ebt_stp.c

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/*
 *  ebt_stp
 *
 *  Authors:
 *  Bart De Schuymer <[email protected]>
 *  Stephen Hemminger <[email protected]>
 *
 *  July, 2003
 */
#include <linux/etherdevice.h>
#include <linux/module.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_stp.h>

#define BPDU_TYPE_CONFIG 0
#define BPDU_TYPE_TCN 0x80

struct stp_header {
    uint8_t dsap;
    uint8_t ssap;
    uint8_t ctrl;
    uint8_t pid;
    uint8_t vers;
    uint8_t type;
};

struct stp_config_pdu {
    uint8_t flags;
    uint8_t root[8];
    uint8_t root_cost[4];
    uint8_t sender[8];
    uint8_t port[2];
    uint8_t msg_age[2];
    uint8_t max_age[2];
    uint8_t hello_time[2];
    uint8_t forward_delay[2];
};

#define NR16(p) (p[0] << 8 | p[1])
#define NR32(p) ((p[0] << 24) | (p[1] << 16) | (p[2] << 8) | p[3])

static bool ebt_filter_config(const struct ebt_stp_info *info,
   const struct stp_config_pdu *stpc)
{
    const struct ebt_stp_config_info *c;
    uint16_t v16;
    uint32_t v32;
    int verdict, i;

    c = &info->config;
    if ((info->bitmask & EBT_STP_FLAGS) &&
        FWINV(c->flags != stpc->flags, EBT_STP_FLAGS))
        return false;
    if (info->bitmask & EBT_STP_ROOTPRIO) {
        v16 = NR16(stpc->root);
        if (FWINV(v16 < c->root_priol ||
            v16 > c->root_priou, EBT_STP_ROOTPRIO))
            return false;
    }
    if (info->bitmask & EBT_STP_ROOTADDR) {
        verdict = 0;
        for (i = 0; i < 6; i++)
            verdict |= (stpc->root[2+i] ^ c->root_addr[i]) &
                   c->root_addrmsk[i];
        if (FWINV(verdict != 0, EBT_STP_ROOTADDR))
            return false;
    }
    if (info->bitmask & EBT_STP_ROOTCOST) {
        v32 = NR32(stpc->root_cost);
        if (FWINV(v32 < c->root_costl ||
            v32 > c->root_costu, EBT_STP_ROOTCOST))
            return false;
    }
    if (info->bitmask & EBT_STP_SENDERPRIO) {
        v16 = NR16(stpc->sender);
        if (FWINV(v16 < c->sender_priol ||
            v16 > c->sender_priou, EBT_STP_SENDERPRIO))
            return false;
    }
    if (info->bitmask & EBT_STP_SENDERADDR) {
        verdict = 0;
        for (i = 0; i < 6; i++)
            verdict |= (stpc->sender[2+i] ^ c->sender_addr[i]) &
                   c->sender_addrmsk[i];
        if (FWINV(verdict != 0, EBT_STP_SENDERADDR))
            return false;
    }
    if (info->bitmask & EBT_STP_PORT) {
        v16 = NR16(stpc->port);
        if (FWINV(v16 < c->portl ||
            v16 > c->portu, EBT_STP_PORT))
            return false;
    }
    if (info->bitmask & EBT_STP_MSGAGE) {
        v16 = NR16(stpc->msg_age);
        if (FWINV(v16 < c->msg_agel ||
            v16 > c->msg_ageu, EBT_STP_MSGAGE))
            return false;
    }
    if (info->bitmask & EBT_STP_MAXAGE) {
        v16 = NR16(stpc->max_age);
        if (FWINV(v16 < c->max_agel ||
            v16 > c->max_ageu, EBT_STP_MAXAGE))
            return false;
    }
    if (info->bitmask & EBT_STP_HELLOTIME) {
        v16 = NR16(stpc->hello_time);
        if (FWINV(v16 < c->hello_timel ||
            v16 > c->hello_timeu, EBT_STP_HELLOTIME))
            return false;
    }
    if (info->bitmask & EBT_STP_FWDD) {
        v16 = NR16(stpc->forward_delay);
        if (FWINV(v16 < c->forward_delayl ||
            v16 > c->forward_delayu, EBT_STP_FWDD))
            return false;
    }
    return true;
}

static bool
ebt_stp_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    const struct ebt_stp_info *info = par->matchinfo;
    const struct stp_header *sp;
    struct stp_header _stph;
    const uint8_t header[6] = {0x42, 0x42, 0x03, 0x00, 0x00, 0x00};

    sp = skb_header_pointer(skb, 0, sizeof(_stph), &_stph);
    if (sp == NULL)
        return false;

    /* The stp code only considers these */
    if (memcmp(sp, header, sizeof(header)))
        return false;

    if (info->bitmask & EBT_STP_TYPE &&
        FWINV(info->type != sp->type, EBT_STP_TYPE))
        return false;

    if (sp->type == BPDU_TYPE_CONFIG &&
        info->bitmask & EBT_STP_CONFIG_MASK) {
        const struct stp_config_pdu *st;
        struct stp_config_pdu _stpc;

        st = skb_header_pointer(skb, sizeof(_stph),
                    sizeof(_stpc), &_stpc);
        if (st == NULL)
            return false;
        return ebt_filter_config(info, st);
    }
    return true;
}

static int ebt_stp_mt_check(const struct xt_mtchk_param *par)
{
    const struct ebt_stp_info *info = par->matchinfo;
    const uint8_t bridge_ula[6] = {0x01, 0x80, 0xc2, 0x00, 0x00, 0x00};
    const uint8_t msk[6] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};
    const struct ebt_entry *e = par->entryinfo;

    if (info->bitmask & ~EBT_STP_MASK || info->invflags & ~EBT_STP_MASK ||
        !(info->bitmask & EBT_STP_MASK))
        return -EINVAL;
    /* Make sure the match only receives stp frames */
    if (!ether_addr_equal(e->destmac, bridge_ula) ||
        !ether_addr_equal(e->destmsk, msk) || !(e->bitmask & EBT_DESTMAC))
        return -EINVAL;

    return 0;
}

static struct xt_match ebt_stp_mt_reg __read_mostly = {
    .name       = "stp",
    .revision   = 0,
    .family     = NFPROTO_BRIDGE,
    .match      = ebt_stp_mt,
    .checkentry = ebt_stp_mt_check,
    .matchsize  = sizeof(struct ebt_stp_info),
    .me     = THIS_MODULE,
};

static int __init ebt_stp_init(void)
{
    return xt_register_match(&ebt_stp_mt_reg);
}

static void __exit ebt_stp_fini(void)
{
    xt_unregister_match(&ebt_stp_mt_reg);
}

module_init(ebt_stp_init);
module_exit(ebt_stp_fini);
MODULE_DESCRIPTION("Ebtables: Spanning Tree Protocol packet match");
MODULE_LICENSE("GPL");