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 <linux/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_DESCRIPTION("PPP async serial channel module");
  91MODULE_LICENSE("GPL");
  92MODULE_ALIAS_LDISC(N_PPP);
  93
  94/*
  95 * Prototypes.
  96 */
  97static int ppp_async_encode(struct asyncppp *ap);
  98static int ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb);
  99static int ppp_async_push(struct asyncppp *ap);
 100static void ppp_async_flush_output(struct asyncppp *ap);
 101static void ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
 102			    const u8 *flags, int count);
 103static int ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd,
 104			   unsigned long arg);
 105static void ppp_async_process(struct tasklet_struct *t);
 106
 107static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
 108			   int len, int inbound);
 109
 110static const struct ppp_channel_ops async_ops = {
 111	.start_xmit = ppp_async_send,
 112	.ioctl      = ppp_async_ioctl,
 113};
 114
 115/*
 116 * Routines implementing the PPP line discipline.
 117 */
 118
 119/*
 120 * We have a potential race on dereferencing tty->disc_data,
 121 * because the tty layer provides no locking at all - thus one
 122 * cpu could be running ppp_asynctty_receive while another
 123 * calls ppp_asynctty_close, which zeroes tty->disc_data and
 124 * frees the memory that ppp_asynctty_receive is using.  The best
 125 * way to fix this is to use a rwlock in the tty struct, but for now
 126 * we use a single global rwlock for all ttys in ppp line discipline.
 127 *
 128 * FIXME: this is no longer true. The _close path for the ldisc is
 129 * now guaranteed to be sane.
 130 */
 131static DEFINE_RWLOCK(disc_data_lock);
 132
 133static struct asyncppp *ap_get(struct tty_struct *tty)
 134{
 135	struct asyncppp *ap;
 136
 137	read_lock(&disc_data_lock);
 138	ap = tty->disc_data;
 139	if (ap != NULL)
 140		refcount_inc(&ap->refcnt);
 141	read_unlock(&disc_data_lock);
 142	return ap;
 143}
 144
 145static void ap_put(struct asyncppp *ap)
 146{
 147	if (refcount_dec_and_test(&ap->refcnt))
 148		complete(&ap->dead);
 149}
 150
 151/*
 152 * Called when a tty is put into PPP line discipline. Called in process
 153 * context.
 154 */
 155static int
 156ppp_asynctty_open(struct tty_struct *tty)
 157{
 158	struct asyncppp *ap;
 159	int err;
 160	int speed;
 161
 162	if (tty->ops->write == NULL)
 163		return -EOPNOTSUPP;
 164
 165	err = -ENOMEM;
 166	ap = kzalloc(sizeof(*ap), GFP_KERNEL);
 167	if (!ap)
 168		goto out;
 169
 170	/* initialize the asyncppp structure */
 171	ap->tty = tty;
 172	ap->mru = PPP_MRU;
 173	spin_lock_init(&ap->xmit_lock);
 174	spin_lock_init(&ap->recv_lock);
 175	ap->xaccm[0] = ~0U;
 176	ap->xaccm[3] = 0x60000000U;
 177	ap->raccm = ~0U;
 178	ap->optr = ap->obuf;
 179	ap->olim = ap->obuf;
 180	ap->lcp_fcs = -1;
 181
 182	skb_queue_head_init(&ap->rqueue);
 183	tasklet_setup(&ap->tsk, ppp_async_process);
 184
 185	refcount_set(&ap->refcnt, 1);
 186	init_completion(&ap->dead);
 187
 188	ap->chan.private = ap;
 189	ap->chan.ops = &async_ops;
 190	ap->chan.mtu = PPP_MRU;
 191	speed = tty_get_baud_rate(tty);
 192	ap->chan.speed = speed;
 193	err = ppp_register_channel(&ap->chan);
 194	if (err)
 195		goto out_free;
 196
 197	tty->disc_data = ap;
 198	tty->receive_room = 65536;
 199	return 0;
 200
 201 out_free:
 202	kfree(ap);
 203 out:
 204	return err;
 205}
 206
 207/*
 208 * Called when the tty is put into another line discipline
 209 * or it hangs up.  We have to wait for any cpu currently
 210 * executing in any of the other ppp_asynctty_* routines to
 211 * finish before we can call ppp_unregister_channel and free
 212 * the asyncppp struct.  This routine must be called from
 213 * process context, not interrupt or softirq context.
