fs/ecryptfs/miscdev.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * eCryptfs: Linux filesystem encryption layer
  *
  * Copyright (C) 2008 International Business Machines Corp.
  *   Author(s): Michael A. Halcrow <mhalcrow@us.ibm.com>
  */

 #include <linux/fs.h>
 #include <linux/hash.h>
 #include <linux/random.h>
 #include <linux/miscdevice.h>
 #include <linux/poll.h>
 #include <linux/slab.h>
 #include <linux/wait.h>
 #include <linux/module.h>
 #include "ecryptfs_kernel.h"

 static atomic_t ecryptfs_num_miscdev_opens;

 /**
  * ecryptfs_miscdev_poll
  * @file: dev file
  * @pt: dev poll table (ignored)
  *
  * Returns the poll mask
  */
 static __poll_t
 ecryptfs_miscdev_poll(struct file *file, poll_table *pt)
 {
 	struct ecryptfs_daemon *daemon = file->private_data;
 	__poll_t mask = 0;

 	mutex_lock(&daemon->mux);
 	if (daemon->flags & ECRYPTFS_DAEMON_ZOMBIE) {
 		printk(KERN_WARNING "%s: Attempt to poll on zombified "
 		       "daemon\n", __func__);
 		goto out_unlock_daemon;
 	}
 	if (daemon->flags & ECRYPTFS_DAEMON_IN_READ)
 		goto out_unlock_daemon;
 	if (daemon->flags & ECRYPTFS_DAEMON_IN_POLL)
 		goto out_unlock_daemon;
 	daemon->flags |= ECRYPTFS_DAEMON_IN_POLL;
 	mutex_unlock(&daemon->mux);
 	poll_wait(file, &daemon->wait, pt);
 	mutex_lock(&daemon->mux);
 	if (!list_empty(&daemon->msg_ctx_out_queue))
 		mask |= EPOLLIN | EPOLLRDNORM;
 out_unlock_daemon:
 	daemon->flags &= ~ECRYPTFS_DAEMON_IN_POLL;
 	mutex_unlock(&daemon->mux);
 	return mask;
 }

 /**
  * ecryptfs_miscdev_open
  * @inode: inode of miscdev handle (ignored)
  * @file: file for miscdev handle
  *
  * Returns zero on success; non-zero otherwise
  */
 static int
 ecryptfs_miscdev_open(struct inode *inode, struct file *file)
 {
 	struct ecryptfs_daemon *daemon = NULL;
 	int rc;

 	mutex_lock(&ecryptfs_daemon_hash_mux);
 	rc = ecryptfs_find_daemon_by_euid(&daemon);
 	if (!rc) {
 		rc = -EINVAL;
 		goto out_unlock_daemon_list;
 	}
 	rc = ecryptfs_spawn_daemon(&daemon, file);
 	if (rc) {
 		printk(KERN_ERR "%s: Error attempting to spawn daemon; "
 		       "rc = [%d]\n", __func__, rc);
 		goto out_unlock_daemon_list;
 	}
 	mutex_lock(&daemon->mux);
 	if (daemon->flags & ECRYPTFS_DAEMON_MISCDEV_OPEN) {
 		rc = -EBUSY;
 		goto out_unlock_daemon;
 	}
 	daemon->flags |= ECRYPTFS_DAEMON_MISCDEV_OPEN;
 	file->private_data = daemon;
 	atomic_inc(&ecryptfs_num_miscdev_opens);
 out_unlock_daemon:
 	mutex_unlock(&daemon->mux);
 out_unlock_daemon_list:
 	mutex_unlock(&ecryptfs_daemon_hash_mux);
 	return rc;
 }

 /**
  * ecryptfs_miscdev_release
  * @inode: inode of fs/ecryptfs/euid handle (ignored)
  * @file: file for fs/ecryptfs/euid handle
  *
  * This keeps the daemon registered until the daemon sends another
  * ioctl to fs/ecryptfs/ctl or until the kernel module unregisters.
  *
  * Returns zero on success; non-zero otherwise
  */
 static int
 ecryptfs_miscdev_release(struct inode *inode, struct file *file)
 {
 	struct ecryptfs_daemon *daemon = file->private_data;
 	int rc;

 	mutex_lock(&daemon->mux);
 	BUG_ON(!(daemon->flags & ECRYPTFS_DAEMON_MISCDEV_OPEN));
 	daemon->flags &= ~ECRYPTFS_DAEMON_MISCDEV_OPEN;
 	atomic_dec(&ecryptfs_num_miscdev_opens);
 	mutex_unlock(&daemon->mux);

 	mutex_lock(&ecryptfs_daemon_hash_mux);
 	rc = ecryptfs_exorcise_daemon(daemon);
 	mutex_unlock(&ecryptfs_daemon_hash_mux);
 	if (rc) {
 		printk(KERN_CRIT "%s: Fatal error whilst attempting to "
 		       "shut down daemon; rc = [%d]. Please report this "
 		       "bug.\n", __func__, rc);
 		BUG();
 	}
 	return rc;
 }

