// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * PPP synchronous tty channel driver for Linux.
 *
 * This is a ppp channel driver that can be used with tty device drivers
 * that are frame oriented, such as synchronous HDLC devices.
 *
 * Complete PPP frames without encoding/decoding are exchanged between
 * the channel driver and the device driver.
 *
 * The async map IOCTL codes are implemented to keep the user mode
 * applications happy if they call them. Synchronous PPP does not use
 * the async maps.
 *
 * Copyright 1999 Paul Mackerras.
 *
 * Also touched by the grubby hands of Paul Fulghum paulkf@microgate.com
 *
 * This driver provides the encapsulation and framing for sending
 * and receiving PPP frames over sync serial lines.  It relies on
 * the generic PPP layer to give it frames to send and to process
 * received frames.  It implements the PPP line discipline.
 *
 * Part of the code in this driver was inspired by the old async-only
 * PPP driver, written by Michael Callahan and Al Longyear, and
 * subsequently hacked by Paul Mackerras.
 *
 * ==FILEVERSION 20040616==
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/tty.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/ppp_defs.h>
#include <linux/ppp-ioctl.h>
#include <linux/ppp_channel.h>
#include <linux/spinlock.h>
#include <linux/completion.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/refcount.h>
#include <linux/unaligned.h>
#include <linux/uaccess.h>

#define PPP_VERSION     "2.4.2"

/* Structure for storing local state. */
struct syncppp {
        struct tty_struct *tty;
        unsigned int    flags;
        unsigned int    rbits;
        int             mru;
        spinlock_t      xmit_lock;
        spinlock_t      recv_lock;
        unsigned long   xmit_flags;
        u32             xaccm[8];
        u32             raccm;
        unsigned int    bytes_sent;
        unsigned int    bytes_rcvd;

        struct sk_buff  *tpkt;
        unsigned long   last_xmit;

        struct sk_buff_head rqueue;

        struct tasklet_struct tsk;

        refcount_t      refcnt;
        struct completion dead_cmp;
        struct ppp_channel chan;        /* interface to generic ppp layer */
};

/* Bit numbers in xmit_flags */
#define XMIT_WAKEUP     0
#define XMIT_FULL       1

/* Bits in rbits */
#define SC_RCV_BITS     (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)

#define PPPSYNC_MAX_RQLEN       32      /* arbitrary */

/*
 * Prototypes.
 */
static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
                          unsigned long arg);
static void ppp_sync_process(struct tasklet_struct *t);
static int ppp_sync_push(struct syncppp *ap);
static void ppp_sync_flush_output(struct syncppp *ap);
static void ppp_sync_input(struct syncppp *ap, const u8 *buf, const u8 *flags,
                           int count);

static const struct ppp_channel_ops sync_ops = {
        .start_xmit = ppp_sync_send,
        .ioctl      = ppp_sync_ioctl,
};

/*
 * Utility procedure to print a buffer in hex/ascii
 */
static void
ppp_print_buffer (const char *name, const __u8 *buf, int count)
{
        if (name != NULL)
                printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);

        print_hex_dump_bytes("", DUMP_PREFIX_NONE, buf, count);
}


/*
 * Routines implementing the synchronous PPP line discipline.
 */

/*
 * We have a potential race on dereferencing tty->disc_data,
 * because the tty layer provides no locking at all - thus one
 * cpu could be running ppp_synctty_receive while another
 * calls ppp_synctty_close, which zeroes tty->disc_data and
 * frees the memory that ppp_synctty_receive is using.  The best
 * way to fix this is to use a rwlock in the tty struct, but for now
 * we use a single global rwlock for all ttys in ppp line discipline.
 *
 * FIXME: Fixed in tty_io nowadays.
 */
static DEFINE_RWLOCK(disc_data_lock);

static struct syncppp *sp_get(struct tty_struct *tty)
{
        struct syncppp *ap;

        read_lock(&disc_data_lock);
        ap = tty->disc_data;
        if (ap != NULL)
                refcount_inc(&ap->refcnt);
        read_unlock(&disc_data_lock);
        return ap;
}

static void sp_put(struct syncppp *ap)
{
        if (refcount_dec_and_test(&ap->refcnt))
                complete(&ap->dead_cmp);
}

