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![Eric Biggers](/assets/img/avatar_default.png)
Master keys can be in one of three states: present, incompletely removed, and absent (as per FSCRYPT_KEY_STATUS_* used in the UAPI). Currently, the way that "present" is distinguished from "incompletely removed" internally is by whether ->mk_secret exists or not. With extent-based encryption, it will be necessary to allow per-extent keys to be derived while the master key is incompletely removed, so that I/O on open files will reliably continue working after removal of the key has been initiated. (We could allow I/O to sometimes fail in that case, but that seems problematic for reasons such as writes getting silently thrown away and diverging from the existing fscrypt semantics.) Therefore, when the filesystem is using extent-based encryption, ->mk_secret can't be wiped when the key becomes incompletely removed. As a prerequisite for doing that, this patch makes the "present" state be tracked using a new field, ->mk_present. No behavior is changed yet. The basic idea here is borrowed from Josef Bacik's patch "fscrypt: use a flag to indicate that the master key is being evicted" (https://lore.kernel.org/r/e86c16dddc049ff065f877d793ad773e4c6bfad9.1696970227.git.josef@toxicpanda.com). I reimplemented it using a "present" bool instead of an "evicted" flag, fixed a couple bugs, and tried to update everything to be consistent. Note: I considered adding a ->mk_status field instead, holding one of FSCRYPT_KEY_STATUS_*. At first that seemed nice, but it ended up being more complex (despite simplifying FS_IOC_GET_ENCRYPTION_KEY_STATUS), since it would have introduced redundancy and had weird locking rules. Reviewed-by: Neal Gompa <neal@gompa.dev> Reviewed-by: Josef Bacik <josef@toxicpanda.com> Link: https://lore.kernel.org/r/20231015061055.62673-1-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
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=====================================
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Filesystem-level encryption (fscrypt)
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=====================================
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Introduction
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============
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fscrypt is a library which filesystems can hook into to support
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transparent encryption of files and directories.
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Note: "fscrypt" in this document refers to the kernel-level portion,
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implemented in ``fs/crypto/``, as opposed to the userspace tool
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`fscrypt <https://github.com/google/fscrypt>`_. This document only
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covers the kernel-level portion. For command-line examples of how to
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use encryption, see the documentation for the userspace tool `fscrypt
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<https://github.com/google/fscrypt>`_. Also, it is recommended to use
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the fscrypt userspace tool, or other existing userspace tools such as
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`fscryptctl <https://github.com/google/fscryptctl>`_ or `Android's key
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management system
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<https://source.android.com/security/encryption/file-based>`_, over
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using the kernel's API directly. Using existing tools reduces the
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chance of introducing your own security bugs. (Nevertheless, for
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completeness this documentation covers the kernel's API anyway.)
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Unlike dm-crypt, fscrypt operates at the filesystem level rather than
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at the block device level. This allows it to encrypt different files
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with different keys and to have unencrypted files on the same
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filesystem. This is useful for multi-user systems where each user's
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data-at-rest needs to be cryptographically isolated from the others.
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However, except for filenames, fscrypt does not encrypt filesystem
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metadata.
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Unlike eCryptfs, which is a stacked filesystem, fscrypt is integrated
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directly into supported filesystems --- currently ext4, F2FS, and
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UBIFS. This allows encrypted files to be read and written without
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caching both the decrypted and encrypted pages in the pagecache,
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thereby nearly halving the memory used and bringing it in line with
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unencrypted files. Similarly, half as many dentries and inodes are
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needed. eCryptfs also limits encrypted filenames to 143 bytes,
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causing application compatibility issues; fscrypt allows the full 255
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bytes (NAME_MAX). Finally, unlike eCryptfs, the fscrypt API can be
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used by unprivileged users, with no need to mount anything.
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fscrypt does not support encrypting files in-place. Instead, it
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supports marking an empty directory as encrypted. Then, after
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userspace provides the key, all regular files, directories, and
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symbolic links created in that directory tree are transparently
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encrypted.
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Threat model
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============
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Offline attacks
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---------------
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Provided that userspace chooses a strong encryption key, fscrypt
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protects the confidentiality of file contents and filenames in the
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event of a single point-in-time permanent offline compromise of the
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block device content. fscrypt does not protect the confidentiality of
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non-filename metadata, e.g. file sizes, file permissions, file
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timestamps, and extended attributes. Also, the existence and location
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of holes (unallocated blocks which logically contain all zeroes) in
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files is not protected.
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fscrypt is not guaranteed to protect confidentiality or authenticity
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if an attacker is able to manipulate the filesystem offline prior to
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an authorized user later accessing the filesystem.
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Online attacks
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--------------
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fscrypt (and storage encryption in general) can only provide limited
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protection, if any at all, against online attacks. In detail:
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Side-channel attacks
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~~~~~~~~~~~~~~~~~~~~
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fscrypt is only resistant to side-channel attacks, such as timing or
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electromagnetic attacks, to the extent that the underlying Linux
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Cryptographic API algorithms or inline encryption hardware are. If a
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vulnerable algorithm is used, such as a table-based implementation of
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AES, it may be possible for an attacker to mount a side channel attack
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against the online system. Side channel attacks may also be mounted
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against applications consuming decrypted data.
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Unauthorized file access
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~~~~~~~~~~~~~~~~~~~~~~~~
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After an encryption key has been added, fscrypt does not hide the
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plaintext file contents or filenames from other users on the same
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system. Instead, existing access control mechanisms such as file mode
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bits, POSIX ACLs, LSMs, or namespaces should be used for this purpose.
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(For the reasoning behind this, understand that while the key is
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added, the confidentiality of the data, from the perspective of the
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system itself, is *not* protected by the mathematical properties of
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encryption but rather only by the correctness of the kernel.
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Therefore, any encryption-specific access control checks would merely
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be enforced by kernel *code* and therefore would be largely redundant
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with the wide variety of access control mechanisms already available.)
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Kernel memory compromise
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~~~~~~~~~~~~~~~~~~~~~~~~
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An attacker who compromises the system enough to read from arbitrary
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memory, e.g. by mounting a physical attack or by exploiting a kernel
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security vulnerability, can compromise all encryption keys that are
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currently in use.
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However, fscrypt allows encryption keys to be removed from the kernel,
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which may protect them from later compromise.
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In more detail, the FS_IOC_REMOVE_ENCRYPTION_KEY ioctl (or the
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FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS ioctl) can wipe a master
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encryption key from kernel memory. If it does so, it will also try to
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evict all cached inodes which had been "unlocked" using the key,
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thereby wiping their per-file keys and making them once again appear
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"locked", i.e. in ciphertext or encrypted form.
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However, these ioctls have some limitations:
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- Per-file keys for in-use files will *not* be removed or wiped.
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Therefore, for maximum effect, userspace should close the relevant
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encrypted files and directories before removing a master key, as
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well as kill any processes whose working directory is in an affected
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encrypted directory.
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- The kernel cannot magically wipe copies of the master key(s) that
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userspace might have as well. Therefore, userspace must wipe all
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copies of the master key(s) it makes as well; normally this should
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be done immediately after FS_IOC_ADD_ENCRYPTION_KEY, without waiting
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for FS_IOC_REMOVE_ENCRYPTION_KEY. Naturally, the same also applies
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to all higher levels in the key hierarchy. Userspace should also
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follow other security precautions such as mlock()ing memory
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containing keys to prevent it from being swapped out.
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- In general, decrypted contents and filenames in the kernel VFS
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caches are freed but not wiped. Therefore, portions thereof may be
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recoverable from freed memory, even after the corresponding key(s)
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were wiped. To partially solve this, you can set
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CONFIG_PAGE_POISONING=y in your kernel config and add page_poison=1
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to your kernel command line. However, this has a performance cost.
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- Secret keys might still exist in CPU registers, in crypto
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accelerator hardware (if used by the crypto API to implement any of
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the algorithms), or in other places not explicitly considered here.
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Limitations of v1 policies
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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v1 encryption policies have some weaknesses with respect to online
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attacks:
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- There is no verification that the provided master key is correct.
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Therefore, a malicious user can temporarily associate the wrong key
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with another user's encrypted files to which they have read-only
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access. Because of filesystem caching, the wrong key will then be
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used by the other user's accesses to those files, even if the other
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user has the correct key in their own keyring. This violates the
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meaning of "read-only access".
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- A compromise of a per-file key also compromises the master key from
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which it was derived.
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- Non-root users cannot securely remove encryption keys.
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All the above problems are fixed with v2 encryption policies. For
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this reason among others, it is recommended to use v2 encryption
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policies on all new encrypted directories.
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Key hierarchy
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=============
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Master Keys
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-----------
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Each encrypted directory tree is protected by a *master key*. Master
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keys can be up to 64 bytes long, and must be at least as long as the
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greater of the security strength of the contents and filenames
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encryption modes being used. For example, if any AES-256 mode is
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used, the master key must be at least 256 bits, i.e. 32 bytes. A
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stricter requirement applies if the key is used by a v1 encryption
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policy and AES-256-XTS is used; such keys must be 64 bytes.
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To "unlock" an encrypted directory tree, userspace must provide the
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appropriate master key. There can be any number of master keys, each
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of which protects any number of directory trees on any number of
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filesystems.
