linux/net/llc/llc_input.c
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   1/*
   2 * llc_input.c - Minimal input path for LLC
   3 *
   4 * Copyright (c) 1997 by Procom Technology, Inc.
   5 *               2001-2003 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
   6 *
   7 * This program can be redistributed or modified under the terms of the
   8 * GNU General Public License as published by the Free Software Foundation.
   9 * This program is distributed without any warranty or implied warranty
  10 * of merchantability or fitness for a particular purpose.
  11 *
  12 * See the GNU General Public License for more details.
  13 */
  14#include <linux/netdevice.h>
  15#include <linux/slab.h>
  16#include <linux/export.h>
  17#include <net/net_namespace.h>
  18#include <net/llc.h>
  19#include <net/llc_pdu.h>
  20#include <net/llc_sap.h>
  21
  22#if 0
  23#define dprintk(args...) printk(KERN_DEBUG args)
  24#else
  25#define dprintk(args...)
  26#endif
  27
  28/*
  29 * Packet handler for the station, registerable because in the minimal
  30 * LLC core that is taking shape only the very minimal subset of LLC that
  31 * is needed for things like IPX, Appletalk, etc will stay, with all the
  32 * rest in the llc1 and llc2 modules.
  33 */
  34static void (*llc_station_handler)(struct sk_buff *skb);
  35
  36/*
  37 * Packet handlers for LLC_DEST_SAP and LLC_DEST_CONN.
  38 */
  39static void (*llc_type_handlers[2])(struct llc_sap *sap,
  40                                    struct sk_buff *skb);
  41
  42void llc_add_pack(int type, void (*handler)(struct llc_sap *sap,
  43                                            struct sk_buff *skb))
  44{
  45        smp_wmb(); /* ensure initialisation is complete before it's called */
  46        if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
  47                llc_type_handlers[type - 1] = handler;
  48}
  49
  50void llc_remove_pack(int type)
  51{
  52        if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
  53                llc_type_handlers[type - 1] = NULL;
  54        synchronize_net();
  55}
  56
  57void llc_set_station_handler(void (*handler)(struct sk_buff *skb))
  58{
  59        /* Ensure initialisation is complete before it's called */
  60        if (handler)
  61                smp_wmb();
  62
  63        llc_station_handler = handler;
  64
  65        if (!handler)
  66                synchronize_net();
  67}
  68
  69/**
  70 *      llc_pdu_type - returns which LLC component must handle for PDU
  71 *      @skb: input skb
  72 *
  73 *      This function returns which LLC component must handle this PDU.
  74 */
  75static __inline__ int llc_pdu_type(struct sk_buff *skb)
  76{
  77        int type = LLC_DEST_CONN; /* I-PDU or S-PDU type */
  78        struct llc_pdu_sn *pdu = llc_pdu_sn_hdr(skb);
  79
  80        if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) != LLC_PDU_TYPE_U)
  81                goto out;
  82        switch (LLC_U_PDU_CMD(pdu)) {
  83        case LLC_1_PDU_CMD_XID:
  84        case LLC_1_PDU_CMD_UI:
  85        case LLC_1_PDU_CMD_TEST:
  86                type = LLC_DEST_SAP;
  87                break;
  88        case LLC_2_PDU_CMD_SABME:
  89        case LLC_2_PDU_CMD_DISC:
  90        case LLC_2_PDU_RSP_UA:
  91        case LLC_2_PDU_RSP_DM:
  92        case LLC_2_PDU_RSP_FRMR:
  93                break;
  94        default:
  95                type = LLC_DEST_INVALID;
  96                break;
  97        }
  98out:
  99        return type;
 100}
 101
 102/**
 103 *      llc_fixup_skb - initializes skb pointers
 104 *      @skb: This argument points to incoming skb
 105 *
 106 *      Initializes internal skb pointer to start of network layer by deriving
 107 *      length of LLC header; finds length of LLC control field in LLC header
 108 *      by looking at the two lowest-order bits of the first control field
 109 *      byte; field is either 3 or 4 bytes long.
