1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * PPP async serial channel driver for Linux.
   4 *
   5 * Copyright 1999 Paul Mackerras.
   6 *
   7 * This driver provides the encapsulation and framing for sending
   8 * and receiving PPP frames over async serial lines.  It relies on
   9 * the generic PPP layer to give it frames to send and to process
  10 * received frames.  It implements the PPP line discipline.
  11 *
  12 * Part of the code in this driver was inspired by the old async-only
  13 * PPP driver, written by Michael Callahan and Al Longyear, and
  14 * subsequently hacked by Paul Mackerras.
  15 */
  16
  17#include <linux/module.h>
  18#include <linux/kernel.h>
  19#include <linux/skbuff.h>
  20#include <linux/tty.h>
  21#include <linux/netdevice.h>
  22#include <linux/poll.h>
  23#include <linux/crc-ccitt.h>
  24#include <linux/ppp_defs.h>
  25#include <linux/ppp-ioctl.h>
  26#include <linux/ppp_channel.h>
  27#include <linux/spinlock.h>
  28#include <linux/init.h>
  29#include <linux/interrupt.h>
  30#include <linux/jiffies.h>
  31#include <linux/slab.h>
  32#include <asm/unaligned.h>
  33#include <linux/uaccess.h>
  34#include <asm/string.h>
  35
  36#define PPP_VERSION	"2.4.2"
  37
  38#define OBUFSIZE	4096
  39
  40/* Structure for storing local state. */
  41struct asyncppp {
  42	struct tty_struct *tty;
  43	unsigned int	flags;
  44	unsigned int	state;
  45	unsigned int	rbits;
  46	int		mru;
  47	spinlock_t	xmit_lock;
  48	spinlock_t	recv_lock;
  49	unsigned long	xmit_flags;
  50	u32		xaccm[8];
  51	u32		raccm;
  52	unsigned int	bytes_sent;
  53	unsigned int	bytes_rcvd;
  54
  55	struct sk_buff	*tpkt;
  56	int		tpkt_pos;
  57	u16		tfcs;
  58	unsigned char	*optr;
  59	unsigned char	*olim;
  60	unsigned long	last_xmit;
  61
  62	struct sk_buff	*rpkt;
  63	int		lcp_fcs;
  64	struct sk_buff_head rqueue;
  65
  66	struct tasklet_struct tsk;
  67
  68	refcount_t	refcnt;
  69	struct completion dead;
  70	struct ppp_channel chan;	/* interface to generic ppp layer */
  71	unsigned char	obuf[OBUFSIZE];
  72};
  73
  74/* Bit numbers in xmit_flags */
  75#define XMIT_WAKEUP	0
  76#define XMIT_FULL	1
  77#define XMIT_BUSY	2
  78
  79/* State bits */
  80#define SC_TOSS		1
  81#define SC_ESCAPE	2
  82#define SC_PREV_ERROR	4
  83
  84/* Bits in rbits */
  85#define SC_RCV_BITS	(SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
  86
  87static int flag_time = HZ;
  88module_param(flag_time, int, 0);
  89MODULE_PARM_DESC(flag_time, "ppp_async: interval between flagged packets (in clock ticks)");
  90MODULE_LICENSE("GPL");
  91MODULE_ALIAS_LDISC(N_PPP);
  92
  93/*
  94 * Prototypes.
  95 */
  96static int ppp_async_encode(struct asyncppp *ap);
  97static int ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb);
  98static int ppp_async_push(struct asyncppp *ap);
  99static void ppp_async_flush_output(struct asyncppp *ap);
 100static void ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
 101			    char *flags, int count);
 102static int ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd,
 103			   unsigned long arg);
 104static void ppp_async_process(unsigned long arg);
 105
 106static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
 107			   int len, int inbound);
 108
 109static const struct ppp_channel_ops async_ops = {
 110	.start_xmit = ppp_async_send,
 111	.ioctl      = ppp_async_ioctl,
 112};
 113
 114/*
 115 * Routines implementing the PPP line discipline.
 116 */
 117
 118/*
 119 * We have a potential race on dereferencing tty->disc_data,
 120 * because the tty layer provides no locking at all - thus one
 121 * cpu could be running ppp_asynctty_receive while another
 122 * calls ppp_asynctty_close, which zeroes tty->disc_data and
 123 * frees the memory that ppp_asynctty_receive is using.  The best
 124 * way to fix this is to use a rwlock in the tty struct, but for now
 125 * we use a single global rwlock for all ttys in ppp line discipline.
