// SPDX-License-Identifier: GPL-2.0-or-later
/* Large capacity key type
*
* Copyright (C) 2017-2020 Jason A. Donenfeld <[email protected]>. All Rights Reserved.
* Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
* Written by David Howells ([email protected])
*/
#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/random.h>
#include <keys/user-type.h>
#include <keys/big_key-type.h>
#include <crypto/chacha20poly1305.h>
/*
* Layout of key payload words.
*/
struct big_key_payload {
u8 *data;
struct path path;
size_t length;
};
#define to_big_key_payload(payload) \
(struct big_key_payload *)((payload).data)
/*
* 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))
/*
* 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,
.update = big_key_update,
};
/*
* Preparse a big key
*/
int big_key_preparse(struct key_preparsed_payload *prep)
{
struct big_key_payload *payload = to_big_key_payload(prep->payload);
struct file *file;
u8 *buf, *enckey;
ssize_t written;
size_t datalen = prep->datalen;
size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
int ret;
BUILD_BUG_ON(sizeof(*payload) != sizeof(prep->payload.data));
if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
return -EINVAL;
/* Set an arbitrary quota */
prep->quotalen = 16;
payload->length = 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.
* Since the key is random for each file, we can set the nonce
* to zero, provided we never define a ->update() call.
*/
loff_t pos = 0;
buf = kvmalloc(enclen, GFP_KERNEL);
if (!buf)
return -ENOMEM;
/* generate random key */
enckey = kmalloc(CHACHA20POLY1305_KEY_SIZE, GFP_KERNEL);
if (!enckey) {
ret = -ENOMEM;
goto error;
}
ret = get_random_bytes_wait(enckey, CHACHA20POLY1305_KEY_SIZE);
if (unlikely(ret))
goto err_enckey;
/* encrypt data */
chacha20poly1305_encrypt(buf, prep->data, datalen, NULL, 0,
0, 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, buf, enclen, &pos);
if (written != enclen) {
ret = written;
if (written >= 0)
ret = -EIO;
goto err_fput;
}
/* Pin the mount and dentry to the key so that we can open it again
* later
*/
payload->data = enckey;
payload->path = file->f_path;
path_get(&payload->path);
fput(file);
kvfree_sensitive(buf, enclen);
} else {
/* Just store the data in a buffer */
void *data = kmalloc(datalen, GFP_KERNEL);
if (!data)
return -ENOMEM;
payload->data = data;
memcpy(data, prep->data, prep->datalen);
}
return 0;
err_fput:
fput(file);
err_enckey:
kfree_sensitive(enckey);
error:
kvfree_sensitive(buf, enclen);
return ret;
}
/*
* Clear preparsement.
*/
void big_key_free_preparse(struct key_preparsed_payload *prep)
{
struct big_key_payload *payload = to_big_key_payload(prep->payload);
if (prep->datalen > BIG_KEY_FILE_THRESHOLD)
path_put(&payload->path);
kfree_sensitive(payload->data);
}
/*
* dispose of the links from a revoked keyring
* - called with the key sem write-locked
*/
void big_key_revoke(struct key *key)
{
struct big_key_payload *payload = to_big_key_payload(key->payload);
/* clear the quota */
key_payload_reserve(key, 0);
if (key_is_positive(key) && payload->length > BIG_KEY_FILE_THRESHOLD)
vfs_truncate(&payload->path, 0);
}
/*
* dispose of the data dangling from the corpse of a big_key key
*/
void big_key_destroy(struct key *key)
{
struct big_key_payload *payload = to_big_key_payload(key->payload);
if (payload->length > BIG_KEY_FILE_THRESHOLD) {
path_put(&payload->path);
payload->path.mnt = NULL;
payload->path.dentry = NULL;
}
kfree_sensitive(payload->data);
payload->data = NULL;
}
/*
* Update a big key
*/
int big_key_update(struct key *key, struct key_preparsed_payload *prep)
{
int ret;
ret = key_payload_reserve(key, prep->datalen);
if (ret < 0)
return ret;
if (key_is_positive(key))
big_key_destroy(key);
return generic_key_instantiate(key, prep);
}
/*
* describe the big_key key
*/
void big_key_describe(const struct key *key, struct seq_file *m)
{
struct big_key_payload *payload = to_big_key_payload(key->payload);
seq_puts(m, key->description);
if (key_is_positive(key))
seq_printf(m, ": %zu [%s]",
payload->length,
payload->length > 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 *buffer, size_t buflen)
{
struct big_key_payload *payload = to_big_key_payload(key->payload);
size_t datalen = payload->length;
long ret;
if (!buffer || buflen < datalen)
return datalen;
if (datalen > BIG_KEY_FILE_THRESHOLD) {
struct file *file;
u8 *buf, *enckey = payload->data;
size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
loff_t pos = 0;
buf = kvmalloc(enclen, GFP_KERNEL);
if (!buf)
return -ENOMEM;
file = dentry_open(&payload->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, buf, enclen, &pos);
if (ret != enclen) {
if (ret >= 0)
ret = -EIO;
goto err_fput;
}
ret = chacha20poly1305_decrypt(buf, buf, enclen, NULL, 0, 0,
enckey) ? 0 : -EBADMSG;
if (unlikely(ret))
goto err_fput;
ret = datalen;
/* copy out decrypted data */
memcpy(buffer, buf, datalen);
err_fput:
fput(file);
error:
kvfree_sensitive(buf, enclen);
} else {
ret = datalen;
memcpy(buffer, payload->data, datalen);
}
return ret;
}
/*
* Register key type
*/
static int __init big_key_init(void)
{
return register_key_type(&key_type_big_key);
}
late_initcall(big_key_init);
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