 110 */
 111static inline int llc_fixup_skb(struct sk_buff *skb)
 112{
 113        u8 llc_len = 2;
 114        struct llc_pdu_un *pdu;
 115
 116        if (unlikely(!pskb_may_pull(skb, sizeof(*pdu))))
 117                return 0;
 118
 119        pdu = (struct llc_pdu_un *)skb->data;
 120        if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) == LLC_PDU_TYPE_U)
 121                llc_len = 1;
 122        llc_len += 2;
 123
 124        if (unlikely(!pskb_may_pull(skb, llc_len)))
 125                return 0;
 126
 127        skb->transport_header += llc_len;
 128        skb_pull(skb, llc_len);
 129        if (skb->protocol == htons(ETH_P_802_2)) {
 130                __be16 pdulen = eth_hdr(skb)->h_proto;
 131                s32 data_size = ntohs(pdulen) - llc_len;
 132
 133                if (data_size < 0 ||
 134                    !pskb_may_pull(skb, data_size))
 135                        return 0;
 136                if (unlikely(pskb_trim_rcsum(skb, data_size)))
 137                        return 0;
 138        }
 139        return 1;
 140}
 141
 142/**
 143 *      llc_rcv - 802.2 entry point from net lower layers
 144 *      @skb: received pdu
 145 *      @dev: device that receive pdu
 146 *      @pt: packet type
 147 *
 148 *      When the system receives a 802.2 frame this function is called. It
 149 *      checks SAP and connection of received pdu and passes frame to
 150 *      llc_{station,sap,conn}_rcv for sending to proper state machine. If
 151 *      the frame is related to a busy connection (a connection is sending
 152 *      data now), it queues this frame in the connection's backlog.
 153 */
 154int llc_rcv(struct sk_buff *skb, struct net_device *dev,
 155            struct packet_type *pt, struct net_device *orig_dev)
 156{
 157        struct llc_sap *sap;
 158        struct llc_pdu_sn *pdu;
 159        int dest;
 160        int (*rcv)(struct sk_buff *, struct net_device *,
 161                   struct packet_type *, struct net_device *);
 162        void (*sta_handler)(struct sk_buff *skb);
 163        void (*sap_handler)(struct llc_sap *sap, struct sk_buff *skb);
 164
 165        if (!net_eq(dev_net(dev), &init_net))
 166                goto drop;
 167
 168        /*
 169         * When the interface is in promisc. mode, drop all the crap that it
 170         * receives, do not try to analyse it.
 171         */
 172        if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) {
 173                dprintk("%s: PACKET_OTHERHOST\n", __func__);
 174                goto drop;
 175        }
 176        skb = skb_share_check(skb, GFP_ATOMIC);
 177        if (unlikely(!skb))
 178                goto out;
 179        if (unlikely(!llc_fixup_skb(skb)))
 180                goto drop;
 181        pdu = llc_pdu_sn_hdr(skb);
 182        if (unlikely(!pdu->dsap)) /* NULL DSAP, refer to station */
 183               goto handle_station;
 184        sap = llc_sap_find(pdu->dsap);
 185        if (unlikely(!sap)) {/* unknown SAP */
 186                dprintk("%s: llc_sap_find(%02X) failed!\n", __func__,
 187                        pdu->dsap);
 188                goto drop;
 189        }
 190        /*
 191         * First the upper layer protocols that don't need the full
 192         * LLC functionality
 193         */
 194        rcv = rcu_dereference(sap->rcv_func);
 195        dest = llc_pdu_type(skb);
 196        sap_handler = dest ? ACCESS_ONCE(llc_type_handlers[dest - 1]) : NULL;
 197        if (unlikely(!sap_handler)) {
 198                if (rcv)
 199                        rcv(skb, dev, pt, orig_dev);
 200                else
 201                        kfree_skb(skb);
 202        } else {
 203                if (rcv) {
 204                        struct sk_buff *cskb = skb_clone(skb, GFP_ATOMIC);
 205                        if (cskb)
 206                                rcv(cskb, dev, pt, orig_dev);
 207                }
 208                sap_handler(sap, skb);
 209        }
 210        llc_sap_put(sap);
 211out:
 212        return 0;
 213drop:
 214        kfree_skb(skb);
 215        goto out;
 216handle_station:
 217        sta_handler = ACCESS_ONCE(llc_station_handler);
 218        if (!sta_handler)
 219                goto drop;
 220        sta_handler(skb);
 221        goto out;
 222}
 223
 224EXPORT_SYMBOL(llc_add_pack);
 225EXPORT_SYMBOL(llc_remove_pack);
 226EXPORT_SYMBOL(llc_set_station_handler);
 227
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