/*
 * llc_input.c - Minimal input path for LLC
 *
 * Copyright (c) 1997 by Procom Technology, Inc.
 *               2001-2003 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 *
 * This program can be redistributed or modified under the terms of the
 * GNU General Public License as published by the Free Software Foundation.
 * This program is distributed without any warranty or implied warranty
 * of merchantability or fitness for a particular purpose.
 *
 * See the GNU General Public License for more details.
 */
#include <linux/netdevice.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <net/net_namespace.h>
#include <net/llc.h>
#include <net/llc_pdu.h>
#include <net/llc_sap.h>

#if 0
#define dprintk(args...) printk(KERN_DEBUG args)
#else
#define dprintk(args...)
#endif

/*
 * Packet handler for the station, registerable because in the minimal
 * LLC core that is taking shape only the very minimal subset of LLC that
 * is needed for things like IPX, Appletalk, etc will stay, with all the
 * rest in the llc1 and llc2 modules.
 */
static void (*llc_station_handler)(struct sk_buff *skb);

/*
 * Packet handlers for LLC_DEST_SAP and LLC_DEST_CONN.
 */
static void (*llc_type_handlers[2])(struct llc_sap *sap,
                                    struct sk_buff *skb);

void llc_add_pack(int type, void (*handler)(struct llc_sap *sap,
                                            struct sk_buff *skb))
{
        smp_wmb(); /* ensure initialisation is complete before it's called */
        if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
                llc_type_handlers[type - 1] = handler;
}

void llc_remove_pack(int type)
{
        if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
                llc_type_handlers[type - 1] = NULL;
        synchronize_net();
}

void llc_set_station_handler(void (*handler)(struct sk_buff *skb))
{
        /* Ensure initialisation is complete before it's called */
        if (handler)
                smp_wmb();

        llc_station_handler = handler;

        if (!handler)
                synchronize_net();
}

/**
 *      llc_pdu_type - returns which LLC component must handle for PDU
 *      @skb: input skb
 *
 *      This function returns which LLC component must handle this PDU.
 */
static __inline__ int llc_pdu_type(struct sk_buff *skb)
{
        int type = LLC_DEST_CONN; /* I-PDU or S-PDU type */
        struct llc_pdu_sn *pdu = llc_pdu_sn_hdr(skb);

        if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) != LLC_PDU_TYPE_U)
                goto out;
        switch (LLC_U_PDU_CMD(pdu)) {
        case LLC_1_PDU_CMD_XID:
        case LLC_1_PDU_CMD_UI:
        case LLC_1_PDU_CMD_TEST:
                type = LLC_DEST_SAP;
                break;
        case LLC_2_PDU_CMD_SABME:
        case LLC_2_PDU_CMD_DISC:
        case LLC_2_PDU_RSP_UA:
        case LLC_2_PDU_RSP_DM:
        case LLC_2_PDU_RSP_FRMR:
                break;
        default:
                type = LLC_DEST_INVALID;
                break;
        }
out:
        return type;
}

/**
 *      llc_fixup_skb - initializes skb pointers
 *      @skb: This argument points to incoming skb
 *
 *      Initializes internal skb pointer to start of network layer by deriving
 *      length of LLC header; finds length of LLC control field in LLC header
 *      by looking at the two lowest-order bits of the first control field
 *      byte; field is either 3 or 4 bytes long.
 */
static inline int llc_fixup_skb(struct sk_buff *skb)
{
        u8 llc_len = 2;
        struct llc_pdu_un *pdu;

        if (unlikely(!pskb_may_pull(skb, sizeof(*pdu))))
                return 0;

        pdu = (struct llc_pdu_un *)skb->data;
        if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) == LLC_PDU_TYPE_U)
                llc_len = 1;
        llc_len += 2;

        if (unlikely(!pskb_may_pull(skb, llc_len)))
                return 0;

        skb->transport_header += llc_len;
        skb_pull(skb, llc_len);
        if (skb->protocol == htons(ETH_P_802_2)) {
                __be16 pdulen = eth_hdr(skb)->h_proto;
                s32 data_size = ntohs(pdulen) - llc_len;

                if (data_size < 0 ||
                    !pskb_may_pull(skb, data_size))
                        return 0;
                if (unlikely(pskb_trim_rcsum(skb, data_size)))
                        return 0;
        }
        return 1;
}

/**
 *      llc_rcv - 802.2 entry point from net lower layers
 *      @skb: received pdu
 *      @dev: device that receive pdu
 *      @pt: packet type
 *
 *      When the system receives a 802.2 frame this function is called. It
 *      checks SAP and connection of received pdu and passes frame to
 *      llc_{station,sap,conn}_rcv for sending to proper state machine. If
 *      the frame is related to a busy connection (a connection is sending
 *      data now), it queues this frame in the connection's backlog.
 */
int llc_rcv(struct sk_buff *skb, struct net_device *dev,
            struct packet_type *pt, struct net_device *orig_dev)
{
        struct llc_sap *sap;
        struct llc_pdu_sn *pdu;
        int dest;
        int (*rcv)(struct sk_buff *, struct net_device *,
                   struct packet_type *, struct net_device *);
        void (*sta_handler)(struct sk_buff *skb);
        void (*sap_handler)(struct llc_sap *sap, struct sk_buff *skb);

        if (!net_eq(dev_net(dev), &init_net))
                goto drop;

        /*
         * When the interface is in promisc. mode, drop all the crap that it
         * receives, do not try to analyse it.
         */
        if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) {
                dprintk("%s: PACKET_OTHERHOST\n", __func__);
                goto drop;
        }
        skb = skb_share_check(skb, GFP_ATOMIC);
        if (unlikely(!skb))
                goto out;
        if (unlikely(!llc_fixup_skb(skb)))
                goto drop;
        pdu = llc_pdu_sn_hdr(skb);
        if (unlikely(!pdu->dsap)) /* NULL DSAP, refer to station */
               goto handle_station;
        sap = llc_sap_find(pdu->dsap);
        if (unlikely(!sap)) {/* unknown SAP */
                dprintk("%s: llc_sap_find(%02X) failed!\n", __func__,
                        pdu->dsap);
                goto drop;
        }
        /*
         * First the upper layer protocols that don't need the full
         * LLC functionality
         */
        rcv = rcu_dereference(sap->rcv_func);
        dest = llc_pdu_type(skb);
        sap_handler = dest ? READ_ONCE(llc_type_handlers[dest - 1]) : NULL;
        if (unlikely(!sap_handler)) {
                if (rcv)
                        rcv(skb, dev, pt, orig_dev);
                else
                        kfree_skb(skb);
        } else {
                if (rcv) {
                        struct sk_buff *cskb = skb_clone(skb, GFP_ATOMIC);
                        if (cskb)
                                rcv(cskb, dev, pt, orig_dev);
                }
                sap_handler(sap, skb);
        }
        llc_sap_put(sap);
out:
        return 0;
drop:
        kfree_skb(skb);
        goto out;
handle_station:
        sta_handler = READ_ONCE(llc_station_handler);
        if (!sta_handler)
                goto drop;
        sta_handler(skb);
        goto out;
}

EXPORT_SYMBOL(llc_add_pack);
EXPORT_SYMBOL(llc_remove_pack);
EXPORT_SYMBOL(llc_set_station_handler);