/* Xtables module to match packets using a BPF filter.
 * Copyright 2013 Google Inc.
 * Written by Willem de Bruijn <willemb@google.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/module.h>
#include <linux/syscalls.h>
#include <linux/skbuff.h>
#include <linux/filter.h>
#include <linux/bpf.h>

#include <linux/netfilter/xt_bpf.h>
#include <linux/netfilter/x_tables.h>

MODULE_AUTHOR("Willem de Bruijn <willemb@google.com>");
MODULE_DESCRIPTION("Xtables: BPF filter match");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_bpf");
MODULE_ALIAS("ip6t_bpf");

static int __bpf_mt_check_bytecode(struct sock_filter *insns, __u16 len,
				   struct bpf_prog **ret)
{
	struct sock_fprog_kern program;

	if (len > XT_BPF_MAX_NUM_INSTR)
		return -EINVAL;

	program.len = len;
	program.filter = insns;

	if (bpf_prog_create(ret, &program)) {
		pr_info("bpf: check failed: parse error\n");
		return -EINVAL;
	}

	return 0;
}

static int __bpf_mt_check_fd(int fd, struct bpf_prog **ret)
{
	struct bpf_prog *prog;

	prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_SOCKET_FILTER);
	if (IS_ERR(prog))
		return PTR_ERR(prog);

	*ret = prog;
	return 0;
}

static int __bpf_mt_check_path(const char *path, struct bpf_prog **ret)
{
	mm_segment_t oldfs = get_fs();
	int retval, fd;

	if (strnlen(path, XT_BPF_PATH_MAX) == XT_BPF_PATH_MAX)
		return -EINVAL;

	set_fs(KERNEL_DS);
	fd = bpf_obj_get_user(path);
	set_fs(oldfs);
	if (fd < 0)
		return fd;

	retval = __bpf_mt_check_fd(fd, ret);
	sys_close(fd);
	return retval;
}

static int bpf_mt_check(const struct xt_mtchk_param *par)
{
	struct xt_bpf_info *info = par->matchinfo;

	return __bpf_mt_check_bytecode(info->bpf_program,
				       info->bpf_program_num_elem,
				       &info->filter);
}

static int bpf_mt_check_v1(const struct xt_mtchk_param *par)
{
	struct xt_bpf_info_v1 *info = par->matchinfo;

	if (info->mode == XT_BPF_MODE_BYTECODE)
		return __bpf_mt_check_bytecode(info->bpf_program,
					       info->bpf_program_num_elem,
					       &info->filter);
	else if (info->mode == XT_BPF_MODE_FD_ELF)
		return __bpf_mt_check_fd(info->fd, &info->filter);
	else if (info->mode == XT_BPF_MODE_PATH_PINNED)
		return __bpf_mt_check_path(info->path, &info->filter);
	else
		return -EINVAL;
}

static bool bpf_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
	const struct xt_bpf_info *info = par->matchinfo;

	return BPF_PROG_RUN(info->filter, skb);
}

static bool bpf_mt_v1(const struct sk_buff *skb, struct xt_action_param *par)
{
	const struct xt_bpf_info_v1 *info = par->matchinfo;

	return !!bpf_prog_run_save_cb(info->filter, (struct sk_buff *) skb);
}

static void bpf_mt_destroy(const struct xt_mtdtor_param *par)
{
	const struct xt_bpf_info *info = par->matchinfo;

	bpf_prog_destroy(info->filter);
}

static void bpf_mt_destroy_v1(const struct xt_mtdtor_param *par)
{
	const struct xt_bpf_info_v1 *info = par->matchinfo;

	bpf_prog_destroy(info->filter);
}

static struct xt_match bpf_mt_reg[] __read_mostly = {
	{
		.name		= "bpf",
		.revision	= 0,
		.family		= NFPROTO_UNSPEC,
		.checkentry	= bpf_mt_check,
		.match		= bpf_mt,
		.destroy	= bpf_mt_destroy,
		.matchsize	= sizeof(struct xt_bpf_info),
		.usersize	= offsetof(struct xt_bpf_info, filter),
		.me		= THIS_MODULE,
	},
	{
		.name		= "bpf",
		.revision	= 1,
		.family		= NFPROTO_UNSPEC,
		.checkentry	= bpf_mt_check_v1,
		.match		= bpf_mt_v1,
		.destroy	= bpf_mt_destroy_v1,
		.matchsize	= sizeof(struct xt_bpf_info_v1),
		.usersize	= offsetof(struct xt_bpf_info_v1, filter),
		.me		= THIS_MODULE,
	},
};

static int __init bpf_mt_init(void)
{
	return xt_register_matches(bpf_mt_reg, ARRAY_SIZE(bpf_mt_reg));
}

static void __exit bpf_mt_exit(void)
{
	xt_unregister_matches(bpf_mt_reg, ARRAY_SIZE(bpf_mt_reg));
}

module_init(bpf_mt_init);
module_exit(bpf_mt_exit);