 126 *
 127 * FIXME: this is no longer true. The _close path for the ldisc is
 128 * now guaranteed to be sane.
 129 */
 130static DEFINE_RWLOCK(disc_data_lock);
 131
 132static struct asyncppp *ap_get(struct tty_struct *tty)
 133{
 134	struct asyncppp *ap;
 135
 136	read_lock(&disc_data_lock);
 137	ap = tty->disc_data;
 138	if (ap != NULL)
 139		refcount_inc(&ap->refcnt);
 140	read_unlock(&disc_data_lock);
 141	return ap;
 142}
 143
 144static void ap_put(struct asyncppp *ap)
 145{
 146	if (refcount_dec_and_test(&ap->refcnt))
 147		complete(&ap->dead);
 148}
 149
 150/*
 151 * Called when a tty is put into PPP line discipline. Called in process
 152 * context.
 153 */
 154static int
 155ppp_asynctty_open(struct tty_struct *tty)
 156{
 157	struct asyncppp *ap;
 158	int err;
 159	int speed;
 160
 161	if (tty->ops->write == NULL)
 162		return -EOPNOTSUPP;
 163
 164	err = -ENOMEM;
 165	ap = kzalloc(sizeof(*ap), GFP_KERNEL);
 166	if (!ap)
 167		goto out;
 168
 169	/* initialize the asyncppp structure */
 170	ap->tty = tty;
 171	ap->mru = PPP_MRU;
 172	spin_lock_init(&ap->xmit_lock);
 173	spin_lock_init(&ap->recv_lock);
 174	ap->xaccm[0] = ~0U;
 175	ap->xaccm[3] = 0x60000000U;
 176	ap->raccm = ~0U;
 177	ap->optr = ap->obuf;
 178	ap->olim = ap->obuf;
 179	ap->lcp_fcs = -1;
 180
 181	skb_queue_head_init(&ap->rqueue);
 182	tasklet_init(&ap->tsk, ppp_async_process, (unsigned long) ap);
 183
 184	refcount_set(&ap->refcnt, 1);
 185	init_completion(&ap->dead);
 186
 187	ap->chan.private = ap;
 188	ap->chan.ops = &async_ops;
 189	ap->chan.mtu = PPP_MRU;
 190	speed = tty_get_baud_rate(tty);
 191	ap->chan.speed = speed;
 192	err = ppp_register_channel(&ap->chan);
 193	if (err)
 194		goto out_free;
 195
 196	tty->disc_data = ap;
 197	tty->receive_room = 65536;
 198	return 0;
 199
 200 out_free:
 201	kfree(ap);
 202 out:
 203	return err;
 204}
 205
 206/*
 207 * Called when the tty is put into another line discipline
 208 * or it hangs up.  We have to wait for any cpu currently
 209 * executing in any of the other ppp_asynctty_* routines to
 210 * finish before we can call ppp_unregister_channel and free
 211 * the asyncppp struct.  This routine must be called from
 212 * process context, not interrupt or softirq context.
 213 */
 214static void
 215ppp_asynctty_close(struct tty_struct *tty)
 216{
 217	struct asyncppp *ap;
 218
 219	write_lock_irq(&disc_data_lock);
 220	ap = tty->disc_data;
 221	tty->disc_data = NULL;
 222	write_unlock_irq(&disc_data_lock);
 223	if (!ap)
 224		return;
 225
 226	/*
 227	 * We have now ensured that nobody can start using ap from now
 228	 * on, but we have to wait for all existing users to finish.
 229	 * Note that ppp_unregister_channel ensures that no calls to
 230	 * our channel ops (i.e. ppp_async_send/ioctl) are in progress
 231	 * by the time it returns.
 232	 */
 233	if (!refcount_dec_and_test(&ap->refcnt))
 234		wait_for_completion(&ap->dead);
 235	tasklet_kill(&ap->tsk);
 236
 237	ppp_unregister_channel(&ap->chan);
 238	kfree_skb(ap->rpkt);
 239	skb_queue_purge(&ap->rqueue);
 240	kfree_skb(ap->tpkt);
 241	kfree(ap);
 242}
 243
 244/*
 245 * Called on tty hangup in process context.
 246 *
 247 * Wait for I/O to driver to complete and unregister PPP channel.
