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@@ -1,79 +1,201 @@ # fscrypt [](https://github.com/google/fscrypt/releases) -[](https://travis-ci.org/google/fscrypt) -[](https://coveralls.io/github/google/fscrypt?branch=master) +[](https://github.com/google/fscrypt/actions?query=workflow%3ACI+branch%3Amaster) [](https://godoc.org/github.com/google/fscrypt) [](https://goreportcard.com/report/github.com/google/fscrypt) [](http://www.apache.org/licenses/LICENSE-2.0.html) -fscrypt is a high-level tool for the management of -[Linux filesystem encryption](https://lwn.net/Articles/639427). -This tool manages metadata, key generation, key wrapping, PAM integration, and +`fscrypt` is a high-level tool for the management of [Linux native filesystem +encryption](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html). +`fscrypt` manages metadata, key generation, key wrapping, PAM integration, and provides a uniform interface for creating and modifying encrypted directories. For a small low-level tool that directly sets policies, see -[fscryptctl](https://github.com/google/fscryptctl). - -To use fscrypt, you must have a filesystem with encryption enabled and a -kernel that supports reading/writing from that filesystem. Currently, -[ext4](https://en.wikipedia.org/wiki/Ext4), -[F2FS](https://en.wikipedia.org/wiki/F2FS), and -[UBIFS](https://en.wikipedia.org/wiki/UBIFS) support Linux filesystem -encryption. Ext4 has supported Linux filesystem encryption -[since v4.1](https://lwn.net/Articles/639427), F2FS -[added support in v4.2](https://lwn.net/Articles/649652), and UBIFS -[added support in v4.10](https://lwn.net/Articles/707900). Other filesystems -may add support for native encryption in the future. Filesystems may -additionally require certain kernel configuration options to be set to use -native encryption. - -Most of the testing for fscrypt has been done with ext4 filesystems. However, -the kernel uses a common userspace interface, so this tool should work with all -existing and future filesystems which support encryption. If there is a problem -using fscrypt with other filesystems, please open an issue. - -### Other encryption solutions - -It is important to distinguish Linux filesystem encryption from two other -encryption solutions: [eCryptfs](https://en.wikipedia.org/wiki/ECryptfs) and -[dm-crypt](https://en.wikipedia.org/wiki/Dm-crypt). - -Currently, dm-crypt encrypts an entire block device with a single master key. -dm-crypt can be used with or without fscrypt. All filesystem data (including all -filesystem metadata) is encrypted with this single key when using dm-crypt, -while fscrypt only encrypts the filenames and file contents in a specified -directory. Note that using both dm-crypt and fscrypt simultaneously will give -the protections and benefits of both; however, this may cause a decrease in -your performance, as file contents are encrypted twice. - -One example of a reasonable setup could involve using dm-crypt with a TPM or -Secure boot key, while using fscrypt for the contents of a home directory. This -would still encrypt the entire drive, but would also tie the encryption of a -user's personal documents to their passphrase. - -On the other hand, eCryptfs is another form of filesystem encryption on Linux; -it encrypts a filesystem directory with some key or passphrase. eCryptfs sits on -top of an existing filesystem. This makes eCryptfs an alternative choice if your -filesystem or kernel does not support native filesystem encryption. - -Also note that fscrypt does not support or setup either eCryptfs or dm-crypt. -For these tools, use -[ecryptfs-utils](https://packages.debian.org/source/jessie/ecryptfs-utils) for -eCryptfs or [cryptsetup](https://linux.die.net/man/8/cryptsetup) for dm-crypt. +[`fscryptctl`](https://github.com/google/fscryptctl). + +To use `fscrypt`, you must have a filesystem that supports the Linux native +filesystem encryption API (which is also sometimes called "fscrypt"; this +documentation calls it "Linux native filesystem encryption" to avoid confusion). +Only certain filesystems, such as [ext4](https://en.wikipedia.org/wiki/Ext4) and +[f2fs](https://en.wikipedia.org/wiki/F2FS), support this API. For a full list +of supported filesystems and how to enable encryption support on each one, see +[Runtime dependencies](#runtime-dependencies). + +For the release notes, see the [NEWS file](NEWS.md). + +## Table of contents + +- [Alternatives to consider](#alternatives-to-consider) +- [Threat model](#threat-model) +- [Features](#features) +- [Building and installing](#building-and-installing) +- [Runtime dependencies](#runtime-dependencies) +- [Configuration file](#configuration-file) +- [Setting up `fscrypt` on a filesystem](#setting-up-fscrypt-on-a-filesystem) +- [Setting up for login protectors](#setting-up-for-login-protectors) + - [Securing your login passphrase](#securing-your-login-passphrase) + - [Enabling the PAM module](#enabling-the-pam-module) + - [Enabling the PAM module on Debian or Ubuntu](#enabling-the-pam-module-on-debian-or-ubuntu) + - [Enabling the PAM module on Arch Linux](#enabling-the-pam-module-on-arch-linux) + - [Enabling the PAM module on other Linux distros](#enabling-the-pam-module-on-other-linux-distros) + - [Allowing `fscrypt` to check your login passphrase](#allowing-fscrypt-to-check-your-login-passphrase) +- [Backup, restore, and recovery](#backup-restore-and-recovery) +- [Encrypting existing files](#encrypting-existing-files) +- [Example usage](#example-usage) + - [Setting up fscrypt on a directory](#setting-up-fscrypt-on-a-directory) + - [Locking and unlocking a directory](#locking-and-unlocking-a-directory) + - [Protecting a directory with your login passphrase](#protecting-a-directory-with-your-login-passphrase) + - [Changing a custom passphrase](#changing-a-custom-passphrase) + - [Using a raw key protector](#using-a-raw-key-protector) + - [Using multiple protectors for a policy](#using-multiple-protectors-for-a-policy) +- [Contributing](#contributing) +- [Troubleshooting](#troubleshooting) + - [I changed my login passphrase, now all my directories are inaccessible](#i-changed-my-login-passphrase-now-all-my-directories-are-inaccessible) + - [Directories using my login passphrase are not automatically unlocking](#directories-using-my-login-passphrase-are-not-automatically-unlocking) + - [Getting "encryption not enabled" on an ext4 filesystem](#getting-encryption-not-enabled-on-an-ext4-filesystem) + - [Getting "user keyring not linked into session keyring"](#getting-user-keyring-not-linked-into-session-keyring) + - [Getting "Operation not permitted" when moving files into an encrypted directory](#getting-operation-not-permitted-when-moving-files-into-an-encrypted-directory) + - [Getting "Package not installed" when trying to use an encrypted directory](#getting-package-not-installed-when-trying-to-use-an-encrypted-directory) + - [Some processes can't access unlocked encrypted files](#some-processes-cant-access-unlocked-encrypted-files) + - [Users can access other users' unlocked encrypted files](#users-can-access-other-users-unlocked-encrypted-files) + - [Getting "Required key not available" when backing up locked encrypted files](#getting-required-key-not-available-when-backing-up-locked-encrypted-files) + - [The reported size of encrypted symlinks is wrong](#the-reported-size-of-encrypted-symlinks-is-wrong) +- [Legal](#legal) + +## Alternatives to consider + +Operating-system level storage encryption solutions work at either the +filesystem or block device level. [Linux native filesystem +encryption](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html) +(the solution configured by `fscrypt`) is filesystem-level; it encrypts +individual directories. Only file contents and filenames are encrypted; +non-filename metadata, such as timestamps, the sizes and number of files, and +extended attributes, is **not** encrypted. Users choose which directories will +be encrypted, and with what keys. + +Before using `fscrypt`, you should consider other solutions: + +* [**dm-crypt/LUKS**](https://en.wikipedia.org/wiki/Dm-crypt) is block device + level encryption: it encrypts an entire block device (and hence an entire + filesystem) with one key. Unlocking this key will unlock the entire block + device. dm-crypt/LUKS is usually configured using + [cryptsetup](https://gitlab.com/cryptsetup/cryptsetup/-/wikis/home). + +* [`systemd-homed`](https://systemd.io/HOME_DIRECTORY/) supports encrypting home + directories using the same Linux native filesystem encryption API that + `fscrypt` uses. Note that while the `systemd-homed` documentation refers to + this as fscrypt support, it does not use the `fscrypt` tool; directories set + up using `systemd-homed` cannot be managed by `fscrypt` and vice versa. + `systemd-homed` has better integration with systemd than `fscrypt` does. + However, `systemd-homed` (as of systemd v255) uses the + ["V1" Linux kernel encryption API](https://www.kernel.org/doc/html/v6.8/filesystems/fscrypt.html#limitations-of-v1-policies), + while `fscrypt` prefers the "V2" API. The older