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Security: Keys: Big keys stored encrypted
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Solved TODO task: big keys saved to shmem file are now stored encrypted.
The encryption key is randomly generated and saved to payload[big_key_data].

Signed-off-by: Kirill Marinushkin <k.marinushkin@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
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Kirill Marinushkin authored and David Howells committed Apr 12, 2016
1 parent 898de7d commit 13100a7
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Showing 2 changed files with 184 additions and 18 deletions.
4 changes: 4 additions & 0 deletions security/keys/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,10 @@ config BIG_KEYS
bool "Large payload keys"
depends on KEYS
depends on TMPFS
select CRYPTO
select CRYPTO_AES
select CRYPTO_ECB
select CRYPTO_RNG
help
This option provides support for holding large keys within the kernel
(for example Kerberos ticket caches). The data may be stored out to
Expand Down
198 changes: 180 additions & 18 deletions security/keys/big_key.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -14,8 +14,10 @@
#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>

/*
* Layout of key payload words.
Expand All @@ -27,13 +29,26 @@ enum {
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
Expand All @@ -49,13 +64,63 @@ struct key_type key_type_big_key = {
.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_blkcipher *big_key_blkcipher;

/*
* 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;
struct blkcipher_desc desc;

if (crypto_blkcipher_setkey(big_key_blkcipher, key, ENC_KEY_SIZE)) {
ret = -EAGAIN;
goto error;
}

desc.flags = 0;
desc.tfm = big_key_blkcipher;

sg_init_one(&sgio, data, datalen);

if (op == BIG_KEY_ENC)
ret = crypto_blkcipher_encrypt(&desc, &sgio, &sgio, datalen);
else
ret = crypto_blkcipher_decrypt(&desc, &sgio, &sgio, datalen);

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;
Expand All @@ -73,16 +138,43 @@ int big_key_preparse(struct key_preparsed_payload *prep)
/* Create a shmem file to store the data in. This will permit the data
* to be swapped out if needed.
*
* TODO: Encrypt the stored data with a temporary key.
* File content is stored encrypted with randomly generated key.
*/
file = shmem_kernel_file_setup("", datalen, 0);
size_t enclen = ALIGN(datalen, crypto_blkcipher_blocksize(big_key_blkcipher));

/* 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 error;
goto err_enckey;
}

written = kernel_write(file, prep->data, prep->datalen, 0);
if (written != datalen) {
written = kernel_write(file, data, enclen, 0);
if (written != enclen) {
ret = written;
if (written >= 0)
ret = -ENOMEM;
Expand All @@ -92,12 +184,15 @@ int big_key_preparse(struct key_preparsed_payload *prep)
/* 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;

Expand All @@ -108,7 +203,10 @@ int big_key_preparse(struct key_preparsed_payload *prep)

err_fput:
fput(file);
err_enckey:
kfree(enckey);
error:
kfree(data);
return ret;
}

Expand All @@ -119,10 +217,10 @@ 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);
} else {
kfree(prep->payload.data[big_key_data]);
}
kfree(prep->payload.data[big_key_data]);
}

/*
Expand All @@ -147,15 +245,15 @@ void big_key_destroy(struct key *key)
{
size_t datalen = (size_t)key->payload.data[big_key_len];

if (datalen) {
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;
} else {
kfree(key->payload.data[big_key_data]);
key->payload.data[big_key_data] = NULL;
}
kfree(key->payload.data[big_key_data]);
key->payload.data[big_key_data] = NULL;
}

/*
Expand Down Expand Up @@ -188,17 +286,41 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
if (datalen > BIG_KEY_FILE_THRESHOLD) {
struct path *path = (struct path *)&key->payload.data[big_key_path];
struct file *file;
loff_t pos;
u8 *data;
u8 *enckey = (u8 *)key->payload.data[big_key_data];
size_t enclen = ALIGN(datalen, crypto_blkcipher_blocksize(big_key_blkcipher));

data = kmalloc(enclen, GFP_KERNEL);
if (!data)
return -ENOMEM;

file = dentry_open(path, O_RDONLY, current_cred());
if (IS_ERR(file))
return PTR_ERR(file);
if (IS_ERR(file)) {
ret = PTR_ERR(file);
goto error;
}

pos = 0;
ret = vfs_read(file, buffer, datalen, &pos);
fput(file);
if (ret >= 0 && ret != datalen)
/* 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],
Expand All @@ -209,8 +331,48 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
return ret;
}

/*
* Register key type
*/
static int __init big_key_init(void)
{
return register_key_type(&key_type_big_key);
}

/*
* Initialize big_key crypto and RNG algorithms
*/
static int __init big_key_crypto_init(void)
{
int ret = -EINVAL;

/* init RNG */
big_key_rng = crypto_alloc_rng(big_key_rng_name, 0, 0);
if (IS_ERR(big_key_rng)) {
big_key_rng = NULL;
return -EFAULT;
}

/* seed RNG */
ret = crypto_rng_reset(big_key_rng, NULL, crypto_rng_seedsize(big_key_rng));
if (ret)
goto error;

/* init block cipher */
big_key_blkcipher = crypto_alloc_blkcipher(big_key_alg_name, 0, 0);
if (IS_ERR(big_key_blkcipher)) {
big_key_blkcipher = NULL;
ret = -EFAULT;
goto error;
}

return 0;

error:
crypto_free_rng(big_key_rng);
big_key_rng = NULL;
return ret;
}

device_initcall(big_key_init);
late_initcall(big_key_crypto_init);

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