security/keys/big_key.c - arm/linux - Git at Google

 /* 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);
	/* 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);