linux/fs/crypto/keysetup.c
Eric Biggers b103fb7653 fscrypt: add support for IV_INO_LBLK_64 policies
Inline encryption hardware compliant with the UFS v2.1 standard or with
the upcoming version of the eMMC standard has the following properties:

(1) Per I/O request, the encryption key is specified by a previously
    loaded keyslot.  There might be only a small number of keyslots.

(2) Per I/O request, the starting IV is specified by a 64-bit "data unit
    number" (DUN).  IV bits 64-127 are assumed to be 0.  The hardware
    automatically increments the DUN for each "data unit" of
    configurable size in the request, e.g. for each filesystem block.

Property (1) makes it inefficient to use the traditional fscrypt
per-file keys.  Property (2) precludes the use of the existing
DIRECT_KEY fscrypt policy flag, which needs at least 192 IV bits.

Therefore, add a new fscrypt policy flag IV_INO_LBLK_64 which causes the
encryption to modified as follows:

- The encryption keys are derived from the master key, encryption mode
  number, and filesystem UUID.

- The IVs are chosen as (inode_number << 32) | file_logical_block_num.
  For filenames encryption, file_logical_block_num is 0.

Since the file nonces aren't used in the key derivation, many files may
share the same encryption key.  This is much more efficient on the
target hardware.  Including the inode number in the IVs and mixing the
filesystem UUID into the keys ensures that data in different files is
nevertheless still encrypted differently.

Additionally, limiting the inode and block numbers to 32 bits and
placing the block number in the low bits maintains compatibility with
the 64-bit DUN convention (property (2) above).

Since this scheme assumes that inode numbers are stable (which may
preclude filesystem shrinking) and that inode and file logical block
numbers are at most 32-bit, IV_INO_LBLK_64 will only be allowed on
filesystems that meet these constraints.  These are acceptable
limitations for the cases where this format would actually be used.

Note that IV_INO_LBLK_64 is an on-disk format, not an implementation.
This patch just adds support for it using the existing filesystem layer
encryption.  A later patch will add support for inline encryption.

Reviewed-by: Paul Crowley <paulcrowley@google.com>
Co-developed-by: Satya Tangirala <satyat@google.com>
Signed-off-by: Satya Tangirala <satyat@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
2019-11-06 12:34:36 -08:00