API causes + [known issues](#some-processes-cant-access-unlocked-encrypted-files), and + migrating `systemd-home` to the "V2" API is tracked + [in this `systemd` issue](https://github.com/systemd/systemd/issues/18280). + Issues with `systemd-homed` should be reported to the systemd developers. + +* [**eCryptfs**](https://en.wikipedia.org/wiki/ECryptfs) is an alternative + filesystem-level encryption solution. It is a stacked filesystem, which means + it sits on top of a real filesystem, rather than being directly integrated + into the real filesystem. Stacked filesystems have a couple advantages (such + as working on almost any real filesystem), but also some significant + disadvantages. eCryptfs is usually configured using + [ecryptfs-utils](https://packages.debian.org/stretch/ecryptfs-utils). + +* Some Linux filesystems support encryption natively, but not in a way that is + compatible with the common API that `fscrypt` uses. Examples of this are + Bcachefs and ZFS. (Note: ZFS is not part of the upstream kernel.) Bcachefs + encryption is similar to dm-crypt in that it encrypts the full filesystem with + one key. ZFS encryption operates on a per-dataset basis. If you are using + one of these filesystems, refer to the documentation for that filesystem. + +Which solution to use? Here are our recommendations: + +* eCryptfs shouldn't be used, if at all possible. eCryptfs's use of filesystem + stacking causes a number of issues, and eCryptfs is no longer actively + maintained. The original author of eCryptfs recommends using Linux native + filesystem encryption instead. The largest users of eCryptfs (Ubuntu and + Chrome OS) have switched to dm-crypt or Linux native filesystem encryption. + +* If you need fine-grained control of encryption within a filesystem and you are + using a filesystem that supports `fscrypt`, then use `fscrypt`, or `fscrypt` + together with dm-crypt/LUKS. If you don't need this, then use dm-crypt/LUKS. + + To understand this recommendation: consider that the main advantage of + `fscrypt` is to allow different files on the same filesystem to be encrypted + by different keys, and thus be unlockable, lockable, and securely deletable + independently from each other. Therefore, `fscrypt` is useful in cases such + as: + + * Multi-user systems, since each user's files can be encrypted with their + own key that is unlocked by their own passphrase. + + * Single-user systems where it's not possible for all files to have the + strongest level of protection. For example, it might be necessary for the + system to boot up without user interaction. Any files that are needed to + do so can only be encrypted by a hardware-protected (e.g. TPM-bound) key + at best. If the user's personal files are located on the same filesystem, + then with dm-crypt/LUKS the user's personal files would be limited to this + weak level of protection. With `fscrypt`, the user's personal files could + be fully protected using the user's passphrase. + + `fscrypt` isn't very useful in the following cases: + + * Single-user systems where the user is willing to enter a strong passphrase + at boot time to unlock the entire filesystem. In this case, the main + advantage of `fscrypt` would go unused, so dm-crypt/LUKS would be better + as it would provide better security (due to ensuring that all files and + all filesystem metadata are encrypted). + + * Any case where it is feasible to create a separate filesystem for every + encryption key you want to use. + + Note: dm-crypt/LUKS and `fscrypt` aren't mutually exclusive; they can be used + together when the performance hit of double encryption is tolerable. It only + makes sense to do this when the keys for each encryption layer are protected + in different ways, such that each layer serves a different purpose. A + reasonable set-up would be to encrypt the whole filesystem with dm-crypt/LUKS + using a TPM-bound key that is automatically unlocked at boot time, and also + encrypt users' home directories with `fscrypt` using their login passphrases. + +## Threat model + +Like other storage encryption solutions (including dm-crypt/LUKS and eCryptfs), +Linux native filesystem encryption is primarily intended to protect the +confidentiality of data from a single point-in-time permanent offline compromise +of the disk. For a detailed description of the threat model, see the [kernel +documentation](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#threat-model). + +It's worth emphasizing that none of these encryption solutions protect unlocked +encrypted files from other users on the same system (that's the job of OS-level +access control, such as UNIX file permissions), or from the cloud provider you +may be running a virtual machine on. By themselves, they also do not protect +from "evil maid" attacks, i.e. non-permanent offline compromises of the disk. ## Features -fscrypt is intended to improve upon the work in +`fscrypt` is intended to improve upon the work in [e4crypt](http://man7.org/linux/man-pages/man8/e4crypt.8.html) by providing a -more managed environment and handling more functionality in the -background. fscrypt has a [design document](https://goo.gl/55cCrI) specifying -the full architecture of fscrypt. +more managed environment and handling more functionality in the background. +`fscrypt` has a [design document](https://goo.gl/55cCrI) specifying its full +architecture. See also the [kernel documentation for Linux native filesystem +encryption](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html). -Briefly, fscrypt deals with protectors and policies. Protectors represent some +Briefly, `fscrypt` deals with protectors and policies. Protectors represent some secret or information used to protect the confidentiality of your data. The three currently supported protector types are: -1. Your login passphrase, through [PAM](http://www.linux-pam.org/Linux-PAM-html) -2. A custom passphrase -3. A raw key file + +1. Your login passphrase, through [PAM](http://www.linux-pam.org/Linux-PAM-html). + The included PAM module (`pam_fscrypt.so`) can automatically unlock + directories protected by your login passphrase when you log in, and lock them + when you log out. __IMPORTANT:__ before using a login protector, follow + [Setting up for login protectors](#setting-up-for-login-protectors). + +2. A custom passphrase. This passphrase is hashed with + [Argon2id](https://en.wikipedia.org/wiki/Argon2), by default calibrated to + use all CPUs and take about 1 second. + +3. A raw key file. See [Using a raw key protector](#using-a-raw-key-protector). These protectors are mutable, so the information can change without needing to update any of your encrypted directories. @@ -85,90 +207,326 @@ enough to get the policy key and access the data. Which protectors protect a policy can also be changed. This allows a user to change how a directory is protected without needing to reencrypt the directory's contents. -Concretely, fscrypt contains the following functionality: -* `fscrypt setup` - Initializes the `fscrypt.conf` file - * This is the only functionality which requires root privileges +Concretely, `fscrypt` contains the following functionality: +* `fscrypt setup` - Creates `/etc/fscrypt.conf` and the `/.fscrypt` directory + * This is the only functionality which always requires root privileges * `fscrypt setup MOUNTPOINT` - Gets a filesystem ready for use with fscrypt * `fscrypt encrypt DIRECTORY` - Encrypts an empty directory * `fscrypt unlock DIRECTORY` - Unlocks an encrypted directory -* `fscrypt purge MOUNTPOINT` - Removes keys for a filesystem before unmounting +* `fscrypt lock DIRECTORY` - Locks an encrypted directory +* `fscrypt purge MOUNTPOINT` - Locks all encrypted directories on a filesystem * `fscrypt status [PATH]` - Gets detailed info about filesystems or paths * `fscrypt metadata` - Manages policies or protectors directly -The following functionality is planned: -* `fscrypt backup` - Manages backups of the fscrypt metadata -* `fscrypt recovery` - Manages recovery keys for directories -* `fscrypt cleanup` - Scans filesystem for unused policies/protectors - See the example usage section below or run `fscrypt COMMAND --help` for more information about each of the commands. -## Building and Installing +## Building and installing -fscrypt has the following build dependencies: -* [Go](https://golang.org/doc/install) +`fscrypt` has a minimal set of build dependencies: +* [Go](https://golang.org/doc/install) 1.23 or higher. Older versions may work + but they are not tested or supported. * A C compiler (`gcc` or `clang`) * `make` -* The [Argon2 Passphrase Hash](https://github.com/P-H-C/phc-winner-argon2) - library, which can be - [directly installed on Artful Ubuntu](https://packages.ubuntu.com/artful/libargon2-0-dev), - or installed from source by running: - ```bash - >>>>> git clone https://github.com/P-H-C/phc-winner-argon2 argon2 - >>>>> cd argon2 - >>>>> make - >>>>> sudo make install - ``` -* Headers for `libpam`. Install them with the appropriate package manager. - - `sudo apt-get install libpam0g-dev` - - `sudo yum install