llc_input.c revision d57b1869b231c56de441db35c647879d51c5d29e 
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 <net/llc.h>
16#include <net/llc_pdu.h>
17#include <net/llc_sap.h>
18
19#if 0
20#define dprintk(args...) printk(KERN_DEBUG args)
21#else
22#define dprintk(args...)
23#endif
24
25/*
26 * Packet handler for the station, registerable because in the minimal
27 * LLC core that is taking shape only the very minimal subset of LLC that
28 * is needed for things like IPX, Appletalk, etc will stay, with all the
29 * rest in the llc1 and llc2 modules.
30 */
31static void (*llc_station_handler)(struct sk_buff *skb);
32
33/*
34 * Packet handlers for LLC_DEST_SAP and LLC_DEST_CONN.
35 */
36static void (*llc_type_handlers[2])(struct llc_sap *sap,
37				    struct sk_buff *skb);
38
39void llc_add_pack(int type, void (*handler)(struct llc_sap *sap,
40					    struct sk_buff *skb))
41{
42	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
43		llc_type_handlers[type - 1] = handler;
44}
45
46void llc_remove_pack(int type)
47{
48	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
49		llc_type_handlers[type - 1] = NULL;
50}
51
52void llc_set_station_handler(void (*handler)(struct sk_buff *skb))
53{
54	llc_station_handler = handler;
55}
56
57/**
58 *	llc_pdu_type - returns which LLC component must handle for PDU
59 *	@skb: input skb
60 *
61 *	This function returns which LLC component must handle this PDU.
62 */
63static __inline__ int llc_pdu_type(struct sk_buff *skb)
64{
65	int type = LLC_DEST_CONN; /* I-PDU or S-PDU type */
66	struct llc_pdu_sn *pdu = llc_pdu_sn_hdr(skb);
67
68	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) != LLC_PDU_TYPE_U)
69		goto out;
70	switch (LLC_U_PDU_CMD(pdu)) {
71	case LLC_1_PDU_CMD_XID:
72	case LLC_1_PDU_CMD_UI:
73	case LLC_1_PDU_CMD_TEST:
74		type = LLC_DEST_SAP;
75		break;
76	case LLC_2_PDU_CMD_SABME:
77	case LLC_2_PDU_CMD_DISC:
78	case LLC_2_PDU_RSP_UA:
79	case LLC_2_PDU_RSP_DM:
80	case LLC_2_PDU_RSP_FRMR:
81		break;
82	default:
83		type = LLC_DEST_INVALID;
84		break;
85	}
86out:
87	return type;
88}
89
90/**
91 *	llc_fixup_skb - initializes skb pointers
92 *	@skb: This argument points to incoming skb
93 *
94 *	Initializes internal skb pointer to start of network layer by deriving
95 *	length of LLC header; finds length of LLC control field in LLC header
96 *	by looking at the two lowest-order bits of the first control field
97 *	byte; field is either 3 or 4 bytes long.
98 */
99static inline int llc_fixup_skb(struct sk_buff *skb)
100{
101	u8 llc_len = 2;
102	struct llc_pdu_un *pdu;
103
104	if (unlikely(!pskb_may_pull(skb, sizeof(*pdu))))
105		return 0;
106
107	pdu = (struct llc_pdu_un *)skb->data;
108	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) == LLC_PDU_TYPE_U)
109		llc_len = 1;
110	llc_len += 2;
111
112	if (unlikely(!pskb_may_pull(skb, llc_len)))
113		return 0;
114
115	skb->h.raw += llc_len;
116	skb_pull(skb, llc_len);
117	if (skb->protocol == htons(ETH_P_802_2)) {
118		__be16 pdulen = eth_hdr(skb)->h_proto;
119		u16 data_size = ntohs(pdulen) - llc_len;
120
121		if (unlikely(pskb_trim_rcsum(skb, data_size)))
122			return 0;
123	}
124	return 1;
125}
126
127/**
128 *	llc_rcv - 802.2 entry point from net lower layers
129 *	@skb: received pdu
130 *	@dev: device that receive pdu
131 *	@pt: packet type
132 *
133 *	When the system receives a 802.2 frame this function is called. It
134 *	checks SAP and connection of received pdu and passes frame to
135 *	llc_{station,sap,conn}_rcv for sending to proper state machine. If
136 *	the frame is related to a busy connection (a connection is sending
137 *	data now), it queues this frame in the connection's backlog.
138 */
139int llc_rcv(struct sk_buff *skb, struct net_device *dev,
140	    struct packet_type *pt, struct net_device *orig_dev)
141{
142	struct llc_sap *sap;
143	struct llc_pdu_sn *pdu;
144	int dest;
145	int (*rcv)(struct sk_buff *, struct net_device *,
146		   struct packet_type *, struct net_device *);
147
148	/*
149	 * When the interface is in promisc. mode, drop all the crap that it
150	 * receives, do not try to analyse it.
151	 */
152	if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) {
153		dprintk("%s: PACKET_OTHERHOST\n", __FUNCTION__);
154		goto drop;
155	}
156	skb = skb_share_check(skb, GFP_ATOMIC);
157	if (unlikely(!skb))
158		goto out;
159	if (unlikely(!llc_fixup_skb(skb)))
160		goto drop;
161	pdu = llc_pdu_sn_hdr(skb);
162	if (unlikely(!pdu->dsap)) /* NULL DSAP, refer to station */
163	       goto handle_station;
164	sap = llc_sap_find(pdu->dsap);
165	if (unlikely(!sap)) {/* unknown SAP */
166		dprintk("%s: llc_sap_find(%02X) failed!\n", __FUNCTION__,
167			pdu->dsap);
168		goto drop;
169	}
170	/*
171	 * First the upper layer protocols that don't need the full
172	 * LLC functionality
173	 */
174	rcv = rcu_dereference(sap->rcv_func);
175	if (rcv) {
176		struct sk_buff *cskb = skb_clone(skb, GFP_ATOMIC);
177		if (cskb)
178			rcv(cskb, dev, pt, orig_dev);
179	}
180	dest = llc_pdu_type(skb);
181	if (unlikely(!dest || !llc_type_handlers[dest - 1]))
182		goto drop_put;
183	llc_type_handlers[dest - 1](sap, skb);
184out_put:
185	llc_sap_put(sap);
186out:
187	return 0;
188drop:
189	kfree_skb(skb);
190	goto out;
191drop_put:
192	kfree_skb(skb);
193	goto out_put;
194handle_station:
195	if (!llc_station_handler)
196		goto drop;
197	llc_station_handler(skb);
198	goto out;
199}
200
201EXPORT_SYMBOL(llc_add_pack);
202EXPORT_SYMBOL(llc_remove_pack);
203EXPORT_SYMBOL(llc_set_station_handler);
204