 248 * This is already done by the close routine, so just call that.
 249 */
 250static int ppp_asynctty_hangup(struct tty_struct *tty)
 251{
 252	ppp_asynctty_close(tty);
 253	return 0;
 254}
 255
 256/*
 257 * Read does nothing - no data is ever available this way.
 258 * Pppd reads and writes packets via /dev/ppp instead.
 259 */
 260static ssize_t
 261ppp_asynctty_read(struct tty_struct *tty, struct file *file,
 262		  unsigned char __user *buf, size_t count)
 
 263{
 264	return -EAGAIN;
 265}
 266
 267/*
 268 * Write on the tty does nothing, the packets all come in
 269 * from the ppp generic stuff.
 270 */
 271static ssize_t
 272ppp_asynctty_write(struct tty_struct *tty, struct file *file,
 273		   const unsigned char *buf, size_t count)
 274{
 275	return -EAGAIN;
 276}
 277
 278/*
 279 * Called in process context only. May be re-entered by multiple
 280 * ioctl calling threads.
 281 */
 282
 283static int
 284ppp_asynctty_ioctl(struct tty_struct *tty, struct file *file,
 285		   unsigned int cmd, unsigned long arg)
 286{
 287	struct asyncppp *ap = ap_get(tty);
 288	int err, val;
 289	int __user *p = (int __user *)arg;
 290
 291	if (!ap)
 292		return -ENXIO;
 293	err = -EFAULT;
 294	switch (cmd) {
 295	case PPPIOCGCHAN:
 296		err = -EFAULT;
 297		if (put_user(ppp_channel_index(&ap->chan), p))
 298			break;
 299		err = 0;
 300		break;
 301
 302	case PPPIOCGUNIT:
 303		err = -EFAULT;
 304		if (put_user(ppp_unit_number(&ap->chan), p))
 305			break;
 306		err = 0;
 307		break;
 308
 309	case TCFLSH:
 310		/* flush our buffers and the serial port's buffer */
 311		if (arg == TCIOFLUSH || arg == TCOFLUSH)
 312			ppp_async_flush_output(ap);
 313		err = n_tty_ioctl_helper(tty, file, cmd, arg);
 314		break;
 315
 316	case FIONREAD:
 317		val = 0;
 318		if (put_user(val, p))
 319			break;
 320		err = 0;
 321		break;
 322
 323	default:
 324		/* Try the various mode ioctls */
 325		err = tty_mode_ioctl(tty, file, cmd, arg);
 326	}
 327
 328	ap_put(ap);
 329	return err;
 330}
 331
 332/* No kernel lock - fine */
 333static __poll_t
 334ppp_asynctty_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
 335{
 336	return 0;
 337}
 338
 339/* May sleep, don't call from interrupt level or with interrupts disabled */
 340static void
 341ppp_asynctty_receive(struct tty_struct *tty, const unsigned char *buf,
 342		  char *cflags, int count)
 343{
 344	struct asyncppp *ap = ap_get(tty);
 345	unsigned long flags;
 346
 347	if (!ap)
 348		return;
 349	spin_lock_irqsave(&ap->recv_lock, flags);
 350	ppp_async_input(ap, buf, cflags, count);
 351	spin_unlock_irqrestore(&ap->recv_lock, flags);
 352	if (!skb_queue_empty(&ap->rqueue))
 353		tasklet_schedule(&ap->tsk);
 354	ap_put(ap);
 355	tty_unthrottle(tty);
 356}
 357
 358static void
 359ppp_asynctty_wakeup(struct tty_struct *tty)
 360{
 361	struct asyncppp *ap = ap_get(tty);
 362
 363	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 364	if (!ap)
 365		return;
 366	set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 367	tasklet_schedule(&ap->tsk);
 368	ap_put(ap);
 369}
 370
 371
 372static struct tty_ldisc_ops ppp_ldisc = {
 373	.owner  = THIS_MODULE,
 374	.magic	= TTY_LDISC_MAGIC,
 375	.name	= "ppp",
 376	.open	= ppp_asynctty_open,
 377	.close	= ppp_asynctty_close,
 378	.hangup	= ppp_asynctty_hangup,
 379	.read	= ppp_asynctty_read,
 380	.write	= ppp_asynctty_write,
 381	.ioctl	= ppp_asynctty_ioctl,
 382	.poll	= ppp_asynctty_poll,
 383	.receive_buf = ppp_asynctty_receive,
 384	.write_wakeup = ppp_asynctty_wakeup,
 385};
 386
 387static int __init
 388ppp_async_init(void)
 389{
 390	int err;
 391
 392	err = tty_register_ldisc(N_PPP, &ppp_ldisc);
 393	if (err != 0)
 394		printk(KERN_ERR "PPP_async: error %d registering line disc.\n",
 395		       err);
 396	return err;
 397}
 398
 399/*
 400 * The following routines provide the PPP channel interface.
