linux/security/keys/big_key.c

390 lines
8.5 KiB
C

/* Large capacity key type
*
* Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#define pr_fmt(fmt) "big_key: "fmt
#include <linux/init.h>
#include <linux/seq_file.h>
#include <linux/file.h>
#include <linux/shmem_fs.h>
#include <linux/err.h>
#include <linux/scatterlist.h>
#include <keys/user-type.h>
#include <keys/big_key-type.h>
#include <crypto/rng.h>
#include <crypto/skcipher.h>
/*
* Layout of key payload words.
*/
enum {
big_key_data,
big_key_path,
big_key_path_2nd_part,
big_key_len,
};
/*
* Crypto operation with big_key data
*/
enum big_key_op {
BIG_KEY_ENC,
BIG_KEY_DEC,
};
/*
* If the data is under this limit, there's no point creating a shm file to
* hold it as the permanently resident metadata for the shmem fs will be at
* least as large as the data.
*/
#define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
/*
* Key size for big_key data encryption
*/
#define ENC_KEY_SIZE 16
/*
* big_key defined keys take an arbitrary string as the description and an
* arbitrary blob of data as the payload
*/
struct key_type key_type_big_key = {
.name = "big_key",
.preparse = big_key_preparse,
.free_preparse = big_key_free_preparse,
.instantiate = generic_key_instantiate,
.revoke = big_key_revoke,
.destroy = big_key_destroy,
.describe = big_key_describe,
.read = big_key_read,
};
/*
* Crypto names for big_key data encryption
*/
static const char big_key_rng_name[] = "stdrng";
static const char big_key_alg_name[] = "ecb(aes)";
/*
* Crypto algorithms for big_key data encryption
*/
static struct crypto_rng *big_key_rng;
static struct crypto_skcipher *big_key_skcipher;
/*
* Generate random key to encrypt big_key data
*/
static inline int big_key_gen_enckey(u8 *key)
{
return crypto_rng_get_bytes(big_key_rng, key, ENC_KEY_SIZE);
}
/*
* Encrypt/decrypt big_key data
*/
static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
{
int ret = -EINVAL;
struct scatterlist sgio;
SKCIPHER_REQUEST_ON_STACK(req, big_key_skcipher);
if (crypto_skcipher_setkey(big_key_skcipher, key, ENC_KEY_SIZE)) {
ret = -EAGAIN;
goto error;
}
skcipher_request_set_tfm(req, big_key_skcipher);
skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP,
NULL, NULL);
sg_init_one(&sgio, data, datalen);
skcipher_request_set_crypt(req, &sgio, &sgio, datalen, NULL);
if (op == BIG_KEY_ENC)
ret = crypto_skcipher_encrypt(req);
else
ret = crypto_skcipher_decrypt(req);
skcipher_request_zero(req);
error:
return ret;
}
/*
* Preparse a big key
*/
int big_key_preparse(struct key_preparsed_payload *prep)
{
struct path *path = (struct path *)&prep->payload.data[big_key_path];
struct file *file;
u8 *enckey;
u8 *data = NULL;
ssize_t written;
size_t datalen = prep->datalen;
int ret;
ret = -EINVAL;
if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
goto error;
/* Set an arbitrary quota */
prep->quotalen = 16;
prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
if (datalen > BIG_KEY_FILE_THRESHOLD) {
/* Create a shmem file to store the data in. This will permit the data
* to be swapped out if needed.
*
* File content is stored encrypted with randomly generated key.
*/
size_t enclen = ALIGN(datalen, crypto_skcipher_blocksize(big_key_skcipher));
/* prepare aligned data to encrypt */
data = kmalloc(enclen, GFP_KERNEL);
if (!data)
return -ENOMEM;
memcpy(data, prep->data, datalen);
memset(data + datalen, 0x00, enclen - datalen);
/* generate random key */
enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
if (!enckey) {
ret = -ENOMEM;
goto error;
}
ret = big_key_gen_enckey(enckey);
if (ret)
goto err_enckey;
/* encrypt aligned data */
ret = big_key_crypt(BIG_KEY_ENC, data, enclen, enckey);
if (ret)
goto err_enckey;
/* save aligned data to file */
file = shmem_kernel_file_setup("", enclen, 0);
if (IS_ERR(file)) {
ret = PTR_ERR(file);
goto err_enckey;
}
written = kernel_write(file, data, enclen, 0);
if (written != enclen) {
ret = written;
if (written >= 0)
ret = -ENOMEM;
goto err_fput;
}
/* Pin the mount and dentry to the key so that we can open it again
* later
*/
prep->payload.data[big_key_data] = enckey;
*path = file->f_path;
path_get(path);
fput(file);
kfree(data);
} else {
/* Just store the data in a buffer */
void *data = kmalloc(datalen, GFP_KERNEL);
if (!data)
return -ENOMEM;
prep->payload.data[big_key_data] = data;
memcpy(data, prep->data, prep->datalen);
}
return 0;
err_fput:
fput(file);
err_enckey:
kfree(enckey);
error:
kfree(data);
return ret;
}
/*
* Clear preparsement.
