/* 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_kernel_file_setup("", datalen, 0);
  		if (IS_ERR(file)) {
  			ret = PTR_ERR(file);
  			goto err_quota;
  		}
  
  		written = kernel_write(file, prep->data, prep->datalen, 0);
  		if (written != datalen) {
  			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
  		 */
  		*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);