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fscrypt: refactor key setup code in preparation for v2 policies 

Do some more refactoring of the key setup code, in preparation for
introducing a filesystem-level keyring and v2 encryption policies:

- Now that ci_inode exists, don't pass around the inode unnecessarily.

- Define a function setup_file_encryption_key() which handles the crypto
  key setup given an under-construction fscrypt_info.  Don't pass the
  fscrypt_context, since everything is in the fscrypt_info.
  [This will be extended for v2 policies and the fs-level keyring.]

- Define a function fscrypt_set_derived_key() which sets the per-file
  key, without depending on anything specific to v1 policies.
  [This will also be used for v2 policies.]

- Define a function fscrypt_setup_v1_file_key() which takes the raw
  master key, thus separating finding the key from using it.
  [This will also be used if the key is found in the fs-level keyring.]

Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
This commit is contained in:
Eric Biggers 2019-08-04 19:35:45 -07:00
parent a828daabb2
commit 3ec4f2a629
2 changed files with 146 additions and 112 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
fs/crypto/fscrypt_private.h
View File

@ -4,9 +4,8 @@
*
* Copyright (C) 2015, Google, Inc.
*
* This contains encryption key functions.
*
* Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
* Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
* Heavily modified since then.
*/
#ifndef _FSCRYPT_PRIVATE_H
@ -168,4 +167,10 @@ struct fscrypt_mode {
bool needs_essiv;
};
static inline bool
fscrypt_mode_supports_direct_key(const struct fscrypt_mode *mode)
{
return mode->ivsize >= offsetofend(union fscrypt_iv, nonce);
}
#endif /* _FSCRYPT_PRIVATE_H */

