/*
 * Copyright (C) 2013 Kay Sievers
 * Copyright (C) 2013 Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 * Copyright (C) 2013 Daniel Mack <daniel@zonque.org>
 * Copyright (C) 2013 Linux Foundation
 *
 * kdbus is free software; you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the
 * Free Software Foundation; either version 2.1 of the License, or (at
 * your option) any later version.
 */

#define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/device.h>
#include <linux/idr.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/mutex.h>
#include <linux/init.h>
#include <linux/poll.h>
#include <linux/sizes.h>

#include "policy.h"
#include "connection.h"
#include "names.h"

struct kdbus_policy_db_cache_entry {
	struct kdbus_conn	*conn_a;
	struct kdbus_conn	*conn_b;
	struct hlist_node	hentry;
	u64			deadline_ns;
	struct list_head	timeout_entry;
};

struct kdbus_policy_db_entry_access {
	u8			type;	/* USER, GROUP, WORLD */
	u8			bits;	/* RECV, SEND, OWN */
	u64			id;	/* uid, gid, 0 */
	struct list_head	list;
};

struct kdbus_policy_db_entry {
	char			*name;
	struct hlist_node	hentry;
	struct list_head	access_list;
};

static void kdbus_policy_db_scan_timeout(struct kdbus_policy_db *db)
{
	struct kdbus_policy_db_cache_entry *ce, *tmp;
	struct timespec ts;
	u64 deadline = -1;
	u64 now;

	ktime_get_ts(&ts);
	now = timespec_to_ns(&ts);

	mutex_lock(&db->cache_lock);
	list_for_each_entry_safe(ce, tmp, &db->timeout_list, timeout_entry) {
		if (ce->deadline_ns <= now) {
			list_del(&ce->timeout_entry);
			hash_del(&ce->hentry);
			kfree(ce);
		} else if (ce->deadline_ns < deadline) {
			deadline = ce->deadline_ns;
		}
	}
	mutex_unlock(&db->cache_lock);

	if (deadline != -1) {
		u64 usecs = deadline - now;
		do_div(usecs, 1000ULL);
		mod_timer(&db->timer, jiffies + usecs_to_jiffies(usecs));
	}
}

static void kdbus_policy_db_work(struct work_struct *work)
{
	struct kdbus_policy_db *db = container_of(work, struct kdbus_policy_db, work);
	kdbus_policy_db_scan_timeout(db);
}

static void kdbus_policy_db_schedule_timeout_scan(struct kdbus_policy_db *db)
{
	schedule_work(&db->work);
}

static void kdbus_policy_db_timer_func(unsigned long val)
{
	struct kdbus_policy_db *db = (struct kdbus_policy_db *) val;
	kdbus_policy_db_schedule_timeout_scan(db);
}

static void __kdbus_policy_db_free(struct kref *kref)
{
	struct kdbus_policy_db_entry *e;
	struct kdbus_policy_db_cache_entry *ce;
	struct hlist_node *tmp;
	struct kdbus_policy_db *db =
		container_of(kref, struct kdbus_policy_db, kref);
	unsigned int i;

	/* purge entries */
	mutex_lock(&db->entries_lock);
	hash_for_each_safe(db->entries_hash, i, tmp, e, hentry) {
		struct kdbus_policy_db_entry_access *a, *tmp;

		list_for_each_entry_safe(a, tmp, &e->access_list, list) {
			list_del(&a->list);
			kfree(a);
		}

		hash_del(&e->hentry);
		kfree(e->name);
		kfree(e);
	}
	mutex_unlock(&db->entries_lock);

	/* purge cache */
	mutex_lock(&db->cache_lock);
	hash_for_each_safe(db->send_access_hash, i, tmp, ce, hentry) {
		hash_del(&ce->hentry);
		kfree(ce);
	}
	mutex_unlock(&db->cache_lock);

	kfree(db);
}

void kdbus_policy_db_unref(struct kdbus_policy_db *db)
{
	kref_put(&db->kref, __kdbus_policy_db_free);
}

struct kdbus_policy_db *kdbus_policy_db_new(void)
{
	struct kdbus_policy_db *db;

	db = kzalloc(sizeof(*db), GFP_KERNEL);
	if (!db)
		return NULL;

	kref_init(&db->kref);
	hash_init(db->entries_hash);
	hash_init(db->send_access_hash);
	INIT_LIST_HEAD(&db->timeout_list);
	mutex_init(&db->entries_lock);
	mutex_init(&db->cache_lock);