 /**
  * ecryptfs_send_miscdev
  * @data: Data to send to daemon; may be NULL
  * @data_size: Amount of data to send to daemon
  * @msg_ctx: Message context, which is used to handle the reply. If
  *           this is NULL, then we do not expect a reply.
  * @msg_type: Type of message
  * @msg_flags: Flags for message
  * @daemon: eCryptfs daemon object
  *
  * Add msg_ctx to queue and then, if it exists, notify the blocked
  * miscdevess about the data being available. Must be called with
  * ecryptfs_daemon_hash_mux held.
  *
  * Returns zero on success; non-zero otherwise
  */
 int ecryptfs_send_miscdev(char *data, size_t data_size,
 			  struct ecryptfs_msg_ctx *msg_ctx, u8 msg_type,
 			  u16 msg_flags, struct ecryptfs_daemon *daemon)
 {
 	struct ecryptfs_message *msg;

 	msg = kmalloc((sizeof(*msg) + data_size), GFP_KERNEL);
 	if (!msg)
 		return -ENOMEM;

 	mutex_lock(&msg_ctx->mux);
 	msg_ctx->msg = msg;
 	msg_ctx->msg->index = msg_ctx->index;
 	msg_ctx->msg->data_len = data_size;
 	msg_ctx->type = msg_type;
 	memcpy(msg_ctx->msg->data, data, data_size);
 	msg_ctx->msg_size = (sizeof(*msg_ctx->msg) + data_size);
 	list_add_tail(&msg_ctx->daemon_out_list, &daemon->msg_ctx_out_queue);
 	mutex_unlock(&msg_ctx->mux);

 	mutex_lock(&daemon->mux);
 	daemon->num_queued_msg_ctx++;
 	wake_up_interruptible(&daemon->wait);
 	mutex_unlock(&daemon->mux);

 	return 0;
 }

 /*
  * miscdevfs packet format:
  *  Octet 0: Type
  *  Octets 1-4: network byte order msg_ctx->counter
  *  Octets 5-N0: Size of struct ecryptfs_message to follow
  *  Octets N0-N1: struct ecryptfs_message (including data)
  *
  *  Octets 5-N1 not written if the packet type does not include a message
  */
 #define PKT_TYPE_SIZE		1
 #define PKT_CTR_SIZE		4
 #define MIN_NON_MSG_PKT_SIZE	(PKT_TYPE_SIZE + PKT_CTR_SIZE)
 #define MIN_MSG_PKT_SIZE	(PKT_TYPE_SIZE + PKT_CTR_SIZE \
 				 + ECRYPTFS_MIN_PKT_LEN_SIZE)
 /* 4 + ECRYPTFS_MAX_ENCRYPTED_KEY_BYTES comes from tag 65 packet format */
 #define MAX_MSG_PKT_SIZE	(PKT_TYPE_SIZE + PKT_CTR_SIZE \
 				 + ECRYPTFS_MAX_PKT_LEN_SIZE \
 				 + sizeof(struct ecryptfs_message) \
 				 + 4 + ECRYPTFS_MAX_ENCRYPTED_KEY_BYTES)
 #define PKT_TYPE_OFFSET		0
 #define PKT_CTR_OFFSET		PKT_TYPE_SIZE
 #define PKT_LEN_OFFSET		(PKT_TYPE_SIZE + PKT_CTR_SIZE)

 /**
  * ecryptfs_miscdev_read - format and send message from queue
  * @file: miscdevfs handle
  * @buf: User buffer into which to copy the next message on the daemon queue
  * @count: Amount of space available in @buf
  * @ppos: Offset in file (ignored)
  *
  * Pulls the most recent message from the daemon queue, formats it for
  * being sent via a miscdevfs handle, and copies it into @buf
  *
  * Returns the number of bytes copied into the user buffer
  */
 static ssize_t
 ecryptfs_miscdev_read(struct file *file, char __user *buf, size_t count,
 		      loff_t *ppos)
 {
 	struct ecryptfs_daemon *daemon = file->private_data;
 	struct ecryptfs_msg_ctx *msg_ctx;
 	size_t packet_length_size;
 	char packet_length[ECRYPTFS_MAX_PKT_LEN_SIZE];
 	size_t i;
 	size_t total_length;
 	int rc;