 401 */
 402static int
 403ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 404{
 405	struct asyncppp *ap = chan->private;
 406	void __user *argp = (void __user *)arg;
 407	int __user *p = argp;
 408	int err, val;
 409	u32 accm[8];
 410
 411	err = -EFAULT;
 412	switch (cmd) {
 413	case PPPIOCGFLAGS:
 414		val = ap->flags | ap->rbits;
 415		if (put_user(val, p))
 416			break;
 417		err = 0;
 418		break;
 419	case PPPIOCSFLAGS:
 420		if (get_user(val, p))
 421			break;
 422		ap->flags = val & ~SC_RCV_BITS;
 423		spin_lock_irq(&ap->recv_lock);
 424		ap->rbits = val & SC_RCV_BITS;
 425		spin_unlock_irq(&ap->recv_lock);
 426		err = 0;
 427		break;
 428
 429	case PPPIOCGASYNCMAP:
 430		if (put_user(ap->xaccm[0], (u32 __user *)argp))
 431			break;
 432		err = 0;
 433		break;
 434	case PPPIOCSASYNCMAP:
 435		if (get_user(ap->xaccm[0], (u32 __user *)argp))
 436			break;
 437		err = 0;
 438		break;
 439
 440	case PPPIOCGRASYNCMAP:
 441		if (put_user(ap->raccm, (u32 __user *)argp))
 442			break;
 443		err = 0;
 444		break;
 445	case PPPIOCSRASYNCMAP:
 446		if (get_user(ap->raccm, (u32 __user *)argp))
 447			break;
 448		err = 0;
 449		break;
 450
 451	case PPPIOCGXASYNCMAP:
 452		if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
 453			break;
 454		err = 0;
 455		break;
 456	case PPPIOCSXASYNCMAP:
 457		if (copy_from_user(accm, argp, sizeof(accm)))
 458			break;
 459		accm[2] &= ~0x40000000U;	/* can't escape 0x5e */
 460		accm[3] |= 0x60000000U;		/* must escape 0x7d, 0x7e */
 461		memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
 462		err = 0;
 463		break;
 464
 465	case PPPIOCGMRU:
 466		if (put_user(ap->mru, p))
 467			break;
 468		err = 0;
 469		break;
 470	case PPPIOCSMRU:
 471		if (get_user(val, p))
 472			break;
 473		if (val < PPP_MRU)
 474			val = PPP_MRU;
 475		ap->mru = val;
 476		err = 0;
 477		break;
 478
 479	default:
 480		err = -ENOTTY;
 481	}
 482
 483	return err;
 484}
 485
 486/*
 487 * This is called at softirq level to deliver received packets
 488 * to the ppp_generic code, and to tell the ppp_generic code
 489 * if we can accept more output now.
 490 */
 491static void ppp_async_process(unsigned long arg)
 492{
 493	struct asyncppp *ap = (struct asyncppp *) arg;
 494	struct sk_buff *skb;
 495
 496	/* process received packets */
 497	while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
 498		if (skb->cb[0])
 499			ppp_input_error(&ap->chan, 0);
 500		ppp_input(&ap->chan, skb);
 501	}
 502
 503	/* try to push more stuff out */
 504	if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_async_push(ap))
 505		ppp_output_wakeup(&ap->chan);
 506}
 507
 508/*
 509 * Procedures for encapsulation and framing.
 510 */
 511
 512/*
 513 * Procedure to encode the data for async serial transmission.
 514 * Does octet stuffing (escaping), puts the address/control bytes
 515 * on if A/C compression is disabled, and does protocol compression.
 516 * Assumes ap->tpkt != 0 on entry.
 517 * Returns 1 if we finished the current frame, 0 otherwise.