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Master keys must be real cryptographic keys, i.e. indistinguishable
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from random bytestrings of the same length. This implies that users
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**must not** directly use a password as a master key, zero-pad a
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shorter key, or repeat a shorter key. Security cannot be guaranteed
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if userspace makes any such error, as the cryptographic proofs and
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analysis would no longer apply.
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Instead, users should generate master keys either using a
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cryptographically secure random number generator, or by using a KDF
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(Key Derivation Function). The kernel does not do any key stretching;
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therefore, if userspace derives the key from a low-entropy secret such
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as a passphrase, it is critical that a KDF designed for this purpose
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be used, such as scrypt, PBKDF2, or Argon2.
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Key derivation function
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-----------------------
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With one exception, fscrypt never uses the master key(s) for
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encryption directly. Instead, they are only used as input to a KDF
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(Key Derivation Function) to derive the actual keys.
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The KDF used for a particular master key differs depending on whether
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the key is used for v1 encryption policies or for v2 encryption
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policies. Users **must not** use the same key for both v1 and v2
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encryption policies. (No real-world attack is currently known on this
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specific case of key reuse, but its security cannot be guaranteed
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since the cryptographic proofs and analysis would no longer apply.)
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For v1 encryption policies, the KDF only supports deriving per-file
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encryption keys. It works by encrypting the master key with
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AES-128-ECB, using the file's 16-byte nonce as the AES key. The
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resulting ciphertext is used as the derived key. If the ciphertext is
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longer than needed, then it is truncated to the needed length.
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For v2 encryption policies, the KDF is HKDF-SHA512. The master key is
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passed as the "input keying material", no salt is used, and a distinct
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"application-specific information string" is used for each distinct
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key to be derived. For example, when a per-file encryption key is
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derived, the application-specific information string is the file's
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nonce prefixed with "fscrypt\\0" and a context byte. Different
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context bytes are used for other types of derived keys.
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HKDF-SHA512 is preferred to the original AES-128-ECB based KDF because
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HKDF is more flexible, is nonreversible, and evenly distributes
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entropy from the master key. HKDF is also standardized and widely
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used by other software, whereas the AES-128-ECB based KDF is ad-hoc.
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Per-file encryption keys
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------------------------
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Since each master key can protect many files, it is necessary to
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"tweak" the encryption of each file so that the same plaintext in two
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files doesn't map to the same ciphertext, or vice versa. In most
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cases, fscrypt does this by deriving per-file keys. When a new
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encrypted inode (regular file, directory, or symlink) is created,
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fscrypt randomly generates a 16-byte nonce and stores it in the
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inode's encryption xattr. Then, it uses a KDF (as described in `Key
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derivation function`_) to derive the file's key from the master key
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and nonce.
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Key derivation was chosen over key wrapping because wrapped keys would
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require larger xattrs which would be less likely to fit in-line in the
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filesystem's inode table, and there didn't appear to be any
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significant advantages to key wrapping. In particular, currently
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there is no requirement to support unlocking a file with multiple
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alternative master keys or to support rotating master keys. Instead,
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the master keys may be wrapped in userspace, e.g. as is done by the
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`fscrypt <https://github.com/google/fscrypt>`_ tool.
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DIRECT_KEY policies
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-------------------
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The Adiantum encryption mode (see `Encryption modes and usage`_) is
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suitable for both contents and filenames encryption, and it accepts
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long IVs --- long enough to hold both an 8-byte data unit index and a
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16-byte per-file nonce. Also, the overhead of each Adiantum key is
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greater than that of an AES-256-XTS key.
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Therefore, to improve performance and save memory, for Adiantum a
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"direct key" configuration is supported. When the user has enabled
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this by setting FSCRYPT_POLICY_FLAG_DIRECT_KEY in the fscrypt policy,
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per-file encryption keys are not used. Instead, whenever any data
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(contents or filenames) is encrypted, the file's 16-byte nonce is
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included in the IV. Moreover:
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- For v1 encryption policies, the encryption is done directly with the
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master key. Because of this, users **must not** use the same master
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key for any other purpose, even for other v1 policies.
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- For v2 encryption policies, the encryption is done with a per-mode
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key derived using the KDF. Users may use the same master key for
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other v2 encryption policies.
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IV_INO_LBLK_64 policies
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-----------------------
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When FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64 is set in the fscrypt policy,
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the encryption keys are derived from the master key, encryption mode
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number, and filesystem UUID. This normally results in all files
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protected by the same master key sharing a single contents encryption
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key and a single filenames encryption key. To still encrypt different
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files' data differently, inode numbers are included in the IVs.
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Consequently, shrinking the filesystem may not be allowed.
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This format is optimized for use with inline encryption hardware
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compliant with the UFS standard, which supports only 64 IV bits per
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I/O request and may have only a small number of keyslots.
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IV_INO_LBLK_32 policies
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-----------------------
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IV_INO_LBLK_32 policies work like IV_INO_LBLK_64, except that for
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IV_INO_LBLK_32, the inode number is hashed with SipHash-2-4 (where the
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SipHash key is derived from the master key) and added to the file data
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unit index mod 2^32 to produce a 32-bit IV.
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This format is optimized for use with inline encryption hardware
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compliant with the eMMC v5.2 standard, which supports only 32 IV bits
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per I/O request and may have only a small number of keyslots. This
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format results in some level of IV reuse, so it should only be used
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when necessary due to hardware limitations.
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Key identifiers
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---------------
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For master keys used for v2 encryption policies, a unique 16-byte "key
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identifier" is also derived using the KDF. This value is stored in
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the clear, since it is needed to reliably identify the key itself.
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Dirhash keys
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------------
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For directories that are indexed using a secret-keyed dirhash over the
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plaintext filenames, the KDF is also used to derive a 128-bit
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SipHash-2-4 key per directory in order to hash filenames. This works
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just like deriving a per-file encryption key, except that a different
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KDF context is used. Currently, only casefolded ("case-insensitive")
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encrypted directories use this style of hashing.
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Encryption modes and usage
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==========================
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fscrypt allows one encryption mode to be specified for file contents
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and one encryption mode to be specified for filenames. Different
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directory trees are permitted to use different encryption modes.
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Supported modes
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---------------
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Currently, the following pairs of encryption modes are supported:
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- AES-256-XTS for contents and AES-256-CTS-CBC for filenames
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- AES-256-XTS for contents and AES-256-HCTR2 for filenames
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- Adiantum for both contents and filenames
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- AES-128-CBC-ESSIV for contents and AES-128-CTS-CBC for filenames
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- SM4-XTS for contents and SM4-CTS-CBC for filenames
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Authenticated encryption modes are not currently supported because of
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the difficulty of dealing with ciphertext expansion. Therefore,
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contents encryption uses a block cipher in `XTS mode
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<https://en.wikipedia.org/wiki/Disk_encryption_theory#XTS>`_ or
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`CBC-ESSIV mode
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<https://en.wikipedia.org/wiki/Disk_encryption_theory#Encrypted_salt-sector_initialization_vector_(ESSIV)>`_,
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or a wide-block cipher. Filenames encryption uses a
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block cipher in `CTS-CBC mode
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<https://en.wikipedia.org/wiki/Ciphertext_stealing>`_ or a wide-block
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cipher.
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The (AES-256-XTS, AES-256-CTS-CBC) pair is the recommended default.
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It is also the only option that is *guaranteed* to always be supported
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if the kernel supports fscrypt at all; see `Kernel config options`_.
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The (AES-256-XTS, AES-256-HCTR2) pair is also a good choice that
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upgrades the filenames encryption to use a wide-block cipher. (A
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*wide-block cipher*, also called a tweakable super-pseudorandom
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permutation, has the property that changing one bit scrambles the
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entire result.) As described in `Filenames encryption`_, a wide-block
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cipher is the ideal mode for the problem domain, though CTS-CBC is the
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"least bad" choice among the alternatives. For more information about
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HCTR2, see `the HCTR2 paper <https://eprint.iacr.org/2021/1441.pdf>`_.
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Adiantum is recommended on systems where AES is too slow due to lack
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of hardware acceleration for AES. Adiantum is a wide-block cipher
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that uses XChaCha12 and AES-256 as its underlying components. Most of
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the work is done by XChaCha12, which is much faster than AES when AES
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acceleration is unavailable. For more information about Adiantum, see
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`the Adiantum paper <https://eprint.iacr.org/2018/720.pdf>`_.
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The (AES-128-CBC-ESSIV, AES-128-CTS-CBC) pair exists only to support
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systems whose only form of AES acceleration is an off-CPU crypto
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accelerator such as CAAM or CESA that does not support XTS.
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The remaining mode pairs are the "national pride ciphers":
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- (SM4-XTS, SM4-CTS-CBC)
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Generally speaking, these ciphers aren't "bad" per se, but they
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receive limited security review compared to the usual choices such as
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AES and ChaCha. They also don't bring much new to the table. It is
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suggested to only use these ciphers where their use is mandated.
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Kernel config options
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---------------------
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Enabling fscrypt support (CONFIG_FS_ENCRYPTION) automatically pulls in
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only the basic support from the crypto API needed to use AES-256-XTS
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and AES-256-CTS-CBC encryption. For optimal performance, it is
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strongly recommended to also enable any available platform-specific
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kconfig options that provide acceleration for the algorithm(s) you
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wish to use. Support for any "non-default" encryption modes typically
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requires extra kconfig options as well.
