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 <[email protected]>
---
security/keys/Kconfig | 4 +
security/keys/big_key.c | 198 +++++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 184 insertions(+), 18 deletions(-)
diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index fe4d74e..4582809 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -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
diff --git a/security/keys/big_key.c b/security/keys/big_key.c
index c721e39..9e443fc 100644
--- a/security/keys/big_key.c
+++ b/security/keys/big_key.c
@@ -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.
@@ -28,6 +30,14 @@ enum {
};
/*
+ * 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.
@@ -35,6 +45,11 @@ enum {
#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
*/
@@ -50,12 +65,62 @@ struct key_type key_type_big_key = {
};
/*
+ * 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;
@@ -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;
@@ -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;
@@ -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;
}
@@ -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]);
}
/*
@@ -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;
}
/*
@@ -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],
@@ -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);
--
1.9.1
Kirill Marinushkin <[email protected]> wrote:
> 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 <[email protected]>
Applied.
David