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 <net/net_namespace.h>
17 #include <net/llc.h>
18 #include <net/llc_pdu.h>
19 #include <net/llc_sap.h>
20 
21 #if 0
22 #define dprintk(args...) printk(KERN_DEBUG args)
23 #else
24 #define dprintk(args...)
25 #endif
26 
27 /*
28  * Packet handler for the station, registerable because in the minimal
29  * LLC core that is taking shape only the very minimal subset of LLC that
30  * is needed for things like IPX, Appletalk, etc will stay, with all the
31  * rest in the llc1 and llc2 modules.
32  */
33 static void (*llc_station_handler)(struct sk_buff *skb);
34 
35 /*
36  * Packet handlers for LLC_DEST_SAP and LLC_DEST_CONN.
37  */
38 static void (*llc_type_handlers[2])(struct llc_sap *sap,
39 				    struct sk_buff *skb);
40 
llc_add_pack(int type,void (* handler)(struct llc_sap * sap,struct sk_buff * skb))41 void llc_add_pack(int type, void (*handler)(struct llc_sap *sap,
42 					    struct sk_buff *skb))
43 {
44 	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
45 		llc_type_handlers[type - 1] = handler;
46 }
47 
llc_remove_pack(int type)48 void llc_remove_pack(int type)
49 {
50 	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
51 		llc_type_handlers[type - 1] = NULL;
52 }
53 
llc_set_station_handler(void (* handler)(struct sk_buff * skb))54 void llc_set_station_handler(void (*handler)(struct sk_buff *skb))
55 {
56 	llc_station_handler = handler;
57 }
58 
59 /**
60  *	llc_pdu_type - returns which LLC component must handle for PDU
61  *	@skb: input skb
62  *
63  *	This function returns which LLC component must handle this PDU.
64  */
llc_pdu_type(struct sk_buff * skb)65 static __inline__ int llc_pdu_type(struct sk_buff *skb)
66 {
67 	int type = LLC_DEST_CONN; /* I-PDU or S-PDU type */
68 	struct llc_pdu_sn *pdu = llc_pdu_sn_hdr(skb);
69 
70 	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) != LLC_PDU_TYPE_U)
71 		goto out;
72 	switch (LLC_U_PDU_CMD(pdu)) {
73 	case LLC_1_PDU_CMD_XID:
74 	case LLC_1_PDU_CMD_UI:
75 	case LLC_1_PDU_CMD_TEST:
76 		type = LLC_DEST_SAP;
77 		break;
78 	case LLC_2_PDU_CMD_SABME:
79 	case LLC_2_PDU_CMD_DISC:
80 	case LLC_2_PDU_RSP_UA:
81 	case LLC_2_PDU_RSP_DM:
82 	case LLC_2_PDU_RSP_FRMR:
83 		break;
84 	default:
85 		type = LLC_DEST_INVALID;
86 		break;
87 	}
88 out:
89 	return type;
90 }
91 
92 /**
93  *	llc_fixup_skb - initializes skb pointers
94  *	@skb: This argument points to incoming skb
95  *
96  *	Initializes internal skb pointer to start of network layer by deriving
97  *	length of LLC header; finds length of LLC control field in LLC header
98  *	by looking at the two lowest-order bits of the first control field
99  *	byte; field is either 3 or 4 bytes long.
