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;
131		s32 data_size;
132
133		if (skb->mac_len < ETH_HLEN)
134			return 0;
135
136		pdulen = eth_hdr(skb)->h_proto;
137		data_size = ntohs(pdulen) - llc_len;
138
139		if (data_size < 0 ||
140		    !pskb_may_pull(skb, data_size))
141			return 0;
142		if (unlikely(pskb_trim_rcsum(skb, data_size)))
143			return 0;
144	}
145	return 1;
146}
147
148/**
149 *	llc_rcv - 802.2 entry point from net lower layers
150 *	@skb: received pdu
151 *	@dev: device that receive pdu
152 *	@pt: packet type
153 *	@orig_dev: the original receive net device
154 *
155 *	When the system receives a 802.2 frame this function is called. It
156 *	checks SAP and connection of received pdu and passes frame to
157 *	llc_{station,sap,conn}_rcv for sending to proper state machine. If
158 *	the frame is related to a busy connection (a connection is sending
159 *	data now), it queues this frame in the connection's backlog.
160 */
161int llc_rcv(struct sk_buff *skb, struct net_device *dev,
162	    struct packet_type *pt, struct net_device *orig_dev)
163{
164	struct llc_sap *sap;
165	struct llc_pdu_sn *pdu;
166	int dest;
167	int (*rcv)(struct sk_buff *, struct net_device *,
168		   struct packet_type *, struct net_device *);
169	void (*sta_handler)(struct sk_buff *skb);
170	void (*sap_handler)(struct llc_sap *sap, struct sk_buff *skb);
171
172	/*
173	 * When the interface is in promisc. mode, drop all the crap that it
174	 * receives, do not try to analyse it.
175	 */
176	if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) {
177		dprintk("%s: PACKET_OTHERHOST\n", __func__);
178		goto drop;
179	}
180	skb = skb_share_check(skb, GFP_ATOMIC);
181	if (unlikely(!skb))
182		goto out;
183	if (unlikely(!llc_fixup_skb(skb)))
184		goto drop;
185	pdu = llc_pdu_sn_hdr(skb);
186	if (unlikely(!pdu->dsap)) /* NULL DSAP, refer to station */
187	       goto handle_station;
188	sap = llc_sap_find(pdu->dsap);
189	if (unlikely(!sap)) {/* unknown SAP */
190		dprintk("%s: llc_sap_find(%02X) failed!\n", __func__,
191			pdu->dsap);
192		goto drop;
193	}
194	/*
195	 * First the upper layer protocols that don't need the full
196	 * LLC functionality
197	 */
198	rcv = rcu_dereference(sap->rcv_func);
199	dest = llc_pdu_type(skb);
200	sap_handler = dest ? READ_ONCE(llc_type_handlers[dest - 1]) : NULL;
201	if (unlikely(!sap_handler)) {
202		if (rcv)
203			rcv(skb, dev, pt, orig_dev);
204		else
205			kfree_skb(skb);
206	} else {
207		if (rcv) {
208			struct sk_buff *cskb = skb_clone(skb, GFP_ATOMIC);
209			if (cskb)
210				rcv(cskb, dev, pt, orig_dev);
211		}
212		sap_handler(sap, skb);
213	}
214	llc_sap_put(sap);
215out:
216	return 0;
217drop:
218	kfree_skb(skb);
219	goto out;
220handle_station:
221	sta_handler = READ_ONCE(llc_station_handler);
222	if (!sta_handler)
223		goto drop;
224	sta_handler(skb);
225	goto out;
226}
227
228EXPORT_SYMBOL(llc_add_pack);
229EXPORT_SYMBOL(llc_remove_pack);
230EXPORT_SYMBOL(llc_set_station_handler);
231