llc_input.c

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/*
 * llc_input.c - Minimal input path for LLC
 *
 * Copyright (c) 1997 by Procom Technology, Inc.
 *       2001-2003 by Arnaldo Carvalho de Melo <[email protected]>
 *
 * 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();
}

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;
}

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;
}

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 ? ACCESS_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 = ACCESS_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);