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Below, some relevant options are listed by encryption mode. Note,
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acceleration options not listed below may be available for your
|
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platform; refer to the kconfig menus. File contents encryption can
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also be configured to use inline encryption hardware instead of the
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kernel crypto API (see `Inline encryption support`_); in that case,
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the file contents mode doesn't need to supported in the kernel crypto
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API, but the filenames mode still does.
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- AES-256-XTS and AES-256-CTS-CBC
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- Recommended:
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- arm64: CONFIG_CRYPTO_AES_ARM64_CE_BLK
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- x86: CONFIG_CRYPTO_AES_NI_INTEL
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- AES-256-HCTR2
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- Mandatory:
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- CONFIG_CRYPTO_HCTR2
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- Recommended:
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- arm64: CONFIG_CRYPTO_AES_ARM64_CE_BLK
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- arm64: CONFIG_CRYPTO_POLYVAL_ARM64_CE
|
|
- x86: CONFIG_CRYPTO_AES_NI_INTEL
|
|
- x86: CONFIG_CRYPTO_POLYVAL_CLMUL_NI
|
|
|
|
- Adiantum
|
|
- Mandatory:
|
|
- CONFIG_CRYPTO_ADIANTUM
|
|
- Recommended:
|
|
- arm32: CONFIG_CRYPTO_CHACHA20_NEON
|
|
- arm32: CONFIG_CRYPTO_NHPOLY1305_NEON
|
|
- arm64: CONFIG_CRYPTO_CHACHA20_NEON
|
|
- arm64: CONFIG_CRYPTO_NHPOLY1305_NEON
|
|
- x86: CONFIG_CRYPTO_CHACHA20_X86_64
|
|
- x86: CONFIG_CRYPTO_NHPOLY1305_SSE2
|
|
- x86: CONFIG_CRYPTO_NHPOLY1305_AVX2
|
|
|
|
- AES-128-CBC-ESSIV and AES-128-CTS-CBC:
|
|
- Mandatory:
|
|
- CONFIG_CRYPTO_ESSIV
|
|
- CONFIG_CRYPTO_SHA256 or another SHA-256 implementation
|
|
- Recommended:
|
|
- AES-CBC acceleration
|
|
|
|
fscrypt also uses HMAC-SHA512 for key derivation, so enabling SHA-512
|
|
acceleration is recommended:
|
|
|
|
- SHA-512
|
|
- Recommended:
|
|
- arm64: CONFIG_CRYPTO_SHA512_ARM64_CE
|
|
- x86: CONFIG_CRYPTO_SHA512_SSSE3
|
|
|
|
Contents encryption
|
|
-------------------
|
|
|
|
For contents encryption, each file's contents is divided into "data
|
|
units". Each data unit is encrypted independently. The IV for each
|
|
data unit incorporates the zero-based index of the data unit within
|
|
the file. This ensures that each data unit within a file is encrypted
|
|
differently, which is essential to prevent leaking information.
|
|
|
|
Note: the encryption depending on the offset into the file means that
|
|
operations like "collapse range" and "insert range" that rearrange the
|
|
extent mapping of files are not supported on encrypted files.
|
|
|
|
There are two cases for the sizes of the data units:
|
|
|
|
* Fixed-size data units. This is how all filesystems other than UBIFS
|
|
work. A file's data units are all the same size; the last data unit
|
|
is zero-padded if needed. By default, the data unit size is equal
|
|
to the filesystem block size. On some filesystems, users can select
|
|
a sub-block data unit size via the ``log2_data_unit_size`` field of
|
|
the encryption policy; see `FS_IOC_SET_ENCRYPTION_POLICY`_.
|
|
|
|
* Variable-size data units. This is what UBIFS does. Each "UBIFS
|
|
data node" is treated as a crypto data unit. Each contains variable
|
|
length, possibly compressed data, zero-padded to the next 16-byte
|
|
boundary. Users cannot select a sub-block data unit size on UBIFS.
|
|
|
|
In the case of compression + encryption, the compressed data is
|
|
encrypted. UBIFS compression works as described above. f2fs
|
|
compression works a bit differently; it compresses a number of
|
|
filesystem blocks into a smaller number of filesystem blocks.
|
|
Therefore a f2fs-compressed file still uses fixed-size data units, and
|
|
it is encrypted in a similar way to a file containing holes.
|
|
|
|
As mentioned in `Key hierarchy`_, the default encryption setting uses
|
|
per-file keys. In this case, the IV for each data unit is simply the
|
|
index of the data unit in the file. However, users can select an
|
|
encryption setting that does not use per-file keys. For these, some
|
|
kind of file identifier is incorporated into the IVs as follows:
|
|
|
|
- With `DIRECT_KEY policies`_, the data unit index is placed in bits
|
|
0-63 of the IV, and the file's nonce is placed in bits 64-191.
|
|
|
|
- With `IV_INO_LBLK_64 policies`_, the data unit index is placed in
|
|
bits 0-31 of the IV, and the file's inode number is placed in bits
|
|
32-63. This setting is only allowed when data unit indices and
|
|
inode numbers fit in 32 bits.
|
|
|
|
- With `IV_INO_LBLK_32 policies`_, the file's inode number is hashed
|
|
and added to the data unit index. The resulting value is truncated
|
|
to 32 bits and placed in bits 0-31 of the IV. This setting is only
|
|
allowed when data unit indices and inode numbers fit in 32 bits.
|
|
|
|
The byte order of the IV is always little endian.
|
|
|
|
If the user selects FSCRYPT_MODE_AES_128_CBC for the contents mode, an
|
|
ESSIV layer is automatically included. In this case, before the IV is
|
|
passed to AES-128-CBC, it is encrypted with AES-256 where the AES-256
|
|
key is the SHA-256 hash of the file's contents encryption key.
|
|
|
|
Filenames encryption
|
|
--------------------
|
|
|
|
For filenames, each full filename is encrypted at once. Because of
|
|
the requirements to retain support for efficient directory lookups and
|
|
filenames of up to 255 bytes, the same IV is used for every filename
|
|
in a directory.
|
|
|
|
However, each encrypted directory still uses a unique key, or
|
|
alternatively has the file's nonce (for `DIRECT_KEY policies`_) or
|
|
inode number (for `IV_INO_LBLK_64 policies`_) included in the IVs.
|
|
Thus, IV reuse is limited to within a single directory.
|
|
|
|
With CTS-CBC, the IV reuse means that when the plaintext filenames share a
|
|
common prefix at least as long as the cipher block size (16 bytes for AES), the
|
|
corresponding encrypted filenames will also share a common prefix. This is
|
|
undesirable. Adiantum and HCTR2 do not have this weakness, as they are
|
|
wide-block encryption modes.
|
|
|
|
All supported filenames encryption modes accept any plaintext length
|
|
>= 16 bytes; cipher block alignment is not required. However,
|
|
filenames shorter than 16 bytes are NUL-padded to 16 bytes before
|
|
being encrypted. In addition, to reduce leakage of filename lengths
|
|
via their ciphertexts, all filenames are NUL-padded to the next 4, 8,
|
|
16, or 32-byte boundary (configurable). 32 is recommended since this
|
|
provides the best confidentiality, at the cost of making directory
|
|
entries consume slightly more space. Note that since NUL (``\0``) is
|
|
not otherwise a valid character in filenames, the padding will never
|
|
produce duplicate plaintexts.
|
|
|
|
Symbolic link targets are considered a type of filename and are
|
|
encrypted in the same way as filenames in directory entries, except
|
|
that IV reuse is not a problem as each symlink has its own inode.
|
|
|
|
User API
|
|
========
|
|
|
|
Setting an encryption policy
|
|
----------------------------
|
|
|
|
FS_IOC_SET_ENCRYPTION_POLICY
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The FS_IOC_SET_ENCRYPTION_POLICY ioctl sets an encryption policy on an
|
|
empty directory or verifies that a directory or regular file already
|
|
has the specified encryption policy. It takes in a pointer to
|
|
struct fscrypt_policy_v1 or struct fscrypt_policy_v2, defined as
|
|
follows::
|
|
|
|
#define FSCRYPT_POLICY_V1 0
|
|
#define FSCRYPT_KEY_DESCRIPTOR_SIZE 8
|
|
struct fscrypt_policy_v1 {
|
|
__u8 version;
|
|
__u8 contents_encryption_mode;
|
|
__u8 filenames_encryption_mode;
|
|
__u8 flags;
|
|
__u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
|
|
};
|
|
#define fscrypt_policy fscrypt_policy_v1
|
|
|
|
#define FSCRYPT_POLICY_V2 2
|
|
#define FSCRYPT_KEY_IDENTIFIER_SIZE 16
|
|
struct fscrypt_policy_v2 {
|
|
__u8 version;
|
|
__u8 contents_encryption_mode;
|
|
__u8 filenames_encryption_mode;
|
|
__u8 flags;
|
|
__u8 log2_data_unit_size;
|
|
__u8 __reserved[3];
|
|
__u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
|
|
};
|
|
|
|
This structure must be initialized as follows:
|
|
|
|
- ``version`` must be FSCRYPT_POLICY_V1 (0) if
|
|
struct fscrypt_policy_v1 is used or FSCRYPT_POLICY_V2 (2) if
|
|
struct fscrypt_policy_v2 is used. (Note: we refer to the original
|
|
policy version as "v1", though its version code is really 0.)