pam-devel` - - `pam` package for Arch (part of the `base` group) - -Once all the dependencies are installed, you can get the repository by running: +* Headers for [`libpam`](http://www.linux-pam.org/). + Install them with the appropriate package manager: + - Debian/Ubuntu: `sudo apt install libpam0g-dev` + - Red Hat: `sudo yum install pam-devel` + - Arch: [`pam`](https://www.archlinux.org/packages/core/x86_64/pam/) + package (usually installed by default) + +Once all the dependencies are installed, clone the repository by running: ```shell -go get -d github.com/google/fscrypt/... +git clone https://github.com/google/fscrypt ``` -and then you can run `make` in `$GOPATH/github.com/google/fscrypt` to build the -executable and PAM moudle in that directory. Running `sudo make install` installs the binary to -`/usr/local/bin`. +Running `make` builds the binary (`fscrypt`) and PAM module (`pam_fscrypt.so`) +in the `bin/` directory. + +Running `sudo make install` installs `fscrypt` into `/usr/local/bin`, +`pam_fscrypt.so` into `/usr/local/lib/security`, and `pam_fscrypt/config` into +`/usr/local/share/pam-configs`. + +On Debian (and Debian derivatives such as Ubuntu), use `sudo make install +PREFIX=/usr` to install into `/usr` instead of the default of `/usr/local`. +Ordinarily you shouldn't manually install software into `/usr`, since `/usr` is +reserved for Debian's own packages. However, Debian's PAM configuration +framework only recognizes configuration files in `/usr`, not in `/usr/local`. +Therefore, the PAM module will only work if you install into `/usr`. Note: if +you later decide to switch to using the Debian package `libpam-fscrypt`, you'll +have to first manually run `sudo make uninstall PREFIX=/usr`. + +It is also possible to use `make install-bin` to only install the `fscrypt` +binary, or `make install-pam` to only install the PAM files. + +Alternatively, if you only want to install the `fscrypt` binary to +`$GOPATH/bin`, simply run: +```shell +go install github.com/google/fscrypt/cmd/fscrypt@latest +``` + +See the `Makefile` for instructions on how to further customize the build. + +## Runtime dependencies + +To run, `fscrypt` needs the following libraries: +* `libpam.so` (almost certainly already on your system) + +In addition, `fscrypt` requires a filesystem that supports the Linux native +filesystem encryption API. Currently, the filesystems that support this are: + +* ext4, with upstream kernel v4.1 or later. The kernel configuration must + contain `CONFIG_FS_ENCRYPTION=y` (for kernels v5.1+) or + `CONFIG_EXT4_ENCRYPTION=y` or `=m` (for older kernels). The filesystem must + also have the `encrypt` feature flag enabled; to enable this flag, see + [here](#getting-encryption-not-enabled-on-an-ext4-filesystem). + +* f2fs, with upstream kernel v4.2 or later. The kernel configuration must + contain `CONFIG_FS_ENCRYPTION=y` (for kernels v5.1+) or + `CONFIG_F2FS_FS_ENCRYPTION=y` (for older kernels). The filesystem must also + have the `encrypt` feature flag enabled; this flag can be enabled at format + time by `mkfs.f2fs -O encrypt` or later by `fsck.f2fs -O encrypt`. + +* UBIFS, with upstream kernel v4.10 or later. The kernel configuration must + contain `CONFIG_FS_ENCRYPTION=y` (for kernels v5.1+) or + `CONFIG_UBIFS_FS_ENCRYPTION=y` (for older kernels). -See the `Makefile` for instructions on how to customize the build. This includes -building a static binary (C libraries used by fscrypt will be dynamically linked -by default). +* CephFS, with upstream kernel v6.6 or later. The kernel configuration must + contain `CONFIG_FS_ENCRYPTION=y`. -Alternatively, if you only want to install the fscrypt binary to `$GOPATH/bin`, -it is enough to just run: +* [Lustre](https://www.lustre.org/), with Lustre v2.14.0 or later. For details, + see the Lustre documentation. Please note that Lustre is not part of the + upstream Linux kernel, and its encryption implementation has not been reviewed + by the authors of `fscrypt`. Questions/issues about Lustre encryption should + be directed to the Lustre developers. Lustre version 2.14 does not encrypt + filenames, even though it claims to, so v2.15.0 or later should be used. + +To check whether the needed option is enabled in your kernel, run: ```shell -go get github.com/google/fscrypt/cmd/fscrypt +zgrep -h ENCRYPTION /proc/config.gz /boot/config-$(uname -r) | sort | uniq ``` -### Runtime Dependencies +It is also recommended to use Linux kernel v5.4 or later, since this +allows the use of v2 encryption policies. v2 policies have several +security and usability improvements over v1 policies. -fscrypt has the following runtime dependencies: -* Kernel support for filesystem encryption (this will depend on your kernel - configuration and specific filesystem) -* `libargon2.so` (see the above installation instructions for Argon2) -* `libpam.so` (almost certainly already on your system) +If you configure `fscrypt` to use non-default features, other kernel +prerequisites may be needed too. See [Configuration +file](#configuration-file). + +## Configuration file + +Running `sudo fscrypt setup` will create the configuration file +`/etc/fscrypt.conf` if it doesn't already exist. It's a JSON file +that looks like the following: + +``` +{ + "source": "custom_passphrase", + "hash_costs": { + "time": "52", + "memory": "131072", + "parallelism": "32" + }, + "options": { + "padding": "32", + "contents": "AES_256_XTS", + "filenames": "AES_256_CTS", + "policy_version": "2" + }, + "use_fs_keyring_for_v1_policies": false, + "allow_cross_user_metadata": false +} +``` + +The fields are: + +* "source" is the default source for new protectors. The choices are + "pam\_passphrase", "custom\_passphrase", and "raw\_key". + +* "hash\_costs" describes how difficult the passphrase hashing is. + By default, `fscrypt setup` calibrates the hashing to use all CPUs + and take about 1 second. The `--time` option to `fscrypt setup` can + be used to customize this time when creating the configuration file. + +* "options" are the encryption options to use for new encrypted + directories: + + * "padding" is the number of bytes by which filenames are padded + before being encrypted. The choices are "32", "16", "8", and + "4". "32" is recommended. + + * "contents" is the algorithm used to encrypt file contents. The + choices are "AES_256_XTS", "AES_128_CBC", and "Adiantum". + Normally, "AES_256_XTS" is recommended. + + * "filenames" is the algorithm used to encrypt file names. The + choices are "AES_256_CTS", "AES_128_CTS", "Adiantum", and + "AES_256_HCTR2". Normally, "AES_256_CTS" is recommended. + + To use algorithms other than "AES_256_XTS" for contents and + "AES_256_CTS" for filenames, the needed algorithm(s) may need to + be enabled in the Linux kernel's cryptography API. For example, + to use Adiantum, `CONFIG_CRYPTO_ADIANTUM` must be set. Also, + not all combinations of algorithms are allowed; for example, + "Adiantum" for contents can only be paired with "Adiantum" for + filenames. See the [kernel + documentation](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#encryption-modes-and-usage) + for more details about the supported algorithms. + + * "policy\_version" is the version of encryption policy to use. + The choices are "1" and "2". If unset, "1" is assumed. + Directories created with policy version "2" are only usable on + kernel v5.4 or later, but are preferable to version "1" if you + don't mind this restriction. + +* "use\_fs\_keyring\_for\_v1\_policies" specifies whether to add keys for v1 + encryption policies to the filesystem keyrings, rather than to user keyrings. + This can solve [issues with processes being unable to access unlocked + encrypted files](#some-processes-cant-access-unlocked-encrypted-files). + However, it requires kernel v5.4 or later, and it makes unlocking and locking + encrypted directories require root. (The PAM module will still work.) + + The purpose of this setting is to allow people to take advantage of some of + the improvements in Linux v5.4 on encrypted directories that are also + compatible with older kernels. If you don't need compatibility with older + kernels, it's better to not use this setting and instead (re-)create your + encrypted directories with `"policy_version": "2"`. + +* "allow\_cross\_user\_metadata" specifies whether `fscrypt` will allow + protectors and policies from other non-root users to be read, e.g. to be + offered as options by `fscrypt encrypt`. The default value is `false`, since + other users might be untrusted and could create malicious files. This can be + set to `true` to restore the old behavior on systems where `fscrypt` metadata + needs to be shared between multiple users. Note that this option is + independent from the permissions on the metadata files themselves, which are + set to 0600 by default; users who wish to share their metadata files with + other users would also need to explicitly change their mode to 0644. + +## Setting up `fscrypt` on a filesystem + +`fscrypt` needs some directories to exist on the filesystem on which encryption +will be used: + +* `MOUNTPOINT/.fscrypt/policies` +* `MOUNTPOINT/.fscrypt/protectors` -The dynamic libraries are not needed if you built a static executable. +(If login protectors are used, these must also exist on the root filesystem.) -### Setting up the PAM module +To create these directories, run `fscrypt setup MOUNTPOINT`. If MOUNTPOINT is +owned by root, as is usually the case, then this command will require root. -Note that to make use of the installed PAM module, your -[PAM configuration files](http://www.linux-pam.org/Linux-PAM-html/sag-configuration.html) -in `/etc/pam.d` must be modified to add fscrypt. +There will be one decision you'll need to make: whether non-root users will be +allowed to create `fscrypt` metadata (policies and protectors). -#### Automatic setup on Ubuntu +If you say `y`, then these directories will be made world-writable, with the +sticky bit set so that users can't delete each other's files -- just like +`/tmp`. If you say `N`, then these directories will be writable only by root. -fscrypt automatically installs the -[PAM config file](https://wiki.ubuntu.com/PAMConfigFrameworkSpec) -`pam_fscrypt/config` to `/usr/share/pam-configs/fscrypt`. This file contains -reasonable defaults for the PAM module. To automatically apply these changes, -run `sudo pam-auth-update` and follow the on-screen instructions. +Saying `y` maximizes the usability of `fscrypt`, and on most systems it's fine +to say `y`. However, on some systems this may be inappropriate, as it will +allow malicious users to fill the entire filesystem unless filesystem quotas +have been configured -- similar to problems that have historically existed with +other world-writable directories, e.g. `/tmp`. If you are concerned about this, +say `N`. If you say `N`, then you'll only be able to run `fscrypt` as root to +set up encryption on users' behalf, unless you manually set custom permissions +on the metadata directories to grant write access to specific users or groups. -#### Manual setup +If you chose the wrong mode at `fscrypt setup` time, you can change the +directory permissions at any time. To enable single-user writable mode, run: -The fscrypt PAM module implements the Auth, Session, and Password + sudo chmod 0755 MOUNTPOINT/.fscrypt/* + +To enable world-writable mode, run: + + sudo chmod 1777 MOUNTPOINT/.fscrypt/* + +## Setting up for login protectors + +If you want any encrypted directories to be protected by your login passphrase, +you'll need to: + +1. Secure your login passphrase (optional, but strongly recommended) +2. Enable the PAM module (`pam_fscrypt.so`) + +If you installed `fscrypt` from source rather than from your distro's package +manager, you may also need to allow `fscrypt` to check your login passphrase. + +### Securing your login passphrase + +Although `fscrypt` uses a strong passphrase hash algorithm, the security of +login protectors is also limited by the strength of your system's passphrase +hashing in `/etc/shadow`. On most Linux distributions, `/etc/shadow` by default +uses SHA-512 with 5000 rounds, which is much weaker than what `fscrypt` uses. + +To mitigate this, you should use a strong login passphrase. + +If using a strong login passphrase is annoying because it needs to be entered +frequently to run `sudo`, consider increasing the `sudo` timeout. That can be +done by adding the following to `/etc/sudoers`: +``` +Defaults timestamp_timeout=60 +``` + +You should also increase the number of rounds that your system's passphrase +hashing uses (though this doesn't increase security as much as choosing a strong +passphrase). To do this, find the line in `/etc/pam.d/passwd` that looks like: +``` +password required pam_unix.so sha512 shadow nullok +``` + +Append `rounds=1000000` (or another number of your choice; the goal is to make +the passphrase hashing take about 1 second, similar to `fscrypt`'s default): +``` +password required pam_unix.so sha512 shadow nullok rounds=1000000 +``` + +Then, change your login passphrase to a new, strong passphrase: +``` +passwd +``` + +If you'd like to keep the same login passphrase (not recommended, as the old +passphrase hash may still be recoverable from disk), then instead run +`sudo passwd $USER` and enter your existing passphrase. This re-hashes your +existing passphrase with the new `rounds`. + +### Enabling the PAM module + +To enable the PAM module `pam_fscrypt.so`, follow the directions for your Linux +distro below. Enabling the PAM module is needed for login passphrase-protected +directories to be automatically unlocked when you log in (and be automatically +locked when you log out), and for login passphrase-protected directories to +remain accessible when you change your login passphrase. + +#### Enabling the PAM module on Debian or Ubuntu + +The official `libpam-fscrypt` package for Debian (and Debian derivatives such as +Ubuntu) will install a configuration file for [Debian's PAM configuration +framework](https://wiki.ubuntu.com/PAMConfigFrameworkSpec) to +`/usr/share/pam-configs/fscrypt`. This file contains reasonable defaults for +the PAM module. To automatically apply these defaults, run +`sudo pam-auth-update` and follow the on-screen instructions. + +This file also gets installed if you build and install `fscrypt` from source, +but it is only installed to the correct location if you use `make install +PREFIX=/usr` to install into `/usr` instead of the default of `/usr/local`. + +#### Enabling the PAM module on Arch Linux + +On Arch Linux, follow the recommendations at the [Arch Linux +Wiki](https://wiki.archlinux.org/index.php/Fscrypt#Auto-unlocking_directories). + +We recommend using the Arch Linux package, either `fscrypt` (official) or +`fscrypt-git` (AUR). If you instead install `fscrypt` manually using `sudo make +install`, then in addition to the steps on the Wiki you'll also need to [create +`/etc/pam.d/fscrypt`](#allowing-fscrypt-to-check-your-login-passphrase). + +#### Enabling the PAM module on other Linux distros + +On all other Linux distros, follow the general guidance below to edit +your PAM configuration files. + +The `fscrypt` PAM module implements the Auth, Session, and Password [types](http://www.linux-pam.org/Linux-PAM-html/sag-configuration-file.html). The Password functionality of `pam_fscrypt.so` is used to automatically rewrap @@ -180,65 +538,198 @@ password optional pam_fscrypt.so after `pam_unix.so` in `/etc/pam.d/common-password` or similar. The Auth and Session functionality of `pam_fscrypt.so` are used to automatically -unlock directories when logging in as a user. An easy way to get this working is -to add the line: +unlock directories when logging in as a user, and lock them when logging out. +An easy way to get this working is to add the line: ``` auth optional pam_fscrypt.so ``` after `pam_unix.so` in `/etc/pam.d/common-auth` or similar, and to add the line: ``` -session optional pam_fscrypt.so drop_caches lock_policies +session optional pam_fscrypt.so ``` -after `pam_unix.so` in `/etc/pam.d/common-session` or similar. The -`lock_policies` option locks the directories protected with the user's login -passphrase when the last session ends. The `drop_caches` option tells fscrypt to -clear the filesystem caches when the last session closes, ensuring all the -locked data is inaccessible. All the types also support the `debug` option which -prints additional debug information to the syslog. +after `pam_unix.so` in `/etc/pam.d/common-session` or similar, but before +`pam_systemd.so` or any other module that accesses the user's home directory or +which starts processes that access the user's home directory during their +session. + +`pam_fscrypt.so` accepts several options: -## Note about stability +* `debug`: print additional debug messages to the syslog. All hook types accept + this option. -fscrypt follows [semantic versioning](http://semver.org). As such, all versions -below `1.0.0` should be considered development versions. This means no -guarantees are make about the stability of APIs or formats of config files. As -the on-disk metadata structures use -[Protocol Buffers](https://github.com/google/protobuf), we don't expect to break -backwards compatibility for metadata, but we give no guarantees. +* `unlock_only`: only unlock directories (at log-in); don't also lock them (at + log-out). This is only relevant for the "session" hook. Note that in + `fscrypt` v0.2.9 and earlier, unlock-only was the default behavior, and + `lock_policies` needed to be specified to enable locking. -## Example Usage +### Allowing `fscrypt` to check your login passphrase -All these examples assume we have ext4 filesystems mounted at `/` and -`/mnt/disk` which both support encryption and that `/mnt/disk` contains -directories we want to encrypt. +This step is only needed if you installed `fscrypt` from source code. + +Some Linux distros use restrictive settings in `/etc/pam.d/other` that prevent +programs from checking your login passphrase unless a per-program PAM +configuration file grants access. This prevents `fscrypt` from creating any +login passphrase-protected directories, even without auto-unlocking. To