net/llc/llc_input.c

// SPDX-License-Identifier: GPL-2.0
/*
 * llc_input.c - Minimal input path for LLC
 *
 * Copyright (c) 1997 by Procom Technology, Inc.
 * 		 2001-2003 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 */
#include <linux/netdevice.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <net/net_namespace.h>
#include <net/llc.h>
#include <net/llc_pdu.h>
#include <net/llc_sap.h>

#if 0
#define dprintk(args...) printk(KERN_DEBUG args)
#else
#define dprintk(args...)
#endif

/*
 * Packet handler for the station, registerable because in the minimal
 * LLC core that is taking shape only the very minimal subset of LLC that
 * is needed for things like IPX, Appletalk, etc will stay, with all the
 * rest in the llc1 and llc2 modules.
 */
static void (*llc_station_handler)(struct sk_buff *skb);

/*
 * Packet handlers for LLC_DEST_SAP and LLC_DEST_CONN.
 */
static void (*llc_type_handlers[2])(struct llc_sap *sap,
				    struct sk_buff *skb);

void llc_add_pack(int type, void (*handler)(struct llc_sap *sap,
					    struct sk_buff *skb))
{
	smp_wmb(); /* ensure initialisation is complete before it's called */
	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
		llc_type_handlers[type - 1] = handler;
}

void llc_remove_pack(int type)
{
	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
		llc_type_handlers[type - 1] = NULL;
	synchronize_net();
}

void llc_set_station_handler(void (*handler)(struct sk_buff *skb))
{
	/* Ensure initialisation is complete before it's called */
	if (handler)
		smp_wmb();

	llc_station_handler = handler;

	if (!handler)
		synchronize_net();
}

/**
 *	llc_pdu_type - returns which LLC component must handle for PDU
 *	@skb: input skb
 *
 *	This function returns which LLC component must handle this PDU.
 */
static __inline__ int llc_pdu_type(struct sk_buff *skb)
{
	int type = LLC_DEST_CONN; /* I-PDU or S-PDU type */
	struct llc_pdu_sn *pdu = llc_pdu_sn_hdr(skb);

	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) != LLC_PDU_TYPE_U)
		goto out;
	switch (LLC_U_PDU_CMD(pdu)) {
	case LLC_1_PDU_CMD_XID:
	case LLC_1_PDU_CMD_UI:
	case LLC_1_PDU_CMD_TEST:
		type = LLC_DEST_SAP;
		break;
	case LLC_2_PDU_CMD_SABME:
	case LLC_2_PDU_CMD_DISC:
	case LLC_2_PDU_RSP_UA:
	case LLC_2_PDU_RSP_DM:
	case LLC_2_PDU_RSP_FRMR:
		break;
	default:
		type = LLC_DEST_INVALID;
		break;
	}
out:
	return type;
}

/**
 *	llc_fixup_skb - initializes skb pointers
 *	@skb: This argument points to incoming skb
 *
 *	Initializes internal skb pointer to start of network layer by deriving
 *	length of LLC header; finds length of LLC control field in LLC header
 *	by looking at the two lowest-order bits of the first control field
 *	byte; field is either 3 or 4 bytes long.
 */
static inline int llc_fixup_skb(struct sk_buff *skb)
{
	u8 llc_len = 2;
	struct llc_pdu_un *pdu;

	if (unlikely(!pskb_may_pull(skb, sizeof(*pdu))))
		return 0;

	pdu = (struct llc_pdu_un *)skb->data;
	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) == LLC_PDU_TYPE_U)
		llc_len = 1;
	llc_len += 2;

	if (unlikely(!pskb_may_pull(skb, llc_len)))
		return 0;

	skb_pull(skb, llc_len);
	skb_reset_transport_header(skb);
	if (skb->protocol == htons(ETH_P_802_2)) {
		__be16 pdulen;
		s32 data_size;

		if (skb->mac_len < ETH_HLEN)
			return 0;

		pdulen = eth_hdr(skb)->h_proto;
		data_size = ntohs(pdulen) - llc_len;

		if (data_size < 0 ||
		    !pskb_may_pull(skb, data_size))
			return 0;
		if (unlikely(pskb_trim_rcsum(skb, data_size)))
			return 0;
	}
	return 1;
}

/**
 *	llc_rcv - 802.2 entry point from net lower layers
 *	@skb: received pdu
 *	@dev: device that receive pdu
 *	@pt: packet type
 *	@orig_dev: the original receive net device
 *
 *	When the system receives a 802.2 frame this function is called. It
 *	checks SAP and connection of received pdu and passes frame to
 *	llc_{station,sap,conn}_rcv for sending to proper state machine. If
 *	the frame is related to a busy connection (a connection is sending
 *	data now), it queues this frame in the connection's backlog.
 */
int llc_rcv(struct sk_buff *skb, struct net_device *dev,
	    struct packet_type *pt, struct net_device *orig_dev)
{
	struct llc_sap *sap;
	struct llc_pdu_sn *pdu;
	int dest;
	int (*rcv)(struct sk_buff *, struct net_device *,
		   struct packet_type *, struct net_device *);
	void (*sta_handler)(struct sk_buff *skb);
	void (*sap_handler)(struct llc_sap *sap, struct sk_buff *skb);

	/*
	 * When the interface is in promisc. mode, drop all the crap that it
	 * receives, do not try to analyse it.
	 */
	if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) {
		dprintk("%s: PACKET_OTHERHOST\n", __func__);
		goto drop;
	}
	skb = skb_share_check(skb, GFP_ATOMIC);
	if (unlikely(!skb))
		goto out;
	if (unlikely(!llc_fixup_skb(skb)))
		goto drop;
	pdu = llc_pdu_sn_hdr(skb);
	if (unlikely(!pdu->dsap)) /* NULL DSAP, refer to station */
	       goto handle_station;
	sap = llc_sap_find(pdu->dsap);
	if (unlikely(!sap)) {/* unknown SAP */
		dprintk("%s: llc_sap_find(%02X) failed!\n", __func__,
			pdu->dsap);
		goto drop;
	}
	/*
	 * First the upper layer protocols that don't need the full
	 * LLC functionality
	 */
	rcv = rcu_dereference(sap->rcv_func);
	dest = llc_pdu_type(skb);
	sap_handler = dest ? READ_ONCE(llc_type_handlers[dest - 1]) : NULL;
	if (unlikely(!sap_handler)) {
		if (rcv)
			rcv(skb, dev, pt, orig_dev);
		else
			kfree_skb(skb);
	} else {
		if (rcv) {
			struct sk_buff *cskb = skb_clone(skb, GFP_ATOMIC);
			if (cskb)
				rcv(cskb, dev, pt, orig_dev);
		}
		sap_handler(sap, skb);
	}
	llc_sap_put(sap);
out:
	return 0;
drop:
	kfree_skb(skb);
	goto out;
handle_station:
	sta_handler = READ_ONCE(llc_station_handler);
	if (!sta_handler)
		goto drop;
	sta_handler(skb);
	goto out;
}

EXPORT_SYMBOL(llc_add_pack);
EXPORT_SYMBOL(llc_remove_pack);
EXPORT_SYMBOL(llc_set_station_handler);