|
|
For new encrypted directories, use v2 policies.
|
|
|
|
- ``contents_encryption_mode`` and ``filenames_encryption_mode`` must
|
|
be set to constants from ``<linux/fscrypt.h>`` which identify the
|
|
encryption modes to use. If unsure, use FSCRYPT_MODE_AES_256_XTS
|
|
(1) for ``contents_encryption_mode`` and FSCRYPT_MODE_AES_256_CTS
|
|
(4) for ``filenames_encryption_mode``. For details, see `Encryption
|
|
modes and usage`_.
|
|
|
|
v1 encryption policies only support three combinations of modes:
|
|
(FSCRYPT_MODE_AES_256_XTS, FSCRYPT_MODE_AES_256_CTS),
|
|
(FSCRYPT_MODE_AES_128_CBC, FSCRYPT_MODE_AES_128_CTS), and
|
|
(FSCRYPT_MODE_ADIANTUM, FSCRYPT_MODE_ADIANTUM). v2 policies support
|
|
all combinations documented in `Supported modes`_.
|
|
|
|
- ``flags`` contains optional flags from ``<linux/fscrypt.h>``:
|
|
|
|
- FSCRYPT_POLICY_FLAGS_PAD_*: The amount of NUL padding to use when
|
|
encrypting filenames. If unsure, use FSCRYPT_POLICY_FLAGS_PAD_32
|
|
(0x3).
|
|
- FSCRYPT_POLICY_FLAG_DIRECT_KEY: See `DIRECT_KEY policies`_.
|
|
- FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64: See `IV_INO_LBLK_64
|
|
policies`_.
|
|
- FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32: See `IV_INO_LBLK_32
|
|
policies`_.
|
|
|
|
v1 encryption policies only support the PAD_* and DIRECT_KEY flags.
|
|
The other flags are only supported by v2 encryption policies.
|
|
|
|
The DIRECT_KEY, IV_INO_LBLK_64, and IV_INO_LBLK_32 flags are
|
|
mutually exclusive.
|
|
|
|
- ``log2_data_unit_size`` is the log2 of the data unit size in bytes,
|
|
or 0 to select the default data unit size. The data unit size is
|
|
the granularity of file contents encryption. For example, setting
|
|
``log2_data_unit_size`` to 12 causes file contents be passed to the
|
|
underlying encryption algorithm (such as AES-256-XTS) in 4096-byte
|
|
data units, each with its own IV.
|
|
|
|
Not all filesystems support setting ``log2_data_unit_size``. ext4
|
|
and f2fs support it since Linux v6.7. On filesystems that support
|
|
it, the supported nonzero values are 9 through the log2 of the
|
|
filesystem block size, inclusively. The default value of 0 selects
|
|
the filesystem block size.
|
|
|
|
The main use case for ``log2_data_unit_size`` is for selecting a
|
|
data unit size smaller than the filesystem block size for
|
|
compatibility with inline encryption hardware that only supports
|
|
smaller data unit sizes. ``/sys/block/$disk/queue/crypto/`` may be
|
|
useful for checking which data unit sizes are supported by a
|
|
particular system's inline encryption hardware.
|
|
|
|
Leave this field zeroed unless you are certain you need it. Using
|
|
an unnecessarily small data unit size reduces performance.
|
|
|
|
- For v2 encryption policies, ``__reserved`` must be zeroed.
|
|
|
|
- For v1 encryption policies, ``master_key_descriptor`` specifies how
|
|
to find the master key in a keyring; see `Adding keys`_. It is up
|
|
to userspace to choose a unique ``master_key_descriptor`` for each
|
|
master key. The e4crypt and fscrypt tools use the first 8 bytes of
|
|
``SHA-512(SHA-512(master_key))``, but this particular scheme is not
|
|
required. Also, the master key need not be in the keyring yet when
|
|
FS_IOC_SET_ENCRYPTION_POLICY is executed. However, it must be added
|
|
before any files can be created in the encrypted directory.
|
|
|
|
For v2 encryption policies, ``master_key_descriptor`` has been
|
|
replaced with ``master_key_identifier``, which is longer and cannot
|
|
be arbitrarily chosen. Instead, the key must first be added using
|
|
`FS_IOC_ADD_ENCRYPTION_KEY`_. Then, the ``key_spec.u.identifier``
|
|
the kernel returned in the struct fscrypt_add_key_arg must
|
|
be used as the ``master_key_identifier`` in
|
|
struct fscrypt_policy_v2.
|
|
|
|
If the file is not yet encrypted, then FS_IOC_SET_ENCRYPTION_POLICY
|
|
verifies that the file is an empty directory. If so, the specified
|
|
encryption policy is assigned to the directory, turning it into an
|
|
encrypted directory. After that, and after providing the
|
|
corresponding master key as described in `Adding keys`_, all regular
|
|
files, directories (recursively), and symlinks created in the
|
|
directory will be encrypted, inheriting the same encryption policy.
|
|
The filenames in the directory's entries will be encrypted as well.
|
|
|
|
Alternatively, if the file is already encrypted, then
|
|
FS_IOC_SET_ENCRYPTION_POLICY validates that the specified encryption
|
|
policy exactly matches the actual one. If they match, then the ioctl
|
|
returns 0. Otherwise, it fails with EEXIST. This works on both
|
|
regular files and directories, including nonempty directories.
|
|
|
|
When a v2 encryption policy is assigned to a directory, it is also
|
|
required that either the specified key has been added by the current
|
|
user or that the caller has CAP_FOWNER in the initial user namespace.
|
|
(This is needed to prevent a user from encrypting their data with
|
|
another user's key.) The key must remain added while
|
|
FS_IOC_SET_ENCRYPTION_POLICY is executing. However, if the new
|
|
encrypted directory does not need to be accessed immediately, then the
|
|
key can be removed right away afterwards.
|
|
|
|
Note that the ext4 filesystem does not allow the root directory to be
|
|
encrypted, even if it is empty. Users who want to encrypt an entire
|
|
filesystem with one key should consider using dm-crypt instead.
|
|
|
|
FS_IOC_SET_ENCRYPTION_POLICY can fail with the following errors:
|
|
|
|
- ``EACCES``: the file is not owned by the process's uid, nor does the
|
|
process have the CAP_FOWNER capability in a namespace with the file
|
|
owner's uid mapped
|
|
- ``EEXIST``: the file is already encrypted with an encryption policy
|
|
different from the one specified
|
|
- ``EINVAL``: an invalid encryption policy was specified (invalid
|
|
version, mode(s), or flags; or reserved bits were set); or a v1
|
|
encryption policy was specified but the directory has the casefold
|
|
flag enabled (casefolding is incompatible with v1 policies).
|
|
- ``ENOKEY``: a v2 encryption policy was specified, but the key with
|
|
the specified ``master_key_identifier`` has not been added, nor does
|
|
the process have the CAP_FOWNER capability in the initial user
|
|
namespace
|
|
- ``ENOTDIR``: the file is unencrypted and is a regular file, not a
|
|
directory
|
|
- ``ENOTEMPTY``: the file is unencrypted and is a nonempty directory
|
|
- ``ENOTTY``: this type of filesystem does not implement encryption
|
|
- ``EOPNOTSUPP``: the kernel was not configured with encryption
|
|
support for filesystems, or the filesystem superblock has not
|
|
had encryption enabled on it. (For example, to use encryption on an
|
|
ext4 filesystem, CONFIG_FS_ENCRYPTION must be enabled in the
|
|
kernel config, and the superblock must have had the "encrypt"
|
|
feature flag enabled using ``tune2fs -O encrypt`` or ``mkfs.ext4 -O
|
|
encrypt``.)
|
|
- ``EPERM``: this directory may not be encrypted, e.g. because it is
|
|
the root directory of an ext4 filesystem
|
|
- ``EROFS``: the filesystem is readonly
|
|
|
|
Getting an encryption policy
|
|
----------------------------
|
|
|
|
Two ioctls are available to get a file's encryption policy:
|
|
|
|
- `FS_IOC_GET_ENCRYPTION_POLICY_EX`_
|
|
- `FS_IOC_GET_ENCRYPTION_POLICY`_
|
|
|
|
The extended (_EX) version of the ioctl is more general and is
|
|
recommended to use when possible. However, on older kernels only the
|
|
original ioctl is available. Applications should try the extended
|
|
version, and if it fails with ENOTTY fall back to the original
|
|
version.
|
|
|
|
FS_IOC_GET_ENCRYPTION_POLICY_EX
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The FS_IOC_GET_ENCRYPTION_POLICY_EX ioctl retrieves the encryption
|
|
policy, if any, for a directory or regular file. No additional
|
|
permissions are required beyond the ability to open the file. It
|
|
takes in a pointer to struct fscrypt_get_policy_ex_arg,
|
|
defined as follows::
|
|
|
|
struct fscrypt_get_policy_ex_arg {
|
|
__u64 policy_size; /* input/output */
|
|
union {
|
|
__u8 version;
|
|
struct fscrypt_policy_v1 v1;
|
|
struct fscrypt_policy_v2 v2;
|
|
} policy; /* output */
|
|
};
|
|
|
|
The caller must initialize ``policy_size`` to the size available for
|
|
the policy struct, i.e. ``sizeof(arg.policy)``.
