Commit Graph

15 Commits

Author SHA1 Message Date
Eric Biggers
c1f1f5bf41 fscrypt: document that CephFS supports fscrypt now
The help text for CONFIG_FS_ENCRYPTION and the fscrypt.rst documentation
file both list the filesystems that support fscrypt.  CephFS added
support for fscrypt in v6.6, so add CephFS to the list.

Link: https://lore.kernel.org/r/20231227045158.87276-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
2023-12-26 22:55:42 -06:00
Ard Biesheuvel
a0fc20333e fscrypt: relax Kconfig dependencies for crypto API algorithms
Even if FS encryption has strict functional dependencies on various
crypto algorithms and chaining modes. those dependencies could potentially
be satisified by other implementations than the generic ones, and no link
time dependency exists on the 'depends on' claused defined by
CONFIG_FS_ENCRYPTION_ALGS.

So let's relax these clauses to 'imply', so that the default behavior
is still to pull in those generic algorithms, but in a way that permits
them to be disabled again in Kconfig.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2021-04-22 17:31:32 +10:00
Eric Biggers
bd0d97b719 fscrypt: switch fscrypt_do_sha256() to use the SHA-256 library
fscrypt_do_sha256() is only used for hashing encrypted filenames to
create no-key tokens, which isn't performance-critical.  Therefore a C
implementation of SHA-256 is sufficient.

Also, the logic to create no-key tokens is always potentially needed.
This differs from fscrypt's other dependencies on crypto API algorithms,
which are conditionally needed depending on what encryption policies
userspace is using.  Therefore, for fscrypt there isn't much benefit to
allowing SHA-256 to be a loadable module.

So, make fscrypt_do_sha256() use the SHA-256 library instead of the
crypto_shash API.  This is much simpler, since it avoids having to
implement one-time-init (which is hard to do correctly, and in fact was
implemented incorrectly) and handle failures to allocate the
crypto_shash object.

Fixes: edc440e3d2 ("fscrypt: improve format of no-key names")
Cc: Daniel Rosenberg <drosen@google.com>
Link: https://lore.kernel.org/r/20200721225920.114347-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
2020-07-21 16:02:13 -07:00
Satya Tangirala
5fee36095c fscrypt: add inline encryption support
Add support for inline encryption to fs/crypto/.  With "inline
encryption", the block layer handles the decryption/encryption as part
of the bio, instead of the filesystem doing the crypto itself via
Linux's crypto API. This model is needed in order to take advantage of
the inline encryption hardware present on most modern mobile SoCs.

To use inline encryption, the filesystem needs to be mounted with
'-o inlinecrypt'. Blk-crypto will then be used instead of the traditional
filesystem-layer crypto whenever possible to encrypt the contents
of any encrypted files in that filesystem. Fscrypt still provides the key
and IV to use, and the actual ciphertext on-disk is still the same;
therefore it's testable using the existing fscrypt ciphertext verification
tests.

Note that since blk-crypto has a fallback to Linux's crypto API, and
also supports all the encryption modes currently supported by fscrypt,
this feature is usable and testable even without actual inline
encryption hardware.

Per-filesystem changes will be needed to set encryption contexts when
submitting bios and to implement the 'inlinecrypt' mount option.  This
patch just adds the common code.

Signed-off-by: Satya Tangirala <satyat@google.com>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20200702015607.1215430-3-satyat@google.com
Co-developed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
2020-07-08 10:29:30 -07:00
Daniel Rosenberg
edc440e3d2 fscrypt: improve format of no-key names
When an encrypted directory is listed without the key, the filesystem
must show "no-key names" that uniquely identify directory entries, are
at most 255 (NAME_MAX) bytes long, and don't contain '/' or '\0'.
Currently, for short names the no-key name is the base64 encoding of the
ciphertext filename, while for long names it's the base64 encoding of
the ciphertext filename's dirhash and second-to-last 16-byte block.

This format has the following problems:

- Since it doesn't always include the dirhash, it's incompatible with
  directories that will use a secret-keyed dirhash over the plaintext
  filenames.  In this case, the dirhash won't be computable from the
  ciphertext name without the key, so it instead must be retrieved from
  the directory entry and always included in the no-key name.
  Casefolded encrypted directories will use this type of dirhash.

- It's ambiguous: it's possible to craft two filenames that map to the
  same no-key name, since the method used to abbreviate long filenames
  doesn't use a proper cryptographic hash function.

Solve both these problems by switching to a new no-key name format that
is the base64 encoding of a variable-length structure that contains the
dirhash, up to 149 bytes of the ciphertext filename, and (if any bytes
remain) the SHA-256 of the remaining bytes of the ciphertext filename.