 	mutex_lock(&daemon->mux);
 	if (daemon->flags & ECRYPTFS_DAEMON_ZOMBIE) {
 		rc = 0;
 		printk(KERN_WARNING "%s: Attempt to read from zombified "
 		       "daemon\n", __func__);
 		goto out_unlock_daemon;
 	}
 	if (daemon->flags & ECRYPTFS_DAEMON_IN_READ) {
 		rc = 0;
 		goto out_unlock_daemon;
 	}
 	/* This daemon will not go away so long as this flag is set */
 	daemon->flags |= ECRYPTFS_DAEMON_IN_READ;
 check_list:
 	if (list_empty(&daemon->msg_ctx_out_queue)) {
 		mutex_unlock(&daemon->mux);
 		rc = wait_event_interruptible(
 			daemon->wait, !list_empty(&daemon->msg_ctx_out_queue));
 		mutex_lock(&daemon->mux);
 		if (rc < 0) {
 			rc = 0;
 			goto out_unlock_daemon;
 		}
 	}
 	if (daemon->flags & ECRYPTFS_DAEMON_ZOMBIE) {
 		rc = 0;
 		goto out_unlock_daemon;
 	}
 	if (list_empty(&daemon->msg_ctx_out_queue)) {
 		/* Something else jumped in since the
 		 * wait_event_interruptable() and removed the
 		 * message from the queue; try again */
 		goto check_list;
 	}
 	msg_ctx = list_first_entry(&daemon->msg_ctx_out_queue,
 				   struct ecryptfs_msg_ctx, daemon_out_list);
 	BUG_ON(!msg_ctx);
 	mutex_lock(&msg_ctx->mux);
 	if (msg_ctx->msg) {
 		rc = ecryptfs_write_packet_length(packet_length,
 						  msg_ctx->msg_size,
 						  &packet_length_size);
 		if (rc) {
 			rc = 0;
 			printk(KERN_WARNING "%s: Error writing packet length; "
 			       "rc = [%d]\n", __func__, rc);
 			goto out_unlock_msg_ctx;
 		}
 	} else {
 		packet_length_size = 0;
 		msg_ctx->msg_size = 0;
 	}
 	total_length = (PKT_TYPE_SIZE + PKT_CTR_SIZE + packet_length_size
 			+ msg_ctx->msg_size);
 	if (count < total_length) {
 		rc = 0;
 		printk(KERN_WARNING "%s: Only given user buffer of "
 		       "size [%zd], but we need [%zd] to read the "
 		       "pending message\n", __func__, count, total_length);
 		goto out_unlock_msg_ctx;
 	}
 	rc = -EFAULT;
 	if (put_user(msg_ctx->type, buf))
 		goto out_unlock_msg_ctx;
 	if (put_user(cpu_to_be32(msg_ctx->counter),
 		     (__be32 __user *)(&buf[PKT_CTR_OFFSET])))
 		goto out_unlock_msg_ctx;
 	i = PKT_TYPE_SIZE + PKT_CTR_SIZE;
 	if (msg_ctx->msg) {
 		if (copy_to_user(&buf[i], packet_length, packet_length_size))
 			goto out_unlock_msg_ctx;
 		i += packet_length_size;
 		if (copy_to_user(&buf[i], msg_ctx->msg, msg_ctx->msg_size))
 			goto out_unlock_msg_ctx;
 		i += msg_ctx->msg_size;
 	}
 	rc = i;
 	list_del(&msg_ctx->daemon_out_list);
 	kfree(msg_ctx->msg);
 	msg_ctx->msg = NULL;
 	/* We do not expect a reply from the userspace daemon for any
 	 * message type other than ECRYPTFS_MSG_REQUEST */
 	if (msg_ctx->type != ECRYPTFS_MSG_REQUEST)
 		ecryptfs_msg_ctx_alloc_to_free(msg_ctx);
 out_unlock_msg_ctx:
 	mutex_unlock(&msg_ctx->mux);
 out_unlock_daemon:
 	daemon->flags &= ~ECRYPTFS_DAEMON_IN_READ;
 	mutex_unlock(&daemon->mux);
 	return rc;
 }

 /**
  * ecryptfs_miscdev_response - miscdevess response to message previously sent to daemon
  * @daemon: eCryptfs daemon object
  * @data: Bytes comprising struct ecryptfs_message
  * @data_size: sizeof(struct ecryptfs_message) + data len
  * @seq: Sequence number for miscdev response packet
  *
  * Returns zero on success; non-zero otherwise
  */
 static int ecryptfs_miscdev_response(struct ecryptfs_daemon *daemon, char *data,
 				     size_t data_size, u32 seq)
 {
 	struct ecryptfs_message *msg = (struct ecryptfs_message *)data;
 	int rc;

 	if ((sizeof(*msg) + msg->data_len) != data_size) {
 		printk(KERN_WARNING "%s: (sizeof(*msg) + msg->data_len) = "
 		       "[%zd]; data_size = [%zd]. Invalid packet.\n", __func__,
 		       (sizeof(*msg) + msg->data_len), data_size);
 		rc = -EINVAL;
 		goto out;
 	}
 	rc = ecryptfs_process_response(daemon, msg, seq);
 	if (rc)
 		printk(KERN_ERR
 		       "Error processing response message; rc = [%d]\n", rc);
 out:
 	return rc;
 }

