// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      X.25 Packet Layer release 002
 *
 *      This is ALPHA test software. This code may break your machine, randomly fail to work with new
 *      releases, misbehave and/or generally screw up. It might even work.
 *
 *      This code REQUIRES 2.1.15 or higher
 *
 *      History
 *      X.25 001        Jonathan Naylor Started coding.
 *      2000-09-04      Henner Eisen    Prevent freeing a dangling skb.
 */

#define pr_fmt(fmt) "X25: " fmt

#include <linux/kernel.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/if_arp.h>
#include <net/x25.h>
#include <net/x25device.h>

static int x25_receive_data(struct sk_buff *skb, struct x25_neigh *nb)
{
        struct sock *sk;
        unsigned short frametype;
        unsigned int lci;

        if (!pskb_may_pull(skb, X25_STD_MIN_LEN))
                return 0;

        frametype = skb->data[2];
        lci = ((skb->data[0] << 8) & 0xF00) + ((skb->data[1] << 0) & 0x0FF);

        /*
         *      LCI of zero is always for us, and its always a link control
         *      frame.
         */
        if (lci == 0) {
                x25_link_control(skb, nb, frametype);
                return 0;
        }

        /*
         *      Find an existing socket.
         */
        if ((sk = x25_find_socket(lci, nb)) != NULL) {
                int queued = 1;

                skb_reset_transport_header(skb);
                bh_lock_sock(sk);
                if (!sock_owned_by_user(sk)) {
                        queued = x25_process_rx_frame(sk, skb);
                } else {
                        queued = !sk_add_backlog(sk, skb, READ_ONCE(sk->sk_rcvbuf));
                }
                bh_unlock_sock(sk);
                sock_put(sk);
                return queued;
        }

        /*
         *      Is is a Call Request ? if so process it.
         */
        if (frametype == X25_CALL_REQUEST)
                return x25_rx_call_request(skb, nb, lci);

        /*
         *      Its not a Call Request, nor is it a control frame.
         *      Can we forward it?
         */

        if (x25_forward_data(lci, nb, skb)) {
                if (frametype == X25_CLEAR_CONFIRMATION) {
                        x25_clear_forward_by_lci(lci);
                }
                kfree_skb(skb);
                return 1;
        }

/*
        x25_transmit_clear_request(nb, lci, 0x0D);
*/

        if (frametype != X25_CLEAR_CONFIRMATION)
                pr_debug("x25_receive_data(): unknown frame type %2x\n",frametype);

        return 0;
}

int x25_lapb_receive_frame(struct sk_buff *skb, struct net_device *dev,
                           struct packet_type *ptype, struct net_device *orig_dev)
{
        struct sk_buff *nskb;
        struct x25_neigh *nb;

        if (!net_eq(dev_net(dev), &init_net))
                goto drop;

        nskb = skb_copy(skb, GFP_ATOMIC);
        if (!nskb)
                goto drop;
        kfree_skb(skb);
        skb = nskb;

        /*
         * Packet received from unrecognised device, throw it away.
         */
        nb = x25_get_neigh(dev);
        if (!nb) {
                pr_debug("unknown neighbour - %s\n", dev->name);
                goto drop;
        }

        if (!pskb_may_pull(skb, 1)) {
                x25_neigh_put(nb);
                goto drop;
        }

        switch (skb->data[0]) {

        case X25_IFACE_DATA:
                skb_pull(skb, 1);
                if (x25_receive_data(skb, nb)) {
                        x25_neigh_put(nb);
                        goto out;
                }
                break;

        case X25_IFACE_CONNECT:
                x25_link_established(nb);
                break;

        case X25_IFACE_DISCONNECT:
                x25_link_terminated(nb);
                break;
        }
        x25_neigh_put(nb);
drop:
        kfree_skb(skb);
out:
        return 0;
}

void x25_establish_link(struct x25_neigh *nb)
{
        struct sk_buff *skb;
        unsigned char *ptr;

        switch (nb->dev->type) {
        case ARPHRD_X25:
                if ((skb = alloc_skb(1, GFP_ATOMIC)) == NULL) {
                        pr_err("x25_dev: out of memory\n");
                        return;
                }
                ptr  = skb_put(skb, 1);
                *ptr = X25_IFACE_CONNECT;
                break;

        default:
                return;
        }

        skb->protocol = htons(ETH_P_X25);
        skb->dev      = nb->dev;

        dev_queue_xmit(skb);
}

void x25_send_frame(struct sk_buff *skb, struct x25_neigh *nb)
{
        unsigned char *dptr;

        skb_reset_network_header(skb);

        switch (nb->dev->type) {
        case ARPHRD_X25:
                dptr  = skb_push(skb, 1);
                *dptr = X25_IFACE_DATA;
                break;

        default:
                kfree_skb(skb);
                return;
        }

        skb->protocol = htons(ETH_P_X25);
        skb->dev      = nb->dev;

        dev_queue_xmit(skb);
}