This ensures that each no-key name contains everything needed to find
the directory entry again, contains only legal characters, doesn't
exceed NAME_MAX, is unambiguous unless there's a SHA-256 collision, and
that we only take the performance hit of SHA-256 on very long filenames.

Note: this change does *not* address the existing issue where users can
modify the 'dirhash' part of a no-key name and the filesystem may still
accept the name.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
[EB: improved comments and commit message, fixed checking return value
 of base64_decode(), check for SHA-256 error, continue to set disk_name
 for short names to keep matching simpler, and many other cleanups]
Link: https://lore.kernel.org/r/20200120223201.241390-7-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
2020-01-22 14:50:03 -08:00
Herbert Xu
ede7a09fc8 fscrypt: Allow modular crypto algorithms
The commit 643fa9612b ("fscrypt: remove filesystem specific
build config option") removed modular support for fs/crypto.  This
causes the Crypto API to be built-in whenever fscrypt is enabled.
This makes it very difficult for me to test modular builds of
the Crypto API without disabling fscrypt which is a pain.

As fscrypt is still evolving and it's developing new ties with the
fs layer, it's hard to build it as a module for now.

However, the actual algorithms are not required until a filesystem
is mounted.  Therefore we can allow them to be built as modules.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Link: https://lore.kernel.org/r/20191227024700.7vrzuux32uyfdgum@gondor.apana.org.au
Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-12-31 10:33:51 -06:00
Eric Biggers
c1144c9b8a fscrypt: add an HKDF-SHA512 implementation
Add an implementation of HKDF (RFC 5869) to fscrypt, for the purpose of
deriving additional key material from the fscrypt master keys for v2
encryption policies.  HKDF is a key derivation function built on top of
HMAC.  We choose SHA-512 for the underlying unkeyed hash, and use an
"hmac(sha512)" transform allocated from the crypto API.

We'll be using this to replace the AES-ECB based KDF currently used to
derive the per-file encryption keys.  While the AES-ECB based KDF is
believed to meet the original security requirements, it is nonstandard
and has problems that don't exist in modern KDFs such as HKDF:

1. It's reversible.  Given a derived key and nonce, an attacker can
   easily compute the master key.  This is okay if the master key and
   derived keys are equally hard to compromise, but now we'd like to be
   more robust against threats such as a derived key being compromised
   through a timing attack, or a derived key for an in-use file being
   compromised after the master key has already been removed.

2. It doesn't evenly distribute the entropy from the master key; each 16
   input bytes only affects the corresponding 16 output bytes.

3. It isn't easily extensible to deriving other values or keys, such as
   a public hash for securely identifying the key, or per-mode keys.
   Per-mode keys will be immediately useful for Adiantum encryption, for
   which fscrypt currently uses the master key directly, introducing
   unnecessary usage constraints.  Per-mode keys will also be useful for
   hardware inline encryption, which is currently being worked on.

HKDF solves all the above problems.

Reviewed-by: Paul Crowley <paulcrowley@google.com>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-08-12 19:18:50 -07:00
Eric Biggers
adbd9b4dee fscrypt: remove selection of CONFIG_CRYPTO_SHA256
fscrypt only uses SHA-256 for AES-128-CBC-ESSIV, which isn't the default
and is only recommended on platforms that have hardware accelerated
AES-CBC but not AES-XTS.  There's no link-time dependency, since SHA-256
is requested via the crypto API on first use.

To reduce bloat, we should limit FS_ENCRYPTION to selecting the default
algorithms only.  SHA-256 by itself isn't that much bloat, but it's
being discussed to move ESSIV into a crypto API template, which would
incidentally bring in other things like "authenc" support, which would
all end up being built-in since FS_ENCRYPTION is now a bool.

For Adiantum encryption we already just document that users who want to
use it have to enable CONFIG_CRYPTO_ADIANTUM themselves.  So, let's do
the same for AES-128-CBC-ESSIV and CONFIG_CRYPTO_SHA256.

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-06-27 10:29:33 -07:00
Thomas Gleixner
ec8f24b7fa treewide: Add SPDX license identifier - Makefile/Kconfig
Add SPDX license identifiers to all Make/Kconfig files which:

 - Have no license information of any form

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

  GPL-2.0-only

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-05-21 10:50:46 +02:00
Chandan Rajendra
643fa9612b fscrypt: remove filesystem specific build config option
In order to have a common code base for fscrypt "post read" processing
for all filesystems which support encryption, this commit removes
filesystem specific build config option (e.g. CONFIG_EXT4_FS_ENCRYPTION)
and replaces it with a build option (i.e. CONFIG_FS_ENCRYPTION) whose
value affects all the filesystems making use of fscrypt.

Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-01-23 23:56:43 -05:00
Eric Biggers
1058ef0dcb fscrypt: remove CRYPTO_CTR dependency
fscrypt doesn't use the CTR mode of operation for anything, so there's
no need to select CRYPTO_CTR.  It was added by commit 71dea01ea2
("ext4 crypto: require CONFIG_CRYPTO_CTR if ext4 encryption is
enabled").  But, I've been unable to identify the arm64 crypto bug it
was supposedly working around.

I suspect the issue was seen only on some old Android device kernel
(circa 3.10?).  So if the fix wasn't mistaken, the real bug is probably
already fixed.  Or maybe it was actually a bug in a non-upstream crypto
driver.

So, remove the dependency.  If it turns out there's actually still a
bug, we'll fix it properly.

Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-01-23 23:56:43 -05:00
Daniel Walter
b7e7cf7a66 fscrypt: add support for AES-128-CBC
fscrypt provides facilities to use different encryption algorithms which
are selectable by userspace when setting the encryption policy. Currently,
only AES-256-XTS for file contents and AES-256-CBC-CTS for file names are
implemented. This is a clear case of kernel offers the mechanism and
userspace selects a policy. Similar to what dm-crypt and ecryptfs have.

This patch adds support for using AES-128-CBC for file contents and
AES-128-CBC-CTS for file name encryption. To mitigate watermarking
attacks, IVs are generated using the ESSIV algorithm. While AES-CBC is
actually slightly less secure than AES-XTS from a security point of view,
there is more widespread hardware support. Using AES-CBC gives us the
acceptable performance while still providing a moderate level of security
for persistent storage.

Especially low-powered embedded devices with crypto accelerators such as
CAAM or CESA often only support AES-CBC. Since using AES-CBC over AES-XTS
is basically thought of a last resort, we use AES-128-CBC over AES-256-CBC
since it has less encryption rounds and yields noticeable better
performance starting from a file size of just a few kB.

Signed-off-by: Daniel Walter <dwalter@sigma-star.at>
[david@sigma-star.at: addressed review comments]
Signed-off-by: David Gstir <david@sigma-star.at>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2017-06-23 20:05:07 -04:00
Richard Weinberger
58ae74683a fscrypt: factor out bio specific functions
That way we can get rid of the direct dependency on CONFIG_BLOCK.

Fixes: d475a50745 ("ubifs: Add skeleton for fscrypto")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Gstir <david@sigma-star.at>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2017-01-01 16:18:49 -05:00
Eric Biggers
8048123576 fscrypto: remove unneeded Kconfig dependencies
SHA256 and ENCRYPTED_KEYS are not needed.  CTR shouldn't be needed
either, but I left it for now because it was intentionally added by
commit 71dea01ea2 ("ext4 crypto: require CONFIG_CRYPTO_CTR if ext4
encryption is enabled").  So it sounds like there may be a dependency
problem elsewhere, which I have not been able to identify specifically,
that must be solved before CTR can be removed.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2016-12-11 16:26:07 -05:00
Jaegeuk Kim
0b81d07790 fs crypto: move per-file encryption from f2fs tree to fs/crypto
This patch adds the renamed functions moved from the f2fs crypto files.

1. definitions for per-file encryption used by ext4 and f2fs.

2. crypto.c for encrypt/decrypt functions
 a. IO preparation:
  - fscrypt_get_ctx / fscrypt_release_ctx
 b. before IOs:
  - fscrypt_encrypt_page
  - fscrypt_decrypt_page
  - fscrypt_zeroout_range
 c. after IOs:
  - fscrypt_decrypt_bio_pages
  - fscrypt_pullback_bio_page
  - fscrypt_restore_control_page

3. policy.c supporting context management.
 a. For ioctls:
  - fscrypt_process_policy
  - fscrypt_get_policy
 b. For context permission
  - fscrypt_has_permitted_context
  - fscrypt_inherit_context

4. keyinfo.c to handle permissions
  - fscrypt_get_encryption_info
  - fscrypt_free_encryption_info

5. fname.c to support filename encryption
 a. general wrapper functions
  - fscrypt_fname_disk_to_usr
  - fscrypt_fname_usr_to_disk
  - fscrypt_setup_filename
  - fscrypt_free_filename

 b. specific filename handling functions
  - fscrypt_fname_alloc_buffer
  - fscrypt_fname_free_buffer

6. Makefile and Kconfig

Cc: Al Viro <viro@ftp.linux.org.uk>
Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Ildar Muslukhov <ildarm@google.com>
Signed-off-by: Uday Savagaonkar <savagaon@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
2016-03-17 21:19:33 -07:00