|
|
|
|
On success, the policy struct is returned in ``policy``, and its
|
|
actual size is returned in ``policy_size``. ``policy.version`` should
|
|
be checked to determine the version of policy returned. Note that the
|
|
version code for the "v1" policy is actually 0 (FSCRYPT_POLICY_V1).
|
|
|
|
FS_IOC_GET_ENCRYPTION_POLICY_EX can fail with the following errors:
|
|
|
|
- ``EINVAL``: the file is encrypted, but it uses an unrecognized
|
|
encryption policy version
|
|
- ``ENODATA``: the file is not encrypted
|
|
- ``ENOTTY``: this type of filesystem does not implement encryption,
|
|
or this kernel is too old to support FS_IOC_GET_ENCRYPTION_POLICY_EX
|
|
(try FS_IOC_GET_ENCRYPTION_POLICY instead)
|
|
- ``EOPNOTSUPP``: the kernel was not configured with encryption
|
|
support for this filesystem, or the filesystem superblock has not
|
|
had encryption enabled on it
|
|
- ``EOVERFLOW``: the file is encrypted and uses a recognized
|
|
encryption policy version, but the policy struct does not fit into
|
|
the provided buffer
|
|
|
|
Note: if you only need to know whether a file is encrypted or not, on
|
|
most filesystems it is also possible to use the FS_IOC_GETFLAGS ioctl
|
|
and check for FS_ENCRYPT_FL, or to use the statx() system call and
|
|
check for STATX_ATTR_ENCRYPTED in stx_attributes.
|
|
|
|
FS_IOC_GET_ENCRYPTION_POLICY
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The FS_IOC_GET_ENCRYPTION_POLICY ioctl can also retrieve the
|
|
encryption policy, if any, for a directory or regular file. However,
|
|
unlike `FS_IOC_GET_ENCRYPTION_POLICY_EX`_,
|
|
FS_IOC_GET_ENCRYPTION_POLICY only supports the original policy
|
|
version. It takes in a pointer directly to struct fscrypt_policy_v1
|
|
rather than struct fscrypt_get_policy_ex_arg.
|
|
|
|
The error codes for FS_IOC_GET_ENCRYPTION_POLICY are the same as those
|
|
for FS_IOC_GET_ENCRYPTION_POLICY_EX, except that
|
|
FS_IOC_GET_ENCRYPTION_POLICY also returns ``EINVAL`` if the file is
|
|
encrypted using a newer encryption policy version.
|
|
|
|
Getting the per-filesystem salt
|
|
-------------------------------
|
|
|
|
Some filesystems, such as ext4 and F2FS, also support the deprecated
|
|
ioctl FS_IOC_GET_ENCRYPTION_PWSALT. This ioctl retrieves a randomly
|
|
generated 16-byte value stored in the filesystem superblock. This
|
|
value is intended to used as a salt when deriving an encryption key
|
|
from a passphrase or other low-entropy user credential.
|
|
|
|
FS_IOC_GET_ENCRYPTION_PWSALT is deprecated. Instead, prefer to
|
|
generate and manage any needed salt(s) in userspace.
|
|
|
|
Getting a file's encryption nonce
|
|
---------------------------------
|
|
|
|
Since Linux v5.7, the ioctl FS_IOC_GET_ENCRYPTION_NONCE is supported.
|
|
On encrypted files and directories it gets the inode's 16-byte nonce.
|
|
On unencrypted files and directories, it fails with ENODATA.
|
|
|
|
This ioctl can be useful for automated tests which verify that the
|
|
encryption is being done correctly. It is not needed for normal use
|
|
of fscrypt.
|
|
|
|
Adding keys
|
|
-----------
|
|
|
|
FS_IOC_ADD_ENCRYPTION_KEY
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The FS_IOC_ADD_ENCRYPTION_KEY ioctl adds a master encryption key to
|
|
the filesystem, making all files on the filesystem which were
|
|
encrypted using that key appear "unlocked", i.e. in plaintext form.
|
|
It can be executed on any file or directory on the target filesystem,
|
|
but using the filesystem's root directory is recommended. It takes in
|
|
a pointer to struct fscrypt_add_key_arg, defined as follows::
|
|
|
|
struct fscrypt_add_key_arg {
|
|
struct fscrypt_key_specifier key_spec;
|
|
__u32 raw_size;
|
|
__u32 key_id;
|
|
__u32 __reserved[8];
|
|
__u8 raw[];
|
|
};
|
|
|
|
#define FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR 1
|
|
#define FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER 2
|
|
|
|
struct fscrypt_key_specifier {
|
|
__u32 type; /* one of FSCRYPT_KEY_SPEC_TYPE_* */
|
|
__u32 __reserved;
|
|
union {
|
|
__u8 __reserved[32]; /* reserve some extra space */
|
|
__u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
|
|
__u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
|
|
} u;
|
|
};
|
|
|
|
struct fscrypt_provisioning_key_payload {
|
|
__u32 type;
|
|
__u32 __reserved;
|
|
__u8 raw[];
|
|
};
|
|
|
|
struct fscrypt_add_key_arg must be zeroed, then initialized
|
|
as follows:
|
|
|
|
- If the key is being added for use by v1 encryption policies, then
|
|
``key_spec.type`` must contain FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR, and
|
|
``key_spec.u.descriptor`` must contain the descriptor of the key
|
|
being added, corresponding to the value in the
|
|
``master_key_descriptor`` field of struct fscrypt_policy_v1.
|
|
To add this type of key, the calling process must have the
|
|
CAP_SYS_ADMIN capability in the initial user namespace.
|
|
|
|
Alternatively, if the key is being added for use by v2 encryption
|
|
policies, then ``key_spec.type`` must contain
|
|
FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER, and ``key_spec.u.identifier`` is
|
|
an *output* field which the kernel fills in with a cryptographic
|
|
hash of the key. To add this type of key, the calling process does
|
|
not need any privileges. However, the number of keys that can be
|
|
added is limited by the user's quota for the keyrings service (see
|
|
``Documentation/security/keys/core.rst``).
|
|
|
|
- ``raw_size`` must be the size of the ``raw`` key provided, in bytes.
|
|
Alternatively, if ``key_id`` is nonzero, this field must be 0, since
|
|
in that case the size is implied by the specified Linux keyring key.
|
|
|
|
- ``key_id`` is 0 if the raw key is given directly in the ``raw``
|
|
field. Otherwise ``key_id`` is the ID of a Linux keyring key of
|
|
type "fscrypt-provisioning" whose payload is
|
|
struct fscrypt_provisioning_key_payload whose ``raw`` field contains
|
|
the raw key and whose ``type`` field matches ``key_spec.type``.
|
|
Since ``raw`` is variable-length, the total size of this key's
|
|
payload must be ``sizeof(struct fscrypt_provisioning_key_payload)``
|
|
plus the raw key size. The process must have Search permission on
|
|
this key.
|
|
|
|
Most users should leave this 0 and specify the raw key directly.
|
|
The support for specifying a Linux keyring key is intended mainly to
|
|
allow re-adding keys after a filesystem is unmounted and re-mounted,
|
|
without having to store the raw keys in userspace memory.
|
|
|
|
- ``raw`` is a variable-length field which must contain the actual
|
|
key, ``raw_size`` bytes long. Alternatively, if ``key_id`` is
|
|
nonzero, then this field is unused.
|
|
|
|
For v2 policy keys, the kernel keeps track of which user (identified
|
|
by effective user ID) added the key, and only allows the key to be
|
|
removed by that user --- or by "root", if they use
|
|
`FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS`_.
|
|
|
|
However, if another user has added the key, it may be desirable to
|
|
prevent that other user from unexpectedly removing it. Therefore,
|
|
FS_IOC_ADD_ENCRYPTION_KEY may also be used to add a v2 policy key
|
|
*again*, even if it's already added by other user(s). In this case,
|
|
FS_IOC_ADD_ENCRYPTION_KEY will just install a claim to the key for the
|
|
current user, rather than actually add the key again (but the raw key
|
|
must still be provided, as a proof of knowledge).
|
|
|
|
FS_IOC_ADD_ENCRYPTION_KEY returns 0 if either the key or a claim to
|
|
the key was either added or already exists.
|
|
|
|
FS_IOC_ADD_ENCRYPTION_KEY can fail with the following errors:
|
|
|
|
- ``EACCES``: FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR was specified, but the
|
|
caller does not have the CAP_SYS_ADMIN capability in the initial
|
|
user namespace; or the raw key was specified by Linux key ID but the
|
|
process lacks Search permission on the key.
