1/* Large capacity key type
  2 *
  3 * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
  4 * Written by David Howells (dhowells@redhat.com)
  5 *
  6 * This program is free software; you can redistribute it and/or
  7 * modify it under the terms of the GNU General Public Licence
  8 * as published by the Free Software Foundation; either version
  9 * 2 of the Licence, or (at your option) any later version.
 10 */
 11
 12#include <linux/init.h>
 13#include <linux/seq_file.h>
 14#include <linux/file.h>
 15#include <linux/shmem_fs.h>
 16#include <linux/err.h>
 17#include <keys/user-type.h>
 18#include <keys/big_key-type.h>
 19
 20/*
 21 * Layout of key payload words.
 22 */
 23enum {
 24	big_key_data,
 25	big_key_path,
 26	big_key_path_2nd_part,
 27	big_key_len,
 28};
 29
 30/*
 31 * If the data is under this limit, there's no point creating a shm file to
 32 * hold it as the permanently resident metadata for the shmem fs will be at
 33 * least as large as the data.
 34 */
 35#define BIG_KEY_FILE_THRESHOLD (sizeof(struct inode) + sizeof(struct dentry))
 36
 37/*
 38 * big_key defined keys take an arbitrary string as the description and an
 39 * arbitrary blob of data as the payload
 40 */
 41struct key_type key_type_big_key = {
 42	.name			= "big_key",
 43	.preparse		= big_key_preparse,
 44	.free_preparse		= big_key_free_preparse,
 45	.instantiate		= generic_key_instantiate,
 46	.revoke			= big_key_revoke,
 47	.destroy		= big_key_destroy,
 48	.describe		= big_key_describe,
 49	.read			= big_key_read,
 50};
 51
 52/*
 53 * Preparse a big key
 54 */
 55int big_key_preparse(struct key_preparsed_payload *prep)
 56{
 57	struct path *path = (struct path *)&prep->payload.data[big_key_path];
 58	struct file *file;
 59	ssize_t written;
 60	size_t datalen = prep->datalen;
 61	int ret;
 62
 63	ret = -EINVAL;
 64	if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
 65		goto error;
 66
 67	/* Set an arbitrary quota */
 68	prep->quotalen = 16;
 69
 70	prep->payload.data[big_key_len] = (void *)(unsigned long)datalen;
 71
 72	if (datalen > BIG_KEY_FILE_THRESHOLD) {
 73		/* Create a shmem file to store the data in.  This will permit the data
 74		 * to be swapped out if needed.
 75		 *
 76		 * TODO: Encrypt the stored data with a temporary key.
 77		 */
 78		file = shmem_kernel_file_setup("", datalen, 0);
 79		if (IS_ERR(file)) {
 80			ret = PTR_ERR(file);
 81			goto error;
 82		}
 83
 84		written = kernel_write(file, prep->data, prep->datalen, 0);
 85		if (written != datalen) {
 86			ret = written;
 87			if (written >= 0)
 88				ret = -ENOMEM;
 89			goto err_fput;
 90		}
 91
 92		/* Pin the mount and dentry to the key so that we can open it again
 93		 * later
 94		 */
 95		*path = file->f_path;
 96		path_get(path);
 97		fput(file);
 98	} else {
 99		/* Just store the data in a buffer */
100		void *data = kmalloc(datalen, GFP_KERNEL);
101		if (!data)
102			return -ENOMEM;
103
104		prep->payload.data[big_key_data] = data;
105		memcpy(data, prep->data, prep->datalen);
106	}
107	return 0;
108
109err_fput:
110	fput(file);
111error:
112	return ret;
113}
114
115/*
116 * Clear preparsement.
117 */
118void big_key_free_preparse(struct key_preparsed_payload *prep)
119{
120	if (prep->datalen > BIG_KEY_FILE_THRESHOLD) {
121		struct path *path = (struct path *)&prep->payload.data[big_key_path];
122		path_put(path);
123	} else {
124		kfree(prep->payload.data[big_key_data]);
125	}
126}
127
128/*
129 * dispose of the links from a revoked keyring
130 * - called with the key sem write-locked
131 */
132void big_key_revoke(struct key *key)
133{
134	struct path *path = (struct path *)&key->payload.data[big_key_path];
135
136	/* clear the quota */
137	key_payload_reserve(key, 0);
138	if (key_is_instantiated(key) &&
139	    (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
140		vfs_truncate(path, 0);
141}
142
143/*
144 * dispose of the data dangling from the corpse of a big_key key
145 */
146void big_key_destroy(struct key *key)
147{
148	size_t datalen = (size_t)key->payload.data[big_key_len];
149
150	if (datalen) {
151		struct path *path = (struct path *)&key->payload.data[big_key_path];
152		path_put(path);
153		path->mnt = NULL;
154		path->dentry = NULL;
155	} else {
156		kfree(key->payload.data[big_key_data]);
157		key->payload.data[big_key_data] = NULL;
158	}
159}
160
161/*
162 * describe the big_key key
163 */
164void big_key_describe(const struct key *key, struct seq_file *m)
165{
166	size_t datalen = (size_t)key->payload.data[big_key_len];
167
168	seq_puts(m, key->description);
169
170	if (key_is_instantiated(key))
171		seq_printf(m, ": %zu [%s]",
172			   datalen,
173			   datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");
174}
175
176/*
177 * read the key data
178 * - the key's semaphore is read-locked
179 */
180long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
181{
182	size_t datalen = (size_t)key->payload.data[big_key_len];
183	long ret;
184
185	if (!buffer || buflen < datalen)
186		return datalen;
187
188	if (datalen > BIG_KEY_FILE_THRESHOLD) {
189		struct path *path = (struct path *)&key->payload.data[big_key_path];
190		struct file *file;
191		loff_t pos;
192
193		file = dentry_open(path, O_RDONLY, current_cred());
194		if (IS_ERR(file))
195			return PTR_ERR(file);
196
197		pos = 0;
198		ret = vfs_read(file, buffer, datalen, &pos);
199		fput(file);
200		if (ret >= 0 && ret != datalen)
201			ret = -EIO;
202	} else {
203		ret = datalen;
204		if (copy_to_user(buffer, key->payload.data[big_key_data],
205				 datalen) != 0)
206			ret = -EFAULT;
207	}
208
209	return ret;
210}
211
212static int __init big_key_init(void)
213{
214	return register_key_type(&key_type_big_key);
215}
216device_initcall(big_key_init);