llc_input.c revision 0dc47877a3de00ceadea0005189656ae8dc52669 
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/net_namespace.h>
16#include <net/llc.h>
17#include <net/llc_pdu.h>
18#include <net/llc_sap.h>
19
20#if 0
21#define dprintk(args...) printk(KERN_DEBUG args)
22#else
23#define dprintk(args...)
24#endif
25
26/*
27 * Packet handler for the station, registerable because in the minimal
28 * LLC core that is taking shape only the very minimal subset of LLC that
29 * is needed for things like IPX, Appletalk, etc will stay, with all the
30 * rest in the llc1 and llc2 modules.
31 */
32static void (*llc_station_handler)(struct sk_buff *skb);
33
34/*
35 * Packet handlers for LLC_DEST_SAP and LLC_DEST_CONN.
36 */
37static void (*llc_type_handlers[2])(struct llc_sap *sap,
38				    struct sk_buff *skb);
39
40void llc_add_pack(int type, void (*handler)(struct llc_sap *sap,
41					    struct sk_buff *skb))
42{
43	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
44		llc_type_handlers[type - 1] = handler;
45}
46
47void llc_remove_pack(int type)
48{
49	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
50		llc_type_handlers[type - 1] = NULL;
51}
52
53void llc_set_station_handler(void (*handler)(struct sk_buff *skb))
54{
55	llc_station_handler = handler;
56}
57
58/**
59 *	llc_pdu_type - returns which LLC component must handle for PDU
60 *	@skb: input skb
61 *
62 *	This function returns which LLC component must handle this PDU.
63 */
64static __inline__ int llc_pdu_type(struct sk_buff *skb)
65{
66	int type = LLC_DEST_CONN; /* I-PDU or S-PDU type */
67	struct llc_pdu_sn *pdu = llc_pdu_sn_hdr(skb);
68
69	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) != LLC_PDU_TYPE_U)
70		goto out;
71	switch (LLC_U_PDU_CMD(pdu)) {
72	case LLC_1_PDU_CMD_XID:
73	case LLC_1_PDU_CMD_UI:
74	case LLC_1_PDU_CMD_TEST:
75		type = LLC_DEST_SAP;
76		break;
77	case LLC_2_PDU_CMD_SABME:
78	case LLC_2_PDU_CMD_DISC:
79	case LLC_2_PDU_RSP_UA:
80	case LLC_2_PDU_RSP_DM:
81	case LLC_2_PDU_RSP_FRMR:
82		break;
83	default:
84		type = LLC_DEST_INVALID;
85		break;
86	}
87out:
88	return type;
89}
90
91/**
92 *	llc_fixup_skb - initializes skb pointers
93 *	@skb: This argument points to incoming skb
94 *
95 *	Initializes internal skb pointer to start of network layer by deriving
96 *	length of LLC header; finds length of LLC control field in LLC header
97 *	by looking at the two lowest-order bits of the first control field
98 *	byte; field is either 3 or 4 bytes long.
99 */
100static inline int llc_fixup_skb(struct sk_buff *skb)
101{
102	u8 llc_len = 2;
103	struct llc_pdu_un *pdu;
104
105	if (unlikely(!pskb_may_pull(skb, sizeof(*pdu))))
106		return 0;
107
108	pdu = (struct llc_pdu_un *)skb->data;
109	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) == LLC_PDU_TYPE_U)
110		llc_len = 1;
111	llc_len += 2;
112
113	if (unlikely(!pskb_may_pull(skb, llc_len)))
114		return 0;
115
116	skb->transport_header += llc_len;
117	skb_pull(skb, llc_len);
118	if (skb->protocol == htons(ETH_P_802_2)) {
119		__be16 pdulen = eth_hdr(skb)->h_proto;
120		u16 data_size = ntohs(pdulen) - llc_len;
121
122		if (unlikely(pskb_trim_rcsum(skb, data_size)))
123			return 0;
124	}
125	return 1;
126}
127
128/**
129 *	llc_rcv - 802.2 entry point from net lower layers
130 *	@skb: received pdu
131 *	@dev: device that receive pdu
132 *	@pt: packet type
133 *
134 *	When the system receives a 802.2 frame this function is called. It
135 *	checks SAP and connection of received pdu and passes frame to
136 *	llc_{station,sap,conn}_rcv for sending to proper state machine. If
137 *	the frame is related to a busy connection (a connection is sending
138 *	data now), it queues this frame in the connection's backlog.
139 */
140int llc_rcv(struct sk_buff *skb, struct net_device *dev,
141	    struct packet_type *pt, struct net_device *orig_dev)
142{
143	struct llc_sap *sap;
144	struct llc_pdu_sn *pdu;
145	int dest;
146	int (*rcv)(struct sk_buff *, struct net_device *,
147		   struct packet_type *, struct net_device *);
148
149	if (dev->nd_net != &init_net)
150		goto drop;
151
152	/*
153	 * When the interface is in promisc. mode, drop all the crap that it
154	 * receives, do not try to analyse it.
155	 */
156	if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) {
157		dprintk("%s: PACKET_OTHERHOST\n", __func__);
158		goto drop;
159	}
160	skb = skb_share_check(skb, GFP_ATOMIC);
161	if (unlikely(!skb))
162		goto out;
163	if (unlikely(!llc_fixup_skb(skb)))
164		goto drop;
165	pdu = llc_pdu_sn_hdr(skb);
166	if (unlikely(!pdu->dsap)) /* NULL DSAP, refer to station */
167	       goto handle_station;
168	sap = llc_sap_find(pdu->dsap);
169	if (unlikely(!sap)) {/* unknown SAP */
170		dprintk("%s: llc_sap_find(%02X) failed!\n", __func__,
171			pdu->dsap);
172		goto drop;
173	}
174	/*
175	 * First the upper layer protocols that don't need the full
176	 * LLC functionality
177	 */
178	rcv = rcu_dereference(sap->rcv_func);
179	if (rcv) {
180		struct sk_buff *cskb = skb_clone(skb, GFP_ATOMIC);
181		if (cskb)
182			rcv(cskb, dev, pt, orig_dev);
183	}
184	dest = llc_pdu_type(skb);
185	if (unlikely(!dest || !llc_type_handlers[dest - 1]))
186		goto drop_put;
187	llc_type_handlers[dest - 1](sap, skb);
188out_put:
189	llc_sap_put(sap);
190out:
191	return 0;
192drop:
193	kfree_skb(skb);
194	goto out;
195drop_put:
196	kfree_skb(skb);
197	goto out_put;
198handle_station:
199	if (!llc_station_handler)
200		goto drop;
201	llc_station_handler(skb);
202	goto out;
203}
204
205EXPORT_SYMBOL(llc_add_pack);
206EXPORT_SYMBOL(llc_remove_pack);
207EXPORT_SYMBOL(llc_set_station_handler);
208