xt_SECMARK.c

Go to the documentation of this file.

/*
 * Module for modifying the secmark field of the skb, for use by
 * security subsystems.
 *
 * Based on the nfmark match by:
 * (C) 1999-2001 Marc Boucher <[email protected]>
 *
 * (C) 2006,2008 Red Hat, Inc., James Morris <[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.
 *
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/security.h>
#include <linux/skbuff.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_SECMARK.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("James Morris <[email protected]>");
MODULE_DESCRIPTION("Xtables: packet security mark modification");
MODULE_ALIAS("ipt_SECMARK");
MODULE_ALIAS("ip6t_SECMARK");

#define PFX "SECMARK: "

static u8 mode;

static unsigned int
secmark_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
    u32 secmark = 0;
    const struct xt_secmark_target_info *info = par->targinfo;

    BUG_ON(info->mode != mode);

    switch (mode) {
    case SECMARK_MODE_SEL:
        secmark = info->secid;
        break;
    default:
        BUG();
    }

    skb->secmark = secmark;
    return XT_CONTINUE;
}

static int checkentry_lsm(struct xt_secmark_target_info *info)
{
    int err;

    info->secctx[SECMARK_SECCTX_MAX - 1] = '\0';
    info->secid = 0;

    err = security_secctx_to_secid(info->secctx, strlen(info->secctx),
                       &info->secid);
    if (err) {
        if (err == -EINVAL)
            pr_info("invalid security context \'%s\'\n", info->secctx);
        return err;
    }

    if (!info->secid) {
        pr_info("unable to map security context \'%s\'\n", info->secctx);
        return -ENOENT;
    }

    err = security_secmark_relabel_packet(info->secid);
    if (err) {
        pr_info("unable to obtain relabeling permission\n");
        return err;
    }

    security_secmark_refcount_inc();
    return 0;
}

static int secmark_tg_check(const struct xt_tgchk_param *par)
{
    struct xt_secmark_target_info *info = par->targinfo;
    int err;

    if (strcmp(par->table, "mangle") != 0 &&
        strcmp(par->table, "security") != 0) {
        pr_info("target only valid in the \'mangle\' "
            "or \'security\' tables, not \'%s\'.\n", par->table);
        return -EINVAL;
    }

    if (mode && mode != info->mode) {
        pr_info("mode already set to %hu cannot mix with "
            "rules for mode %hu\n", mode, info->mode);
        return -EINVAL;
    }

    switch (info->mode) {
    case SECMARK_MODE_SEL:
        break;
    default:
        pr_info("invalid mode: %hu\n", info->mode);
        return -EINVAL;
    }

    err = checkentry_lsm(info);
    if (err)
        return err;

    if (!mode)
        mode = info->mode;
    return 0;
}

static void secmark_tg_destroy(const struct xt_tgdtor_param *par)
{
    switch (mode) {
    case SECMARK_MODE_SEL:
        security_secmark_refcount_dec();
    }
}

static struct xt_target secmark_tg_reg __read_mostly = {
    .name       = "SECMARK",
    .revision   = 0,
    .family     = NFPROTO_UNSPEC,
    .checkentry = secmark_tg_check,
    .destroy    = secmark_tg_destroy,
    .target     = secmark_tg,
    .targetsize = sizeof(struct xt_secmark_target_info),
    .me         = THIS_MODULE,
};

static int __init secmark_tg_init(void)
{
    return xt_register_target(&secmark_tg_reg);
}

static void __exit secmark_tg_exit(void)
{
    xt_unregister_target(&secmark_tg_reg);
}

module_init(secmark_tg_init);
module_exit(secmark_tg_exit);