KEYS: Implement a big key type that can save to tmpfs (ab3c3587) · Commits · EulixOS / Software / Kernel

include/keys/big_key-type.h

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		/* Big capacity key type.
		*
		* 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 License
		* as published by the Free Software Foundation; either version
		* 2 of the License, or (at your option) any later version.
		*/

		#ifndef _KEYS_BIG_KEY_TYPE_H
		#define _KEYS_BIG_KEY_TYPE_H

		#include <linux/key-type.h>

		extern struct key_type key_type_big_key;

		extern int big_key_instantiate(struct key key, struct key_preparsed_payload prep);
		extern void big_key_revoke(struct key *key);
		extern void big_key_destroy(struct key *key);
		extern void big_key_describe(const struct key big_key, struct seq_file m);
		extern long big_key_read(const struct key key, char __user buffer, size_t buflen);

		#endif /* _KEYS_BIG_KEY_TYPE_H */

include/linux/key.h

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		@@ -201,6 +201,7 @@ struct key {
		unsigned long value;
		void __rcu *rcudata;
		void *data;
		void *data2[2];
		} payload;
		struct assoc_array keys;
		};

security/keys/Kconfig

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		@@ -20,6 +20,17 @@ config KEYS

		If you are unsure as to whether this is required, answer N.

		config BIG_KEYS
		tristate "Large payload keys"
		depends on KEYS
		depends on TMPFS
		help
		This option provides support for holding large keys within the kernel
		(for example Kerberos ticket caches). The data may be stored out to
		swapspace by tmpfs.

		If you are unsure as to whether this is required, answer N.

		config TRUSTED_KEYS
		tristate "TRUSTED KEYS"
		depends on KEYS && TCG_TPM

security/keys/Makefile

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		@@ -22,5 +22,6 @@ obj-$(CONFIG_SYSCTL) += sysctl.o
		#
		# Key types
		#
		obj-$(CONFIG_BIG_KEYS) += big_key.o
		obj-$(CONFIG_TRUSTED_KEYS) += trusted.o
		obj-$(CONFIG_ENCRYPTED_KEYS) += encrypted-keys/

security/keys/big_key.c

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		/* Large capacity key type
		*
		* 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.
		*/

		#include <linux/module.h>
		#include <linux/init.h>
		#include <linux/seq_file.h>
		#include <linux/file.h>
		#include <linux/shmem_fs.h>
		#include <linux/err.h>
		#include <keys/user-type.h>
		#include <keys/big_key-type.h>

		MODULE_LICENSE("GPL");

		/*
		* 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",
		.def_lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
		.instantiate = big_key_instantiate,
		.match = user_match,
		.revoke = big_key_revoke,
		.destroy = big_key_destroy,
		.describe = big_key_describe,
		.read = big_key_read,
		};

		/*
		* Instantiate a big key
		*/
		int big_key_instantiate(struct key key, struct key_preparsed_payload prep)
		{
		struct path path = (struct path )&key->payload.data2;
		struct file *file;
		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 */
		ret = key_payload_reserve(key, 16);
		if (ret < 0)
		goto error;

		key->type_data.x[1] = 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.
		*
		* TODO: Encrypt the stored data with a temporary key.
		*/
		file = shmem_file_setup("", datalen, 0);
		if (IS_ERR(file))
		goto err_quota;

		written = kernel_write(file, prep->data, prep->datalen, 0);
		if (written != datalen) {
		if (written >= 0)
		ret = -ENOMEM;
		goto err_fput;
		}

		/* Pin the mount and dentry to the key so that we can open it again
		* later
		*/
		*path = file->f_path;
		path_get(path);
		fput(file);
		} else {
		/* Just store the data in a buffer */
		void *data = kmalloc(datalen, GFP_KERNEL);
		if (!data) {
		ret = -ENOMEM;
		goto err_quota;
		}

		key->payload.data = memcpy(data, prep->data, prep->datalen);
		}
		return 0;

		err_fput:
		fput(file);
		err_quota:
		key_payload_reserve(key, 0);
		error:
		return ret;
		}

		/*
		* 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.data2;

		/* clear the quota */
		key_payload_reserve(key, 0);
		if (key_is_instantiated(key) && key->type_data.x[1] > 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)
		{
		if (key->type_data.x[1] > BIG_KEY_FILE_THRESHOLD) {
		struct path path = (struct path )&key->payload.data2;
		path_put(path);
		path->mnt = NULL;
		path->dentry = NULL;
		} else {
		kfree(key->payload.data);
		key->payload.data = NULL;
		}
		}

		/*
		* describe the big_key key
		*/
		void big_key_describe(const struct key key, struct seq_file m)
		{
		unsigned long datalen = key->type_data.x[1];

		seq_puts(m, key->description);

		if (key_is_instantiated(key))
		seq_printf(m, ": %lu [%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)
		{
		unsigned long datalen = key->type_data.x[1];
		long ret;

		if (!buffer \|\| buflen < datalen)
		return datalen;

		if (datalen > BIG_KEY_FILE_THRESHOLD) {
		struct path path = (struct path )&key->payload.data2;
		struct file *file;
		loff_t pos;

		file = dentry_open(path, O_RDONLY, current_cred());
		if (IS_ERR(file))
		return PTR_ERR(file);

		pos = 0;
		ret = vfs_read(file, buffer, datalen, &pos);
		fput(file);
		if (ret >= 0 && ret != datalen)
		ret = -EIO;
		} else {
		ret = datalen;
		if (copy_to_user(buffer, key->payload.data, datalen) != 0)
		ret = -EFAULT;
		}

		return ret;
		}

		/*
		* Module stuff
		*/
		static int __init big_key_init(void)
		{
		return register_key_type(&key_type_big_key);
		}

		static void __exit big_key_cleanup(void)
		{
		unregister_key_type(&key_type_big_key);
		}

		module_init(big_key_init);
		module_exit(big_key_cleanup);