/*
 * Called when a tty is put into sync-PPP line discipline.
 */
static int
ppp_sync_open(struct tty_struct *tty)
{
        struct syncppp *ap;
        int err;
        int speed;

        if (tty->ops->write == NULL)
                return -EOPNOTSUPP;

        ap = kzalloc_obj(*ap);
        err = -ENOMEM;
        if (!ap)
                goto out;

        /* initialize the syncppp structure */
        ap->tty = tty;
        ap->mru = PPP_MRU;
        spin_lock_init(&ap->xmit_lock);
        spin_lock_init(&ap->recv_lock);
        ap->xaccm[0] = ~0U;
        ap->xaccm[3] = 0x60000000U;
        ap->raccm = ~0U;

        skb_queue_head_init(&ap->rqueue);
        tasklet_setup(&ap->tsk, ppp_sync_process);

        refcount_set(&ap->refcnt, 1);
        init_completion(&ap->dead_cmp);

        ap->chan.private = ap;
        ap->chan.ops = &sync_ops;
        ap->chan.mtu = PPP_MRU;
        ap->chan.hdrlen = 2;    /* for A/C bytes */
        speed = tty_get_baud_rate(tty);
        ap->chan.speed = speed;
        err = ppp_register_channel(&ap->chan);
        if (err)
                goto out_free;

        tty->disc_data = ap;
        tty->receive_room = 65536;
        return 0;

 out_free:
        kfree(ap);
 out:
        return err;
}

/*
 * Called when the tty is put into another line discipline
 * or it hangs up.  We have to wait for any cpu currently
 * executing in any of the other ppp_synctty_* routines to
 * finish before we can call ppp_unregister_channel and free
 * the syncppp struct.  This routine must be called from
 * process context, not interrupt or softirq context.
 */
static void
ppp_sync_close(struct tty_struct *tty)
{
        struct syncppp *ap;

        write_lock_irq(&disc_data_lock);
        ap = tty->disc_data;
        tty->disc_data = NULL;
        write_unlock_irq(&disc_data_lock);
        if (!ap)
                return;

        /*
         * We have now ensured that nobody can start using ap from now
         * on, but we have to wait for all existing users to finish.
         * Note that ppp_unregister_channel ensures that no calls to
         * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
         * by the time it returns.
         */
        if (!refcount_dec_and_test(&ap->refcnt))
                wait_for_completion(&ap->dead_cmp);
        tasklet_kill(&ap->tsk);

        ppp_unregister_channel(&ap->chan);
        skb_queue_purge(&ap->rqueue);
        kfree_skb(ap->tpkt);
        kfree(ap);
}

/*
 * Called on tty hangup in process context.
 *
 * Wait for I/O to driver to complete and unregister PPP channel.
 * This is already done by the close routine, so just call that.
 */
static void ppp_sync_hangup(struct tty_struct *tty)
{
        ppp_sync_close(tty);
}

/*
 * Read does nothing - no data is ever available this way.
 * Pppd reads and writes packets via /dev/ppp instead.
 */
static ssize_t
ppp_sync_read(struct tty_struct *tty, struct file *file, u8 *buf, size_t count,
              void **cookie, unsigned long offset)
{
        return -EAGAIN;
}

