key_arg { struct fscrypt_key_specifier key_spec; #define FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY 0x00000001 +#define FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS 0x00000002 __u32 removal_status_flags; /* output */ __u32 __reserved[5]; }; @@ -135,7 +136,10 @@ struct fscrypt_get_key_status_arg { #define FSCRYPT_KEY_STATUS_PRESENT 2 #define FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED 3 __u32 status; - __u32 __out_reserved[15]; +#define FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF 0x00000001 + __u32 status_flags; + __u32 user_count; + __u32 __out_reserved[13]; }; #define FS_IOC_SET_ENCRYPTION_POLICY _IOR('f', 19, struct fscrypt_policy) |