 214 */
 215static void
 216ppp_asynctty_close(struct tty_struct *tty)
 217{
 218	struct asyncppp *ap;
 219
 220	write_lock_irq(&disc_data_lock);
 221	ap = tty->disc_data;
 222	tty->disc_data = NULL;
 223	write_unlock_irq(&disc_data_lock);
 224	if (!ap)
 225		return;
 226
 227	/*
 228	 * We have now ensured that nobody can start using ap from now
 229	 * on, but we have to wait for all existing users to finish.
 230	 * Note that ppp_unregister_channel ensures that no calls to
 231	 * our channel ops (i.e. ppp_async_send/ioctl) are in progress
 232	 * by the time it returns.
 233	 */
 234	if (!refcount_dec_and_test(&ap->refcnt))
 235		wait_for_completion(&ap->dead);
 236	tasklet_kill(&ap->tsk);
 237
 238	ppp_unregister_channel(&ap->chan);
 239	kfree_skb(ap->rpkt);
 240	skb_queue_purge(&ap->rqueue);
 241	kfree_skb(ap->tpkt);
 242	kfree(ap);
 243}
 244
 245/*
 246 * Called on tty hangup in process context.
 247 *
 248 * Wait for I/O to driver to complete and unregister PPP channel.
 249 * This is already done by the close routine, so just call that.
 250 */
 251static void ppp_asynctty_hangup(struct tty_struct *tty)
 252{
 253	ppp_asynctty_close(tty);
 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, u8 *buf,
 262		  size_t count, void **cookie, unsigned long offset)
 
 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, const u8 *buf,
 273		   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, unsigned int cmd, unsigned long arg)
 285{
 286	struct asyncppp *ap = ap_get(tty);
 287	int err, val;
 288	int __user *p = (int __user *)arg;
 289
 290	if (!ap)
 291		return -ENXIO;
 292	err = -EFAULT;
 293	switch (cmd) {
 294	case PPPIOCGCHAN:
 295		err = -EFAULT;
 296		if (put_user(ppp_channel_index(&ap->chan), p))
 297			break;
 298		err = 0;
 299		break;
 300
 301	case PPPIOCGUNIT:
 302		err = -EFAULT;
 303		if (put_user(ppp_unit_number(&ap->chan), p))
 304			break;
 305		err = 0;
 306		break;
 307
 308	case TCFLSH:
 309		/* flush our buffers and the serial port's buffer */
 310		if (arg == TCIOFLUSH || arg == TCOFLUSH)
 311			ppp_async_flush_output(ap);
 312		err = n_tty_ioctl_helper(tty, cmd, arg);
 313		break;
 314
 315	case FIONREAD:
 316		val = 0;
 317		if (put_user(val, p))
 318			break;
 319		err = 0;
 320		break;
 321
 322	default:
 323		/* Try the various mode ioctls */
 324		err = tty_mode_ioctl(tty, cmd, arg);
 325	}
 326
 327	ap_put(ap);
 328	return err;
 329}
 330
 
 
 
 
 
 
 
 331/* May sleep, don't call from interrupt level or with interrupts disabled */
 332static void
 333ppp_asynctty_receive(struct tty_struct *tty, const u8 *buf, const u8 *cflags,
 334		     size_t count)
 335{
 336	struct asyncppp *ap = ap_get(tty);
 337	unsigned long flags;
 338
 339	if (!ap)
 340		return;
 341	spin_lock_irqsave(&ap->recv_lock, flags);
 342	ppp_async_input(ap, buf, cflags, count);
 343	spin_unlock_irqrestore(&ap->recv_lock, flags);
 344	if (!skb_queue_empty(&ap->rqueue))
 345		tasklet_schedule(&ap->tsk);
 346	ap_put(ap);
 347	tty_unthrottle(tty);
 348}
 349
 350static void
 351ppp_asynctty_wakeup(struct tty_struct *tty)
 352{
 353	struct asyncppp *ap = ap_get(tty);
 354
 355	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 356	if (!ap)
 357		return;
 358	set_bit(XMIT_WAKEUP, &ap->xmit_flags);
 359	tasklet_schedule(&ap->tsk);
 360	ap_put(ap);
 361}
 362
 363
 364static struct tty_ldisc_ops ppp_ldisc = {
 365	.owner  = THIS_MODULE,
 366	.num	= N_PPP,
 367	.name	= "ppp",
 368	.open	= ppp_asynctty_open,
 369	.close	= ppp_asynctty_close,
 370	.hangup	= ppp_asynctty_hangup,
 371	.read	= ppp_asynctty_read,
 372	.write	= ppp_asynctty_write,
 373	.ioctl	= ppp_asynctty_ioctl,
 
 374	.receive_buf = ppp_asynctty_receive,
 375	.write_wakeup = ppp_asynctty_wakeup,
 376};
 377
 378static int __init
 379ppp_async_init(void)
 380{
 381	int err;
 382
 383	err = tty_register_ldisc(&ppp_ldisc);
 384	if (err != 0)
 385		printk(KERN_ERR "PPP_async: error %d registering line disc.\n",
 386		       err);
 387	return err;
 388}
 389
 390/*
 391 * The following routines provide the PPP channel interface.
