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fscrypt updates for 6.9

Browse Source 
Fix flakiness in a test by releasing the quota synchronously when a key
 is removed, and other minor cleanups.
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Merge tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/linux

Pull fscrypt updates from Eric Biggers:
 "Fix flakiness in a test by releasing the quota synchronously when a
  key is removed, and other minor cleanups"

* tag 'fscrypt-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/linux:
  fscrypt: shrink the size of struct fscrypt_inode_info slightly
  fscrypt: write CBC-CTS instead of CTS-CBC
  fscrypt: clear keyring before calling key_put()
  fscrypt: explicitly require that inode->i_blkbits be set
This commit is contained in:
Linus Torvalds 2024-03-12 13:17:36 -07:00
commit 3bf95d567d
4 changed files with 36 additions and 24 deletions
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27
Documentation/filesystems/fscrypt.rst
View File

@ -338,11 +338,14 @@ Supported modes
Currently, the following pairs of encryption modes are supported:
- AES-256-XTS for contents and AES-256-CTS-CBC for filenames
- AES-256-XTS for contents and AES-256-CBC-CTS for filenames
- AES-256-XTS for contents and AES-256-HCTR2 for filenames
- Adiantum for both contents and filenames
- AES-128-CBC-ESSIV for contents and AES-128-CTS-CBC for filenames
- SM4-XTS for contents and SM4-CTS-CBC for filenames
- AES-128-CBC-ESSIV for contents and AES-128-CBC-CTS for filenames
- SM4-XTS for contents and SM4-CBC-CTS for filenames
Note: in the API, "CBC" means CBC-ESSIV, and "CTS" means CBC-CTS.
So, for example, FSCRYPT_MODE_AES_256_CTS means AES-256-CBC-CTS.
Authenticated encryption modes are not currently supported because of
the difficulty of dealing with ciphertext expansion. Therefore,
@ -351,11 +354,11 @@ contents encryption uses a block cipher in `XTS mode
`CBC-ESSIV mode
<https://en.wikipedia.org/wiki/Disk_encryption_theory#Encrypted_salt-sector_initialization_vector_(ESSIV)>`_,
or a wide-block cipher. Filenames encryption uses a
block cipher in `CTS-CBC mode
block cipher in `CBC-CTS mode
<https://en.wikipedia.org/wiki/Ciphertext_stealing>`_ or a wide-block
cipher.
The (AES-256-XTS, AES-256-CTS-CBC) pair is the recommended default.
The (AES-256-XTS, AES-256-CBC-CTS) pair is the recommended default.
It is also the only option that is *guaranteed* to always be supported
if the kernel supports fscrypt at all; see `Kernel config options`_.
@ -364,7 +367,7 @@ upgrades the filenames encryption to use a wide-block cipher. (A
*wide-block cipher*, also called a tweakable super-pseudorandom
permutation, has the property that changing one bit scrambles the
entire result.) As described in `Filenames encryption`_, a wide-block
cipher is the ideal mode for the problem domain, though CTS-CBC is the
cipher is the ideal mode for the problem domain, though CBC-CTS is the
"least bad" choice among the alternatives. For more information about
HCTR2, see `the HCTR2 paper <https://eprint.iacr.org/2021/1441.pdf>`_.
@ -375,13 +378,13 @@ the work is done by XChaCha12, which is much faster than AES when AES
acceleration is unavailable. For more information about Adiantum, see
`the Adiantum paper <https://eprint.iacr.org/2018/720.pdf>`_.
The (AES-128-CBC-ESSIV, AES-128-CTS-CBC) pair exists only to support
The (AES-128-CBC-ESSIV, AES-128-CBC-CTS) pair exists only to support
systems whose only form of AES acceleration is an off-CPU crypto
accelerator such as CAAM or CESA that does not support XTS.
The remaining mode pairs are the "national pride ciphers":
- (SM4-XTS, SM4-CTS-CBC)
- (SM4-XTS, SM4-CBC-CTS)
Generally speaking, these ciphers aren't "bad" per se, but they
receive limited security review compared to the usual choices such as
@ -393,7 +396,7 @@ Kernel config options
Enabling fscrypt support (CONFIG_FS_ENCRYPTION) automatically pulls in
only the basic support from the crypto API needed to use AES-256-XTS
and AES-256-CTS-CBC encryption. For optimal performance, it is
and AES-256-CBC-CTS encryption. For optimal performance, it is
strongly recommended to also enable any available platform-specific
kconfig options that provide acceleration for the algorithm(s) you
wish to use. Support for any "non-default" encryption modes typically
@ -407,7 +410,7 @@ kernel crypto API (see `Inline encryption support`_); in that case,
the file contents mode doesn't need to supported in the kernel crypto
API, but the filenames mode still does.
- AES-256-XTS and AES-256-CTS-CBC
- AES-256-XTS and AES-256-CBC-CTS
- Recommended:
- arm64: CONFIG_CRYPTO_AES_ARM64_CE_BLK
- x86: CONFIG_CRYPTO_AES_NI_INTEL
@ -433,7 +436,7 @@ API, but the filenames mode still does.
- x86: CONFIG_CRYPTO_NHPOLY1305_SSE2
- x86: CONFIG_CRYPTO_NHPOLY1305_AVX2
- AES-128-CBC-ESSIV and AES-128-CTS-CBC:
- AES-128-CBC-ESSIV and AES-128-CBC-CTS:
- Mandatory:
- CONFIG_CRYPTO_ESSIV
- CONFIG_CRYPTO_SHA256 or another SHA-256 implementation
@ -521,7 +524,7 @@ 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
With CBC-CTS, 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

