// 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.
 *      X.25 002        Jonathan Naylor   Centralised disconnection processing.
 *      mar/20/00       Daniela Squassoni Disabling/enabling of facilities
 *                                        negotiation.
 *      jun/24/01       Arnaldo C. Melo   use skb_queue_purge, cleanups
 *      apr/04/15       Shaun Pereira           Fast select with no
 *                                              restriction on response.
 */

#define pr_fmt(fmt) "X25: " fmt

#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <net/tcp_states.h>
#include <net/x25.h>

/*
 *      This routine purges all of the queues of frames.
 */
void x25_clear_queues(struct sock *sk)
{
        struct x25_sock *x25 = x25_sk(sk);

        skb_queue_purge(&sk->sk_write_queue);
        skb_queue_purge(&x25->ack_queue);
        skb_queue_purge(&x25->interrupt_in_queue);
        skb_queue_purge(&x25->interrupt_out_queue);
        skb_queue_purge(&x25->fragment_queue);
}


/*
 * This routine purges the input queue of those frames that have been
 * acknowledged. This replaces the boxes labelled "V(a) <- N(r)" on the
 * SDL diagram.
*/
void x25_frames_acked(struct sock *sk, unsigned short nr)
{
        struct sk_buff *skb;
        struct x25_sock *x25 = x25_sk(sk);
        int modulus = x25->neighbour->extended ? X25_EMODULUS : X25_SMODULUS;

        /*
         * Remove all the ack-ed frames from the ack queue.
         */
        if (x25->va != nr)
                while (skb_peek(&x25->ack_queue) && x25->va != nr) {
                        skb = skb_dequeue(&x25->ack_queue);
                        kfree_skb(skb);
                        x25->va = (x25->va + 1) % modulus;
                }
}

void x25_requeue_frames(struct sock *sk)
{
        struct sk_buff *skb, *skb_prev = NULL;

        /*
         * Requeue all the un-ack-ed frames on the output queue to be picked
         * up by x25_kick. This arrangement handles the possibility of an empty
         * output queue.
         */
        while ((skb = skb_dequeue(&x25_sk(sk)->ack_queue)) != NULL) {
                if (!skb_prev)
                        skb_queue_head(&sk->sk_write_queue, skb);
                else
                        skb_append(skb_prev, skb, &sk->sk_write_queue);
                skb_prev = skb;
        }
}

/*
 *      Validate that the value of nr is between va and vs. Return true or
 *      false for testing.
 */
int x25_validate_nr(struct sock *sk, unsigned short nr)
{
        struct x25_sock *x25 = x25_sk(sk);
        unsigned short vc = x25->va;
        int modulus = x25->neighbour->extended ? X25_EMODULUS : X25_SMODULUS;

        while (vc != x25->vs) {
                if (nr == vc)
                        return 1;
                vc = (vc + 1) % modulus;
        }

        return nr == x25->vs ? 1 : 0;
}

/*
 *  This routine is called when the packet layer internally generates a
 *  control frame.
 */
void x25_write_internal(struct sock *sk, int frametype)
{
        struct x25_sock *x25 = x25_sk(sk);
        struct sk_buff *skb;
        unsigned char  *dptr;
        unsigned char  facilities[X25_MAX_FAC_LEN];
        unsigned char  addresses[1 + X25_ADDR_LEN];
        unsigned char  lci1, lci2;
        /*
         *      Default safe frame size.
         */
        int len = X25_MAX_L2_LEN + X25_EXT_MIN_LEN;

        /*
         *      Adjust frame size.
         */
        switch (frametype) {
        case X25_CALL_REQUEST:
                len += 1 + X25_ADDR_LEN + X25_MAX_FAC_LEN + X25_MAX_CUD_LEN;
                break;
        case X25_CALL_ACCEPTED: /* fast sel with no restr on resp */
                if (x25->facilities.reverse & 0x80) {
                        len += 1 + X25_MAX_FAC_LEN + X25_MAX_CUD_LEN;
                } else {
                        len += 1 + X25_MAX_FAC_LEN;
                }
                break;
        case X25_CLEAR_REQUEST:
        case X25_RESET_REQUEST:
                len += 2;
                break;
        case X25_RR:
        case X25_RNR:
        case X25_REJ:
        case X25_CLEAR_CONFIRMATION:
        case X25_INTERRUPT_CONFIRMATION:
        case X25_RESET_CONFIRMATION:
                break;
        default:
                pr_err("invalid frame type %02X\n", frametype);
                return;
        }

        if ((skb = alloc_skb(len, GFP_ATOMIC)) == NULL)
                return;