	INIT_WORK(&db->work, kdbus_policy_db_work);

	init_timer(&db->timer);
	db->timer.expires = 0;
	db->timer.function = kdbus_policy_db_timer_func;
	db->timer.data = (unsigned long) db;
	add_timer(&db->timer);

	return db;
}

static inline u64 kdbus_collect_entry_accesses(struct kdbus_policy_db_entry *db_entry,
					 struct kdbus_conn *conn)
{
	struct kdbus_policy_db_entry_access *a;
	u64 access = 0;

	list_for_each_entry(a, &db_entry->access_list, list) {
		switch (a->type) {
		case KDBUS_POLICY_ACCESS_USER:
			if (conn->creds.uid == a->id)
				access |= a->bits;
			break;
		case KDBUS_POLICY_ACCESS_GROUP:
			if (conn->creds.gid == a->id)
				access |= a->bits;
			break;
		case KDBUS_POLICY_ACCESS_WORLD:
			access |= a->bits;
			break;
		}
	}

	return access;
}

static int __kdbus_policy_db_check_send_access(struct kdbus_policy_db *db,
					       struct kdbus_conn *conn_src,
					       struct kdbus_conn *conn_dst)
{
	struct kdbus_name_entry *name_entry;
	struct kdbus_policy_db_entry *db_entry;
	u64 access;
	u32 hash;

	/*
	 * send access is granted if either the source connection has a
	 * matching SEND rule or the receiver connection has a matching
	 * RECV rule.
	 * Hence, we walk the list of the names registered for each
	 * connection.
	 */
	list_for_each_entry(name_entry, &conn_src->names_list, conn_entry) {
		hash = kdbus_str_hash(name_entry->name);
		hash_for_each_possible(db->entries_hash, db_entry, hentry, hash) {
			if (strcmp(db_entry->name, name_entry->name) != 0)
				continue;

			access = kdbus_collect_entry_accesses(db_entry, conn_src);
			if (access & KDBUS_POLICY_SEND)
				return 0;
		}
	}

	list_for_each_entry(name_entry, &conn_dst->names_list, conn_entry) {
		hash = kdbus_str_hash(name_entry->name);
		hash_for_each_possible(db->entries_hash, db_entry, hentry, hash) {
			if (strcmp(db_entry->name, name_entry->name) != 0)
				continue;

			access = kdbus_collect_entry_accesses(db_entry, conn_dst);
			if (access & KDBUS_POLICY_RECV)
				return 0;
		}
	}

	return 0;
}

static struct kdbus_policy_db_cache_entry *
kdbus_policy_cache_entry_new(struct kdbus_conn *conn_a,
			     struct kdbus_conn *conn_b)
{
	struct kdbus_policy_db_cache_entry *ce;

	ce = kzalloc(sizeof(*ce), GFP_KERNEL);
	if (!ce)
		return NULL;

	ce->conn_a = conn_a;
	ce->conn_b = conn_b;
	INIT_LIST_HEAD(&ce->timeout_entry);

	return ce;
}

static int kdbus_add_reverse_cache_entry(struct kdbus_policy_db *db,
				   struct kdbus_policy_db_cache_entry *ce,
				   u64 reply_deadline_ns)
{
	struct kdbus_policy_db_cache_entry *new;
	unsigned int hash = 0;

	/* note that the entries are given in reverse order (b, a) */
	new = kdbus_policy_cache_entry_new(ce->conn_b, ce->conn_a);
	if (!new)
		return -ENOMEM;

	hash ^= hash_ptr(ce->conn_b, sizeof(ce->conn_b) * 8);
	hash ^= hash_ptr(ce->conn_a, sizeof(ce->conn_a) * 8);
	new->deadline_ns = reply_deadline_ns;

	mutex_lock(&db->cache_lock);
	hash_add(db->send_access_hash, &new->hentry, hash);
	list_add_tail(&new->timeout_entry, &db->timeout_list);
	mutex_unlock(&db->cache_lock);

	kdbus_policy_db_scan_timeout(db);

	return 0;
}

int kdbus_policy_db_check_send_access(struct kdbus_policy_db *db,
				      struct kdbus_conn *conn_src,
				      struct kdbus_conn *conn_dst,
				      u64 reply_deadline_ns)
{
	int ret = 0;
	unsigned int hash = 0;
	struct kdbus_policy_db_cache_entry *ce;

	/* FIXME */
	hash ^= hash_ptr(conn_src, sizeof(conn_src) * 8);
	hash ^= hash_ptr(conn_dst, sizeof(conn_dst) * 8);

	mutex_lock(&db->cache_lock);
	hash_for_each_possible(db->send_access_hash, ce, hentry, hash)
		if (ce->conn_a == conn_src && ce->conn_b == conn_dst) {
			mutex_unlock(&db->cache_lock);
			/* do we need a temporaty rule for replies? */
			if (reply_deadline_ns)
				ret = kdbus_add_reverse_cache_entry(db, ce, reply_deadline_ns);
			return ret;
		}
	mutex_unlock(&db->cache_lock);

	mutex_lock(&db->entries_lock);
	ret = __kdbus_policy_db_check_send_access(db, conn_src, conn_dst);
	if (ret == 0) {
		/* add to cache */
		ce = kdbus_policy_cache_entry_new(conn_src, conn_dst);
		if (!ce) {
			ret = -ENOMEM;
			goto exit_unlock_entries;
		}

		mutex_lock(&db->cache_lock);
		hash_add(db->send_access_hash, &ce->hentry, hash);
		mutex_unlock(&db->cache_lock);