100  */
llc_fixup_skb(struct sk_buff * skb)101 static inline int llc_fixup_skb(struct sk_buff *skb)
102 {
103 	u8 llc_len = 2;
104 	struct llc_pdu_un *pdu;
105 
106 	if (unlikely(!pskb_may_pull(skb, sizeof(*pdu))))
107 		return 0;
108 
109 	pdu = (struct llc_pdu_un *)skb->data;
110 	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) == LLC_PDU_TYPE_U)
111 		llc_len = 1;
112 	llc_len += 2;
113 
114 	if (unlikely(!pskb_may_pull(skb, llc_len)))
115 		return 0;
116 
117 	skb->transport_header += llc_len;
118 	skb_pull(skb, llc_len);
119 	if (skb->protocol == htons(ETH_P_802_2)) {
120 		__be16 pdulen = eth_hdr(skb)->h_proto;
121 		s32 data_size = ntohs(pdulen) - llc_len;
122 
123 		if (data_size < 0 ||
124 		    !pskb_may_pull(skb, data_size))
125 			return 0;
126 		if (unlikely(pskb_trim_rcsum(skb, data_size)))
127 			return 0;
128 	}
129 	return 1;
130 }
131 
132 /**
133  *	llc_rcv - 802.2 entry point from net lower layers
134  *	@skb: received pdu
135  *	@dev: device that receive pdu
136  *	@pt: packet type
137  *
138  *	When the system receives a 802.2 frame this function is called. It
139  *	checks SAP and connection of received pdu and passes frame to
140  *	llc_{station,sap,conn}_rcv for sending to proper state machine. If
141  *	the frame is related to a busy connection (a connection is sending
142  *	data now), it queues this frame in the connection's backlog.
143  */
llc_rcv(struct sk_buff * skb,struct net_device * dev,struct packet_type * pt,struct net_device * orig_dev)144 int llc_rcv(struct sk_buff *skb, struct net_device *dev,
145 	    struct packet_type *pt, struct net_device *orig_dev)
146 {
147 	struct llc_sap *sap;
148 	struct llc_pdu_sn *pdu;
149 	int dest;
150 	int (*rcv)(struct sk_buff *, struct net_device *,
151 		   struct packet_type *, struct net_device *);
152 
153 	if (!net_eq(dev_net(dev), &init_net))
154 		goto drop;
155 
156 	/*
157 	 * When the interface is in promisc. mode, drop all the crap that it
158 	 * receives, do not try to analyse it.
159 	 */
160 	if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) {
161 		dprintk("%s: PACKET_OTHERHOST\n", __func__);
162 		goto drop;
163 	}
164 	skb = skb_share_check(skb, GFP_ATOMIC);
165 	if (unlikely(!skb))
166 		goto out;
167 	if (unlikely(!llc_fixup_skb(skb)))
168 		goto drop;
169 	pdu = llc_pdu_sn_hdr(skb);
170 	if (unlikely(!pdu->dsap)) /* NULL DSAP, refer to station */
171 	       goto handle_station;
172 	sap = llc_sap_find(pdu->dsap);
173 	if (unlikely(!sap)) {/* unknown SAP */
174 		dprintk("%s: llc_sap_find(%02X) failed!\n", __func__,
175 			pdu->dsap);
176 		goto drop;
177 	}
178 	/*
179 	 * First the upper layer protocols that don't need the full
180 	 * LLC functionality
181 	 */
182 	rcv = rcu_dereference(sap->rcv_func);
183 	dest = llc_pdu_type(skb);
184 	if (unlikely(!dest || !llc_type_handlers[dest - 1])) {
185 		if (rcv)
186 			rcv(skb, dev, pt, orig_dev);
187 		else
188 			kfree_skb(skb);
189 	} else {
190 		if (rcv) {
191 			struct sk_buff *cskb = skb_clone(skb, GFP_ATOMIC);
192 			if (cskb)
193 				rcv(cskb, dev, pt, orig_dev);
194 		}
195 		llc_type_handlers[dest - 1](sap, skb);
196 	}
197 	llc_sap_put(sap);
198 out:
199 	return 0;
200 drop:
201 	kfree_skb(skb);
202 	goto out;
203 handle_station:
204 	if (!llc_station_handler)
205 		goto drop;
206 	llc_station_handler(skb);
207 	goto out;
208 }
209 
210 EXPORT_SYMBOL(llc_add_pack);
211 EXPORT_SYMBOL(llc_remove_pack);
212 EXPORT_SYMBOL(llc_set_station_handler);
213