528 lines
15 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Key setup facility for FS encryption support.
*
* Copyright (C) 2015, Google, Inc.
*
* Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
* Heavily modified since then.
*/
#include <crypto/skcipher.h>
#include <linux/key.h>
#include "fscrypt_private.h"
static struct fscrypt_mode available_modes[] = {
[FSCRYPT_MODE_AES_256_XTS] = {
.friendly_name = "AES-256-XTS",
.cipher_str = "xts(aes)",
.keysize = 64,
.ivsize = 16,
},
[FSCRYPT_MODE_AES_256_CTS] = {
.friendly_name = "AES-256-CTS-CBC",
.cipher_str = "cts(cbc(aes))",
.keysize = 32,
.ivsize = 16,
},
[FSCRYPT_MODE_AES_128_CBC] = {
.friendly_name = "AES-128-CBC-ESSIV",
.cipher_str = "essiv(cbc(aes),sha256)",
.keysize = 16,
.ivsize = 16,
},
[FSCRYPT_MODE_AES_128_CTS] = {
.friendly_name = "AES-128-CTS-CBC",
.cipher_str = "cts(cbc(aes))",
.keysize = 16,
.ivsize = 16,
},
[FSCRYPT_MODE_ADIANTUM] = {
.friendly_name = "Adiantum",
.cipher_str = "adiantum(xchacha12,aes)",
.keysize = 32,
.ivsize = 32,
},
};
static struct fscrypt_mode *
select_encryption_mode(const union fscrypt_policy *policy,
const struct inode *inode)
{
if (S_ISREG(inode->i_mode))
return &available_modes[fscrypt_policy_contents_mode(policy)];
if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
return &available_modes[fscrypt_policy_fnames_mode(policy)];
WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
inode->i_ino, (inode->i_mode & S_IFMT));
return ERR_PTR(-EINVAL);
}
/* Create a symmetric cipher object for the given encryption mode and key */
struct crypto_skcipher *fscrypt_allocate_skcipher(struct fscrypt_mode *mode,
const u8 *raw_key,
const struct inode *inode)
{
struct crypto_skcipher *tfm;
int err;
tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
if (IS_ERR(tfm)) {
if (PTR_ERR(tfm) == -ENOENT) {
fscrypt_warn(inode,
"Missing crypto API support for %s (API name: \"%s\")",
mode->friendly_name, mode->cipher_str);
return ERR_PTR(-ENOPKG);
}
fscrypt_err(inode, "Error allocating '%s' transform: %ld",
mode->cipher_str, PTR_ERR(tfm));
return tfm;
}
if (!xchg(&mode->logged_impl_name, 1)) {
/*
* fscrypt performance can vary greatly depending on which
* crypto algorithm implementation is used. Help people debug
* performance problems by logging the ->cra_driver_name the
* first time a mode is used.
*/
pr_info("fscrypt: %s using implementation \"%s\"\n",
mode->friendly_name,
crypto_skcipher_alg(tfm)->base.cra_driver_name);
}
crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
if (err)
goto err_free_tfm;
return tfm;
err_free_tfm:
crypto_free_skcipher(tfm);
return ERR_PTR(err);
}
/* Given the per-file key, set up the file's crypto transform object */
int fscrypt_set_derived_key(struct fscrypt_info *ci, const u8 *derived_key)
{
struct crypto_skcipher *tfm;
tfm = fscrypt_allocate_skcipher(ci->ci_mode, derived_key, ci->ci_inode);
if (IS_ERR(tfm))
return PTR_ERR(tfm);
ci->ci_ctfm = tfm;
ci->ci_owns_key = true;
return 0;
}
static int setup_per_mode_key(struct fscrypt_info *ci,
struct fscrypt_master_key *mk,
struct crypto_skcipher **tfms,
u8 hkdf_context, bool include_fs_uuid)
{
const struct inode *inode = ci->ci_inode;
const struct super_block *sb = inode->i_sb;
struct fscrypt_mode *mode = ci->ci_mode;
u8 mode_num = mode - available_modes;
struct crypto_skcipher *tfm, *prev_tfm;
u8 mode_key[FSCRYPT_MAX_KEY_SIZE];
u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
unsigned int hkdf_infolen = 0;
int err;
if (WARN_ON(mode_num > __FSCRYPT_MODE_MAX))
return -EINVAL;
/* pairs with cmpxchg() below */
tfm = READ_ONCE(tfms[mode_num]);
if (likely(tfm != NULL))
goto done;
BUILD_BUG_ON(sizeof(mode_num) != 1);
BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
BUILD_BUG_ON(sizeof(hkdf_info) != 17);
hkdf_info[hkdf_infolen++] = mode_num;
if (include_fs_uuid) {
memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
sizeof(sb->s_uuid));
hkdf_infolen += sizeof(sb->s_uuid);
}
err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
hkdf_context, hkdf_info, hkdf_infolen,
mode_key, mode->keysize);
if (err)
return err;
tfm = fscrypt_allocate_skcipher(mode, mode_key, inode);
memzero_explicit(mode_key, mode->keysize);
if (IS_ERR(tfm))
return PTR_ERR(tfm);
/* pairs with READ_ONCE() above */
prev_tfm = cmpxchg(&tfms[mode_num], NULL, tfm);
if (prev_tfm != NULL) {
crypto_free_skcipher(tfm);
tfm = prev_tfm;
}
done:
ci->ci_ctfm = tfm;
return 0;
}
static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,
struct fscrypt_master_key *mk)
{
u8 derived_key[FSCRYPT_MAX_KEY_SIZE];
int err;
if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
/*
* DIRECT_KEY: instead of deriving per-file keys, the per-file
* nonce will be included in all the IVs. But unlike v1