 392 */
 393static int
 394ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
 395{
 396	struct asyncppp *ap = chan->private;
 397	void __user *argp = (void __user *)arg;
 398	int __user *p = argp;
 399	int err, val;
 400	u32 accm[8];
 401
 402	err = -EFAULT;
 403	switch (cmd) {
 404	case PPPIOCGFLAGS:
 405		val = ap->flags | ap->rbits;
 406		if (put_user(val, p))
 407			break;
 408		err = 0;
 409		break;
 410	case PPPIOCSFLAGS:
 411		if (get_user(val, p))
 412			break;
 413		ap->flags = val & ~SC_RCV_BITS;
 414		spin_lock_irq(&ap->recv_lock);
 415		ap->rbits = val & SC_RCV_BITS;
 416		spin_unlock_irq(&ap->recv_lock);
 417		err = 0;
 418		break;
 419
 420	case PPPIOCGASYNCMAP:
 421		if (put_user(ap->xaccm[0], (u32 __user *)argp))
 422			break;
 423		err = 0;
 424		break;
 425	case PPPIOCSASYNCMAP:
 426		if (get_user(ap->xaccm[0], (u32 __user *)argp))
 427			break;
 428		err = 0;
 429		break;
 430
 431	case PPPIOCGRASYNCMAP:
 432		if (put_user(ap->raccm, (u32 __user *)argp))
 433			break;
 434		err = 0;
 435		break;
 436	case PPPIOCSRASYNCMAP:
 437		if (get_user(ap->raccm, (u32 __user *)argp))
 438			break;
 439		err = 0;
 440		break;
 441
 442	case PPPIOCGXASYNCMAP:
 443		if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
 444			break;
 445		err = 0;
 446		break;
 447	case PPPIOCSXASYNCMAP:
 448		if (copy_from_user(accm, argp, sizeof(accm)))
 449			break;
 450		accm[2] &= ~0x40000000U;	/* can't escape 0x5e */
 451		accm[3] |= 0x60000000U;		/* must escape 0x7d, 0x7e */
 452		memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
 453		err = 0;
 454		break;
 455
 456	case PPPIOCGMRU:
 457		if (put_user(ap->mru, p))
 458			break;
 459		err = 0;
 460		break;
 461	case PPPIOCSMRU:
 462		if (get_user(val, p))
 463			break;
 464		if (val > U16_MAX) {
 465			err = -EINVAL;
 466			break;
 467		}
 468		if (val < PPP_MRU)
 469			val = PPP_MRU;
 470		ap->mru = val;
 471		err = 0;
 472		break;
 473
 474	default:
 475		err = -ENOTTY;
 476	}
 477
 478	return err;
 479}
 480
 481/*
 482 * This is called at softirq level to deliver received packets
 483 * to the ppp_generic code, and to tell the ppp_generic code
 484 * if we can accept more output now.