 /**
  * ecryptfs_miscdev_write - handle write to daemon miscdev handle
  * @file: File for misc dev handle
  * @buf: Buffer containing user data
  * @count: Amount of data in @buf
  * @ppos: Pointer to offset in file (ignored)
  *
  * Returns the number of bytes read from @buf
  */
 static ssize_t
 ecryptfs_miscdev_write(struct file *file, const char __user *buf,
 		       size_t count, loff_t *ppos)
 {
 	__be32 counter_nbo;
 	u32 seq;
 	size_t packet_size, packet_size_length;
 	char *data;
 	unsigned char packet_size_peek[ECRYPTFS_MAX_PKT_LEN_SIZE];
 	ssize_t rc;

 	if (count == 0) {
 		return 0;
 	} else if (count == MIN_NON_MSG_PKT_SIZE) {
 		/* Likely a harmless MSG_HELO or MSG_QUIT - no packet length */
 		goto memdup;
 	} else if (count < MIN_MSG_PKT_SIZE || count > MAX_MSG_PKT_SIZE) {
 		printk(KERN_WARNING "%s: Acceptable packet size range is "
 		       "[%d-%zu], but amount of data written is [%zu].\n",
 		       __func__, MIN_MSG_PKT_SIZE, MAX_MSG_PKT_SIZE, count);
 		return -EINVAL;
 	}

 	if (copy_from_user(packet_size_peek, &buf[PKT_LEN_OFFSET],
 			   sizeof(packet_size_peek))) {
 		printk(KERN_WARNING "%s: Error while inspecting packet size\n",
 		       __func__);
 		return -EFAULT;
 	}

 	rc = ecryptfs_parse_packet_length(packet_size_peek, &packet_size,
 					  &packet_size_length);
 	if (rc) {
 		printk(KERN_WARNING "%s: Error parsing packet length; "
 		       "rc = [%zd]\n", __func__, rc);
 		return rc;
 	}

 	if ((PKT_TYPE_SIZE + PKT_CTR_SIZE + packet_size_length + packet_size)
 	    != count) {
 		printk(KERN_WARNING "%s: Invalid packet size [%zu]\n", __func__,
 		       packet_size);
 		return -EINVAL;
 	}

 memdup:
 	data = memdup_user(buf, count);
 	if (IS_ERR(data)) {
 		printk(KERN_ERR "%s: memdup_user returned error [%ld]\n",
 		       __func__, PTR_ERR(data));
 		return PTR_ERR(data);
 	}
 	switch (data[PKT_TYPE_OFFSET]) {
 	case ECRYPTFS_MSG_RESPONSE:
 		if (count < (MIN_MSG_PKT_SIZE
 			     + sizeof(struct ecryptfs_message))) {
 			printk(KERN_WARNING "%s: Minimum acceptable packet "
 			       "size is [%zd], but amount of data written is "
 			       "only [%zd]. Discarding response packet.\n",
 			       __func__,
 			       (MIN_MSG_PKT_SIZE
 				+ sizeof(struct ecryptfs_message)), count);
 			rc = -EINVAL;
 			goto out_free;
 		}
 		memcpy(&counter_nbo, &data[PKT_CTR_OFFSET], PKT_CTR_SIZE);
 		seq = be32_to_cpu(counter_nbo);
 		rc = ecryptfs_miscdev_response(file->private_data,
 				&data[PKT_LEN_OFFSET + packet_size_length],
 				packet_size, seq);
 		if (rc) {
 			printk(KERN_WARNING "%s: Failed to deliver miscdev "
 			       "response to requesting operation; rc = [%zd]\n",
 			       __func__, rc);
 			goto out_free;
 		}
 		break;
 	case ECRYPTFS_MSG_HELO:
 	case ECRYPTFS_MSG_QUIT:
 		break;
 	default:
 		ecryptfs_printk(KERN_WARNING, "Dropping miscdev "
 				"message of unrecognized type [%d]\n",
 				data[0]);
 		rc = -EINVAL;
 		goto out_free;
 	}
 	rc = count;
 out_free:
 	kfree(data);
 	return rc;
 }


 static const struct file_operations ecryptfs_miscdev_fops = {
 	.owner   = THIS_MODULE,
 	.open    = ecryptfs_miscdev_open,
 	.poll    = ecryptfs_miscdev_poll,
 	.read    = ecryptfs_miscdev_read,
 	.write   = ecryptfs_miscdev_write,
 	.release = ecryptfs_miscdev_release,
 	.llseek  = noop_llseek,
 };

 static struct miscdevice ecryptfs_miscdev = {
 	.minor = MISC_DYNAMIC_MINOR,
 	.name  = "ecryptfs",
 	.fops  = &ecryptfs_miscdev_fops
 };

 /**
  * ecryptfs_init_ecryptfs_miscdev
  *
  * Messages sent to the userspace daemon from the kernel are placed on
  * a queue associated with the daemon. The next read against the
  * miscdev handle by that daemon will return the oldest message placed
  * on the message queue for the daemon.
  *
  * Returns zero on success; non-zero otherwise
  */
 int __init ecryptfs_init_ecryptfs_miscdev(void)
 {
 	int rc;

 	atomic_set(&ecryptfs_num_miscdev_opens, 0);
 	rc = misc_register(&ecryptfs_miscdev);
 	if (rc)
 		printk(KERN_ERR "%s: Failed to register miscellaneous device "
 		       "for communications with userspace daemons; rc = [%d]\n",
 		       __func__, rc);
 	return rc;
 }