|
|
- ``EDQUOT``: the key quota for this user would be exceeded by adding
|
|
the key
|
|
- ``EINVAL``: invalid key size or key specifier type, or reserved bits
|
|
were set
|
|
- ``EKEYREJECTED``: the raw key was specified by Linux key ID, but the
|
|
key has the wrong type
|
|
- ``ENOKEY``: the raw key was specified by Linux key ID, but no key
|
|
exists with that ID
|
|
- ``ENOTTY``: this type of filesystem does not implement encryption
|
|
- ``EOPNOTSUPP``: the kernel was not configured with encryption
|
|
support for this filesystem, or the filesystem superblock has not
|
|
had encryption enabled on it
|
|
|
|
Legacy method
|
|
~~~~~~~~~~~~~
|
|
|
|
For v1 encryption policies, a master encryption key can also be
|
|
provided by adding it to a process-subscribed keyring, e.g. to a
|
|
session keyring, or to a user keyring if the user keyring is linked
|
|
into the session keyring.
|
|
|
|
This method is deprecated (and not supported for v2 encryption
|
|
policies) for several reasons. First, it cannot be used in
|
|
combination with FS_IOC_REMOVE_ENCRYPTION_KEY (see `Removing keys`_),
|
|
so for removing a key a workaround such as keyctl_unlink() in
|
|
combination with ``sync; echo 2 > /proc/sys/vm/drop_caches`` would
|
|
have to be used. Second, it doesn't match the fact that the
|
|
locked/unlocked status of encrypted files (i.e. whether they appear to
|
|
be in plaintext form or in ciphertext form) is global. This mismatch
|
|
has caused much confusion as well as real problems when processes
|
|
running under different UIDs, such as a ``sudo`` command, need to
|
|
access encrypted files.
|
|
|
|
Nevertheless, to add a key to one of the process-subscribed keyrings,
|
|
the add_key() system call can be used (see:
|
|
``Documentation/security/keys/core.rst``). The key type must be
|
|
"logon"; keys of this type are kept in kernel memory and cannot be
|
|
read back by userspace. The key description must be "fscrypt:"
|
|
followed by the 16-character lower case hex representation of the
|
|
``master_key_descriptor`` that was set in the encryption policy. The
|
|
key payload must conform to the following structure::
|
|
|
|
#define FSCRYPT_MAX_KEY_SIZE 64
|
|
|
|
struct fscrypt_key {
|
|
__u32 mode;
|
|
__u8 raw[FSCRYPT_MAX_KEY_SIZE];
|
|
__u32 size;
|
|
};
|
|
|
|
``mode`` is ignored; just set it to 0. The actual key is provided in
|
|
``raw`` with ``size`` indicating its size in bytes. That is, the
|
|
bytes ``raw[0..size-1]`` (inclusive) are the actual key.
|
|
|
|
The key description prefix "fscrypt:" may alternatively be replaced
|
|
with a filesystem-specific prefix such as "ext4:". However, the
|
|
filesystem-specific prefixes are deprecated and should not be used in
|
|
new programs.
|
|
|
|
Removing keys
|
|
-------------
|
|
|
|
Two ioctls are available for removing a key that was added by
|
|
`FS_IOC_ADD_ENCRYPTION_KEY`_:
|
|
|
|
- `FS_IOC_REMOVE_ENCRYPTION_KEY`_
|
|
- `FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS`_
|
|
|
|
These two ioctls differ only in cases where v2 policy keys are added
|
|
or removed by non-root users.
|
|
|
|
These ioctls don't work on keys that were added via the legacy
|
|
process-subscribed keyrings mechanism.
|
|
|
|
Before using these ioctls, read the `Kernel memory compromise`_
|
|
section for a discussion of the security goals and limitations of
|
|
these ioctls.
|
|
|
|
FS_IOC_REMOVE_ENCRYPTION_KEY
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The FS_IOC_REMOVE_ENCRYPTION_KEY ioctl removes a claim to a master
|
|
encryption key from the filesystem, and possibly removes the key
|
|
itself. It can be executed on any file or directory on the target
|
|
filesystem, but using the filesystem's root directory is recommended.
|
|
It takes in a pointer to struct fscrypt_remove_key_arg, defined
|
|
as follows::
|
|
|
|
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];
|
|
};
|
|
|
|
This structure must be zeroed, then initialized as follows:
|
|
|
|
- The key to remove is specified by ``key_spec``:
|
|
|
|
- To remove a key used by v1 encryption policies, set
|
|
``key_spec.type`` to FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR and fill
|
|
in ``key_spec.u.descriptor``. To remove this type of key, the
|
|
calling process must have the CAP_SYS_ADMIN capability in the
|
|
initial user namespace.
|
|
|
|
- To remove a key used by v2 encryption policies, set
|
|
``key_spec.type`` to FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER and fill
|
|
in ``key_spec.u.identifier``.
|
|
|
|
For v2 policy keys, this ioctl is usable by non-root users. However,
|
|
to make this possible, it actually just removes the current user's
|
|
claim to the key, undoing a single call to FS_IOC_ADD_ENCRYPTION_KEY.
|
|
Only after all claims are removed is the key really removed.
|
|
|
|
For example, if FS_IOC_ADD_ENCRYPTION_KEY was called with uid 1000,
|
|
then the key will be "claimed" by uid 1000, and
|
|
FS_IOC_REMOVE_ENCRYPTION_KEY will only succeed as uid 1000. Or, if
|
|
both uids 1000 and 2000 added the key, then for each uid
|
|
FS_IOC_REMOVE_ENCRYPTION_KEY will only remove their own claim. Only
|
|
once *both* are removed is the key really removed. (Think of it like
|
|
unlinking a file that may have hard links.)
|
|
|
|
If FS_IOC_REMOVE_ENCRYPTION_KEY really removes the key, it will also
|
|
try to "lock" all files that had been unlocked with the key. It won't
|
|
lock files that are still in-use, so this ioctl is expected to be used
|
|
in cooperation with userspace ensuring that none of the files are
|
|
still open. However, if necessary, this ioctl can be executed again
|
|
later to retry locking any remaining files.
|
|
|
|
FS_IOC_REMOVE_ENCRYPTION_KEY returns 0 if either the key was removed
|
|
(but may still have files remaining to be locked), the user's claim to
|
|
the key was removed, or the key was already removed but had files
|
|
remaining to be the locked so the ioctl retried locking them. In any
|
|
of these cases, ``removal_status_flags`` is filled in with the
|
|
following informational status flags:
|
|
|
|
- ``FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY``: set if some file(s)
|
|
are still in-use. Not guaranteed to be set in the case where only
|
|
the user's claim to the key was removed.
|
|
- ``FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS``: set if only the
|
|
user's claim to the key was removed, not the key itself
|
|
|
|
FS_IOC_REMOVE_ENCRYPTION_KEY can fail with the following errors:
|
|
|
|
- ``EACCES``: The FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR key specifier type
|
|
was specified, but the caller does not have the CAP_SYS_ADMIN
|
|
capability in the initial user namespace
|
|
- ``EINVAL``: invalid key specifier type, or reserved bits were set
|
|
- ``ENOKEY``: the key object was not found at all, i.e. it was never
|
|
added in the first place or was already fully removed including all
|
|
files locked; or, the user does not have a claim to the key (but
|
|
someone else does).
|
|
- ``ENOTTY``: this type of filesystem does not implement encryption
|
|
- ``EOPNOTSUPP``: the kernel was not configured with encryption
|
|
support for this filesystem, or the filesystem superblock has not
|
|
had encryption enabled on it
|
|
|
|
FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS is exactly the same as
|
|
`FS_IOC_REMOVE_ENCRYPTION_KEY`_, except that for v2 policy keys, the
|
|
ALL_USERS version of the ioctl will remove all users' claims to the
|
|
key, not just the current user's. I.e., the key itself will always be
|
|
removed, no matter how many users have added it. This difference is
|
|
only meaningful if non-root users are adding and removing keys.
|
|
|
|
Because of this, FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS also requires
|
|
"root", namely the CAP_SYS_ADMIN capability in the initial user
|
|
namespace. Otherwise it will fail with EACCES.
|
|
|
|
Getting key status
|
|
------------------
|
|
|
|
FS_IOC_GET_ENCRYPTION_KEY_STATUS
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
The FS_IOC_GET_ENCRYPTION_KEY_STATUS ioctl retrieves the status of a
|
|
master encryption key. It can be executed on any file or directory on
|
|
the target filesystem, but using the filesystem's root directory is
|
|
recommended. It takes in a pointer to
|
|
struct fscrypt_get_key_status_arg, defined as follows::
|
|
|
|
struct fscrypt_get_key_status_arg {
|
|
/* input */
|
|
struct fscrypt_key_specifier key_spec;
|
|
__u32 __reserved[6];
|
|
|
|
/* output */
|
|
#define FSCRYPT_KEY_STATUS_ABSENT 1
|
|
#define FSCRYPT_KEY_STATUS_PRESENT 2
|
|
#define FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED 3
|
|
__u32 status;
|
|
#define FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF 0x00000001
|
|
__u32 status_flags;
|
|
__u32 user_count;
|
|
__u32 __out_reserved[13];
|
|
};
|
|
|
|
The caller must zero all input fields, then fill in ``key_spec``:
|
|
|
|
- To get the status of a key for v1 encryption policies, set
|
|
``key_spec.type`` to FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR and fill
|
|
in ``key_spec.u.descriptor``.
|
|
|
|
- To get the status of a key for v2 encryption policies, set
|
|
``key_spec.type`` to FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER and fill
|
|
in ``key_spec.u.identifier``.