 518 */
 519
 520#define PUT_BYTE(ap, buf, c, islcp)	do {		\
 521	if ((islcp && c < 0x20) || (ap->xaccm[c >> 5] & (1 << (c & 0x1f)))) {\
 522		*buf++ = PPP_ESCAPE;			\
 523		*buf++ = c ^ PPP_TRANS;			\
 524	} else						\
 525		*buf++ = c;				\
 526} while (0)
 527
 528static int
 529ppp_async_encode(struct asyncppp *ap)
 530{
 531	int fcs, i, count, c, proto;
 532	unsigned char *buf, *buflim;
 533	unsigned char *data;
 534	int islcp;
 535
 536	buf = ap->obuf;
 537	ap->olim = buf;
 538	ap->optr = buf;
 539	i = ap->tpkt_pos;
 540	data = ap->tpkt->data;
 541	count = ap->tpkt->len;
 542	fcs = ap->tfcs;
 543	proto = get_unaligned_be16(data);
 544
 545	/*
 546	 * LCP packets with code values between 1 (configure-reqest)
 547	 * and 7 (code-reject) must be sent as though no options
 548	 * had been negotiated.
 549	 */
 550	islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
 551
 552	if (i == 0) {
 553		if (islcp)
 554			async_lcp_peek(ap, data, count, 0);
 555
 556		/*
 557		 * Start of a new packet - insert the leading FLAG
 558		 * character if necessary.
 559		 */
 560		if (islcp || flag_time == 0 ||
 561		    time_after_eq(jiffies, ap->last_xmit + flag_time))
 562			*buf++ = PPP_FLAG;
 563		ap->last_xmit = jiffies;
 564		fcs = PPP_INITFCS;
 565
 566		/*
 567		 * Put in the address/control bytes if necessary
 568		 */
 569		if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
 570			PUT_BYTE(ap, buf, 0xff, islcp);
 571			fcs = PPP_FCS(fcs, 0xff);
 572			PUT_BYTE(ap, buf, 0x03, islcp);
 573			fcs = PPP_FCS(fcs, 0x03);
 574		}
 575	}
 576
 577	/*
 578	 * Once we put in the last byte, we need to put in the FCS
 579	 * and closing flag, so make sure there is at least 7 bytes
 580	 * of free space in the output buffer.
 581	 */
 582	buflim = ap->obuf + OBUFSIZE - 6;
 583	while (i < count && buf < buflim) {
 584		c = data[i++];
 585		if (i == 1 && c == 0 && (ap->flags & SC_COMP_PROT))
 586			continue;	/* compress protocol field */
 587		fcs = PPP_FCS(fcs, c);
 588		PUT_BYTE(ap, buf, c, islcp);
 589	}
 590
 591	if (i < count) {
 592		/*
 593		 * Remember where we are up to in this packet.
 594		 */
 595		ap->olim = buf;
 596		ap->tpkt_pos = i;
 597		ap->tfcs = fcs;
 598		return 0;
 599	}
 600
 601	/*
 602	 * We have finished the packet.  Add the FCS and flag.
 603	 */
 604	fcs = ~fcs;
 605	c = fcs & 0xff;
 606	PUT_BYTE(ap, buf, c, islcp);
 607	c = (fcs >> 8) & 0xff;
 608	PUT_BYTE(ap, buf, c, islcp);
 609	*buf++ = PPP_FLAG;
 610	ap->olim = buf;
 611
 612	consume_skb(ap->tpkt);
 613	ap->tpkt = NULL;
 614	return 1;
 615}
 616
 617/*
 618 * Transmit-side routines.
 619 */
 620
 621/*
 622 * Send a packet to the peer over an async tty line.
 623 * Returns 1 iff the packet was accepted.
 624 * If the packet was not accepted, we will call ppp_output_wakeup
 625 * at some later time.
 626 */
 627static int
 628ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb)
 629{
 630	struct asyncppp *ap = chan->private;
 631
 632	ppp_async_push(ap);
 633
 634	if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
 635		return 0;	/* already full */
 636	ap->tpkt = skb;
 637	ap->tpkt_pos = 0;
 638
 639	ppp_async_push(ap);
 640	return 1;
 641}
 642
 643/*
 644 * Push as much data as possible out to the tty.
 645 */
 646static int
 647ppp_async_push(struct asyncppp *ap)
 648{
 649	int avail, sent, done = 0;
 650	struct tty_struct *tty = ap->tty;
 651	int tty_stuffed = 0;
 652
 653	/*
 654	 * We can get called recursively here if the tty write
 655	 * function calls our wakeup function.  This can happen
 656	 * for example on a pty with both the master and slave
 657	 * set to PPP line discipline.
