/* Large capacity key type
*
* Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
* 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 <linux/random.h>
#include <keys/user-type.h>
#include <keys/big_key-type.h>
#include <crypto/aead.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 32
/*
* Authentication tag length
*/
#define ENC_AUTHTAG_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,
/* no ->update(); don't add it without changing big_key_crypt() nonce */
};
/*
* Crypto names for big_key data authenticated encryption
*/
static const char big_key_alg_name[] = "gcm(aes)";
/*
* Crypto algorithms for big_key data authenticated encryption
*/
static struct crypto_aead *big_key_aead;
/*
* Since changing the key affects the entire object, we need a mutex.
*/
static DEFINE_MUTEX(big_key_aead_lock);
/*
* Encrypt/decrypt big_key data
*/
static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
{
int ret;
struct scatterlist sgio;
struct aead_request *aead_req;
/* We always use a zero nonce. The reason we can get away with this is
* because we're using a different randomly generated key for every
* different encryption. Notably, too, key_type_big_key doesn't define
* an .update function, so there's no chance we'll wind up reusing the
* key to encrypt updated data. Simply put: one key, one encryption.
*/
u8 zero_nonce[crypto_aead_ivsize(big_key_aead)];
aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
if (!aead_req)
return -ENOMEM;
memset(zero_nonce, 0, sizeof(zero_nonce));
sg_init_one(&sgio, data, datalen + (op == BIG_KEY_ENC ? ENC_AUTHTAG_SIZE : 0));
aead_request_set_crypt(aead_req, &sgio, &sgio, datalen, zero_nonce);
aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
aead_request_set_ad(aead_req, 0);
mutex_lock(&big_key_aead_lock);
if (crypto_aead_setkey(big_key_aead, key, ENC_KEY_SIZE)) {
ret = -EAGAIN;
goto error;
}
if (op == BIG_KEY_ENC)
ret = crypto_aead_encrypt(aead_req);
else
ret = crypto_aead_decrypt(aead_req);
error:
mutex_unlock(&big_key_aead_lock);
aead_request_free(aead_req);
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 = datalen + ENC_AUTHTAG_SIZE;
loff_t pos = 0;
data = kmalloc(enclen, GFP_KERNEL);
if (!data)
return -ENOMEM;
memcpy(data, prep->data, datalen);
/* generate random key */
enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
if (!enckey) {
ret = -ENOMEM;
goto error;
}
ret = get_random_bytes_wait(enckey, ENC_KEY_SIZE);
if (unlikely(ret))
goto err_enckey;
/* encrypt aligned data */
ret = big_key_crypt(BIG_KEY_ENC, data, datalen, 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, &pos);
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);
kzfree(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:
kzfree(enckey);
error:
kzfree(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);
}
kzfree(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;
}
kzfree(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 = datalen + ENC_AUTHTAG_SIZE;
loff_t pos = 0;
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, data, enclen, &pos);
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:
kzfree(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)
{
int ret;
/* init block cipher */
big_key_aead = crypto_alloc_aead(big_key_alg_name, 0, CRYPTO_ALG_ASYNC);
if (IS_ERR(big_key_aead)) {
ret = PTR_ERR(big_key_aead);
pr_err("Can't alloc crypto: %d\n", ret);
return ret;
}
ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE);
if (ret < 0) {
pr_err("Can't set crypto auth tag len: %d\n", ret);
goto free_aead;
}
ret = register_key_type(&key_type_big_key);
if (ret < 0) {
pr_err("Can't register type: %d\n", ret);
goto free_aead;
}
return 0;
free_aead:
crypto_free_aead(big_key_aead);
return ret;
}
late_initcall(big_key_init);
