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

 // SPDX-License-Identifier: GPL-2.0-or-later
 /* Large capacity key type
  *
  * Copyright (C) 2017-2020 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)
  */

 #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.
  */
 enum {
 	big_key_data,
 	big_key_path,
 	big_key_path_2nd_part,
 	big_key_len,
 };

 /*
  * 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 path *path = (struct path *)&prep->payload.data[big_key_path];
 	struct file *file;
 	u8 *buf, *enckey;
 	ssize_t written;
 	size_t datalen = prep->datalen;
 	size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
 	int ret;

 	if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
 		return -EINVAL;

 	/* 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.
 		 * 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
 		 */
 		prep->payload.data[big_key_data] = enckey;
 		*path = file->f_path;
 		path_get(path);
 		fput(file);
 		memzero_explicit(buf, enclen);
 		kvfree(buf);
 	} 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:
 	memzero_explicit(buf, enclen);
 	kvfree(buf);
 	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_positive(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;
 }

 /*
  * 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)
 {
 	size_t datalen = (size_t)key->payload.data[big_key_len];

 	seq_puts(m, key->description);

 	if (key_is_positive(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 *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 *buf, *enckey = (u8 *)key->payload.data[big_key_data];
 		size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
 		loff_t pos = 0;

 		buf = kvmalloc(enclen, GFP_KERNEL);
 		if (!buf)
 			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, 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:
 		memzero_explicit(buf, enclen);
 		kvfree(buf);
 	} else {
 		ret = datalen;
 		memcpy(buffer, key->payload.data[big_key_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);
	// SPDX-License-Identifier: GPL-2.0-or-later
	/* Large capacity key type
	*
	* Copyright (C) 2017-2020 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)
	*/

	#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.
	*/
	enum {
	big_key_data,
	big_key_path,
	big_key_path_2nd_part,
	big_key_len,
	};

	/*
	* 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 path path = (struct path )&prep->payload.data[big_key_path];
	struct file *file;
	u8 buf, enckey;
	ssize_t written;
	size_t datalen = prep->datalen;
	size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
	int ret;

	if (datalen <= 0 \|\| datalen > 1024 * 1024 \|\| !prep->data)
	return -EINVAL;

	/* 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.
	* 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
	*/
	prep->payload.data[big_key_data] = enckey;
	*path = file->f_path;
	path_get(path);
	fput(file);
	memzero_explicit(buf, enclen);
	kvfree(buf);
	} 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:
	memzero_explicit(buf, enclen);
	kvfree(buf);
	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_positive(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;
	}

	/*
	* 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)
	{
	size_t datalen = (size_t)key->payload.data[big_key_len];

	seq_puts(m, key->description);

	if (key_is_positive(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 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 buf, enckey = (u8 *)key->payload.data[big_key_data];
	size_t enclen = datalen + CHACHA20POLY1305_AUTHTAG_SIZE;
	loff_t pos = 0;

	buf = kvmalloc(enclen, GFP_KERNEL);
	if (!buf)
	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, 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:
	memzero_explicit(buf, enclen);
	kvfree(buf);
	} else {
	ret = datalen;
	memcpy(buffer, key->payload.data[big_key_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);