 658	 * We use the XMIT_BUSY bit to detect this and get out,
 659	 * leaving the XMIT_WAKEUP bit set to tell the other
 660	 * instance that it may now be able to write more now.
 661	 */
 662	if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
 663		return 0;
 664	spin_lock_bh(&ap->xmit_lock);
 665	for (;;) {
 666		if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
 667			tty_stuffed = 0;
 668		if (!tty_stuffed && ap->optr < ap->olim) {
 669			avail = ap->olim - ap->optr;
 670			set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 671			sent = tty->ops->write(tty, ap->optr, avail);
 672			if (sent < 0)
 673				goto flush;	/* error, e.g. loss of CD */
 674			ap->optr += sent;
 675			if (sent < avail)
 676				tty_stuffed = 1;
 677			continue;
 678		}
 679		if (ap->optr >= ap->olim && ap->tpkt) {
 680			if (ppp_async_encode(ap)) {
 681				/* finished processing ap->tpkt */
 682				clear_bit(XMIT_FULL, &ap->xmit_flags);
 683				done = 1;
 684			}
 685			continue;
 686		}
 687		/*
 688		 * We haven't made any progress this time around.
 689		 * Clear XMIT_BUSY to let other callers in, but
 690		 * after doing so we have to check if anyone set
 691		 * XMIT_WAKEUP since we last checked it.  If they
 692		 * did, we should try again to set XMIT_BUSY and go
 693		 * around again in case XMIT_BUSY was still set when
 694		 * the other caller tried.
 695		 */
 696		clear_bit(XMIT_BUSY, &ap->xmit_flags);
 697		/* any more work to do? if not, exit the loop */
 698		if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) ||
 699		      (!tty_stuffed && ap->tpkt)))
 700			break;
 701		/* more work to do, see if we can do it now */
 702		if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
 703			break;
 704	}
 705	spin_unlock_bh(&ap->xmit_lock);
 706	return done;
 707
 708flush:
 709	clear_bit(XMIT_BUSY, &ap->xmit_flags);
 710	if (ap->tpkt) {
 711		kfree_skb(ap->tpkt);
 712		ap->tpkt = NULL;
 713		clear_bit(XMIT_FULL, &ap->xmit_flags);
 714		done = 1;
 715	}
 716	ap->optr = ap->olim;
 717	spin_unlock_bh(&ap->xmit_lock);
 718	return done;
 719}
 720
 721/*
 722 * Flush output from our internal buffers.
 723 * Called for the TCFLSH ioctl. Can be entered in parallel
 724 * but this is covered by the xmit_lock.
 725 */
 726static void
 727ppp_async_flush_output(struct asyncppp *ap)
 728{
 729	int done = 0;
 730
 731	spin_lock_bh(&ap->xmit_lock);
 732	ap->optr = ap->olim;
 733	if (ap->tpkt != NULL) {
 734		kfree_skb(ap->tpkt);
 735		ap->tpkt = NULL;
 736		clear_bit(XMIT_FULL, &ap->xmit_flags);
 737		done = 1;
 738	}
 739	spin_unlock_bh(&ap->xmit_lock);
 740	if (done)
 741		ppp_output_wakeup(&ap->chan);
 742}
 743
 744/*
 745 * Receive-side routines.
