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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  */
 34 static void (*llc_station_handler)(struct sk_buff *skb);
 35 
 36 /*
 37  * Packet handlers for LLC_DEST_SAP and LLC_DEST_CONN.
 38  */
 39 static void (*llc_type_handlers[2])(struct llc_sap *sap,
 40                                     struct sk_buff *skb);
 41 
 42 void 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 
 50 void 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 
 57 void 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  */
 75 static __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         }
 98 out:
 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  */
111 static 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  */
154 int 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);
211 out:
212         return 0;
213 drop:
214         kfree_skb(skb);
215         goto out;
216 handle_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 
224 EXPORT_SYMBOL(llc_add_pack);
225 EXPORT_SYMBOL(llc_remove_pack);
226 EXPORT_SYMBOL(llc_set_station_handler);
227 

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