        /*
         *      Space for Ethernet and 802.2 LLC headers.
         */
        skb_reserve(skb, X25_MAX_L2_LEN);

        /*
         *      Make space for the GFI and LCI, and fill them in.
         */
        dptr = skb_put(skb, 2);

        lci1 = (x25->lci >> 8) & 0x0F;
        lci2 = (x25->lci >> 0) & 0xFF;

        if (x25->neighbour->extended) {
                *dptr++ = lci1 | X25_GFI_EXTSEQ;
                *dptr++ = lci2;
        } else {
                *dptr++ = lci1 | X25_GFI_STDSEQ;
                *dptr++ = lci2;
        }

        /*
         *      Now fill in the frame type specific information.
         */
        switch (frametype) {

                case X25_CALL_REQUEST:
                        dptr    = skb_put(skb, 1);
                        *dptr++ = X25_CALL_REQUEST;
                        len     = x25_addr_aton(addresses, &x25->dest_addr,
                                                &x25->source_addr);
                        skb_put_data(skb, addresses, len);
                        len     = x25_create_facilities(facilities,
                                        &x25->facilities,
                                        &x25->dte_facilities,
                                        x25->neighbour->global_facil_mask);
                        skb_put_data(skb, facilities, len);
                        skb_put_data(skb, x25->calluserdata.cuddata,
                                     x25->calluserdata.cudlength);
                        x25->calluserdata.cudlength = 0;
                        break;

                case X25_CALL_ACCEPTED:
                        dptr    = skb_put(skb, 2);
                        *dptr++ = X25_CALL_ACCEPTED;
                        *dptr++ = 0x00;         /* Address lengths */
                        len     = x25_create_facilities(facilities,
                                                        &x25->facilities,
                                                        &x25->dte_facilities,
                                                        x25->vc_facil_mask);
                        skb_put_data(skb, facilities, len);

                        /* fast select with no restriction on response
                                allows call user data. Userland must
                                ensure it is ours and not theirs */
                        if(x25->facilities.reverse & 0x80) {
                                skb_put_data(skb,
                                             x25->calluserdata.cuddata,
                                             x25->calluserdata.cudlength);
                        }
                        x25->calluserdata.cudlength = 0;
                        break;

                case X25_CLEAR_REQUEST:
                        dptr    = skb_put(skb, 3);
                        *dptr++ = frametype;
                        *dptr++ = x25->causediag.cause;
                        *dptr++ = x25->causediag.diagnostic;
                        break;

                case X25_RESET_REQUEST:
                        dptr    = skb_put(skb, 3);
                        *dptr++ = frametype;
                        *dptr++ = 0x00;         /* XXX */
                        *dptr++ = 0x00;         /* XXX */
                        break;

                case X25_RR:
                case X25_RNR:
                case X25_REJ:
                        if (x25->neighbour->extended) {
                                dptr     = skb_put(skb, 2);
                                *dptr++  = frametype;
                                *dptr++  = (x25->vr << 1) & 0xFE;
                        } else {
                                dptr     = skb_put(skb, 1);
                                *dptr    = frametype;
                                *dptr++ |= (x25->vr << 5) & 0xE0;
                        }
                        break;

                case X25_CLEAR_CONFIRMATION:
                case X25_INTERRUPT_CONFIRMATION:
                case X25_RESET_CONFIRMATION:
                        dptr  = skb_put(skb, 1);
                        *dptr = frametype;
                        break;
        }

        x25_transmit_link(skb, x25->neighbour);
}

/*
 *      Unpick the contents of the passed X.25 Packet Layer frame.
 */
int x25_decode(struct sock *sk, struct sk_buff *skb, int *ns, int *nr, int *q,
               int *d, int *m)
{
        struct x25_sock *x25 = x25_sk(sk);
        unsigned char *frame;

        if (!pskb_may_pull(skb, X25_STD_MIN_LEN))
                return X25_ILLEGAL;
        frame = skb->data;