 746 */
 747
 748/* see how many ordinary chars there are at the start of buf */
 749static inline int
 750scan_ordinary(struct asyncppp *ap, const unsigned char *buf, int count)
 751{
 752	int i, c;
 753
 754	for (i = 0; i < count; ++i) {
 755		c = buf[i];
 756		if (c == PPP_ESCAPE || c == PPP_FLAG ||
 757		    (c < 0x20 && (ap->raccm & (1 << c)) != 0))
 758			break;
 759	}
 760	return i;
 761}
 762
 763/* called when a flag is seen - do end-of-packet processing */
 764static void
 765process_input_packet(struct asyncppp *ap)
 766{
 767	struct sk_buff *skb;
 768	unsigned char *p;
 769	unsigned int len, fcs;
 770
 771	skb = ap->rpkt;
 772	if (ap->state & (SC_TOSS | SC_ESCAPE))
 773		goto err;
 774
 775	if (skb == NULL)
 776		return;		/* 0-length packet */
 777
 778	/* check the FCS */
 779	p = skb->data;
 780	len = skb->len;
 781	if (len < 3)
 782		goto err;	/* too short */
 783	fcs = PPP_INITFCS;
 784	for (; len > 0; --len)
 785		fcs = PPP_FCS(fcs, *p++);
 786	if (fcs != PPP_GOODFCS)
 787		goto err;	/* bad FCS */
 788	skb_trim(skb, skb->len - 2);
 789
 790	/* check for address/control and protocol compression */
 791	p = skb->data;
 792	if (p[0] == PPP_ALLSTATIONS) {
 793		/* chop off address/control */
 794		if (p[1] != PPP_UI || skb->len < 3)
 795			goto err;
 796		p = skb_pull(skb, 2);
 797	}
 798
 799	/* If protocol field is not compressed, it can be LCP packet */
 800	if (!(p[0] & 0x01)) {
 801		unsigned int proto;
 802
 803		if (skb->len < 2)
 804			goto err;
 805		proto = (p[0] << 8) + p[1];
 806		if (proto == PPP_LCP)
 807			async_lcp_peek(ap, p, skb->len, 1);
 808	}
 809
 810	/* queue the frame to be processed */
 811	skb->cb[0] = ap->state;
 812	skb_queue_tail(&ap->rqueue, skb);
 813	ap->rpkt = NULL;
 814	ap->state = 0;
 815	return;
 816
 817 err:
 818	/* frame had an error, remember that, reset SC_TOSS & SC_ESCAPE */
 819	ap->state = SC_PREV_ERROR;
 820	if (skb) {
 821		/* make skb appear as freshly allocated */
 822		skb_trim(skb, 0);
 823		skb_reserve(skb, - skb_headroom(skb));
 824	}
 825}
 826
 827/* Called when the tty driver has data for us. Runs parallel with the
 828   other ldisc functions but will not be re-entered */
 829
 830static void
 831ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
 832		char *flags, int count)
 833{
 834	struct sk_buff *skb;
 835	int c, i, j, n, s, f;
 836	unsigned char *sp;
 837
 838	/* update bits used for 8-bit cleanness detection */
 839	if (~ap->rbits & SC_RCV_BITS) {
 840		s = 0;
 841		for (i = 0; i < count; ++i) {
 842			c = buf[i];
 843			if (flags && flags[i] != 0)
 844				continue;
 845			s |= (c & 0x80)? SC_RCV_B7_1: SC_RCV_B7_0;
 846			c = ((c >> 4) ^ c) & 0xf;
 847			s |= (0x6996 & (1 << c))? SC_RCV_ODDP: SC_RCV_EVNP;
 848		}
 849		ap->rbits |= s;
 850	}
 851
 852	while (count > 0) {
 853		/* scan through and see how many chars we can do in bulk */
 854		if ((ap->state & SC_ESCAPE) && buf[0] == PPP_ESCAPE)
 855			n = 1;
 856		else
 857			n = scan_ordinary(ap, buf, count);
 858
 859		f = 0;
 860		if (flags && (ap->state & SC_TOSS) == 0) {
 861			/* check the flags to see if any char had an error */
 862			for (j = 0; j < n; ++j)
 863				if ((f = flags[j]) != 0)
 864					break;
 865		}
 866		if (f != 0) {
 867			/* start tossing */
 868			ap->state |= SC_TOSS;
 869
 870		} else if (n > 0 && (ap->state & SC_TOSS) == 0) {
 871			/* stuff the chars in the skb */
 872			skb = ap->rpkt;
 873			if (!skb) {
 874				skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
 875				if (!skb)
 876					goto nomem;
 877				ap->rpkt = skb;
 878			}
 879			if (skb->len == 0) {
 880				/* Try to get the payload 4-byte aligned.
 881				 * This should match the
 882				 * PPP_ALLSTATIONS/PPP_UI/compressed tests in
 883				 * process_input_packet, but we do not have
 884				 * enough chars here to test buf[1] and buf[2].