 /**
  * ecryptfs_destroy_ecryptfs_miscdev
  *
  * All of the daemons must be exorcised prior to calling this
  * function.
  */
 void ecryptfs_destroy_ecryptfs_miscdev(void)
 {
 	BUG_ON(atomic_read(&ecryptfs_num_miscdev_opens) != 0);
 	misc_deregister(&ecryptfs_miscdev);
 }
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* eCryptfs: Linux filesystem encryption layer
	*
	* Copyright (C) 2008 International Business Machines Corp.
	* Author(s): Michael A. Halcrow <mhalcrow@us.ibm.com>
	*/

	#include <linux/fs.h>
	#include <linux/hash.h>
	#include <linux/random.h>
	#include <linux/miscdevice.h>
	#include <linux/poll.h>
	#include <linux/slab.h>
	#include <linux/wait.h>
	#include <linux/module.h>
	#include "ecryptfs_kernel.h"

	static atomic_t ecryptfs_num_miscdev_opens;

	/**
	* ecryptfs_miscdev_poll
	* @file: dev file
	* @pt: dev poll table (ignored)
	*
	* Returns the poll mask
	*/
	static __poll_t
	ecryptfs_miscdev_poll(struct file file, poll_table pt)
	{
	struct ecryptfs_daemon *daemon = file->private_data;
	__poll_t mask = 0;

	mutex_lock(&daemon->mux);
	if (daemon->flags & ECRYPTFS_DAEMON_ZOMBIE) {
	printk(KERN_WARNING "%s: Attempt to poll on zombified "
	"daemon\n", __func__);
	goto out_unlock_daemon;
	}
	if (daemon->flags & ECRYPTFS_DAEMON_IN_READ)
	goto out_unlock_daemon;
	if (daemon->flags & ECRYPTFS_DAEMON_IN_POLL)
	goto out_unlock_daemon;
	daemon->flags \|= ECRYPTFS_DAEMON_IN_POLL;
	mutex_unlock(&daemon->mux);
	poll_wait(file, &daemon->wait, pt);
	mutex_lock(&daemon->mux);
	if (!list_empty(&daemon->msg_ctx_out_queue))
	mask \|= EPOLLIN \| EPOLLRDNORM;
	out_unlock_daemon:
	daemon->flags &= ~ECRYPTFS_DAEMON_IN_POLL;
	mutex_unlock(&daemon->mux);
	return mask;
	}

	/**
	* ecryptfs_miscdev_open
	* @inode: inode of miscdev handle (ignored)
	* @file: file for miscdev handle
	*
	* Returns zero on success; non-zero otherwise
	*/
	static int
	ecryptfs_miscdev_open(struct inode inode, struct file file)
	{
	struct ecryptfs_daemon *daemon = NULL;
	int rc;

	mutex_lock(&ecryptfs_daemon_hash_mux);
	rc = ecryptfs_find_daemon_by_euid(&daemon);
	if (!rc) {
	rc = -EINVAL;
	goto out_unlock_daemon_list;
	}
	rc = ecryptfs_spawn_daemon(&daemon, file);
	if (rc) {
	printk(KERN_ERR "%s: Error attempting to spawn daemon; "
	"rc = [%d]\n", __func__, rc);
	goto out_unlock_daemon_list;
	}
	mutex_lock(&daemon->mux);
	if (daemon->flags & ECRYPTFS_DAEMON_MISCDEV_OPEN) {
	rc = -EBUSY;
	goto out_unlock_daemon;
	}
	daemon->flags \|= ECRYPTFS_DAEMON_MISCDEV_OPEN;
	file->private_data = daemon;
	atomic_inc(&ecryptfs_num_miscdev_opens);
	out_unlock_daemon:
	mutex_unlock(&daemon->mux);
	out_unlock_daemon_list:
	mutex_unlock(&ecryptfs_daemon_hash_mux);
	return rc;
	}

	/**
	* ecryptfs_miscdev_release
	* @inode: inode of fs/ecryptfs/euid handle (ignored)
	* @file: file for fs/ecryptfs/euid handle
	*
	* This keeps the daemon registered until the daemon sends another
	* ioctl to fs/ecryptfs/ctl or until the kernel module unregisters.
	*
	* Returns zero on success; non-zero otherwise
	*/
	static int
	ecryptfs_miscdev_release(struct inode inode, struct file file)
	{
	struct ecryptfs_daemon *daemon = file->private_data;
	int rc;

	mutex_lock(&daemon->mux);
	BUG_ON(!(daemon->flags & ECRYPTFS_DAEMON_MISCDEV_OPEN));
	daemon->flags &= ~ECRYPTFS_DAEMON_MISCDEV_OPEN;
	atomic_dec(&ecryptfs_num_miscdev_opens);
	mutex_unlock(&daemon->mux);

	mutex_lock(&ecryptfs_daemon_hash_mux);
	rc = ecryptfs_exorcise_daemon(daemon);
	mutex_unlock(&ecryptfs_daemon_hash_mux);
	if (rc) {
	printk(KERN_CRIT "%s: Fatal error whilst attempting to "
	"shut down daemon; rc = [%d]. Please report this "
	"bug.\n", __func__, rc);
	BUG();
	}
	return rc;
	}