		/* do we need a temporaty rule for replies? */
		if (reply_deadline_ns)
			ret = kdbus_add_reverse_cache_entry(db, ce, reply_deadline_ns);
	}

exit_unlock_entries:
	mutex_unlock(&db->entries_lock);

	return ret;
}

void kdbus_policy_db_remove_conn(struct kdbus_policy_db *db,
				 struct kdbus_conn *conn)
{
	struct kdbus_policy_db_cache_entry *ce;
	struct hlist_node *tmp;
	int i;

	mutex_lock(&db->cache_lock);
	hash_for_each_safe(db->send_access_hash, i, tmp, ce, hentry)
		if (ce->conn_a == conn || ce->conn_b == conn) {
			hash_del(&ce->hentry);
			kfree(ce);
		}
	mutex_unlock(&db->cache_lock);
}

int kdbus_policy_db_check_own_access(struct kdbus_policy_db *db,
				     struct kdbus_conn *conn,
				     const char *name)
{
	struct kdbus_policy_db_entry *db_entry;
	int ret = -EPERM;
	u32 hash = kdbus_str_hash(name);

	/* Walk the list of the names registered for a connection ... */
	mutex_lock(&db->entries_lock);
	hash_for_each_possible(db->entries_hash, db_entry,
			       hentry, hash) {
		u64 access;

		if (strcmp(db_entry->name, name) != 0)
			continue;

		access = kdbus_collect_entry_accesses(db_entry, conn);
		if (access & KDBUS_POLICY_OWN) {
			ret = 0;
			goto exit_unlock;
		}
	}

exit_unlock:
	mutex_unlock(&db->entries_lock);

	return ret;
}

static int kdbus_policy_db_parse(struct kdbus_policy_db *db,
				 const struct kdbus_cmd_policy *cmd,
				 u64 size)
{
	const struct kdbus_policy *pol;
	struct kdbus_policy_db_entry *current_entry = NULL;

	KDBUS_PART_FOREACH(pol, cmd, policies) {
		if (!KDBUS_PART_VALID(pol, cmd))
			return -EINVAL;

		switch (pol->type) {
		case KDBUS_POLICY_NAME: {
			struct kdbus_policy_db_entry *e;
			u32 hash;

			e = kzalloc(sizeof(*e), GFP_KERNEL);
			if (!e)
				return -ENOMEM;

			hash = kdbus_str_hash(pol->name);
			e->name = kstrdup(pol->name, GFP_KERNEL);
			INIT_LIST_HEAD(&e->access_list);

			mutex_lock(&db->entries_lock);
			hash_add(db->entries_hash, &e->hentry, hash);
			mutex_unlock(&db->entries_lock);

			current_entry = e;
			break;
		}

		case KDBUS_POLICY_ACCESS: {
			struct kdbus_policy_db_entry_access *a;

			if (!current_entry)
				return -EINVAL;

			a = kzalloc(sizeof(*a), GFP_KERNEL);
			if (!a)
				return -ENOMEM;

			a->type = pol->access.type;
			a->bits = pol->access.bits;
			a->id   = pol->access.id;
			INIT_LIST_HEAD(&a->list);

			mutex_lock(&db->entries_lock);
			list_add_tail(&a->list, &current_entry->access_list);
			mutex_unlock(&db->entries_lock);
			break;
		}

		default:
			return -EINVAL;
		}
	}

	if (!KDBUS_PART_END(pol, cmd))
		return -EINVAL;

	return 0;
}

int kdbus_cmd_policy_set_from_user(struct kdbus_policy_db *db, void __user *buf)
{
	struct kdbus_cmd_policy *cmd;
	u64 size;
	int ret;

	if (kdbus_size_get_user(&size, buf, struct kdbus_cmd_policy))
		return -EFAULT;

	if (size <= sizeof(struct kdbus_cmd_policy))
		return -EINVAL;

	if (size > KDBUS_POLICY_MAX_SIZE)
		return -EMSGSIZE;

	cmd = memdup_user(buf, size);
	if (IS_ERR(cmd))
		return PTR_ERR(cmd);

	ret = kdbus_policy_db_parse(db, cmd, size);
	kfree(cmd);

	return ret;
}