linux/fs/crypto/keysetup.c
Eric Biggers e3b1078bed fscrypt: add support for IV_INO_LBLK_32 policies
The eMMC inline crypto standard will only specify 32 DUN bits (a.k.a. IV
bits), unlike UFS's 64.  IV_INO_LBLK_64 is therefore not applicable, but
an encryption format which uses one key per policy and permits the
moving of encrypted file contents (as f2fs's garbage collector requires)
is still desirable.

To support such hardware, add a new encryption format IV_INO_LBLK_32
that makes the best use of the 32 bits: the IV is set to
'SipHash-2-4(inode_number) + file_logical_block_number mod 2^32', where
the SipHash key is derived from the fscrypt master key.  We hash only
the inode number and not also the block number, because we need to
maintain contiguity of DUNs to merge bios.

Unlike with IV_INO_LBLK_64, with this format IV reuse is possible; this
is unavoidable given the size of the DUN.  This means this format should
only be used where the requirements of the first paragraph apply.
However, the hash spreads out the IVs in the whole usable range, and the
use of a keyed hash makes it difficult for an attacker to determine
which files use which IVs.

Besides the above differences, this flag works like IV_INO_LBLK_64 in
that on ext4 it is only allowed if the stable_inodes feature has been
enabled to prevent inode numbers and the filesystem UUID from changing.

Link: https://lore.kernel.org/r/20200515204141.251098-1-ebiggers@kernel.org
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Paul Crowley <paulcrowley@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
2020-05-19 09:34:18 -07:00

598 lines
17 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"
struct fscrypt_mode fscrypt_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 DEFINE_MUTEX(fscrypt_mode_key_setup_mutex);
static struct fscrypt_mode *
select_encryption_mode(const union fscrypt_policy *policy,
const struct inode *inode)
{
if (S_ISREG(inode->i_mode))
return &fscrypt_modes[fscrypt_policy_contents_mode(policy)];
if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
return &fscrypt_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_driver_name(tfm));
}
if (WARN_ON(crypto_skcipher_ivsize(tfm) != mode->ivsize)) {
err = -EINVAL;
goto err_free_tfm;
}
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 a per-file encryption key, set up the file's crypto transform object */
int fscrypt_set_per_file_enc_key(struct fscrypt_info *ci, const u8 *raw_key)
{
struct crypto_skcipher *tfm;
tfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_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_enc_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;
const u8 mode_num = mode - fscrypt_modes;
struct crypto_skcipher *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 smp_store_release() below */
tfm = READ_ONCE(tfms[mode_num]);
if (likely(tfm != NULL)) {
ci->ci_ctfm = tfm;
return 0;
}
mutex_lock(&fscrypt_mode_key_setup_mutex);
if (tfms[mode_num])
goto done_unlock;
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)
goto out_unlock;
tfm = fscrypt_allocate_skcipher(mode, mode_key, inode);
memzero_explicit(mode_key, mode->keysize);
if (IS_ERR(tfm)) {
err = PTR_ERR(tfm);
goto out_unlock;
}
/* pairs with READ_ONCE() above */
smp_store_release(&tfms[mode_num], tfm);
done_unlock:
ci->ci_ctfm = tfm;
err = 0;
out_unlock:
mutex_unlock(&fscrypt_mode_key_setup_mutex);
return err;
}
int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
const struct fscrypt_master_key *mk)
{
int err;
err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, HKDF_CONTEXT_DIRHASH_KEY,
ci->ci_nonce, FS_KEY_DERIVATION_NONCE_SIZE,
(u8 *)&ci->ci_dirhash_key,
sizeof(ci->ci_dirhash_key));
if (err)
return err;
ci->ci_dirhash_key_initialized = true;
return 0;
}
static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_info *ci,
struct fscrypt_master_key *mk)
{
int err;
err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_32_keys,
HKDF_CONTEXT_IV_INO_LBLK_32_KEY, true);
if (err)
return err;
/* pairs with smp_store_release() below */
if (!smp_load_acquire(&mk->mk_ino_hash_key_initialized)) {
mutex_lock(&fscrypt_mode_key_setup_mutex);
if (mk->mk_ino_hash_key_initialized)
goto unlock;
err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
HKDF_CONTEXT_INODE_HASH_KEY, NULL, 0,
(u8 *)&mk->mk_ino_hash_key,
sizeof(mk->mk_ino_hash_key));
if (err)
goto unlock;
/* pairs with smp_load_acquire() above */
smp_store_release(&mk->mk_ino_hash_key_initialized, true);
unlock:
mutex_unlock(&fscrypt_mode_key_setup_mutex);
if (err)
return err;
}
ci->ci_hashed_ino = (u32)siphash_1u64(ci->ci_inode->i_ino,
&mk->mk_ino_hash_key);
return 0;
}
static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,
struct fscrypt_master_key *mk)
{
int err;
if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
/*
* DIRECT_KEY: instead of deriving per-file encryption 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
* encryption key. This ensures that the master key is
* consistently used only for HKDF, avoiding key reuse issues.
*/
err = setup_per_mode_enc_key(ci, mk, mk->mk_direct_keys,
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 standard.
*/
err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_64_keys,
HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
true);
} else if (ci->ci_policy.v2.flags &
FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
err = fscrypt_setup_iv_ino_lblk_32_key(ci, mk);
} else {
u8 derived_key[FSCRYPT_MAX_KEY_SIZE];
err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
HKDF_CONTEXT_PER_FILE_ENC_KEY,
ci->ci_nonce,
FS_KEY_DERIVATION_NONCE_SIZE,
derived_key, ci->ci_mode->keysize);
if (err)
return err;
err = fscrypt_set_per_file_enc_key(ci, derived_key);
memzero_explicit(derived_key, ci->ci_mode->keysize);
}
if (err)
return err;
/* Derive a secret dirhash key for directories that need it. */
if (S_ISDIR(ci->ci_inode->i_mode) && IS_CASEFOLDED(ci->ci_inode)) {
err = fscrypt_derive_dirhash_key(ci, mk);
if (err)
return err;
}
return 0;
}
/*
* 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) {
const union fscrypt_context *dummy_ctx =
fscrypt_get_dummy_context(inode->i_sb);
if (IS_ENCRYPTED(inode) || !dummy_ctx) {
fscrypt_warn(inode,
"Error %d getting encryption context",
res);
return res;
}
/* Fake up a context for an unencrypted directory */
res = fscrypt_context_size(dummy_ctx);
memcpy(&ctx, dummy_ctx, res);
}
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;
}
memcpy(crypt_info->ci_nonce, fscrypt_context_nonce(&ctx),
FS_KEY_DERIVATION_NONCE_SIZE);
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
* @inode: an inode being evicted
*
* 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
* @inode: an inode being freed
*
* 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
* @inode: an inode being considered for eviction
*
* 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];
/*
* With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes
* protected by the key were cleaned by sync_filesystem(). But if
* userspace is still using the files, inodes can be dirtied between
* then and now. We mustn't lose any writes, so skip dirty inodes here.
*/
if (inode->i_state & I_DIRTY_ALL)
return 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);