	/**
	* ecryptfs_send_miscdev
	* @data: Data to send to daemon; may be NULL
	* @data_size: Amount of data to send to daemon
	* @msg_ctx: Message context, which is used to handle the reply. If
	* this is NULL, then we do not expect a reply.
	* @msg_type: Type of message
	* @msg_flags: Flags for message
	* @daemon: eCryptfs daemon object
	*
	* Add msg_ctx to queue and then, if it exists, notify the blocked
	* miscdevess about the data being available. Must be called with
	* ecryptfs_daemon_hash_mux held.
	*
	* Returns zero on success; non-zero otherwise
	*/
	int ecryptfs_send_miscdev(char *data, size_t data_size,
	struct ecryptfs_msg_ctx *msg_ctx, u8 msg_type,
	u16 msg_flags, struct ecryptfs_daemon *daemon)
	{
	struct ecryptfs_message *msg;

	msg = kmalloc((sizeof(*msg) + data_size), GFP_KERNEL);
	if (!msg)
	return -ENOMEM;

	mutex_lock(&msg_ctx->mux);
	msg_ctx->msg = msg;
	msg_ctx->msg->index = msg_ctx->index;
	msg_ctx->msg->data_len = data_size;
	msg_ctx->type = msg_type;
	memcpy(msg_ctx->msg->data, data, data_size);
	msg_ctx->msg_size = (sizeof(*msg_ctx->msg) + data_size);
	list_add_tail(&msg_ctx->daemon_out_list, &daemon->msg_ctx_out_queue);
	mutex_unlock(&msg_ctx->mux);

	mutex_lock(&daemon->mux);
	daemon->num_queued_msg_ctx++;
	wake_up_interruptible(&daemon->wait);
	mutex_unlock(&daemon->mux);

	return 0;
	}

	/*
	* miscdevfs packet format:
	* Octet 0: Type
	* Octets 1-4: network byte order msg_ctx->counter
	* Octets 5-N0: Size of struct ecryptfs_message to follow
	* Octets N0-N1: struct ecryptfs_message (including data)
	*
	* Octets 5-N1 not written if the packet type does not include a message
	*/
	#define PKT_TYPE_SIZE 1
	#define PKT_CTR_SIZE 4
	#define MIN_NON_MSG_PKT_SIZE (PKT_TYPE_SIZE + PKT_CTR_SIZE)
	#define MIN_MSG_PKT_SIZE (PKT_TYPE_SIZE + PKT_CTR_SIZE \
	+ ECRYPTFS_MIN_PKT_LEN_SIZE)
	/* 4 + ECRYPTFS_MAX_ENCRYPTED_KEY_BYTES comes from tag 65 packet format */
	#define MAX_MSG_PKT_SIZE (PKT_TYPE_SIZE + PKT_CTR_SIZE \
	+ ECRYPTFS_MAX_PKT_LEN_SIZE \
	+ sizeof(struct ecryptfs_message) \
	+ 4 + ECRYPTFS_MAX_ENCRYPTED_KEY_BYTES)
	#define PKT_TYPE_OFFSET 0
	#define PKT_CTR_OFFSET PKT_TYPE_SIZE
	#define PKT_LEN_OFFSET (PKT_TYPE_SIZE + PKT_CTR_SIZE)

	/**
	* ecryptfs_miscdev_read - format and send message from queue
	* @file: miscdevfs handle
	* @buf: User buffer into which to copy the next message on the daemon queue
	* @count: Amount of space available in @buf
	* @ppos: Offset in file (ignored)
	*
	* Pulls the most recent message from the daemon queue, formats it for
	* being sent via a miscdevfs handle, and copies it into @buf
	*
	* Returns the number of bytes copied into the user buffer
	*/
	static ssize_t
	ecryptfs_miscdev_read(struct file file, char __user buf, size_t count,
	loff_t *ppos)
	{
	struct ecryptfs_daemon *daemon = file->private_data;
	struct ecryptfs_msg_ctx *msg_ctx;
	size_t packet_length_size;
	char packet_length[ECRYPTFS_MAX_PKT_LEN_SIZE];
	size_t i;
	size_t total_length;
	int rc;