ensure +that `fscrypt` will work properly (if you didn't install an official `fscrypt` +package from your distro, which should have already handled this), also create a +file `/etc/pam.d/fscrypt` containing: +``` +auth required pam_unix.so +``` + +## Backup, restore, and recovery + +Encrypted files and directories can't be backed up while they are "locked", i.e. +while they appear in encrypted form. They can only be backed up while they are +unlocked, in which case they can be backed up like any other files. Note that +since the encryption is transparent, the files won't be encrypted in the backup +(unless the backup applies its own encryption). + +For the same reason (and several others), an encrypted directory can't be +directly "moved" to another filesystem. However, it is possible to create a new +encrypted directory on the destination filesystem using `fscrypt encrypt`, then +copy the contents of the source directory into it. + +For directories protected by a `custom_passphrase` or `raw_key` protector, all +metadata needed to unlock the directory (excluding the actual passphrase or raw +key, of course) is located in the `.fscrypt` directory at the root of the +filesystem that contains the encrypted directory. For example, if you have an +encrypted directory `/home/$USER/private` that is protected by a custom +passphrase, all `fscrypt` metadata needed to unlock the directory with that +custom passphrase will be located in `/home/.fscrypt` if you are using a +dedicated `/home` filesystem or in `/.fscrypt` if you aren't. If desired, you +can back up the `fscrypt` metadata by making a copy of this directory, although +this isn't too important since this metadata is located on the same filesystem +as the encrypted directory(s). + +`pam_passphrase` (login passphrase) protectors are a bit different as they are +always stored on the root filesystem, in `/.fscrypt`. This ties them to the +specific system and ensures that each user has only a single login protector. +Therefore, encrypted directories on a non-root filesystem **can't be unlocked +via a login protector if the operating system is reinstalled or if the disk is +connected to another system** -- even if the new system uses the same login +passphrase for the user. + +Because of this, `fscrypt encrypt` will automatically generate a recovery +passphrase when creating a login passphrase-protected directory on a non-root +filesystem. The recovery passphrase is simply a `custom_passphrase` protector +with a randomly generated high-entropy passphrase. Initially, the recovery +passphrase is stored in a file in the encrypted directory itself; therefore, to +use it you **must** record it in another secure location. It is strongly +recommended to do this. Then, if ever needed, you can use `fscrypt unlock` to +unlock the directory with the recovery passphrase (by choosing the recovery +protector instead of the login protector). + +If you really want to disable the generation of a recovery passphrase, use the +`--no-recovery` option. Only do this if you really know what you are doing and +are prepared for potential data loss. + +Alternative approaches to supporting recovery of login passphrase-protected +directories include the following: + +* Manually adding your own recovery protector, using + `fscrypt metadata add-protector-to-policy`. + +* Backing up and restoring the `/.fscrypt` directory on the root filesystem. + Note that after restoring the `/.fscrypt` directory, unlocking the login + protectors will require the passphrases they had at the time the backup was + made **even if they were changed later**, so make sure to remember these + passphrase(s) or record them in a secure location. Also note that if the UUID + of the root filesystem changed, you will need to manually fix the UUID in any + `.fscrypt/protectors/*.link` files on other filesystems. + +The auto-generated recovery passphrases should be enough for most users, though. + +## Encrypting existing files + +`fscrypt` isn't designed to encrypt existing files, as this presents significant +technical challenges and usually is impossible to do securely. Therefore, +`fscrypt encrypt` only works on empty directories. + +Of course, it is still possible to create an encrypted directory, copy files +into it, and delete the original files. The `mv` command will even work, as it +will fall back to a copy and delete ([except on older +kernels](#getting-operation-not-permitted-when-moving-files-into-an-encrypted-directory)). +However, beware that due to the characteristics of filesystems and storage +devices, this may not properly protect the files, as their original contents may +still be forensically recoverable from disk even after being deleted. It's +**much** better to encrypt files from the very beginning. + +There are only a few cases where copying files into an encrypted directory can +really make sense, such as: + +* The source files are located on an in-memory filesystem such as `tmpfs`. + +* The confidentiality of the source files isn't important, e.g. they are + system default files and the user hasn't added any personal files yet. + +* The source files are protected by a different `fscrypt` policy, the old and + new policies are protected by only the same protector(s), and the old policy + uses similar strength encryption. + +If one of the above doesn't apply, then it's probably too late to securely +encrypt your existing files. + +As a best-effort attempt, you can use the `shred` program to try to erase the +original files. Here are the recommended commands for "best-effort" encryption +of an existing directory named "dir": + +```bash +mkdir dir.new +fscrypt encrypt dir.new +cp -a -T dir dir.new +find dir -type f -print0 | xargs -0 shred -n1 --remove=unlink +rm -rf dir +mv dir.new dir +``` + +However, beware that `shred` isn't guaranteed to be effective on all storage +devices and filesystems. For example, if you're using an SSD, "overwrites" of +data typically go to new flash blocks, so they aren't really overwrites. + +Note: for reasons similar to the above, changed or removed `fscrypt` protectors +aren't guaranteed to be forensically unrecoverable from disk either. Thus, the +use of weak or default passphrases should be avoided, even if changed later. + +## Example usage + +All these examples assume there is an ext4 filesystem which supports +encryption mounted at `/mnt/disk`. See +[here](#getting-encryption-not-enabled-on-an-ext4-filesystem) for how +to enable encryption support on an ext4 filesystem. ### Setting up fscrypt on a directory ```bash # Check which directories on our system support encryption >>>>> fscrypt status -2 filesystem(s) on this system support encryption +filesystems supporting encryption: 1 +filesystems with fscrypt metadata: 0 -MOUNTPOINT DEVICE FILESYSTEM STATUS -/ /dev/sda1 ext4 encryption not enabled -/mnt/disk /dev/sdb ext4 not setup with fscrypt +MOUNTPOINT DEVICE FILESYSTEM ENCRYPTION FSCRYPT +/ /dev/sda1 ext4 not enabled No +/mnt/disk /dev/sdb ext4 supported No -# Create the global configuration file. Nothing else needs root. +# Create the global configuration file. Nothing else necessarily needs root. >>>>> sudo fscrypt setup -Create "/etc/fscrypt.conf"? [Y/n] y +Defaulting to policy_version 2 because kernel supports it. Customizing passphrase hashing difficulty for this system... Created global config file at "/etc/fscrypt.conf". +Allow users other than root to create fscrypt metadata on the root filesystem? +(See https://github.com/google/fscrypt#setting-up-fscrypt-on-a-filesystem) [y/N] y +Metadata directories created at "/.fscrypt", writable by everyone. # Start using fscrypt with our filesystem ->>>>> fscrypt setup /mnt/disk -Metadata directories created at "/mnt/disk/.fscrypt". -Filesystem "/mnt/disk" (/dev/sdb) ready for use with ext4 encryption. +>>>>> sudo fscrypt setup /mnt/disk +Allow users other than root to create fscrypt metadata on this filesystem? (See +https://github.com/google/fscrypt#setting-up-fscrypt-on-a-filesystem) [y/N] y +Metadata directories created at "/mnt/disk/.fscrypt", writable by everyone. # Initialize encryption on a new empty directory >>>>> mkdir /mnt/disk/dir1 >>>>> fscrypt encrypt /mnt/disk/dir1 -Should we create a new protector? [Y/n] y -Your data can be protected with one of the following sources: +The following protector sources are available: 1 - Your login passphrase (pam_passphrase) 2 - A custom passphrase (custom_passphrase) 3 - A raw 256-bit key (raw_key) @@ -250,55 +741,50 @@ Confirm passphrase: # We can see this created one policy and one protector for this directory >>>>> fscrypt status /mnt/disk -ext4 filesystem "/mnt/disk" has 1 protector(s) and 1 policy(ies) +ext4 filesystem "/mnt/disk" has 1 protector and 1 policy PROTECTOR LINKED DESCRIPTION 7626382168311a9d No custom protector "Super Secret" -POLICY UNLOCKED PROTECTORS -7626382168311a9d Yes 7626382168311a9d +POLICY UNLOCKED PROTECTORS +16382f282d7b29ee27e6460151d03382 Yes 7626382168311a9d ``` -#### Quiet Version +#### Quiet version ```bash ->>>>> sudo fscrypt setup --quiet --force ->>>>> fscrypt setup /mnt/disk --quiet +>>>>> sudo fscrypt setup --quiet --force --all-users +>>>>> sudo fscrypt setup /mnt/disk --quiet --all-users >>>>> echo "hunter2" | fscrypt encrypt /mnt/disk/dir1 --quiet --source=custom_passphrase --name="Super Secret" ``` ### Locking and unlocking a directory -As noted in the troubleshooting below, we (as of now) have to unmount a -filesystem after purging its keys to clear the necessary caches. - ```bash # Write a file to our encrypted directory. >>>>> echo "Hello World" > /mnt/disk/dir1/secret.txt >>>>> fscrypt status /mnt/disk/dir1 "/mnt/disk/dir1" is encrypted with fscrypt. -Policy: 16382f282d7b29ee +Policy: 16382f282d7b29ee27e6460151d03382 +Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2 Unlocked: Yes -Protected with 1 protector(s): +Protected with 1 protector: PROTECTOR LINKED DESCRIPTION 7626382168311a9d No custom protector "Super Secret" -# Purging, unmounting, and remounting a filesystem locks all the files. ->>>>> fscrypt purge /mnt/disk -WARNING: This may make data encrypted with fscrypt inaccessible. -Purge all policy keys from "/mnt/disk" (this will lock all encrypted directories) [y/N] y -All keys purged for "/mnt/disk". -Filesystem "/mnt/disk" should now be unmounted. ->>>>> umount /mnt/disk ->>>>> mount /mnt/disk +# Lock the directory. Note: if using a v1 encryption policy instead +# of v2, you'll need 'sudo fscrypt lock /mnt/disk/dir1 --user=$USER'. +>>>>> fscrypt lock /mnt/disk/dir1 +"/mnt/disk/dir1" is now locked. >>>>> fscrypt status /mnt/disk/dir1 "/mnt/disk/dir1" is encrypted with fscrypt. -Policy: 16382f282d7b29ee +Policy: 16382f282d7b29ee27e6460151d03382 +Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2 Unlocked: No -Protected with 1 protector(s): +Protected with 1 protector: PROTECTOR LINKED DESCRIPTION 7626382168311a9d No custom protector "Super Secret" @@ -315,41 +801,36 @@ Enter custom passphrase for protector "Super Secret": >>>>> fscrypt status /mnt/disk/dir1 "/mnt/disk/dir1" is encrypted with fscrypt. -Policy: 16382f282d7b29ee +Policy: 16382f282d7b29ee27e6460151d03382 +Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2 Unlocked: Yes -Protected with 1 protector(s): +Protected with 1 protector: PROTECTOR LINKED DESCRIPTION 7626382168311a9d No custom protector "Super Secret" >>>>> cat /mnt/disk/dir1/secret.txt Hello World ``` -#### Quiet Version +#### Quiet version ```bash ->>>>> fscrypt purge /mnt/disk --quiet --force ->>>>> umount /mnt/disk ->>>>> mount /mnt/disk ->>>>> printf "hunter2" | fscrypt unlock /mnt/disk/dir1 --quiet +>>>>> fscrypt lock /mnt/disk/dir1 --quiet +>>>>> echo "hunter2" | fscrypt unlock /mnt/disk/dir1 --quiet ``` ### Protecting a directory with your login passphrase -As noted above and in the troubleshooting below, fscrypt cannot (yet) detect -when your login passphrase changes. So if you protect a directory with your -login passphrase, you may have to do additional work when you change your system -passphrase. +First, ensure that you have properly [set up your system for login +protectors](#setting-up-for-login-protectors). -```bash -# Login passphrases also require that fscrypt is setup on the root directory ->>>>> sudo fscrypt setup / -Filesystem "/" (/dev/dm-1) ready for use with ext4 encryption. +Then, you can protect directories with your login passphrase as follows: +```bash # Select your login passphrase as the desired source. >>>>> mkdir /mnt/disk/dir2 >>>>> fscrypt encrypt /mnt/disk/dir2 -Should we create a new protector? [Y/n] y -Your data can be protected with one of the following sources: +Should we create a new protector? [y/N] y +The following protector sources are available: 1 - Your login passphrase (pam_passphrase) 2 - A custom passphrase (custom_passphrase) 3 - A raw 256-bit key (raw_key) @@ -361,22 +842,23 @@ Enter login passphrase for joerichey: >>>>> fscrypt status /mnt/disk/dir2 "/mnt/disk/dir2" is encrypted with fscrypt. -Policy: fe1c92009abc1cff +Policy: fe1c92009abc1cff4f3257c77e8134e3 +Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2 Unlocked: Yes -Protected with 1 protector(s): +Protected with 1 protector: PROTECTOR LINKED DESCRIPTION 6891f0a901f0065e Yes (/) login protector for joerichey >>>>> fscrypt status /mnt/disk -ext4 filesystem "/mnt/disk" has 3 protector(s) and 3 policy(ies) +ext4 filesystem "/mnt/disk" has 2 protectors and 2 policies PROTECTOR LINKED DESCRIPTION 7626382168311a9d No custom protector "Super Secret" 6891f0a901f0065e Yes (/) login protector for joerichey -POLICY UNLOCKED PROTECTORS -16382f282d7b29ee Yes 7626382168311a9d -fe1c92009abc1cff Yes 6891f0a901f0065e +POLICY UNLOCKED PROTECTORS +16382f282d7b29ee27e6460151d03382 Yes 7626382168311a9d +fe1c92009abc1cff4f3257c77e8134e3 Yes 6891f0a901f0065e >>>>> fscrypt status / ext4 filesystem "/" has 1 protector(s) and 0 policy(ies) @@ -384,10 +866,10 @@ PROTECTOR LINKED DESCRIPTION 6891f0a901f0065e No login protector for joerichey ``` -#### Quiet Version +#### Quiet version ```bash >>>>> mkdir /mnt/disk/dir2 ->>>>> echo "password" | fscrypt encrypt /mnt/disk/dir1 --source=pam_passphrase --quiet +>>>>> echo "password" | fscrypt encrypt /mnt/disk/dir2 --source=pam_passphrase --quiet ``` ### Changing a custom passphrase @@ -396,10 +878,11 @@ PROTECTOR LINKED DESCRIPTION >>>>> fscrypt status /mnt/disk/dir1 "/mnt/disk/dir1" is encrypted with fscrypt. -Policy: 16382f282d7b29ee +Policy: 16382f282d7b29ee27e6460151d03382 +Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2 Unlocked: Yes -Protected with 1 protector(s): +Protected with 1 protector: PROTECTOR LINKED DESCRIPTION 7626382168311a9d No custom protector "Super Secret" @@ -411,14 +894,14 @@ Confirm passphrase: Passphrase for protector 7626382168311a9d successfully changed. ``` -#### Quiet Version +#### Quiet version ```bash >>>>> printf "hunter2\nhunter3" | fscrypt metadata change-passphrase --protector=/mnt/disk:7626382168311a9d --quiet ``` ### Using a raw key protector -fscrypt also supports protectors which use raw key files as the user-provided +`fscrypt` also supports protectors which use raw key files as the user-provided secret. These key files must be exactly 32 bytes long and contain the raw binary data of the key. Obviously, make sure to store the key file securely (and not in the directory you are encrypting with it). If generating the keys on Linux make @@ -434,7 +917,7 @@ sure you are aware of # could also use `fscrypt encrypt --key=secret.key` to achieve the same thing. >>>>> fscrypt metadata create protector /mnt/disk Create new protector on "/mnt/disk" [Y/n] y -Your data can be protected with one of the following sources: +The following protector sources are available: 1 - Your login passphrase (pam_passphrase) 2 - A custom passphrase (custom_passphrase) 3 - A raw 256-bit key (raw_key) @@ -443,16 +926,16 @@ Enter a name for the new protector: Skeleton Enter key file for protector "Skeleton": secret.key Protector 2c75f519b9c9959d created on filesystem "/mnt/disk". >>>>> fscrypt status /mnt/disk -ext4 filesystem "/mnt/disk" has 3 protectors and 3 policies +ext4 filesystem "/mnt/disk" has 3 protectors and 2 policies PROTECTOR LINKED DESCRIPTION 7626382168311a9d No custom protector "Super Secret" 2c75f519b9c9959d No raw key protector "Skeleton" 6891f0a901f0065e Yes (/) login protector for joerichey -POLICY UNLOCKED PROTECTORS -16382f282d7b29ee Yes 7626382168311a9d -fe1c92009abc1cff Yes 6891f0a901f0065e +POLICY UNLOCKED PROTECTORS +16382f282d7b29ee27e6460151d03382 Yes 7626382168311a9d +fe1c92009abc1cff4f3257c77e8134e3 Yes 6891f0a901f0065e # Finally, we could apply this key to a directory >>>>> mkdir /mnt/disk/dir3 @@ -461,7 +944,7 @@ Enter key file for protector "Skeleton": secret.key "/mnt/disk/dir3" is now encrypted, unlocked, and ready for use. ``` -#### Quiet Version +#### Quiet version ```bash >>>>> head --bytes=32 /dev/urandom > secret.key >>>>> fscrypt encrypt /mnt/disk/dir3 --key=secret.key --source=raw_key --name=Skeleton @@ -469,7 +952,7 @@ Enter key file for protector "Skeleton": secret.key ### Using multiple protectors for a policy -fscrypt supports the idea of of protecting a single directory with multiple +`fscrypt` supports the idea of protecting a single directory with multiple protectors. This means having access to any of the protectors is sufficient to decrypt the directory. This is useful for sharing data or setting up access control systems. @@ -484,29 +967,31 @@ PROTECTOR LINKED DESCRIPTION 2c75f519b9c9959d No raw key protector "Skeleton" 6891f0a901f0065e Yes (/) login protector for joerichey -POLICY UNLOCKED PROTECTORS -d03fb894584a4318 No 2c75f519b9c9959d -16382f282d7b29ee No 7626382168311a9d -fe1c92009abc1cff No 6891f0a901f0065e +POLICY UNLOCKED PROTECTORS +d03fb894584a4318d1780e9a7b0b47eb No 2c75f519b9c9959d +16382f282d7b29ee27e6460151d03382 No 7626382168311a9d +fe1c92009abc1cff4f3257c77e8134e3 No 6891f0a901f0065e >>>>> fscrypt status /mnt/disk/dir1 "/mnt/disk/dir1" is encrypted with fscrypt. -Policy: 16382f282d7b29ee +Policy: 16382f282d7b29ee27e6460151d03382 +Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2 Unlocked: No Protected with 1 protector: PROTECTOR LINKED DESCRIPTION 