linux/fs/ext4/crypto_key.c
Theodore Ts'o c936e1ec28 ext4 crypto: use per-inode tfm structure
As suggested by Herbert Xu, we shouldn't allocate a new tfm each time
we read or write a page.  Instead we can use a single tfm hanging off
the inode's crypt_info structure for all of our encryption needs for
that inode, since the tfm can be used by multiple crypto requests in
parallel.

Also use cmpxchg() to avoid races that could result in crypt_info
structure getting doubly allocated or doubly freed.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2015-05-31 13:34:22 -04:00

261 lines
6.9 KiB
C

/*
* linux/fs/ext4/crypto_key.c
*
* Copyright (C) 2015, Google, Inc.
*
* This contains encryption key functions for ext4
*
* Written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar, 2015.
*/
#include <keys/encrypted-type.h>
#include <keys/user-type.h>
#include <linux/random.h>
#include <linux/scatterlist.h>
#include <uapi/linux/keyctl.h>
#include "ext4.h"
#include "xattr.h"
static void derive_crypt_complete(struct crypto_async_request *req, int rc)
{
struct ext4_completion_result *ecr = req->data;
if (rc == -EINPROGRESS)
return;
ecr->res = rc;
complete(&ecr->completion);
}
/**
* ext4_derive_key_aes() - Derive a key using AES-128-ECB
* @deriving_key: Encryption key used for derivatio.
* @source_key: Source key to which to apply derivation.
* @derived_key: Derived key.
*
* Return: Zero on success; non-zero otherwise.
*/
static int ext4_derive_key_aes(char deriving_key[EXT4_AES_128_ECB_KEY_SIZE],
char source_key[EXT4_AES_256_XTS_KEY_SIZE],
char derived_key[EXT4_AES_256_XTS_KEY_SIZE])
{
int res = 0;
struct ablkcipher_request *req = NULL;
DECLARE_EXT4_COMPLETION_RESULT(ecr);
struct scatterlist src_sg, dst_sg;
struct crypto_ablkcipher *tfm = crypto_alloc_ablkcipher("ecb(aes)", 0,
0);
if (IS_ERR(tfm)) {
res = PTR_ERR(tfm);
tfm = NULL;
goto out;
}
crypto_ablkcipher_set_flags(tfm, CRYPTO_TFM_REQ_WEAK_KEY);
req = ablkcipher_request_alloc(tfm, GFP_NOFS);
if (!req) {
res = -ENOMEM;
goto out;
}
ablkcipher_request_set_callback(req,
CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
derive_crypt_complete, &ecr);
res = crypto_ablkcipher_setkey(tfm, deriving_key,
EXT4_AES_128_ECB_KEY_SIZE);
if (res < 0)
goto out;
sg_init_one(&src_sg, source_key, EXT4_AES_256_XTS_KEY_SIZE);
sg_init_one(&dst_sg, derived_key, EXT4_AES_256_XTS_KEY_SIZE);
ablkcipher_request_set_crypt(req, &src_sg, &dst_sg,
EXT4_AES_256_XTS_KEY_SIZE, NULL);
res = crypto_ablkcipher_encrypt(req);
if (res == -EINPROGRESS || res == -EBUSY) {
BUG_ON(req->base.data != &ecr);
wait_for_completion(&ecr.completion);
res = ecr.res;
}
out:
if (req)
ablkcipher_request_free(req);
if (tfm)
crypto_free_ablkcipher(tfm);
return res;
}
void ext4_free_crypt_info(struct ext4_crypt_info *ci)
{
if (!ci)
return;
if (ci->ci_keyring_key)
key_put(ci->ci_keyring_key);
crypto_free_ablkcipher(ci->ci_ctfm);
kmem_cache_free(ext4_crypt_info_cachep, ci);
}
void ext4_free_encryption_info(struct inode *inode,
struct ext4_crypt_info *ci)
{
struct ext4_inode_info *ei = EXT4_I(inode);
struct ext4_crypt_info *prev;
if (ci == NULL)
ci = ACCESS_ONCE(ei->i_crypt_info);
if (ci == NULL)
return;
prev = cmpxchg(&ei->i_crypt_info, ci, NULL);
if (prev != ci)
return;
ext4_free_crypt_info(ci);
}
int _ext4_get_encryption_info(struct inode *inode)
{
struct ext4_inode_info *ei = EXT4_I(inode);
struct ext4_crypt_info *crypt_info;
char full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
(EXT4_KEY_DESCRIPTOR_SIZE * 2) + 1];
struct key *keyring_key = NULL;
struct ext4_encryption_key *master_key;
struct ext4_encryption_context ctx;
struct user_key_payload *ukp;
struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
struct crypto_ablkcipher *ctfm;
const char *cipher_str;
char raw_key[EXT4_MAX_KEY_SIZE];
char mode;
int res;
if (!ext4_read_workqueue) {
res = ext4_init_crypto();
if (res)
return res;
}
retry:
crypt_info = ACCESS_ONCE(ei->i_crypt_info);
if (crypt_info) {
if (!crypt_info->ci_keyring_key ||
key_validate(crypt_info->ci_keyring_key) == 0)
return 0;
ext4_free_encryption_info(inode, crypt_info);
goto retry;
}
res = ext4_xattr_get(inode, EXT4_XATTR_INDEX_ENCRYPTION,
EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
&ctx, sizeof(ctx));
if (res < 0) {
if (!DUMMY_ENCRYPTION_ENABLED(sbi))
return res;
ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
ctx.filenames_encryption_mode =
EXT4_ENCRYPTION_MODE_AES_256_CTS;
ctx.flags = 0;
} else if (res != sizeof(ctx))
return -EINVAL;
res = 0;
crypt_info = kmem_cache_alloc(ext4_crypt_info_cachep, GFP_KERNEL);
if (!crypt_info)
return -ENOMEM;
crypt_info->ci_flags = ctx.flags;
crypt_info->ci_data_mode = ctx.contents_encryption_mode;
crypt_info->ci_filename_mode = ctx.filenames_encryption_mode;
crypt_info->ci_ctfm = NULL;
crypt_info->ci_keyring_key = NULL;
memcpy(crypt_info->ci_master_key, ctx.master_key_descriptor,
sizeof(crypt_info->ci_master_key));
if (S_ISREG(inode->i_mode))
mode = crypt_info->ci_data_mode;
else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
mode = crypt_info->ci_filename_mode;
else
BUG();
switch (mode) {
case EXT4_ENCRYPTION_MODE_AES_256_XTS:
cipher_str = "xts(aes)";
break;
case EXT4_ENCRYPTION_MODE_AES_256_CTS:
cipher_str = "cts(cbc(aes))";
break;
default:
printk_once(KERN_WARNING
"ext4: unsupported key mode %d (ino %u)\n",
mode, (unsigned) inode->i_ino);
res = -ENOKEY;
goto out;
}
if (DUMMY_ENCRYPTION_ENABLED(sbi)) {
memset(raw_key, 0x42, EXT4_AES_256_XTS_KEY_SIZE);
goto got_key;
}
memcpy(full_key_descriptor, EXT4_KEY_DESC_PREFIX,
EXT4_KEY_DESC_PREFIX_SIZE);
sprintf(full_key_descriptor + EXT4_KEY_DESC_PREFIX_SIZE,
"%*phN", EXT4_KEY_DESCRIPTOR_SIZE,
ctx.master_key_descriptor);
full_key_descriptor[EXT4_KEY_DESC_PREFIX_SIZE +
(2 * EXT4_KEY_DESCRIPTOR_SIZE)] = '\0';
keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
if (IS_ERR(keyring_key)) {
res = PTR_ERR(keyring_key);
keyring_key = NULL;
goto out;
}
crypt_info->ci_keyring_key = keyring_key;
BUG_ON(keyring_key->type != &key_type_logon);
ukp = ((struct user_key_payload *)keyring_key->payload.data);
if (ukp->datalen != sizeof(struct ext4_encryption_key)) {
res = -EINVAL;
goto out;
}
master_key = (struct ext4_encryption_key *)ukp->data;
BUILD_BUG_ON(EXT4_AES_128_ECB_KEY_SIZE !=
EXT4_KEY_DERIVATION_NONCE_SIZE);
BUG_ON(master_key->size != EXT4_AES_256_XTS_KEY_SIZE);
res = ext4_derive_key_aes(ctx.nonce, master_key->raw,
raw_key);
got_key:
ctfm = crypto_alloc_ablkcipher(cipher_str, 0, 0);
if (!ctfm || IS_ERR(ctfm)) {
res = ctfm ? PTR_ERR(ctfm) : -ENOMEM;
printk(KERN_DEBUG
"%s: error %d (inode %u) allocating crypto tfm\n",
__func__, res, (unsigned) inode->i_ino);
goto out;
}
crypt_info->ci_ctfm = ctfm;
crypto_ablkcipher_clear_flags(ctfm, ~0);
crypto_tfm_set_flags(crypto_ablkcipher_tfm(ctfm),
CRYPTO_TFM_REQ_WEAK_KEY);
res = crypto_ablkcipher_setkey(ctfm, raw_key,
ext4_encryption_key_size(mode));
if (res)
goto out;
memzero_explicit(raw_key, sizeof(raw_key));
if (cmpxchg(&ei->i_crypt_info, NULL, crypt_info) != NULL) {
ext4_free_crypt_info(crypt_info);
goto retry;
}
return 0;
out:
if (res == -ENOKEY)
res = 0;
ext4_free_crypt_info(crypt_info);
memzero_explicit(raw_key, sizeof(raw_key));
return res;
}
int ext4_has_encryption_key(struct inode *inode)
{
struct ext4_inode_info *ei = EXT4_I(inode);
return (ei->i_crypt_info != NULL);
}