|
|
|
|
On success, 0 is returned and the kernel fills in the output fields:
|
|
|
|
- ``status`` indicates whether the key is absent, present, or
|
|
incompletely removed. Incompletely removed means that removal has
|
|
been initiated, but some files are still in use; i.e.,
|
|
`FS_IOC_REMOVE_ENCRYPTION_KEY`_ returned 0 but set the informational
|
|
status flag FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY.
|
|
|
|
- ``status_flags`` can contain the following flags:
|
|
|
|
- ``FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF`` indicates that the key
|
|
has added by the current user. This is only set for keys
|
|
identified by ``identifier`` rather than by ``descriptor``.
|
|
|
|
- ``user_count`` specifies the number of users who have added the key.
|
|
This is only set for keys identified by ``identifier`` rather than
|
|
by ``descriptor``.
|
|
|
|
FS_IOC_GET_ENCRYPTION_KEY_STATUS can fail with the following errors:
|
|
|
|
- ``EINVAL``: invalid key specifier type, or reserved bits were set
|
|
- ``ENOTTY``: this type of filesystem does not implement encryption
|
|
- ``EOPNOTSUPP``: the kernel was not configured with encryption
|
|
support for this filesystem, or the filesystem superblock has not
|
|
had encryption enabled on it
|
|
|
|
Among other use cases, FS_IOC_GET_ENCRYPTION_KEY_STATUS can be useful
|
|
for determining whether the key for a given encrypted directory needs
|
|
to be added before prompting the user for the passphrase needed to
|
|
derive the key.
|
|
|
|
FS_IOC_GET_ENCRYPTION_KEY_STATUS can only get the status of keys in
|
|
the filesystem-level keyring, i.e. the keyring managed by
|
|
`FS_IOC_ADD_ENCRYPTION_KEY`_ and `FS_IOC_REMOVE_ENCRYPTION_KEY`_. It
|
|
cannot get the status of a key that has only been added for use by v1
|
|
encryption policies using the legacy mechanism involving
|
|
process-subscribed keyrings.
|
|
|
|
Access semantics
|
|
================
|
|
|
|
With the key
|
|
------------
|
|
|
|
With the encryption key, encrypted regular files, directories, and
|
|
symlinks behave very similarly to their unencrypted counterparts ---
|
|
after all, the encryption is intended to be transparent. However,
|
|
astute users may notice some differences in behavior:
|
|
|
|
- Unencrypted files, or files encrypted with a different encryption
|
|
policy (i.e. different key, modes, or flags), cannot be renamed or
|
|
linked into an encrypted directory; see `Encryption policy
|
|
enforcement`_. Attempts to do so will fail with EXDEV. However,
|
|
encrypted files can be renamed within an encrypted directory, or
|
|
into an unencrypted directory.
|
|
|
|
Note: "moving" an unencrypted file into an encrypted directory, e.g.
|
|
with the `mv` program, is implemented in userspace by a copy
|
|
followed by a delete. Be aware that the original unencrypted data
|
|
may remain recoverable from free space on the disk; prefer to keep
|
|
all files encrypted from the very beginning. The `shred` program
|
|
may be used to overwrite the source files but isn't guaranteed to be
|
|
effective on all filesystems and storage devices.
|
|
|
|
- Direct I/O is supported on encrypted files only under some
|
|
circumstances. For details, see `Direct I/O support`_.
|
|
|
|
- The fallocate operations FALLOC_FL_COLLAPSE_RANGE and
|
|
FALLOC_FL_INSERT_RANGE are not supported on encrypted files and will
|
|
fail with EOPNOTSUPP.
|
|
|
|
- Online defragmentation of encrypted files is not supported. The
|
|
EXT4_IOC_MOVE_EXT and F2FS_IOC_MOVE_RANGE ioctls will fail with
|
|
EOPNOTSUPP.
|
|
|
|
- The ext4 filesystem does not support data journaling with encrypted
|
|
regular files. It will fall back to ordered data mode instead.
|
|
|
|
- DAX (Direct Access) is not supported on encrypted files.
|
|
|
|
- The maximum length of an encrypted symlink is 2 bytes shorter than
|
|
the maximum length of an unencrypted symlink. For example, on an
|
|
EXT4 filesystem with a 4K block size, unencrypted symlinks can be up
|
|
to 4095 bytes long, while encrypted symlinks can only be up to 4093
|
|
bytes long (both lengths excluding the terminating null).
|
|
|
|
Note that mmap *is* supported. This is possible because the pagecache
|
|
for an encrypted file contains the plaintext, not the ciphertext.
|
|
|
|
Without the key
|
|
---------------
|
|
|
|
Some filesystem operations may be performed on encrypted regular
|
|
files, directories, and symlinks even before their encryption key has
|
|
been added, or after their encryption key has been removed:
|
|
|
|
- File metadata may be read, e.g. using stat().
|
|
|
|
- Directories may be listed, in which case the filenames will be
|
|
listed in an encoded form derived from their ciphertext. The
|
|
current encoding algorithm is described in `Filename hashing and
|
|
encoding`_. The algorithm is subject to change, but it is
|
|
guaranteed that the presented filenames will be no longer than
|
|
NAME_MAX bytes, will not contain the ``/`` or ``\0`` characters, and
|
|
will uniquely identify directory entries.
|
|
|
|
The ``.`` and ``..`` directory entries are special. They are always
|
|
present and are not encrypted or encoded.
|
|
|
|
- Files may be deleted. That is, nondirectory files may be deleted
|
|
with unlink() as usual, and empty directories may be deleted with
|
|
rmdir() as usual. Therefore, ``rm`` and ``rm -r`` will work as
|
|
expected.
|
|
|
|
- Symlink targets may be read and followed, but they will be presented
|
|
in encrypted form, similar to filenames in directories. Hence, they
|
|
are unlikely to point to anywhere useful.
|
|
|
|
Without the key, regular files cannot be opened or truncated.
|
|
Attempts to do so will fail with ENOKEY. This implies that any
|
|
regular file operations that require a file descriptor, such as
|
|
read(), write(), mmap(), fallocate(), and ioctl(), are also forbidden.
|
|
|
|
Also without the key, files of any type (including directories) cannot
|
|
be created or linked into an encrypted directory, nor can a name in an
|
|
encrypted directory be the source or target of a rename, nor can an
|
|
O_TMPFILE temporary file be created in an encrypted directory. All
|
|
such operations will fail with ENOKEY.
|
|
|
|
It is not currently possible to backup and restore encrypted files
|
|
without the encryption key. This would require special APIs which
|
|
have not yet been implemented.
|
|
|
|
Encryption policy enforcement
|
|
=============================
|
|
|
|
After an encryption policy has been set on a directory, all regular
|
|
files, directories, and symbolic links created in that directory
|
|
(recursively) will inherit that encryption policy. Special files ---
|
|
that is, named pipes, device nodes, and UNIX domain sockets --- will
|
|
not be encrypted.
|
|
|
|
Except for those special files, it is forbidden to have unencrypted
|
|
files, or files encrypted with a different encryption policy, in an
|
|
encrypted directory tree. Attempts to link or rename such a file into
|
|
an encrypted directory will fail with EXDEV. This is also enforced
|
|
during ->lookup() to provide limited protection against offline
|
|
attacks that try to disable or downgrade encryption in known locations
|
|
where applications may later write sensitive data. It is recommended
|
|
that systems implementing a form of "verified boot" take advantage of
|
|
this by validating all top-level encryption policies prior to access.
|
|
|
|
Inline encryption support
|
|
=========================
|
|
|
|
By default, fscrypt uses the kernel crypto API for all cryptographic
|
|
operations (other than HKDF, which fscrypt partially implements
|
|
itself). The kernel crypto API supports hardware crypto accelerators,
|
|
but only ones that work in the traditional way where all inputs and
|
|
outputs (e.g. plaintexts and ciphertexts) are in memory. fscrypt can
|
|
take advantage of such hardware, but the traditional acceleration
|
|
model isn't particularly efficient and fscrypt hasn't been optimized
|
|
for it.
|
|
|
|
Instead, many newer systems (especially mobile SoCs) have *inline
|
|
encryption hardware* that can encrypt/decrypt data while it is on its
|
|
way to/from the storage device. Linux supports inline encryption
|
|
through a set of extensions to the block layer called *blk-crypto*.
|
|
blk-crypto allows filesystems to attach encryption contexts to bios
|
|
(I/O requests) to specify how the data will be encrypted or decrypted
|
|
in-line. For more information about blk-crypto, see
|
|
:ref:`Documentation/block/inline-encryption.rst <inline_encryption>`.
|
|
|
|
On supported filesystems (currently ext4 and f2fs), fscrypt can use
|
|
blk-crypto instead of the kernel crypto API to encrypt/decrypt file
|
|
contents. To enable this, set CONFIG_FS_ENCRYPTION_INLINE_CRYPT=y in
|
|
the kernel configuration, and specify the "inlinecrypt" mount option
|
|
when mounting the filesystem.
|
|
|
|
Note that the "inlinecrypt" mount option just specifies to use inline
|
|
encryption when possible; it doesn't force its use. fscrypt will
|
|
still fall back to using the kernel crypto API on files where the
|
|
inline encryption hardware doesn't have the needed crypto capabilities
|
|
(e.g. support for the needed encryption algorithm and data unit size)
|
|
and where blk-crypto-fallback is unusable. (For blk-crypto-fallback
|
|
to be usable, it must be enabled in the kernel configuration with
|
|
CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK=y.)