	mutex_lock(&daemon->mux);
	if (daemon->flags & ECRYPTFS_DAEMON_ZOMBIE) {
	rc = 0;
	printk(KERN_WARNING "%s: Attempt to read from zombified "
	"daemon\n", __func__);
	goto out_unlock_daemon;
	}
	if (daemon->flags & ECRYPTFS_DAEMON_IN_READ) {
	rc = 0;
	goto out_unlock_daemon;
	}
	/* This daemon will not go away so long as this flag is set */
	daemon->flags \|= ECRYPTFS_DAEMON_IN_READ;
	check_list:
	if (list_empty(&daemon->msg_ctx_out_queue)) {
	mutex_unlock(&daemon->mux);
	rc = wait_event_interruptible(
	daemon->wait, !list_empty(&daemon->msg_ctx_out_queue));
	mutex_lock(&daemon->mux);
	if (rc < 0) {
	rc = 0;
	goto out_unlock_daemon;
	}
	}
	if (daemon->flags & ECRYPTFS_DAEMON_ZOMBIE) {
	rc = 0;
	goto out_unlock_daemon;
	}
	if (list_empty(&daemon->msg_ctx_out_queue)) {
	/* Something else jumped in since the
	* wait_event_interruptable() and removed the
	* message from the queue; try again */
	goto check_list;
	}
	msg_ctx = list_first_entry(&daemon->msg_ctx_out_queue,
	struct ecryptfs_msg_ctx, daemon_out_list);
	BUG_ON(!msg_ctx);
	mutex_lock(&msg_ctx->mux);
	if (msg_ctx->msg) {
	rc = ecryptfs_write_packet_length(packet_length,
	msg_ctx->msg_size,
	&packet_length_size);
	if (rc) {
	rc = 0;
	printk(KERN_WARNING "%s: Error writing packet length; "
	"rc = [%d]\n", __func__, rc);
	goto out_unlock_msg_ctx;
	}
	} else {
	packet_length_size = 0;
	msg_ctx->msg_size = 0;
	}
	total_length = (PKT_TYPE_SIZE + PKT_CTR_SIZE + packet_length_size
	+ msg_ctx->msg_size);
	if (count < total_length) {
	rc = 0;
	printk(KERN_WARNING "%s: Only given user buffer of "
	"size [%zd], but we need [%zd] to read the "
	"pending message\n", __func__, count, total_length);
	goto out_unlock_msg_ctx;
	}
	rc = -EFAULT;
	if (put_user(msg_ctx->type, buf))
	goto out_unlock_msg_ctx;
	if (put_user(cpu_to_be32(msg_ctx->counter),
	(__be32 __user *)(&buf[PKT_CTR_OFFSET])))
	goto out_unlock_msg_ctx;
	i = PKT_TYPE_SIZE + PKT_CTR_SIZE;
	if (msg_ctx->msg) {
	if (copy_to_user(&buf[i], packet_length, packet_length_size))
	goto out_unlock_msg_ctx;
	i += packet_length_size;
	if (copy_to_user(&buf[i], msg_ctx->msg, msg_ctx->msg_size))
	goto out_unlock_msg_ctx;
	i += msg_ctx->msg_size;
	}
	rc = i;
	list_del(&msg_ctx->daemon_out_list);
	kfree(msg_ctx->msg);
	msg_ctx->msg = NULL;
	/* We do not expect a reply from the userspace daemon for any
	* message type other than ECRYPTFS_MSG_REQUEST */
	if (msg_ctx->type != ECRYPTFS_MSG_REQUEST)
	ecryptfs_msg_ctx_alloc_to_free(msg_ctx);
	out_unlock_msg_ctx:
	mutex_unlock(&msg_ctx->mux);
	out_unlock_daemon:
	daemon->flags &= ~ECRYPTFS_DAEMON_IN_READ;
	mutex_unlock(&daemon->mux);
	return rc;
	}

	/**
	* ecryptfs_miscdev_response - miscdevess response to message previously sent to daemon
	* @daemon: eCryptfs daemon object
	* @data: Bytes comprising struct ecryptfs_message
	* @data_size: sizeof(struct ecryptfs_message) + data len
	* @seq: Sequence number for miscdev response packet
	*
	* Returns zero on success; non-zero otherwise
	*/
	static int ecryptfs_miscdev_response(struct ecryptfs_daemon daemon, char data,
	size_t data_size, u32 seq)
	{
	struct ecryptfs_message msg = (struct ecryptfs_message )data;
	int rc;

	if ((sizeof(*msg) + msg->data_len) != data_size) {
	printk(KERN_WARNING "%s: (sizeof(*msg) + msg->data_len) = "
	"[%zd]; data_size = [%zd]. Invalid packet.\n", __func__,
	(sizeof(*msg) + msg->data_len), data_size);
	rc = -EINVAL;
	goto out;
	}
	rc = ecryptfs_process_response(daemon, msg, seq);
	if (rc)
	printk(KERN_ERR
	"Error processing response message; rc = [%d]\n", rc);
	out:
	return rc;
	}

