// SPDX-License-Identifier: GPL-2.0-only
/*
 *      STP SAP demux
 *
 *      Copyright (c) 2008 Patrick McHardy <kaber@trash.net>
 */
#include <linux/mutex.h>
#include <linux/skbuff.h>
#include <linux/etherdevice.h>
#include <linux/llc.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <net/llc.h>
#include <net/llc_pdu.h>
#include <net/stp.h>

/* 01:80:c2:00:00:20 - 01:80:c2:00:00:2F */
#define GARP_ADDR_MIN   0x20
#define GARP_ADDR_MAX   0x2F
#define GARP_ADDR_RANGE (GARP_ADDR_MAX - GARP_ADDR_MIN)

static const struct stp_proto __rcu *garp_protos[GARP_ADDR_RANGE + 1] __read_mostly;
static const struct stp_proto __rcu *stp_proto __read_mostly;

static struct llc_sap *sap __read_mostly;
static unsigned int sap_registered;
static DEFINE_MUTEX(stp_proto_mutex);

/* Called under rcu_read_lock from LLC */
static int stp_pdu_rcv(struct sk_buff *skb, struct net_device *dev,
                       struct packet_type *pt, struct net_device *orig_dev)
{
        const struct ethhdr *eh = eth_hdr(skb);
        const struct llc_pdu_un *pdu = llc_pdu_un_hdr(skb);
        const struct stp_proto *proto;

        if (pdu->ssap != LLC_SAP_BSPAN ||
            pdu->dsap != LLC_SAP_BSPAN ||
            pdu->ctrl_1 != LLC_PDU_TYPE_U)
                goto err;

        if (eh->h_dest[5] >= GARP_ADDR_MIN && eh->h_dest[5] <= GARP_ADDR_MAX) {
                proto = rcu_dereference(garp_protos[eh->h_dest[5] -
                                                    GARP_ADDR_MIN]);
                if (proto &&
                    !ether_addr_equal(eh->h_dest, proto->group_address))
                        goto err;
        } else
                proto = rcu_dereference(stp_proto);

        if (!proto)
                goto err;

        proto->rcv(proto, skb, dev);
        return 0;

err:
        kfree_skb(skb);
        return 0;
}

int stp_proto_register(const struct stp_proto *proto)
{
        int err = 0;

        mutex_lock(&stp_proto_mutex);
        if (sap_registered++ == 0) {
                sap = llc_sap_open(LLC_SAP_BSPAN, stp_pdu_rcv);
                if (!sap) {
                        err = -ENOMEM;
                        goto out;
                }
        }
        if (is_zero_ether_addr(proto->group_address))
                rcu_assign_pointer(stp_proto, proto);
        else
                rcu_assign_pointer(garp_protos[proto->group_address[5] -
                                               GARP_ADDR_MIN], proto);
out:
        mutex_unlock(&stp_proto_mutex);
        return err;
}
EXPORT_SYMBOL_GPL(stp_proto_register);

void stp_proto_unregister(const struct stp_proto *proto)
{
        mutex_lock(&stp_proto_mutex);
        if (is_zero_ether_addr(proto->group_address))
                RCU_INIT_POINTER(stp_proto, NULL);
        else
                RCU_INIT_POINTER(garp_protos[proto->group_address[5] -
                                               GARP_ADDR_MIN], NULL);
        synchronize_rcu();

        if (--sap_registered == 0)
                llc_sap_put(sap);
        mutex_unlock(&stp_proto_mutex);
}
EXPORT_SYMBOL_GPL(stp_proto_unregister);

MODULE_DESCRIPTION("SAP demux for IEEE 802.1D Spanning Tree Protocol (STP)");
MODULE_LICENSE("GPL");