*/
void big_key_free_preparse(struct key_preparsed_payload *prep)
{
if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
struct path *path = (struct path *)&prep->payload.data[big_key_path];
path_put(path);
}
kfree(prep->payload.data[big_key_data]);
}
/*
* dispose of the links from a revoked keyring
* - called with the key sem write-locked
*/
void big_key_revoke(struct key *key)
{
struct path *path = (struct path *)&key->payload.data[big_key_path];
/* clear the quota */
key_payload_reserve(key, 0);
if (key_is_instantiated(key) &&
(size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
vfs_truncate(path, 0);
}
/*
* dispose of the data dangling from the corpse of a big_key key
*/
void big_key_destroy(struct key *key)
{
size_t datalen = (size_t)key->payload.data[big_key_len];
if (datalen > BIG_KEY_FILE_THRESHOLD) {
struct path *path = (struct path *)&key->payload.data[big_key_path];
path_put(path);
path->mnt = NULL;
path->dentry = NULL;
}
kfree(key->payload.data[big_key_data]);
key->payload.data[big_key_data] = NULL;
}
/*
* describe the big_key key
*/
void big_key_describe(const struct key *key, struct seq_file *m)
{
size_t datalen = (size_t)key->payload.data[big_key_len];
seq_puts(m, key->description);
if (key_is_instantiated(key))
seq_printf(m, ": %zu [%s]",
datalen,
datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
}
/*
* read the key data
* - the key's semaphore is read-locked
*/
long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
{
size_t datalen = (size_t)key->payload.data[big_key_len];
long ret;
if (!buffer || buflen < datalen)
return datalen;
if (datalen > BIG_KEY_FILE_THRESHOLD) {
struct path *path = (struct path *)&key->payload.data[big_key_path];
struct file *file;
u8 *data;
u8 *enckey = (u8 *)key->payload.data[big_key_data];
size_t enclen = ALIGN(datalen, crypto_skcipher_blocksize(big_key_skcipher));
data = kmalloc(enclen, GFP_KERNEL);
if (!data)
return -ENOMEM;
file = dentry_open(path, O_RDONLY, current_cred());
if (IS_ERR(file)) {
ret = PTR_ERR(file);
goto error;
}
/* read file to kernel and decrypt */
ret = kernel_read(file, 0, data, enclen);
if (ret >= 0 && ret != enclen) {
ret = -EIO;
goto err_fput;
}
ret = big_key_crypt(BIG_KEY_DEC, data, enclen, enckey);
if (ret)
goto err_fput;
ret = datalen;
/* copy decrypted data to user */
if (copy_to_user(buffer, data, datalen) != 0)
ret = -EFAULT;
err_fput:
fput(file);
error:
kfree(data);
} else {
ret = datalen;
if (copy_to_user(buffer, key->payload.data[big_key_data],
datalen) != 0)
ret = -EFAULT;
}
return ret;
}
/*
* Register key type
*/
static int __init big_key_init(void)
{
struct crypto_skcipher *cipher;
struct crypto_rng *rng;
int ret;
rng = crypto_alloc_rng(big_key_rng_name, 0, 0);
if (IS_ERR(rng)) {
pr_err("Can't alloc rng: %ld\n", PTR_ERR(rng));
return PTR_ERR(rng);
}
big_key_rng = rng;
/* seed RNG */
ret = crypto_rng_reset(rng, NULL, crypto_rng_seedsize(rng));
if (ret) {
pr_err("Can't reset rng: %d\n", ret);
goto error_rng;
}
/* init block cipher */
cipher = crypto_alloc_skcipher(big_key_alg_name, 0, CRYPTO_ALG_ASYNC);
if (IS_ERR(cipher)) {
ret = PTR_ERR(cipher);
pr_err("Can't alloc crypto: %d\n", ret);
goto error_rng;
}
big_key_skcipher = cipher;
ret = register_key_type(&key_type_big_key);
if (ret < 0) {
pr_err("Can't register type: %d\n", ret);
goto error_cipher;
}
return 0;
error_cipher:
crypto_free_skcipher(big_key_skcipher);
error_rng:
crypto_free_rng(big_key_rng);
return ret;
}
late_initcall(big_key_init);