/*
 * Write on the tty does nothing, the packets all come in
 * from the ppp generic stuff.
 */
static ssize_t
ppp_sync_write(struct tty_struct *tty, struct file *file, const u8 *buf,
               size_t count)
{
        return -EAGAIN;
}

static int
ppp_synctty_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
{
        struct syncppp *ap = sp_get(tty);
        int __user *p = (int __user *)arg;
        int err, val;

        if (!ap)
                return -ENXIO;
        err = -EFAULT;
        switch (cmd) {
        case PPPIOCGCHAN:
                err = -EFAULT;
                if (put_user(ppp_channel_index(&ap->chan), p))
                        break;
                err = 0;
                break;

        case PPPIOCGUNIT:
                err = -EFAULT;
                if (put_user(ppp_unit_number(&ap->chan), p))
                        break;
                err = 0;
                break;

        case TCFLSH:
                /* flush our buffers and the serial port's buffer */
                if (arg == TCIOFLUSH || arg == TCOFLUSH)
                        ppp_sync_flush_output(ap);
                err = n_tty_ioctl_helper(tty, cmd, arg);
                break;

        case FIONREAD:
                val = 0;
                if (put_user(val, p))
                        break;
                err = 0;
                break;

        default:
                err = tty_mode_ioctl(tty, cmd, arg);
                break;
        }

        sp_put(ap);
        return err;
}

/* May sleep, don't call from interrupt level or with interrupts disabled */
static void
ppp_sync_receive(struct tty_struct *tty, const u8 *buf, const u8 *cflags,
                 size_t count)
{
        struct syncppp *ap = sp_get(tty);
        unsigned long flags;

        if (!ap)
                return;
        spin_lock_irqsave(&ap->recv_lock, flags);
        ppp_sync_input(ap, buf, cflags, count);
        spin_unlock_irqrestore(&ap->recv_lock, flags);
        if (!skb_queue_empty(&ap->rqueue))
                tasklet_schedule(&ap->tsk);
        sp_put(ap);
        tty_unthrottle(tty);
}

static void
ppp_sync_wakeup(struct tty_struct *tty)
{
        struct syncppp *ap = sp_get(tty);

        clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
        if (!ap)
                return;
        set_bit(XMIT_WAKEUP, &ap->xmit_flags);
        tasklet_schedule(&ap->tsk);
        sp_put(ap);
}


static struct tty_ldisc_ops ppp_sync_ldisc = {
        .owner  = THIS_MODULE,
        .num    = N_SYNC_PPP,
        .name   = "pppsync",
        .open   = ppp_sync_open,
        .close  = ppp_sync_close,
        .hangup = ppp_sync_hangup,
        .read   = ppp_sync_read,
        .write  = ppp_sync_write,
        .ioctl  = ppp_synctty_ioctl,
        .receive_buf = ppp_sync_receive,
        .write_wakeup = ppp_sync_wakeup,
};

static int __init
ppp_sync_init(void)
{
        int err;

        err = tty_register_ldisc(&ppp_sync_ldisc);
        if (err != 0)
                printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
                       err);
        return err;
}

/*
 * The following routines provide the PPP channel interface.
 */
static int
ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
{
        struct syncppp *ap = chan->private;
        int err, val;
        u32 accm[8];
        void __user *argp = (void __user *)arg;
        u32 __user *p = argp;

        err = -EFAULT;
        switch (cmd) {
        case PPPIOCGFLAGS:
                val = ap->flags | ap->rbits;
                if (put_user(val, (int __user *) argp))
                        break;
                err = 0;
                break;
        case PPPIOCSFLAGS:
                if (get_user(val, (int __user *) argp))
                        break;
                ap->flags = val & ~SC_RCV_BITS;
                spin_lock_irq(&ap->recv_lock);
                ap->rbits = val & SC_RCV_BITS;
                spin_unlock_irq(&ap->recv_lock);
                err = 0;
                break;

        case PPPIOCGASYNCMAP:
                if (put_user(ap->xaccm[0], p))
                        break;
                err = 0;
                break;
        case PPPIOCSASYNCMAP:
                if (get_user(ap->xaccm[0], p))
                        break;
                err = 0;
                break;

        case PPPIOCGRASYNCMAP:
                if (put_user(ap->raccm, p))
                        break;
                err = 0;
                break;
        case PPPIOCSRASYNCMAP:
                if (get_user(ap->raccm, p))
                        break;
                err = 0;
                break;