	/**
	* ecryptfs_miscdev_write - handle write to daemon miscdev handle
	* @file: File for misc dev handle
	* @buf: Buffer containing user data
	* @count: Amount of data in @buf
	* @ppos: Pointer to offset in file (ignored)
	*
	* Returns the number of bytes read from @buf
	*/
	static ssize_t
	ecryptfs_miscdev_write(struct file file, const char __user buf,
	size_t count, loff_t *ppos)
	{
	__be32 counter_nbo;
	u32 seq;
	size_t packet_size, packet_size_length;
	char *data;
	unsigned char packet_size_peek[ECRYPTFS_MAX_PKT_LEN_SIZE];
	ssize_t rc;

	if (count == 0) {
	return 0;
	} else if (count == MIN_NON_MSG_PKT_SIZE) {
	/* Likely a harmless MSG_HELO or MSG_QUIT - no packet length */
	goto memdup;
	} else if (count < MIN_MSG_PKT_SIZE \|\| count > MAX_MSG_PKT_SIZE) {
	printk(KERN_WARNING "%s: Acceptable packet size range is "
	"[%d-%zu], but amount of data written is [%zu].\n",
	__func__, MIN_MSG_PKT_SIZE, MAX_MSG_PKT_SIZE, count);
	return -EINVAL;
	}

	if (copy_from_user(packet_size_peek, &buf[PKT_LEN_OFFSET],
	sizeof(packet_size_peek))) {
	printk(KERN_WARNING "%s: Error while inspecting packet size\n",
	__func__);
	return -EFAULT;
	}

	rc = ecryptfs_parse_packet_length(packet_size_peek, &packet_size,
	&packet_size_length);
	if (rc) {
	printk(KERN_WARNING "%s: Error parsing packet length; "
	"rc = [%zd]\n", __func__, rc);
	return rc;
	}

	if ((PKT_TYPE_SIZE + PKT_CTR_SIZE + packet_size_length + packet_size)
	!= count) {
	printk(KERN_WARNING "%s: Invalid packet size [%zu]\n", __func__,
	packet_size);
	return -EINVAL;
	}

	memdup:
	data = memdup_user(buf, count);
	if (IS_ERR(data)) {
	printk(KERN_ERR "%s: memdup_user returned error [%ld]\n",
	__func__, PTR_ERR(data));
	return PTR_ERR(data);
	}
	switch (data[PKT_TYPE_OFFSET]) {
	case ECRYPTFS_MSG_RESPONSE:
	if (count < (MIN_MSG_PKT_SIZE
	+ sizeof(struct ecryptfs_message))) {
	printk(KERN_WARNING "%s: Minimum acceptable packet "
	"size is [%zd], but amount of data written is "
	"only [%zd]. Discarding response packet.\n",
	__func__,
	(MIN_MSG_PKT_SIZE
	+ sizeof(struct ecryptfs_message)), count);
	rc = -EINVAL;
	goto out_free;
	}
	memcpy(&counter_nbo, &data[PKT_CTR_OFFSET], PKT_CTR_SIZE);
	seq = be32_to_cpu(counter_nbo);
	rc = ecryptfs_miscdev_response(file->private_data,
	&data[PKT_LEN_OFFSET + packet_size_length],
	packet_size, seq);
	if (rc) {
	printk(KERN_WARNING "%s: Failed to deliver miscdev "
	"response to requesting operation; rc = [%zd]\n",
	__func__, rc);
	goto out_free;
	}
	break;
	case ECRYPTFS_MSG_HELO:
	case ECRYPTFS_MSG_QUIT:
	break;
	default:
	ecryptfs_printk(KERN_WARNING, "Dropping miscdev "
	"message of unrecognized type [%d]\n",
	data[0]);
	rc = -EINVAL;
	goto out_free;
	}
	rc = count;
	out_free:
	kfree(data);
	return rc;
	}


	static const struct file_operations ecryptfs_miscdev_fops = {
	.owner = THIS_MODULE,
	.open = ecryptfs_miscdev_open,
	.poll = ecryptfs_miscdev_poll,
	.read = ecryptfs_miscdev_read,
	.write = ecryptfs_miscdev_write,
	.release = ecryptfs_miscdev_release,
	.llseek = noop_llseek,
	};

	static struct miscdevice ecryptfs_miscdev = {
	.minor = MISC_DYNAMIC_MINOR,
	.name = "ecryptfs",
	.fops = &ecryptfs_miscdev_fops
	};

	/**
	* ecryptfs_init_ecryptfs_miscdev
	*
	* Messages sent to the userspace daemon from the kernel are placed on
	* a queue associated with the daemon. The next read against the
	* miscdev handle by that daemon will return the oldest message placed
	* on the message queue for the daemon.
	*
	* Returns zero on success; non-zero otherwise
	*/
	int __init ecryptfs_init_ecryptfs_miscdev(void)
	{
	int rc;

	atomic_set(&ecryptfs_num_miscdev_opens, 0);
	rc = misc_register(&ecryptfs_miscdev);
	if (rc)
	printk(KERN_ERR "%s: Failed to register miscellaneous device "
	"for communications with userspace daemons; rc = [%d]\n",
	__func__, rc);
	return rc;
	}

	/**
	* ecryptfs_destroy_ecryptfs_miscdev
	*
	* All of the daemons must be exorcised prior to calling this
	* function.
	*/
	void ecryptfs_destroy_ecryptfs_miscdev(void)
	{
	BUG_ON(atomic_read(&ecryptfs_num_miscdev_opens) != 0);
	misc_deregister(&ecryptfs_miscdev);
	}