* policies, for v2 policies in this case we don't encrypt with
* the master key directly but rather derive a per-mode key.
* This ensures that the master key is consistently used only
* for HKDF, avoiding key reuse issues.
*/
if (!fscrypt_mode_supports_direct_key(ci->ci_mode)) {
fscrypt_warn(ci->ci_inode,
"Direct key flag not allowed with %s",
ci->ci_mode->friendly_name);
return -EINVAL;
}
return setup_per_mode_key(ci, mk, mk->mk_direct_tfms,
HKDF_CONTEXT_DIRECT_KEY, false);
} else if (ci->ci_policy.v2.flags &
FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
/*
* IV_INO_LBLK_64: encryption keys are derived from (master_key,
* mode_num, filesystem_uuid), and inode number is included in
* the IVs. This format is optimized for use with inline
* encryption hardware compliant with the UFS or eMMC standards.
*/
return setup_per_mode_key(ci, mk, mk->mk_iv_ino_lblk_64_tfms,
HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
true);
}
err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
HKDF_CONTEXT_PER_FILE_KEY,
ci->ci_nonce, FS_KEY_DERIVATION_NONCE_SIZE,
derived_key, ci->ci_mode->keysize);
if (err)
return err;
err = fscrypt_set_derived_key(ci, derived_key);
memzero_explicit(derived_key, ci->ci_mode->keysize);
return err;
}
/*
* Find the master key, then set up the inode's actual encryption key.
*
* If the master key is found in the filesystem-level keyring, then the
* corresponding 'struct key' is returned in *master_key_ret with
* ->mk_secret_sem read-locked. This is needed to ensure that only one task
* links the fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race
* to create an fscrypt_info for the same inode), and to synchronize the master
* key being removed with a new inode starting to use it.
*/
static int setup_file_encryption_key(struct fscrypt_info *ci,
struct key **master_key_ret)
{
struct key *key;
struct fscrypt_master_key *mk = NULL;
struct fscrypt_key_specifier mk_spec;
int err;
switch (ci->ci_policy.version) {
case FSCRYPT_POLICY_V1:
mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
memcpy(mk_spec.u.descriptor,
ci->ci_policy.v1.master_key_descriptor,
FSCRYPT_KEY_DESCRIPTOR_SIZE);
break;
case FSCRYPT_POLICY_V2:
mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
memcpy(mk_spec.u.identifier,
ci->ci_policy.v2.master_key_identifier,
FSCRYPT_KEY_IDENTIFIER_SIZE);
break;
default:
WARN_ON(1);
return -EINVAL;
}
key = fscrypt_find_master_key(ci->ci_inode->i_sb, &mk_spec);
if (IS_ERR(key)) {
if (key != ERR_PTR(-ENOKEY) ||
ci->ci_policy.version != FSCRYPT_POLICY_V1)
return PTR_ERR(key);
/*
* As a legacy fallback for v1 policies, search for the key in
* the current task's subscribed keyrings too. Don't move this
* to before the search of ->s_master_keys, since users
* shouldn't be able to override filesystem-level keys.
*/
return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
}
mk = key->payload.data[0];
down_read(&mk->mk_secret_sem);
/* Has the secret been removed (via FS_IOC_REMOVE_ENCRYPTION_KEY)? */
if (!is_master_key_secret_present(&mk->mk_secret)) {
err = -ENOKEY;
goto out_release_key;
}
/*
* Require that the master key be at least as long as the derived key.
* Otherwise, the derived key cannot possibly contain as much entropy as
* that required by the encryption mode it will be used for. For v1
* policies it's also required for the KDF to work at all.
*/
if (mk->mk_secret.size < ci->ci_mode->keysize) {
fscrypt_warn(NULL,
"key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
master_key_spec_type(&mk_spec),
master_key_spec_len(&mk_spec), (u8 *)&mk_spec.u,
mk->mk_secret.size, ci->ci_mode->keysize);
err = -ENOKEY;
goto out_release_key;
}
switch (ci->ci_policy.version) {
case FSCRYPT_POLICY_V1:
err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
break;
case FSCRYPT_POLICY_V2:
err = fscrypt_setup_v2_file_key(ci, mk);
break;
default:
WARN_ON(1);
err = -EINVAL;
break;
}
if (err)
goto out_release_key;
*master_key_ret = key;
return 0;
out_release_key:
up_read(&mk->mk_secret_sem);
key_put(key);
return err;
}
static void put_crypt_info(struct fscrypt_info *ci)
{
struct key *key;
if (!ci)
return;
if (ci->ci_direct_key)
fscrypt_put_direct_key(ci->ci_direct_key);
else if (ci->ci_owns_key)
crypto_free_skcipher(ci->ci_ctfm);
key = ci->ci_master_key;
if (key) {
struct fscrypt_master_key *mk = key->payload.data[0];
/*
* Remove this inode from the list of inodes that were unlocked
* with the master key.
*
* In addition, if we're removing the last inode from a key that
* already had its secret removed, invalidate the key so that it
* gets removed from ->s_master_keys.
*/
spin_lock(&mk->mk_decrypted_inodes_lock);
list_del(&ci->ci_master_key_link);
spin_unlock(&mk->mk_decrypted_inodes_lock);
if (refcount_dec_and_test(&mk->mk_refcount))