7626382168311a9d No custom protector "Super Secret" ->>>>> fscrypt metadata add-protector-to-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee +>>>>> fscrypt metadata add-protector-to-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee27e6460151d03382 WARNING: All files using this policy will be accessible with this protector!! -Protect policy 16382f282d7b29ee with protector 2c75f519b9c9959d? [Y/n] +Protect policy 16382f282d7b29ee27e6460151d03382 with protector 2c75f519b9c9959d? [Y/n] Enter key file for protector "Skeleton": secret.key Enter custom passphrase for protector "Super Secret": -Protector 2c75f519b9c9959d now protecting policy 16382f282d7b29ee. +Protector 2c75f519b9c9959d now protecting policy 16382f282d7b29ee27e6460151d03382. >>>>> fscrypt status /mnt/disk/dir1 "/mnt/disk/dir1" is encrypted with fscrypt. -Policy: 16382f282d7b29ee +Policy: 16382f282d7b29ee27e6460151d03382 +Options: padding:32 contents:AES_256_XTS filenames:AES_256_CTS policy_version:2 Unlocked: No Protected with 2 protectors: @@ -524,91 +1009,279 @@ Enter key file for protector "Skeleton": secret.key "/mnt/disk/dir1" is now unlocked and ready for use. # The protector can also be removed from the policy (if it is not the only one) ->>>>> fscrypt metadata remove-protector-from-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee +>>>>> fscrypt metadata remove-protector-from-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee27e6460151d03382 WARNING: All files using this policy will NO LONGER be accessible with this protector!! -Stop protecting policy 16382f282d7b29ee with protector 2c75f519b9c9959d? [y/N] y -Protector 2c75f519b9c9959d no longer protecting policy 16382f282d7b29ee. +Stop protecting policy 16382f282d7b29ee27e6460151d03382 with protector 2c75f519b9c9959d? [y/N] y +Protector 2c75f519b9c9959d no longer protecting policy 16382f282d7b29ee27e6460151d03382. ``` -#### Quiet Version +#### Quiet version ```bash ->>>>> echo "hunter2" | fscrypt metadata add-protector-to-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee --key=secret.key --quiet ->>>>> fscrypt metadata remove-protector-from-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee --quiet --force +>>>>> echo "hunter2" | fscrypt metadata add-protector-to-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee27e6460151d03382 --key=secret.key --quiet +>>>>> fscrypt metadata remove-protector-from-policy --protector=/mnt/disk:2c75f519b9c9959d --policy=/mnt/disk:16382f282d7b29ee27e6460151d03382 --quiet --force ``` ## Contributing -We would love to accept your contributions to fscrypt. See the `CONTRIBUTING.md` -file for more information about singing the CLA and submitting a pull request. +We would love to accept your contributions to `fscrypt`. See the +`CONTRIBUTING.md` file for more information about signing the CLA and submitting +a pull request. ## Troubleshooting -In general, if you are encountering issues with fscrypt, +In general, if you are encountering issues with `fscrypt`, [open an issue](https://github.com/google/fscrypt/issues/new), following the guidelines in `CONTRIBUTING.md`. We will try our best to help. #### I changed my login passphrase, now all my directories are inaccessible -The PAM module provided by fscrypt (`pam_fscrypt.so`) should automatically -detect changes to a user's login passphrase so that they can still access their -encrypted directories. However, sometimes the login passphrase can become -desynchronized from a user's login protector. This usually happens when the PAM -passphrase is managed by an external system, if the PAM module is not installed, -or if the PAM module is not properly configured. - -To fix your login protector, you first should find the appropriate protector ID -by running `fscrypt status "/"`. Then, change the passphrase for this protector -by running: +Usually, the PAM module `pam_fscrypt.so` will automatically detect changes to a +user's login passphrase and update the user's `fscrypt` login protector so that +they retain access their login-passphrase protected directories. However, +sometimes a user's login passphrase can become desynchronized from their +`fscrypt` login protector. This can happen if `root` assigns the user a new +passphrase without providing the old one, if the user's login passphrase is +managed by an external system such as LDAP, if the PAM module is not installed, +or if the PAM module is not properly configured. See [Enabling the PAM +module](#enabling-the-pam-module) for how to configure the PAM module. + +To fix a user's login protector, find the corresponding protector ID by running +`fscrypt status "/"`. Then, change this protector's passphrase by running: ``` fscrypt metadata change-passphrase --protector=/:ID ``` -#### Directories using my login passphrase are not automatically unlocking. +#### Directories using my login passphrase are not automatically unlocking + +First, directories won't unlock if your session starts without password +authentication. The most common case of this is public-key ssh login. To +trigger a password authentication event, run `su $USER -c exit`. + +If your session did start with password authentication, then the following may +be causing the issue: + +* The PAM module might not be configured correctly. Ensure you have correctly + [configured the PAM module](#enabling-the-pam-module). + +* If your login passphrase recently changed, then it might have gotten out of + sync with your login protector. To fix this, [manually change your login + protector's + passphrase](#i-changed-my-login-passphrase-now-all-my-directories-are-inaccessible) + to get it back in sync with your actual login passphrase. + +* Due to a [bug in sshd](https://bugzilla.mindrot.org/show_bug.cgi?id=2548), + encrypted directories won't auto-unlock when logging in with ssh using the + `ChallengeResponseAuthentication` ssh authentication method, which is also + called `KbdInteractiveAuthentication`. This ssh authentication method + implements password authentication by default, so it might appear similar to + `PasswordAuthentication`. However, only `PasswordAuthentication` works with + `fscrypt`. To avoid this issue, make sure that your `/etc/ssh/sshd_config` + file contains `PasswordAuthentication yes`, `UsePAM yes`, and either + `ChallengeResponseAuthentication no` or `KbdInteractiveAuthentication no`. + +#### Getting "encryption not enabled" on an ext4 filesystem + +This is usually caused by your ext4 filesystem not having the `encrypt` feature +flag enabled. The `encrypt` feature flag allows the filesystem to contain +encrypted files. (It doesn't actually encrypt anything by itself.) + +Before enabling `encrypt` on your ext4 filesystem, first ensure that all of the +following are true for you: -Either the PAM module is not installed correctly, or your login passphrase -changed and things got out of sync. Another reason that these directories might -not unlock is if your session starts without password authentication. The most -common case of this is public-key ssh login. +* You only need to use your filesystem on kernels v4.1 and later. -To trigger a password authentication event, run `su $(whoami) -c exit`. + (Kernels v4.0 and earlier can't mount ext4 filesystems that have the `encrypt` + feature flag.) -#### Getting "encryption not enabled" on an ext4 filesystem. +* Either you only need to use your filesystem on kernels v5.5 and later, or your + kernel page size (run `getconf PAGE_SIZE`) and filesystem block size (run + `tune2fs -l /dev/device | grep 'Block size'`) are the same. -Getting this error on an ext4 system usually means the filesystem has not been -setup for encryption. The only other way to get this error is if filesystem -encryption has been explictly disabled in the kernel config. + (Both values will almost always be 4096, but they may differ if your + filesystem is very small, if your system uses the PowerPC CPU architecture, or + if you overrode the default block size when you created the filesystem. Only + kernels v5.5 and later support ext4 encryption in such cases.) -__IMPORTANT:__ Before enabling encryption on an ext4 filesystem __ALL__ of the -following should be true: - * Your filesystem is formatted as ext4. Other filesystems will have - different ways of enabling encryption. - * Your kernel page size (run `getconf PAGE_SIZE`) and your filesystem - block size (run `tune2fs -l /dev/device | grep 'Block size'`) are the - same. - * You are ok with not being able to mount this filesystem with a v4.0 - kernel or older. - * You are __NOT__ using GRUB to boot directly off this filesystem. If - you have a sperate `/boot` partition, you are fine. -If any of the above is not true, __DO NOT ENABLE FILESYSTEM ENCRYPTION__. +* Either you aren't using GRUB to boot directly off the filesystem in question, + or you are using GRUB 2.04 or later. -To turn on encryption for your filesystem, run + (Old versions of GRUB can't boot from ext4 filesystems that have `encrypt` + enabled. If, like most people, you have a separate `/boot` partition, you are + fine. You are also fine if you are using the GRUB Debian