net/netfilter/xt_string.c

// SPDX-License-Identifier: GPL-2.0-only
/* String matching match for iptables
 *
 * (C) 2005 Pablo Neira Ayuso <pablo@eurodev.net>
 */

#include <linux/gfp.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_string.h>
#include <linux/textsearch.h>

MODULE_AUTHOR("Pablo Neira Ayuso <pablo@eurodev.net>");
MODULE_DESCRIPTION("Xtables: string-based matching");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_string");
MODULE_ALIAS("ip6t_string");
MODULE_ALIAS("ebt_string");

static bool
string_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
	const struct xt_string_info *conf = par->matchinfo;
	bool invert;

	invert = conf->u.v1.flags & XT_STRING_FLAG_INVERT;

	return (skb_find_text((struct sk_buff *)skb, conf->from_offset,
			     conf->to_offset, conf->config)
			     != UINT_MAX) ^ invert;
}

#define STRING_TEXT_PRIV(m) ((struct xt_string_info *)(m))

static int string_mt_check(const struct xt_mtchk_param *par)
{
	struct xt_string_info *conf = par->matchinfo;
	struct ts_config *ts_conf;
	int flags = TS_AUTOLOAD;

	/* Damn, can't handle this case properly with iptables... */
	if (conf->from_offset > conf->to_offset)
		return -EINVAL;
	if (conf->algo[XT_STRING_MAX_ALGO_NAME_SIZE - 1] != '\0')
		return -EINVAL;
	if (conf->patlen > XT_STRING_MAX_PATTERN_SIZE)
		return -EINVAL;
	if (conf->u.v1.flags &
	    ~(XT_STRING_FLAG_IGNORECASE | XT_STRING_FLAG_INVERT))
		return -EINVAL;
	if (conf->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
		flags |= TS_IGNORECASE;
	ts_conf = textsearch_prepare(conf->algo, conf->pattern, conf->patlen,
				     GFP_KERNEL, flags);
	if (IS_ERR(ts_conf))
		return PTR_ERR(ts_conf);

	conf->config = ts_conf;
	return 0;
}

static void string_mt_destroy(const struct xt_mtdtor_param *par)
{
	textsearch_destroy(STRING_TEXT_PRIV(par->matchinfo)->config);
}

static struct xt_match xt_string_mt_reg __read_mostly = {
	.name       = "string",
	.revision   = 1,
	.family     = NFPROTO_UNSPEC,
	.checkentry = string_mt_check,
	.match      = string_mt,
	.destroy    = string_mt_destroy,
	.matchsize  = sizeof(struct xt_string_info),
	.usersize   = offsetof(struct xt_string_info, config),
	.me         = THIS_MODULE,
};

static int __init string_mt_init(void)
{
	return xt_register_match(&xt_string_mt_reg);
}

static void __exit string_mt_exit(void)
{
	xt_unregister_match(&xt_string_mt_reg);
}

module_init(string_mt_init);
module_exit(string_mt_exit);