|
|
|
|
Currently fscrypt always uses the filesystem block size (which is
|
|
usually 4096 bytes) as the data unit size. Therefore, it can only use
|
|
inline encryption hardware that supports that data unit size.
|
|
|
|
Inline encryption doesn't affect the ciphertext or other aspects of
|
|
the on-disk format, so users may freely switch back and forth between
|
|
using "inlinecrypt" and not using "inlinecrypt".
|
|
|
|
Direct I/O support
|
|
==================
|
|
|
|
For direct I/O on an encrypted file to work, the following conditions
|
|
must be met (in addition to the conditions for direct I/O on an
|
|
unencrypted file):
|
|
|
|
* The file must be using inline encryption. Usually this means that
|
|
the filesystem must be mounted with ``-o inlinecrypt`` and inline
|
|
encryption hardware must be present. However, a software fallback
|
|
is also available. For details, see `Inline encryption support`_.
|
|
|
|
* The I/O request must be fully aligned to the filesystem block size.
|
|
This means that the file position the I/O is targeting, the lengths
|
|
of all I/O segments, and the memory addresses of all I/O buffers
|
|
must be multiples of this value. Note that the filesystem block
|
|
size may be greater than the logical block size of the block device.
|
|
|
|
If either of the above conditions is not met, then direct I/O on the
|
|
encrypted file will fall back to buffered I/O.
|
|
|
|
Implementation details
|
|
======================
|
|
|
|
Encryption context
|
|
------------------
|
|
|
|
An encryption policy is represented on-disk by
|
|
struct fscrypt_context_v1 or struct fscrypt_context_v2. It is up to
|
|
individual filesystems to decide where to store it, but normally it
|
|
would be stored in a hidden extended attribute. It should *not* be
|
|
exposed by the xattr-related system calls such as getxattr() and
|
|
setxattr() because of the special semantics of the encryption xattr.
|
|
(In particular, there would be much confusion if an encryption policy
|
|
were to be added to or removed from anything other than an empty
|
|
directory.) These structs are defined as follows::
|
|
|
|
#define FSCRYPT_FILE_NONCE_SIZE 16
|
|
|
|
#define FSCRYPT_KEY_DESCRIPTOR_SIZE 8
|
|
struct fscrypt_context_v1 {
|
|
u8 version;
|
|
u8 contents_encryption_mode;
|
|
u8 filenames_encryption_mode;
|
|
u8 flags;
|
|
u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
|
|
u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
|
|
};
|
|
|
|
#define FSCRYPT_KEY_IDENTIFIER_SIZE 16
|
|
struct fscrypt_context_v2 {
|
|
u8 version;
|
|
u8 contents_encryption_mode;
|
|
u8 filenames_encryption_mode;
|
|
u8 flags;
|
|
u8 __reserved[4];
|
|
u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
|
|
u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
|
|
};
|
|
|
|
The context structs contain the same information as the corresponding
|
|
policy structs (see `Setting an encryption policy`_), except that the
|
|
context structs also contain a nonce. The nonce is randomly generated
|
|
by the kernel and is used as KDF input or as a tweak to cause
|
|
different files to be encrypted differently; see `Per-file encryption
|
|
keys`_ and `DIRECT_KEY policies`_.
|
|
|
|
Data path changes
|
|
-----------------
|
|
|
|
When inline encryption is used, filesystems just need to associate
|
|
encryption contexts with bios to specify how the block layer or the
|
|
inline encryption hardware will encrypt/decrypt the file contents.
|
|
|
|
When inline encryption isn't used, filesystems must encrypt/decrypt
|
|
the file contents themselves, as described below:
|
|
|
|
For the read path (->read_folio()) of regular files, filesystems can
|
|
read the ciphertext into the page cache and decrypt it in-place. The
|
|
folio lock must be held until decryption has finished, to prevent the
|
|
folio from becoming visible to userspace prematurely.
|
|
|
|
For the write path (->writepage()) of regular files, filesystems
|
|
cannot encrypt data in-place in the page cache, since the cached
|
|
plaintext must be preserved. Instead, filesystems must encrypt into a
|
|
temporary buffer or "bounce page", then write out the temporary
|
|
buffer. Some filesystems, such as UBIFS, already use temporary
|
|
buffers regardless of encryption. Other filesystems, such as ext4 and
|
|
F2FS, have to allocate bounce pages specially for encryption.
|
|
|
|
Filename hashing and encoding
|
|
-----------------------------
|
|
|
|
Modern filesystems accelerate directory lookups by using indexed
|
|
directories. An indexed directory is organized as a tree keyed by
|
|
filename hashes. When a ->lookup() is requested, the filesystem
|
|
normally hashes the filename being looked up so that it can quickly
|
|
find the corresponding directory entry, if any.
|
|
|
|
With encryption, lookups must be supported and efficient both with and
|
|
without the encryption key. Clearly, it would not work to hash the
|
|
plaintext filenames, since the plaintext filenames are unavailable
|
|
without the key. (Hashing the plaintext filenames would also make it
|
|
impossible for the filesystem's fsck tool to optimize encrypted
|
|
directories.) Instead, filesystems hash the ciphertext filenames,
|
|
i.e. the bytes actually stored on-disk in the directory entries. When
|
|
asked to do a ->lookup() with the key, the filesystem just encrypts
|
|
the user-supplied name to get the ciphertext.
|
|
|
|
Lookups without the key are more complicated. The raw ciphertext may
|
|
contain the ``\0`` and ``/`` characters, which are illegal in
|
|
filenames. Therefore, readdir() must base64url-encode the ciphertext
|
|
for presentation. For most filenames, this works fine; on ->lookup(),
|
|
the filesystem just base64url-decodes the user-supplied name to get
|
|
back to the raw ciphertext.
|
|
|
|
However, for very long filenames, base64url encoding would cause the
|
|
filename length to exceed NAME_MAX. To prevent this, readdir()
|
|
actually presents long filenames in an abbreviated form which encodes
|
|
a strong "hash" of the ciphertext filename, along with the optional
|
|
filesystem-specific hash(es) needed for directory lookups. This
|
|
allows the filesystem to still, with a high degree of confidence, map
|
|
the filename given in ->lookup() back to a particular directory entry
|
|
that was previously listed by readdir(). See
|
|
struct fscrypt_nokey_name in the source for more details.
|
|
|
|
Note that the precise way that filenames are presented to userspace
|
|
without the key is subject to change in the future. It is only meant
|
|
as a way to temporarily present valid filenames so that commands like
|
|
``rm -r`` work as expected on encrypted directories.
|
|
|
|
Tests
|
|
=====
|
|
|
|
To test fscrypt, use xfstests, which is Linux's de facto standard
|
|
filesystem test suite. First, run all the tests in the "encrypt"
|
|
group on the relevant filesystem(s). One can also run the tests
|
|
with the 'inlinecrypt' mount option to test the implementation for
|
|
inline encryption support. For example, to test ext4 and
|
|
f2fs encryption using `kvm-xfstests
|
|
<https://github.com/tytso/xfstests-bld/blob/master/Documentation/kvm-quickstart.md>`_::
|
|
|
|
kvm-xfstests -c ext4,f2fs -g encrypt
|
|
kvm-xfstests -c ext4,f2fs -g encrypt -m inlinecrypt
|
|
|
|
UBIFS encryption can also be tested this way, but it should be done in
|
|
a separate command, and it takes some time for kvm-xfstests to set up
|
|
emulated UBI volumes::
|
|
|
|
kvm-xfstests -c ubifs -g encrypt
|
|
|
|
No tests should fail. However, tests that use non-default encryption
|
|
modes (e.g. generic/549 and generic/550) will be skipped if the needed
|
|
algorithms were not built into the kernel's crypto API. Also, tests
|
|
that access the raw block device (e.g. generic/399, generic/548,
|
|
generic/549, generic/550) will be skipped on UBIFS.
|
|
|
|
Besides running the "encrypt" group tests, for ext4 and f2fs it's also
|
|
possible to run most xfstests with the "test_dummy_encryption" mount
|
|
option. This option causes all new files to be automatically
|
|
encrypted with a dummy key, without having to make any API calls.
|
|
This tests the encrypted I/O paths more thoroughly. To do this with
|
|
kvm-xfstests, use the "encrypt" filesystem configuration::
|
|
|
|
kvm-xfstests -c ext4/encrypt,f2fs/encrypt -g auto
|
|
kvm-xfstests -c ext4/encrypt,f2fs/encrypt -g auto -m inlinecrypt
|
|
|
|
Because this runs many more tests than "-g encrypt" does, it takes
|
|
much longer to run; so also consider using `gce-xfstests
|
|
<https://github.com/tytso/xfstests-bld/blob/master/Documentation/gce-xfstests.md>`_
|
|
instead of kvm-xfstests::
|
|
|
|
gce-xfstests -c ext4/encrypt,f2fs/encrypt -g auto
|
|
gce-xfstests -c ext4/encrypt,f2fs/encrypt -g auto -m inlinecrypt
|