        *ns = *nr = *q = *d = *m = 0;

        switch (frame[2]) {
        case X25_CALL_REQUEST:
        case X25_CALL_ACCEPTED:
        case X25_CLEAR_REQUEST:
        case X25_CLEAR_CONFIRMATION:
        case X25_INTERRUPT:
        case X25_INTERRUPT_CONFIRMATION:
        case X25_RESET_REQUEST:
        case X25_RESET_CONFIRMATION:
        case X25_RESTART_REQUEST:
        case X25_RESTART_CONFIRMATION:
        case X25_REGISTRATION_REQUEST:
        case X25_REGISTRATION_CONFIRMATION:
        case X25_DIAGNOSTIC:
                return frame[2];
        }

        if (x25->neighbour->extended) {
                if (frame[2] == X25_RR  ||
                    frame[2] == X25_RNR ||
                    frame[2] == X25_REJ) {
                        if (!pskb_may_pull(skb, X25_EXT_MIN_LEN))
                                return X25_ILLEGAL;
                        frame = skb->data;

                        *nr = (frame[3] >> 1) & 0x7F;
                        return frame[2];
                }
        } else {
                if ((frame[2] & 0x1F) == X25_RR  ||
                    (frame[2] & 0x1F) == X25_RNR ||
                    (frame[2] & 0x1F) == X25_REJ) {
                        *nr = (frame[2] >> 5) & 0x07;
                        return frame[2] & 0x1F;
                }
        }

        if (x25->neighbour->extended) {
                if ((frame[2] & 0x01) == X25_DATA) {
                        if (!pskb_may_pull(skb, X25_EXT_MIN_LEN))
                                return X25_ILLEGAL;
                        frame = skb->data;

                        *q  = (frame[0] & X25_Q_BIT) == X25_Q_BIT;
                        *d  = (frame[0] & X25_D_BIT) == X25_D_BIT;
                        *m  = (frame[3] & X25_EXT_M_BIT) == X25_EXT_M_BIT;
                        *nr = (frame[3] >> 1) & 0x7F;
                        *ns = (frame[2] >> 1) & 0x7F;
                        return X25_DATA;
                }
        } else {
                if ((frame[2] & 0x01) == X25_DATA) {
                        *q  = (frame[0] & X25_Q_BIT) == X25_Q_BIT;
                        *d  = (frame[0] & X25_D_BIT) == X25_D_BIT;
                        *m  = (frame[2] & X25_STD_M_BIT) == X25_STD_M_BIT;
                        *nr = (frame[2] >> 5) & 0x07;
                        *ns = (frame[2] >> 1) & 0x07;
                        return X25_DATA;
                }
        }

        pr_debug("invalid PLP frame %3ph\n", frame);

        return X25_ILLEGAL;
}

void x25_disconnect(struct sock *sk, int reason, unsigned char cause,
                    unsigned char diagnostic)
{
        struct x25_sock *x25 = x25_sk(sk);

        x25_clear_queues(sk);
        x25_stop_timer(sk);

        x25->lci   = 0;
        x25->state = X25_STATE_0;

        x25->causediag.cause      = cause;
        x25->causediag.diagnostic = diagnostic;

        sk->sk_state     = TCP_CLOSE;
        sk->sk_err       = reason;
        sk->sk_shutdown |= SEND_SHUTDOWN;

        if (!sock_flag(sk, SOCK_DEAD)) {
                sk->sk_state_change(sk);
                sock_set_flag(sk, SOCK_DEAD);
        }
        if (x25->neighbour) {
                read_lock_bh(&x25_list_lock);
                x25_neigh_put(x25->neighbour);
                x25->neighbour = NULL;
                read_unlock_bh(&x25_list_lock);
        }
}

/*
 * Clear an own-rx-busy condition and tell the peer about this, provided
 * that there is a significant amount of free receive buffer space available.
 */
void x25_check_rbuf(struct sock *sk)
{
        struct x25_sock *x25 = x25_sk(sk);

        if (atomic_read(&sk->sk_rmem_alloc) < (sk->sk_rcvbuf >> 1) &&
            (x25->condition & X25_COND_OWN_RX_BUSY)) {
                x25->condition &= ~X25_COND_OWN_RX_BUSY;
                x25->condition &= ~X25_COND_ACK_PENDING;
                x25->vl         = x25->vr;
                x25_write_internal(sk, X25_RR);
                x25_stop_timer(sk);
        }
}