package `2.02-2` or + later [*not* `2.02_beta*`], including the version in Ubuntu 18.04 and later, + since the patch to support `encrypt` was backported.) + +After verifying all of the above, enable `encrypt` by running: ``` tune2fs -O encrypt /dev/device ``` -To turn off encryption for your filesystem, run + +If you need to undo this, first delete all encrypted files and directories on +the filesystem. Then, run: ``` fsck -fn /dev/device debugfs -w -R "feature -encrypt" /dev/device fsck -fn /dev/device ``` -Note: It is actually possible to get GRUB to boot an encrypted ext4 filesystem. -However, it requires GRUB 2.02 (__NOT__ the 2.02 beta) to be installed as the -bootloader. As this version was released in April 2017, most systems __WILL -FAIL TO BOOT__ with an ext4 encrypted boot directory. Note that this is only -relevant to systems without a seperate boot partition. Sytems with `/boot` on -a different partition than the one being encrypted (including all UEFI systems) -are not effected by this. +If you've enabled `encrypt` but you still get the "encryption not enabled" +error, then the problem is that ext4 encryption isn't enabled in your kernel +config. See [Runtime dependencies](#runtime-dependencies) for how to enable it. + +#### Getting "user keyring not linked into session keyring" + +Some older versions of Ubuntu didn't link the user keyring into the session +keyring, which caused problems with `fscrypt`. + +To avoid this issue, upgrade to Ubuntu 20.04 or later. + +#### Getting "Operation not permitted" when moving files into an encrypted directory + +Originally, filesystems didn't return the correct error code when attempting to +rename unencrypted files (or files with a different encryption policy) into an +encrypted directory. Specifically, they returned `EPERM` instead of `EXDEV`, +which caused `mv` to fail rather than fall back to a copy as expected. + +This bug was fixed in version 5.1 of the mainline Linux kernel, as well as in +versions 4.4 and later of the LTS (Long Term Support) branches of the Linux +kernel; specifically v4.19.155, 4.14.204, v4.9.242, and v4.4.242. + +If the kernel can't be upgraded, this bug can be worked around by explicitly +copying the files instead, e.g. with `cp`. + +__IMPORTANT:__ Encrypting existing files can be insecure. Before doing so, read +[Encrypting existing files](#encrypting-existing-files). + +#### Getting "Package not installed" when trying to use an encrypted directory + +Trying to create or open an encrypted file will fail with `ENOPKG` ("Package not +installed") when the kernel doesn't support one or more of the cryptographic +algorithms used by the file or its directory. Note that `fscrypt encrypt` and +`fscrypt unlock` will still succeed; it's only using the directory afterwards +that will fail. + +The kernel will always support the algorithms that `fscrypt` uses by default. +However, if you changed the contents and/or filenames encryption algorithms in +[`/etc/fscrypt.conf`](#configuration-file), then you may run into this issue. +To fix it, enable the needed `CONFIG_CRYPTO_*` options in your Linux kernel +configuration. See the [kernel +documentation](https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#encryption-modes-and-usage) +for details about which option(s) are required for each encryption mode. + +#### Some processes can't access unlocked encrypted files + +This issue is caused by a limitation in the original design of Linux native +filesystem encryption which made it difficult to ensure that all processes can +access unlocked encrypted files. This issue can manifest in many ways, such as: + +* SSH to a user with an encrypted home directory not working, even when that + directory is already unlocked + +* Docker containers being unable to access encrypted files that were unlocked + from outside the container + +* NetworkManager being unable to access certificates stored in the user's + already-unlocked encrypted home directory + +* Other system services being unable to access already-unlocked encrypted files + +* `sudo` sessions being unable to access already-unlocked encrypted files + +* A user being unable to access encrypted files that were unlocked by root + +If an OS-level error is shown, it is `ENOKEY` ("Required key not available"). + +To fix this issue, first run `fscrypt status $dir`, where `$dir` is your +encrypted directory. If the output contains `policy_version:2`, then your issue +is something else, so stop reading now. If the output contains +`policy_version:1` or doesn't contain any mention of `policy_version`, then +you'll need to upgrade your directory(s) to policy version 2. To do this: + +1. Upgrade to Linux kernel v5.4 or later. + +2. Upgrade to `fscrypt` v0.2.7 or later. + +3. Run `sudo fscrypt setup --force`. + +4. Re-encrypt your encrypted directory(s). Since files cannot be (re-)encrypted + in-place, this requires replacing them with new directories. For example: + ``` + fscrypt unlock dir # if not already unlocked + mkdir dir.new + fscrypt encrypt dir.new + cp -a -T dir dir.new + find dir -type f -print0 | xargs -0 shred -n1 --remove=unlink + rm -rf dir + mv dir.new dir + ``` + + You don't need to create a new protector. I.e., when `fscrypt encrypt` asks + for a protector, just choose the one you were using before. + +5. `fscrypt status` on your directory(s) should now show `policy_version:2`, + and the issue should be gone. + +Note that once your directories are using policy version 2, they will only be +usable with Linux kernel v5.4 and later and `fscrypt` v0.2.6 and later. So be +careful not to downgrade your software past those versions. + +This issue can also be fixed by setting `"use_fs_keyring_for_v1_policies": true` +in `/etc/fscrypt.conf`, as described in [Configuration +file](#configuration-file). This avoids needing to upgrade directories to +policy version 2. However, this has some limitations, and the same kernel and +`fscrypt` prerequisites still apply for this option to take effect. It is +recommended to upgrade your directories to policy version 2 instead. + +#### Users can access other users' unlocked encrypted files + +This is working as intended. When an encrypted directory is unlocked (or +locked), it is unlocked (or locked) for all users. Encryption is not access +control; the Linux kernel already has many access control mechanisms, such as +the standard UNIX file permissions, that can be used to control access to files. + +Setting the mode of your encrypted directory to `0700` will prevent users other +than the directory's owner and `root` from accessing it while it is unlocked. +In `fscrypt` v0.2.5 and later, `fscrypt encrypt` sets this mode automatically. + +Having the locked/unlocked status of directories be global instead of per-user +may seem unintuitive, but it is actually the only logical way. The encryption +is done by the filesystem, so in reality the filesystem either has the key or it +doesn't. And once it has the key, any additional checks of whether particular +users "have" the key would be OS-level access control checks (not cryptography) +that are redundant with existing OS-level access control mechanisms. + +Similarly, any attempt of the filesystem encryption feature to prevent `root` +from accessing unlocked encrypted files would be pointless. On Linux systems, +`root` is usually all-powerful and can always get access to files in ways that +cannot be prevented, e.g. `setuid()` and `ptrace()`. The only reliable way to +limit what `root` can do is via a mandatory access control system, e.g. SELinux. + +The original design of Linux native filesystem encryption actually did put the +keys into per-user keyrings. However, this caused a [massive number of +problems](#some-processes-cant-access-unlocked-encrypted-files), as it's +actually very common that encrypted files need to be accessed by processes +running under different user IDs -- even if it may not be immediately apparent. + +#### Getting "Required key not available" when backing up locked encrypted files + +Encrypted files can't be backed up while locked; you need to unlock them first. +For details, see [Backup, restore, and recovery](#backup-restore-and-recovery). + +#### The reported size of encrypted symlinks is wrong + +Originally, filesystems didn't conform to POSIX when reporting the size of +encrypted symlinks, as they gave the size of the ciphertext symlink target +rather than the size of the plaintext target. This would make the reported size +of symlinks appear to be slightly too large when queried using ``lstat()`` or +similar system calls. Most programs don't care about this, but in rare cases +programs can depend on the filesystem reporting symlink sizes correctly. + +This bug was fixed in version 5.15 of the mainline Linux kernel, as well as in +versions 4.19 and later of the LTS (Long Term Support) branches of the Linux +kernel; specifically v5.10.63, v5.4.145, and v4.19.207. + +If the kernel can't be upgraded, the only workaround for this bug is to update +any affected programs to not depend on symlink sizes being reported correctly. ## Legal |