xt_string.c

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/* String matching match for iptables
 *
 * (C) 2005 Pablo Neira Ayuso <[email protected]>
 *
 * 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/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 <[email protected]>");
MODULE_DESCRIPTION("Xtables: string-based matching");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_string");
MODULE_ALIAS("ip6t_string");

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

    memset(&state, 0, sizeof(struct ts_state));
    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, &state)
                 != 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),
    .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);