        case PPPIOCGXASYNCMAP:
                if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
                        break;
                err = 0;
                break;
        case PPPIOCSXASYNCMAP:
                if (copy_from_user(accm, argp, sizeof(accm)))
                        break;
                accm[2] &= ~0x40000000U;        /* can't escape 0x5e */
                accm[3] |= 0x60000000U;         /* must escape 0x7d, 0x7e */
                memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
                err = 0;
                break;

        case PPPIOCGMRU:
                if (put_user(ap->mru, (int __user *) argp))
                        break;
                err = 0;
                break;
        case PPPIOCSMRU:
                if (get_user(val, (int __user *) argp))
                        break;
                if (val > U16_MAX) {
                        err = -EINVAL;
                        break;
                }
                if (val < PPP_MRU)
                        val = PPP_MRU;
                ap->mru = val;
                err = 0;
                break;

        default:
                err = -ENOTTY;
        }
        return err;
}

/*
 * This is called at softirq level to deliver received packets
 * to the ppp_generic code, and to tell the ppp_generic code
 * if we can accept more output now.
 */
static void ppp_sync_process(struct tasklet_struct *t)
{
        struct syncppp *ap = from_tasklet(ap, t, tsk);
        struct sk_buff *skb;

        /* process received packets */
        while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
                if (skb->len == 0) {
                        /* zero length buffers indicate error */
                        ppp_input_error(&ap->chan, 0);
                        kfree_skb(skb);
                }
                else
                        ppp_input(&ap->chan, skb);
        }

        /* try to push more stuff out */
        if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
                ppp_output_wakeup(&ap->chan);
}

/*
 * Procedures for encapsulation and framing.
 */

static struct sk_buff*
ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
{
        int proto;
        unsigned char *data;
        int islcp;

        /* Ensure we can safely access protocol field and LCP code */
        if (!pskb_may_pull(skb, 3)) {
                kfree_skb(skb);
                return NULL;
        }
        data  = skb->data;
        proto = get_unaligned_be16(data);

        /* LCP packets with codes between 1 (configure-request)
         * and 7 (code-reject) must be sent as though no options
         * have been negotiated.
         */
        islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;

        /* compress protocol field if option enabled */
        if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
                skb_pull(skb,1);

        /* prepend address/control fields if necessary */
        if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
                if (skb_headroom(skb) < 2) {
                        struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
                        if (npkt == NULL) {
                                kfree_skb(skb);
                                return NULL;
                        }
                        skb_reserve(npkt,2);
                        skb_copy_from_linear_data(skb,
                                      skb_put(npkt, skb->len), skb->len);
                        consume_skb(skb);
                        skb = npkt;
                }
                skb_push(skb,2);
                skb->data[0] = PPP_ALLSTATIONS;
                skb->data[1] = PPP_UI;
        }

        ap->last_xmit = jiffies;

        if (skb && ap->flags & SC_LOG_OUTPKT)
                ppp_print_buffer ("send buffer", skb->data, skb->len);

        return skb;
}

/*
 * Transmit-side routines.
 */

/*
 * Send a packet to the peer over an sync tty line.
 * Returns 1 iff the packet was accepted.
 * If the packet was not accepted, we will call ppp_output_wakeup
 * at some later time.
 */
static int
ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
{
        struct syncppp *ap = chan->private;

        ppp_sync_push(ap);

        if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
                return 0;       /* already full */
        skb = ppp_sync_txmunge(ap, skb);
        if (skb != NULL)
                ap->tpkt = skb;
        else
                clear_bit(XMIT_FULL, &ap->xmit_flags);

        ppp_sync_push(ap);
        return 1;
}

/*
 * Push as much data as possible out to the tty.
 */
static int
ppp_sync_push(struct syncppp *ap)
{
        int sent, done = 0;
        struct tty_struct *tty = ap->tty;
        int tty_stuffed = 0;

