// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Description: EBTables 802.1Q match extension kernelspace module.
 * Authors: Nick Fedchik <nick@fedchik.org.ua>
 *          Bart De Schuymer <bdschuym@pandora.be>
 */

#include <linux/if_ether.h>
#include <linux/if_vlan.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_vlan.h>

#define MODULE_VERS "0.6"

MODULE_AUTHOR("Nick Fedchik <nick@fedchik.org.ua>");
MODULE_DESCRIPTION("Ebtables: 802.1Q VLAN tag match");
MODULE_LICENSE("GPL");

#define GET_BITMASK(_BIT_MASK_) info->bitmask & _BIT_MASK_
#define EXIT_ON_MISMATCH(_MATCH_,_MASK_) {if (!((info->_MATCH_ == _MATCH_)^!!(info->invflags & _MASK_))) return false; }

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

        unsigned short TCI;     /* Whole TCI, given from parsed frame */
        unsigned short id;      /* VLAN ID, given from frame TCI */
        unsigned char prio;     /* user_priority, given from frame TCI */
        /* VLAN encapsulated Type/Length field, given from orig frame */
        __be16 encap;

        if (skb_vlan_tag_present(skb)) {
                TCI = skb_vlan_tag_get(skb);
                encap = skb->protocol;
        } else {
                const struct vlan_hdr *fp;
                struct vlan_hdr _frame;

                fp = skb_header_pointer(skb, 0, sizeof(_frame), &_frame);
                if (fp == NULL)
                        return false;

                TCI = ntohs(fp->h_vlan_TCI);
                encap = fp->h_vlan_encapsulated_proto;
        }

        /* Tag Control Information (TCI) consists of the following elements:
         * - User_priority. The user_priority field is three bits in length,
         * interpreted as a binary number.
         * - Canonical Format Indicator (CFI). The Canonical Format Indicator
         * (CFI) is a single bit flag value. Currently ignored.
         * - VLAN Identifier (VID). The VID is encoded as
         * an unsigned binary number.
         */
        id = TCI & VLAN_VID_MASK;
        prio = (TCI >> 13) & 0x7;

        /* Checking VLAN Identifier (VID) */
        if (GET_BITMASK(EBT_VLAN_ID))
                EXIT_ON_MISMATCH(id, EBT_VLAN_ID);

        /* Checking user_priority */
        if (GET_BITMASK(EBT_VLAN_PRIO))
                EXIT_ON_MISMATCH(prio, EBT_VLAN_PRIO);

        /* Checking Encapsulated Proto (Length/Type) field */
        if (GET_BITMASK(EBT_VLAN_ENCAP))
                EXIT_ON_MISMATCH(encap, EBT_VLAN_ENCAP);

        return true;
}

static int ebt_vlan_mt_check(const struct xt_mtchk_param *par)
{
        struct ebt_vlan_info *info = par->matchinfo;
        const struct ebt_entry *e = par->entryinfo;

        /* Is it 802.1Q frame checked? */
        if (e->ethproto != htons(ETH_P_8021Q)) {
                pr_debug("passed entry proto %2.4X is not 802.1Q (8100)\n",
                         ntohs(e->ethproto));
                return -EINVAL;
        }

        /* Check for bitmask range
         * True if even one bit is out of mask
         */
        if (info->bitmask & ~EBT_VLAN_MASK) {
                pr_debug("bitmask %2X is out of mask (%2X)\n",
                         info->bitmask, EBT_VLAN_MASK);
                return -EINVAL;
        }

        /* Check for inversion flags range */
        if (info->invflags & ~EBT_VLAN_MASK) {
                pr_debug("inversion flags %2X is out of mask (%2X)\n",
                         info->invflags, EBT_VLAN_MASK);
                return -EINVAL;
        }

        /* Reserved VLAN ID (VID) values
         * -----------------------------
         * 0 - The null VLAN ID.
         * 1 - The default Port VID (PVID)
         * 0x0FFF - Reserved for implementation use.
         * if_vlan.h: VLAN_N_VID 4096.
         */
        if (GET_BITMASK(EBT_VLAN_ID)) {
                if (!!info->id) { /* if id!=0 => check vid range */
                        if (info->id > VLAN_N_VID) {
                                pr_debug("id %d is out of range (1-4096)\n",
                                         info->id);
                                return -EINVAL;
                        }
                        /* Note: This is valid VLAN-tagged frame point.
                         * Any value of user_priority are acceptable,
                         * but should be ignored according to 802.1Q Std.
                         * So we just drop the prio flag.
                         */
                        info->bitmask &= ~EBT_VLAN_PRIO;
                }
                /* Else, id=0 (null VLAN ID)  => user_priority range (any?) */
        }

        if (GET_BITMASK(EBT_VLAN_PRIO)) {
                if ((unsigned char) info->prio > 7) {
                        pr_debug("prio %d is out of range (0-7)\n",
                                 info->prio);
                        return -EINVAL;
                }
        }
        /* Check for encapsulated proto range - it is possible to be
         * any value for u_short range.
         * if_ether.h:  ETH_ZLEN        60   -  Min. octets in frame sans FCS
         */
        if (GET_BITMASK(EBT_VLAN_ENCAP)) {
                if ((unsigned short) ntohs(info->encap) < ETH_ZLEN) {
                        pr_debug("encap frame length %d is less than "
                                 "minimal\n", ntohs(info->encap));
                        return -EINVAL;
                }
        }

        return 0;
}

static struct xt_match ebt_vlan_mt_reg __read_mostly = {
        .name           = "vlan",
        .revision       = 0,
        .family         = NFPROTO_BRIDGE,
        .match          = ebt_vlan_mt,
        .checkentry     = ebt_vlan_mt_check,
        .matchsize      = sizeof(struct ebt_vlan_info),
        .me             = THIS_MODULE,
};

static int __init ebt_vlan_init(void)
{
        pr_debug("ebtables 802.1Q extension module v" MODULE_VERS "\n");
        return xt_register_match(&ebt_vlan_mt_reg);
}

static void __exit ebt_vlan_fini(void)
{
        xt_unregister_match(&ebt_vlan_mt_reg);
}

module_init(ebt_vlan_init);
module_exit(ebt_vlan_fini);