 885				 */
 886				if (buf[0] != PPP_ALLSTATIONS)
 887					skb_reserve(skb, 2 + (buf[0] & 1));
 888			}
 889			if (n > skb_tailroom(skb)) {
 890				/* packet overflowed MRU */
 891				ap->state |= SC_TOSS;
 892			} else {
 893				sp = skb_put_data(skb, buf, n);
 894				if (ap->state & SC_ESCAPE) {
 895					sp[0] ^= PPP_TRANS;
 896					ap->state &= ~SC_ESCAPE;
 897				}
 898			}
 899		}
 900
 901		if (n >= count)
 902			break;
 903
 904		c = buf[n];
 905		if (flags != NULL && flags[n] != 0) {
 906			ap->state |= SC_TOSS;
 907		} else if (c == PPP_FLAG) {
 908			process_input_packet(ap);
 909		} else if (c == PPP_ESCAPE) {
 910			ap->state |= SC_ESCAPE;
 911		} else if (I_IXON(ap->tty)) {
 912			if (c == START_CHAR(ap->tty))
 913				start_tty(ap->tty);
 914			else if (c == STOP_CHAR(ap->tty))
 915				stop_tty(ap->tty);
 916		}
 917		/* otherwise it's a char in the recv ACCM */
 918		++n;
 919
 920		buf += n;
 921		if (flags)
 922			flags += n;
 923		count -= n;
 924	}
 925	return;
 926
 927 nomem:
 928	printk(KERN_ERR "PPPasync: no memory (input pkt)\n");
 929	ap->state |= SC_TOSS;
 930}
 931
 932/*
 933 * We look at LCP frames going past so that we can notice
 934 * and react to the LCP configure-ack from the peer.
 935 * In the situation where the peer has been sent a configure-ack
 936 * already, LCP is up once it has sent its configure-ack
 937 * so the immediately following packet can be sent with the
 938 * configured LCP options.  This allows us to process the following
 939 * packet correctly without pppd needing to respond quickly.
 940 *
 941 * We only respond to the received configure-ack if we have just
 942 * sent a configure-request, and the configure-ack contains the
 943 * same data (this is checked using a 16-bit crc of the data).
 944 */
 945#define CONFREQ		1	/* LCP code field values */
 946#define CONFACK		2
 947#define LCP_MRU		1	/* LCP option numbers */
 948#define LCP_ASYNCMAP	2
 949
 950static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
 951			   int len, int inbound)
 952{
 953	int dlen, fcs, i, code;
 954	u32 val;
 955
 956	data += 2;		/* skip protocol bytes */
 957	len -= 2;
 958	if (len < 4)		/* 4 = code, ID, length */
 959		return;
 960	code = data[0];
 961	if (code != CONFACK && code != CONFREQ)
 962		return;
 963	dlen = get_unaligned_be16(data + 2);
 964	if (len < dlen)
 965		return;		/* packet got truncated or length is bogus */
 966
 967	if (code == (inbound? CONFACK: CONFREQ)) {
 968		/*
 969		 * sent confreq or received confack:
 970		 * calculate the crc of the data from the ID field on.
 971		 */
 972		fcs = PPP_INITFCS;
 973		for (i = 1; i < dlen; ++i)
 974			fcs = PPP_FCS(fcs, data[i]);
 975
 976		if (!inbound) {
 977			/* outbound confreq - remember the crc for later */
 978			ap->lcp_fcs = fcs;
 979			return;
 980		}
 981
 982		/* received confack, check the crc */
 983		fcs ^= ap->lcp_fcs;
 984		ap->lcp_fcs = -1;
 985		if (fcs != 0)
 986			return;
 987	} else if (inbound)
 988		return;	/* not interested in received confreq */
 989
 990	/* process the options in the confack */
 991	data += 4;
 992	dlen -= 4;
 993	/* data[0] is code, data[1] is length */
 994	while (dlen >= 2 && dlen >= data[1] && data[1] >= 2) {
 995		switch (data[0]) {
 996		case LCP_MRU:
 997			val = get_unaligned_be16(data + 2);
 998			if (inbound)
 999				ap->mru = val;
1000			else
1001				ap->chan.mtu = val;
1002			break;
1003		case LCP_ASYNCMAP:
1004			val = get_unaligned_be32(data + 2);
1005			if (inbound)
1006				ap->raccm = val;
1007			else
1008				ap->xaccm[0] = val;
1009			break;
1010		}
1011		dlen -= data[1];
1012		data += data[1];
1013	}
1014}
1015
1016static void __exit ppp_async_cleanup(void)
1017{
1018	if (tty_unregister_ldisc(N_PPP) != 0)
1019		printk(KERN_ERR "failed to unregister PPP line discipline\n");
1020}
1021
1022module_init(ppp_async_init);
1023module_exit(ppp_async_cleanup);