247
fs/crypto/keyinfo.c
View File

@ -1,12 +1,11 @@
// SPDX-License-Identifier: GPL-2.0
/*
* key management facility for FS encryption support.
* Key setup facility for FS encryption support.
*
* Copyright (C) 2015, Google, Inc.
*
* This contains encryption key functions.
*
* Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
* Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
* Heavily modified since then.
*/
#include <keys/user-type.h>
@ -25,14 +24,19 @@ static DEFINE_HASHTABLE(fscrypt_direct_keys, 6); /* 6 bits = 64 buckets */
static DEFINE_SPINLOCK(fscrypt_direct_keys_lock);
/*
* Key derivation function. This generates the derived key by encrypting the
* master key with AES-128-ECB using the inode's nonce as the AES key.
* v1 key derivation function. This generates the derived key by encrypting the
* master key with AES-128-ECB using the nonce as the AES key. This provides a
* unique derived key with sufficient entropy for each inode. However, it's
* nonstandard, non-extensible, doesn't evenly distribute the entropy from the
* master key, and is trivially reversible: an attacker who compromises a
* derived key can "decrypt" it to get back to the master key, then derive any
* other key. For all new code, use HKDF instead.
*
* The master key must be at least as long as the derived key. If the master
* key is longer, then only the first 'derived_keysize' bytes are used.
*/
static int derive_key_aes(const u8 *master_key,
const struct fscrypt_context *ctx,
const u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE],
u8 *derived_key, unsigned int derived_keysize)
{
int res = 0;
@ -55,7 +59,7 @@ static int derive_key_aes(const u8 *master_key,
skcipher_request_set_callback(req,
CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
crypto_req_done, &wait);
res = crypto_skcipher_setkey(tfm, ctx->nonce, sizeof(ctx->nonce));
res = crypto_skcipher_setkey(tfm, nonce, FS_KEY_DERIVATION_NONCE_SIZE);
if (res < 0)
goto out;
@ -183,54 +187,10 @@ select_encryption_mode(const struct fscrypt_info *ci, const struct inode *inode)
return ERR_PTR(-EINVAL);
}
/* Find the master key, then derive the inode's actual encryption key */
static int find_and_derive_key(const struct inode *inode,
const struct fscrypt_context *ctx,
u8 *derived_key, const struct fscrypt_mode *mode)
{
struct key *key;
const struct fscrypt_key *payload;
int err;
key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
ctx->master_key_descriptor,
mode->keysize, &payload);
if (key == ERR_PTR(-ENOKEY) && inode->i_sb->s_cop->key_prefix) {
key = find_and_lock_process_key(inode->i_sb->s_cop->key_prefix,
ctx->master_key_descriptor,
mode->keysize, &payload);
}
if (IS_ERR(key))
return PTR_ERR(key);
if (ctx->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
if (mode->ivsize < offsetofend(union fscrypt_iv, nonce)) {
fscrypt_warn(inode,
"Direct key mode not allowed with %s",
mode->friendly_name);
err = -EINVAL;
} else if (ctx->contents_encryption_mode !=
ctx->filenames_encryption_mode) {
fscrypt_warn(inode,
"Direct key mode not allowed with different contents and filenames modes");
err = -EINVAL;
} else {
memcpy(derived_key, payload->raw, mode->keysize);
err = 0;
}
} else {
err = derive_key_aes(payload->raw, ctx, derived_key,
mode->keysize);
}
up_read(&key->sem);
key_put(key);
return err;
}
/* Allocate and key a symmetric cipher object for the given encryption mode */
/* Create a symmetric cipher object for the given encryption mode and key */
static struct crypto_skcipher *
allocate_skcipher_for_mode(struct fscrypt_mode *mode, const u8 *raw_key,
const struct inode *inode)
fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
const struct inode *inode)
{
struct crypto_skcipher *tfm;
int err;
@ -308,8 +268,7 @@ static void put_direct_key(struct fscrypt_direct_key *dk)
*/
static struct fscrypt_direct_key *
find_or_insert_direct_key(struct fscrypt_direct_key *to_insert,
const u8 *raw_key, const struct fscrypt_mode *mode,
const struct fscrypt_info *ci)
const u8 *raw_key, const struct fscrypt_info *ci)
{
unsigned long hash_key;
struct fscrypt_direct_key *dk;
@ -328,9 +287,9 @@ find_or_insert_direct_key(struct fscrypt_direct_key *to_insert,
if (memcmp(ci->ci_master_key_descriptor, dk->dk_descriptor,
FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
continue;
if (mode != dk->dk_mode)
if (ci->ci_mode != dk->dk_mode)
continue;
if (crypto_memneq(raw_key, dk->dk_raw, mode->keysize))
if (crypto_memneq(raw_key, dk->dk_raw, ci->ci_mode->keysize))
continue;
/* using existing tfm with same (descriptor, mode, raw_key) */
refcount_inc(&dk->dk_refcount);
@ -346,14 +305,13 @@ find_or_insert_direct_key(struct fscrypt_direct_key *to_insert,
/* Prepare to encrypt directly using the master key in the given mode */
static struct fscrypt_direct_key *
fscrypt_get_direct_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode,
const u8 *raw_key, const struct inode *inode)
fscrypt_get_direct_key(const struct fscrypt_info *ci, const u8 *raw_key)
{
struct fscrypt_direct_key *dk;
int err;
/* Is there already a tfm for this key? */
dk = find_or_insert_direct_key(NULL, raw_key, mode, ci);
dk = find_or_insert_direct_key(NULL, raw_key, ci);
if (dk)
return dk;
@ -362,8 +320,9 @@ fscrypt_get_direct_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode,
if (!dk)
return ERR_PTR(-ENOMEM);
refcount_set(&dk->dk_refcount, 1);
dk->dk_mode = mode;
dk->dk_ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
dk->dk_mode = ci->ci_mode;
dk->dk_ctfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key,
ci->ci_inode);
if (IS_ERR(dk->dk_ctfm)) {
err = PTR_ERR(dk->dk_ctfm);
dk->dk_ctfm = NULL;
@ -371,9 +330,9 @@ fscrypt_get_direct_key(const struct fscrypt_info *ci, struct fscrypt_mode *mode,