key_invalidate(key);
key_put(key);
}
memzero_explicit(ci, sizeof(*ci));
kmem_cache_free(fscrypt_info_cachep, ci);
}
int fscrypt_get_encryption_info(struct inode *inode)
{
struct fscrypt_info *crypt_info;
union fscrypt_context ctx;
struct fscrypt_mode *mode;
struct key *master_key = NULL;
int res;
if (fscrypt_has_encryption_key(inode))
return 0;
res = fscrypt_initialize(inode->i_sb->s_cop->flags);
if (res)
return res;
res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
if (res < 0) {
if (!fscrypt_dummy_context_enabled(inode) ||
IS_ENCRYPTED(inode)) {
fscrypt_warn(inode,
"Error %d getting encryption context",
res);
return res;
}
/* Fake up a context for an unencrypted directory */
memset(&ctx, 0, sizeof(ctx));
ctx.version = FSCRYPT_CONTEXT_V1;
ctx.v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
ctx.v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
memset(ctx.v1.master_key_descriptor, 0x42,
FSCRYPT_KEY_DESCRIPTOR_SIZE);
res = sizeof(ctx.v1);
}
crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
if (!crypt_info)
return -ENOMEM;
crypt_info->ci_inode = inode;
res = fscrypt_policy_from_context(&crypt_info->ci_policy, &ctx, res);
if (res) {
fscrypt_warn(inode,
"Unrecognized or corrupt encryption context");
goto out;
}
switch (ctx.version) {
case FSCRYPT_CONTEXT_V1:
memcpy(crypt_info->ci_nonce, ctx.v1.nonce,
FS_KEY_DERIVATION_NONCE_SIZE);
break;
case FSCRYPT_CONTEXT_V2:
memcpy(crypt_info->ci_nonce, ctx.v2.nonce,
FS_KEY_DERIVATION_NONCE_SIZE);
break;
default:
WARN_ON(1);
res = -EINVAL;
goto out;
}
if (!fscrypt_supported_policy(&crypt_info->ci_policy, inode)) {
res = -EINVAL;
goto out;
}
mode = select_encryption_mode(&crypt_info->ci_policy, inode);
if (IS_ERR(mode)) {
res = PTR_ERR(mode);
goto out;
}
WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
crypt_info->ci_mode = mode;
res = setup_file_encryption_key(crypt_info, &master_key);
if (res)
goto out;
if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL) {
if (master_key) {
struct fscrypt_master_key *mk =
master_key->payload.data[0];
refcount_inc(&mk->mk_refcount);
crypt_info->ci_master_key = key_get(master_key);
spin_lock(&mk->mk_decrypted_inodes_lock);
list_add(&crypt_info->ci_master_key_link,
&mk->mk_decrypted_inodes);
spin_unlock(&mk->mk_decrypted_inodes_lock);
}
crypt_info = NULL;
}
res = 0;
out:
if (master_key) {
struct fscrypt_master_key *mk = master_key->payload.data[0];
up_read(&mk->mk_secret_sem);
key_put(master_key);
}
if (res == -ENOKEY)
res = 0;
put_crypt_info(crypt_info);
return res;
}
EXPORT_SYMBOL(fscrypt_get_encryption_info);
/**
* fscrypt_put_encryption_info - free most of an inode's fscrypt data
*
* Free the inode's fscrypt_info. Filesystems must call this when the inode is
* being evicted. An RCU grace period need not have elapsed yet.
*/
void fscrypt_put_encryption_info(struct inode *inode)
{
put_crypt_info(inode->i_crypt_info);
inode->i_crypt_info = NULL;
}
EXPORT_SYMBOL(fscrypt_put_encryption_info);
/**
* fscrypt_free_inode - free an inode's fscrypt data requiring RCU delay
*
* Free the inode's cached decrypted symlink target, if any. Filesystems must
* call this after an RCU grace period, just before they free the inode.
*/
void fscrypt_free_inode(struct inode *inode)
{
if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
kfree(inode->i_link);
inode->i_link = NULL;
}
}
EXPORT_SYMBOL(fscrypt_free_inode);
/**
* fscrypt_drop_inode - check whether the inode's master key has been removed
*
* Filesystems supporting fscrypt must call this from their ->drop_inode()
* method so that encrypted inodes are evicted as soon as they're no longer in
* use and their master key has been removed.
*
* Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0
*/
int fscrypt_drop_inode(struct inode *inode)
{
const struct fscrypt_info *ci = READ_ONCE(inode->i_crypt_info);
const struct fscrypt_master_key *mk;
/*
* If ci is NULL, then the inode doesn't have an encryption key set up
* so it's irrelevant. If ci_master_key is NULL, then the master key
* was provided via the legacy mechanism of the process-subscribed
* keyrings, so we don't know whether it's been removed or not.
*/
if (!ci || !ci->ci_master_key)
return 0;
mk = ci->ci_master_key->payload.data[0];
/*
* Note: since we aren't holding ->mk_secret_sem, the result here can
* immediately become outdated. But there's no correctness problem with
* unnecessarily evicting. Nor is there a correctness problem with not
* evicting while iput() is racing with the key being removed, since
* then the thread removing the key will either evict the inode itself
* or will correctly detect that it wasn't evicted due to the race.
*/
return !is_master_key_secret_present(&mk->mk_secret);
}
EXPORT_SYMBOL_GPL(fscrypt_drop_inode);