14
fs/crypto/fscrypt_private.h
View File

@ -222,16 +222,19 @@ struct fscrypt_inode_info {
struct fscrypt_prepared_key ci_enc_key;
/* True if ci_enc_key should be freed when this struct is freed */
bool ci_owns_key;
u8 ci_owns_key : 1;
#ifdef CONFIG_FS_ENCRYPTION_INLINE_CRYPT
/*
* True if this inode will use inline encryption (blk-crypto) instead of
* the traditional filesystem-layer encryption.
*/
bool ci_inlinecrypt;
u8 ci_inlinecrypt : 1;
#endif
/* True if ci_dirhash_key is initialized */
u8 ci_dirhash_key_initialized : 1;
/*
* log2 of the data unit size (granularity of contents encryption) of
* this file. This is computable from ci_policy and ci_inode but is
@ -242,6 +245,9 @@ struct fscrypt_inode_info {
/* Cached value: log2 of number of data units per FS block */
u8 ci_data_units_per_block_bits;
/* Hashed inode number. Only set for IV_INO_LBLK_32 */
u32 ci_hashed_ino;
/*
* Encryption mode used for this inode. It corresponds to either the
* contents or filenames encryption mode, depending on the inode type.
@ -276,16 +282,12 @@ struct fscrypt_inode_info {
* the plaintext filenames -- currently just casefolded directories.
*/
siphash_key_t ci_dirhash_key;
bool ci_dirhash_key_initialized;
/* The encryption policy used by this inode */
union fscrypt_policy ci_policy;
/* This inode's nonce, copied from the fscrypt_context */
u8 ci_nonce[FSCRYPT_FILE_NONCE_SIZE];
/* Hashed inode number. Only set for IV_INO_LBLK_32 */
u32 ci_hashed_ino;
};
typedef enum {

8
fs/crypto/keyring.c
View File

@ -74,8 +74,12 @@ void fscrypt_put_master_key(struct fscrypt_master_key *mk)
* that concurrent keyring lookups can no longer find it.
*/
WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 0);
key_put(mk->mk_users);
mk->mk_users = NULL;
if (mk->mk_users) {
/* Clear the keyring so the quota gets released right away. */
keyring_clear(mk->mk_users);
key_put(mk->mk_users);
mk->mk_users = NULL;
}
call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key);
}

11
fs/crypto/keysetup.c
View File

@ -23,7 +23,7 @@ struct fscrypt_mode fscrypt_modes[] = {
.blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_256_XTS,
},
[FSCRYPT_MODE_AES_256_CTS] = {
.friendly_name = "AES-256-CTS-CBC",
.friendly_name = "AES-256-CBC-CTS",
.cipher_str = "cts(cbc(aes))",
.keysize = 32,
.security_strength = 32,
@ -38,7 +38,7 @@ struct fscrypt_mode fscrypt_modes[] = {
.blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_128_CBC_ESSIV,
},
[FSCRYPT_MODE_AES_128_CTS] = {
.friendly_name = "AES-128-CTS-CBC",
.friendly_name = "AES-128-CBC-CTS",
.cipher_str = "cts(cbc(aes))",
.keysize = 16,
.security_strength = 16,
@ -53,7 +53,7 @@ struct fscrypt_mode fscrypt_modes[] = {
.blk_crypto_mode = BLK_ENCRYPTION_MODE_SM4_XTS,
},
[FSCRYPT_MODE_SM4_CTS] = {
.friendly_name = "SM4-CTS-CBC",
.friendly_name = "SM4-CBC-CTS",
.cipher_str = "cts(cbc(sm4))",
.keysize = 16,
.security_strength = 16,
@ -687,7 +687,7 @@ int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported)
/**
* fscrypt_prepare_new_inode() - prepare to create a new inode in a directory
* @dir: a possibly-encrypted directory
* @inode: the new inode. ->i_mode must be set already.
* @inode: the new inode. ->i_mode and ->i_blkbits must be set already.
* ->i_ino doesn't need to be set yet.
* @encrypt_ret: (output) set to %true if the new inode will be encrypted
*
@ -717,6 +717,9 @@ int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
if (IS_ERR(policy))
return PTR_ERR(policy);
if (WARN_ON_ONCE(inode->i_blkbits == 0))
return -EINVAL;
if (WARN_ON_ONCE(inode->i_mode == 0))
return -EINVAL;