}
memcpy(dk->dk_descriptor, ci->ci_master_key_descriptor,
FSCRYPT_KEY_DESCRIPTOR_SIZE);
memcpy(dk->dk_raw, raw_key, mode->keysize);
memcpy(dk->dk_raw, raw_key, ci->ci_mode->keysize);
return find_or_insert_direct_key(dk, raw_key, mode, ci);
return find_or_insert_direct_key(dk, raw_key, ci);
err_free_dk:
free_direct_key(dk);
@ -422,6 +381,9 @@ static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
struct crypto_cipher *essiv_tfm;
u8 salt[SHA256_DIGEST_SIZE];
if (WARN_ON(ci->ci_mode->ivsize != AES_BLOCK_SIZE))
return -EINVAL;
essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
if (IS_ERR(essiv_tfm))
return PTR_ERR(essiv_tfm);
@ -446,41 +408,24 @@ out:
return err;
}
/*
* Given the encryption mode and key (normally the derived key, but for
* DIRECT_KEY mode it's the master key), set up the inode's symmetric cipher
* transform object(s).
*/
static int setup_crypto_transform(struct fscrypt_info *ci,
struct fscrypt_mode *mode,
const u8 *raw_key, const struct inode *inode)
/* Given the per-file key, set up the file's crypto transform object(s) */
static int fscrypt_set_derived_key(struct fscrypt_info *ci,
const u8 *derived_key)
{
struct fscrypt_direct_key *dk;
struct fscrypt_mode *mode = ci->ci_mode;
struct crypto_skcipher *ctfm;
int err;
if (ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
dk = fscrypt_get_direct_key(ci, mode, raw_key, inode);
if (IS_ERR(dk))
return PTR_ERR(dk);
ctfm = dk->dk_ctfm;
} else {
dk = NULL;
ctfm = allocate_skcipher_for_mode(mode, raw_key, inode);
if (IS_ERR(ctfm))
return PTR_ERR(ctfm);
}
ci->ci_direct_key = dk;
ctfm = fscrypt_allocate_skcipher(mode, derived_key, ci->ci_inode);
if (IS_ERR(ctfm))
return PTR_ERR(ctfm);
ci->ci_ctfm = ctfm;
if (mode->needs_essiv) {
/* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
WARN_ON(mode->ivsize != AES_BLOCK_SIZE);
WARN_ON(ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY);
err = init_essiv_generator(ci, raw_key, mode->keysize);
err = init_essiv_generator(ci, derived_key, mode->keysize);
if (err) {
fscrypt_warn(inode,
fscrypt_warn(ci->ci_inode,
"Error initializing ESSIV generator: %d",
err);
return err;
@ -489,6 +434,105 @@ static int setup_crypto_transform(struct fscrypt_info *ci,
return 0;
}
/* v1 policy, DIRECT_KEY: use the master key directly */
static int setup_v1_file_key_direct(struct fscrypt_info *ci,
const u8 *raw_master_key)
{
const struct fscrypt_mode *mode = ci->ci_mode;
struct fscrypt_direct_key *dk;
if (!fscrypt_mode_supports_direct_key(mode)) {
fscrypt_warn(ci->ci_inode,
"Direct key mode not allowed with %s",
mode->friendly_name);
return -EINVAL;
}
if (ci->ci_data_mode != ci->ci_filename_mode) {
fscrypt_warn(ci->ci_inode,
"Direct key mode not allowed with different contents and filenames modes");
return -EINVAL;
}
/* ESSIV implies 16-byte IVs which implies !DIRECT_KEY */
if (WARN_ON(mode->needs_essiv))
return -EINVAL;
dk = fscrypt_get_direct_key(ci, raw_master_key);
if (IS_ERR(dk))
return PTR_ERR(dk);
ci->ci_direct_key = dk;
ci->ci_ctfm = dk->dk_ctfm;
return 0;
}
/* v1 policy, !DIRECT_KEY: derive the file's encryption key */
static int setup_v1_file_key_derived(struct fscrypt_info *ci,
const u8 *raw_master_key)
{
u8 *derived_key;
int err;
/*
* This cannot be a stack buffer because it will be passed to the
* scatterlist crypto API during derive_key_aes().
*/
derived_key = kmalloc(ci->ci_mode->keysize, GFP_NOFS);
if (!derived_key)
return -ENOMEM;
err = derive_key_aes(raw_master_key, ci->ci_nonce,
derived_key, ci->ci_mode->keysize);
if (err)
goto out;
err = fscrypt_set_derived_key(ci, derived_key);
out:
kzfree(derived_key);
return err;
}
static int fscrypt_setup_v1_file_key(struct fscrypt_info *ci,
const u8 *raw_master_key)
{
if (ci->ci_flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
return setup_v1_file_key_direct(ci, raw_master_key);
else
return setup_v1_file_key_derived(ci, raw_master_key);
}
static int fscrypt_setup_v1_file_key_via_subscribed_keyrings(
struct fscrypt_info *ci)
{
struct key *key;
const struct fscrypt_key *payload;
int err;
key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
ci->ci_master_key_descriptor,
ci->ci_mode->keysize, &payload);
if (key == ERR_PTR(-ENOKEY) && ci->ci_inode->i_sb->s_cop->key_prefix) {
key = find_and_lock_process_key(ci->ci_inode->i_sb->s_cop->key_prefix,
ci->ci_master_key_descriptor,
ci->ci_mode->keysize, &payload);
}
if (IS_ERR(key))
return PTR_ERR(key);
err = fscrypt_setup_v1_file_key(ci, payload->raw);
up_read(&key->sem);
key_put(key);
return err;
}
/*
* Find the master key, then set up the inode's actual encryption key.
*/
static int setup_file_encryption_key(struct fscrypt_info *ci)
{
return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
}
static void put_crypt_info(struct fscrypt_info *ci)
{
if (!ci)
@ -508,7 +552,6 @@ int fscrypt_get_encryption_info(struct inode *inode)
struct fscrypt_info *crypt_info;
struct fscrypt_context ctx;
struct fscrypt_mode *mode;
u8 *raw_key = NULL;
int res;
if (fscrypt_has_encryption_key(inode))
@ -573,20 +616,7 @@ int fscrypt_get_encryption_info(struct inode *inode)
WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
crypt_info->ci_mode = mode;
/*
* This cannot be a stack buffer because it may be passed to the
* scatterlist crypto API as part of key derivation.
*/
res = -ENOMEM;
raw_key = kmalloc(mode->keysize, GFP_NOFS);
if (!raw_key)
goto out;
res = find_and_derive_key(inode, &ctx, raw_key, mode);
if (res)
goto out;
res = setup_crypto_transform(crypt_info, mode, raw_key, inode);
res = setup_file_encryption_key(crypt_info);
if (res)
goto out;
@ -596,7 +626,6 @@ out:
if (res == -ENOKEY)
res = 0;
put_crypt_info(crypt_info);
kzfree(raw_key);
return res;
}
EXPORT_SYMBOL(fscrypt_get_encryption_info);