        if (!spin_trylock_bh(&ap->xmit_lock))
                return 0;
        for (;;) {
                if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
                        tty_stuffed = 0;
                if (!tty_stuffed && ap->tpkt) {
                        set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
                        sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len);
                        if (sent < 0)
                                goto flush;     /* error, e.g. loss of CD */
                        if (sent < ap->tpkt->len) {
                                tty_stuffed = 1;
                        } else {
                                consume_skb(ap->tpkt);
                                ap->tpkt = NULL;
                                clear_bit(XMIT_FULL, &ap->xmit_flags);
                                done = 1;
                        }
                        continue;
                }
                /* haven't made any progress */
                spin_unlock_bh(&ap->xmit_lock);
                if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) ||
                      (!tty_stuffed && ap->tpkt)))
                        break;
                if (!spin_trylock_bh(&ap->xmit_lock))
                        break;
        }
        return done;

flush:
        if (ap->tpkt) {
                kfree_skb(ap->tpkt);
                ap->tpkt = NULL;
                clear_bit(XMIT_FULL, &ap->xmit_flags);
                done = 1;
        }
        spin_unlock_bh(&ap->xmit_lock);
        return done;
}

/*
 * Flush output from our internal buffers.
 * Called for the TCFLSH ioctl.
 */
static void
ppp_sync_flush_output(struct syncppp *ap)
{
        int done = 0;

        spin_lock_bh(&ap->xmit_lock);
        if (ap->tpkt != NULL) {
                kfree_skb(ap->tpkt);
                ap->tpkt = NULL;
                clear_bit(XMIT_FULL, &ap->xmit_flags);
                done = 1;
        }
        spin_unlock_bh(&ap->xmit_lock);
        if (done)
                ppp_output_wakeup(&ap->chan);
}

/*
 * Receive-side routines.
 */

/* called when the tty driver has data for us.
 *
 * Data is frame oriented: each call to ppp_sync_input is considered
 * a whole frame. If the 1st flag byte is non-zero then the whole
 * frame is considered to be in error and is tossed.
 */
static void
ppp_sync_input(struct syncppp *ap, const u8 *buf, const u8 *flags, int count)
{
        struct sk_buff *skb;
        unsigned char *p;

        if (count == 0)
                return;

        if (ap->flags & SC_LOG_INPKT)
                ppp_print_buffer ("receive buffer", buf, count);

        /* stuff the chars in the skb */
        skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
        if (!skb) {
                printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
                goto err;
        }
        /* Try to get the payload 4-byte aligned */
        if (buf[0] != PPP_ALLSTATIONS)
                skb_reserve(skb, 2 + (buf[0] & 1));

        if (flags && *flags) {
                /* error flag set, ignore frame */
                goto err;
        } else if (count > skb_tailroom(skb)) {
                /* packet overflowed MRU */
                goto err;
        }

        skb_put_data(skb, buf, count);

        /* strip address/control field if present */
        p = skb->data;
        if (skb->len >= 2 && p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
                /* chop off address/control */
                if (skb->len < 3)
                        goto err;
                p = skb_pull(skb, 2);
        }

        /* PPP packet length should be >= 2 bytes when protocol field is not
         * compressed.
         */
        if (!(p[0] & 0x01) && skb->len < 2)
                goto err;

        /* queue the frame to be processed */
        skb_queue_tail(&ap->rqueue, skb);
        return;

err:
        /* queue zero length packet as error indication */
        if (skb || (skb = dev_alloc_skb(0))) {
                skb_trim(skb, 0);
                skb_queue_tail(&ap->rqueue, skb);
        }
}

static void __exit
ppp_sync_cleanup(void)
{
        tty_unregister_ldisc(&ppp_sync_ldisc);
}

module_init(ppp_sync_init);
module_exit(ppp_sync_cleanup);
MODULE_DESCRIPTION("PPP synchronous TTY channel module");
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_SYNC_PPP);