 485 */
 486static void ppp_async_process(struct tasklet_struct *t)
 487{
 488	struct asyncppp *ap = from_tasklet(ap, t, tsk);
 489	struct sk_buff *skb;
 490
 491	/* process received packets */
 492	while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
 493		if (skb->cb[0])
 494			ppp_input_error(&ap->chan, 0);
 495		ppp_input(&ap->chan, skb);
 496	}
 497
 498	/* try to push more stuff out */
 499	if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_async_push(ap))
 500		ppp_output_wakeup(&ap->chan);
 501}
 502
 503/*
 504 * Procedures for encapsulation and framing.
 505 */
 506
 507/*
 508 * Procedure to encode the data for async serial transmission.
 509 * Does octet stuffing (escaping), puts the address/control bytes
 510 * on if A/C compression is disabled, and does protocol compression.
 511 * Assumes ap->tpkt != 0 on entry.
 512 * Returns 1 if we finished the current frame, 0 otherwise.
 513 */
 514
 515#define PUT_BYTE(ap, buf, c, islcp)	do {		\
 516	if ((islcp && c < 0x20) || (ap->xaccm[c >> 5] & (1 << (c & 0x1f)))) {\
 517		*buf++ = PPP_ESCAPE;			\
 518		*buf++ = c ^ PPP_TRANS;			\
 519	} else						\
 520		*buf++ = c;				\
 521} while (0)
 522
 523static int
 524ppp_async_encode(struct asyncppp *ap)
 525{
 526	int fcs, i, count, c, proto;
 527	unsigned char *buf, *buflim;
 528	unsigned char *data;
 529	int islcp;
 530
 531	buf = ap->obuf;
 532	ap->olim = buf;
 533	ap->optr = buf;
 534	i = ap->tpkt_pos;
 535	data = ap->tpkt->data;
 536	count = ap->tpkt->len;
 537	fcs = ap->tfcs;
 538	proto = get_unaligned_be16(data);
 539
 540	/*
 541	 * LCP packets with code values between 1 (configure-request)
 542	 * and 7 (code-reject) must be sent as though no options
 543	 * had been negotiated.
 544	 */
 545	islcp = proto == PPP_LCP && count >= 3 && 1 <= data[2] && data[2] <= 7;
 546
 547	if (i == 0) {
 548		if (islcp)
 549			async_lcp_peek(ap, data, count, 0);
 550
 551		/*
 552		 * Start of a new packet - insert the leading FLAG
 553		 * character if necessary.
 554		 */
 555		if (islcp || flag_time == 0 ||
 556		    time_after_eq(jiffies, ap->last_xmit + flag_time))
 557			*buf++ = PPP_FLAG;
 558		ap->last_xmit = jiffies;
 559		fcs = PPP_INITFCS;
 560
 561		/*
 562		 * Put in the address/control bytes if necessary
 563		 */
 564		if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
 565			PUT_BYTE(ap, buf, 0xff, islcp);
 566			fcs = PPP_FCS(fcs, 0xff);
 567			PUT_BYTE(ap, buf, 0x03, islcp);
 568			fcs = PPP_FCS(fcs, 0x03);
 569		}
 570	}
 571
 572	/*
 573	 * Once we put in the last byte, we need to put in the FCS
 574	 * and closing flag, so make sure there is at least 7 bytes
 575	 * of free space in the output buffer.
 576	 */
 577	buflim = ap->obuf + OBUFSIZE - 6;
 578	while (i < count && buf < buflim) {
 579		c = data[i++];
 580		if (i == 1 && c == 0 && (ap->flags & SC_COMP_PROT))
 581			continue;	/* compress protocol field */
 582		fcs = PPP_FCS(fcs, c);
 583		PUT_BYTE(ap, buf, c, islcp);
 584	}
 585
 586	if (i < count) {
 587		/*
 588		 * Remember where we are up to in this packet.
 589		 */
 590		ap->olim = buf;
 591		ap->tpkt_pos = i;
 592		ap->tfcs = fcs;
 593		return 0;
 594	}
 595
 596	/*
 597	 * We have finished the packet.  Add the FCS and flag.
 598	 */
 599	fcs = ~fcs;
 600	c = fcs & 0xff;
 601	PUT_BYTE(ap, buf, c, islcp);
 602	c = (fcs >> 8) & 0xff;
 603	PUT_BYTE(ap, buf, c, islcp);
 604	*buf++ = PPP_FLAG;
 605	ap->olim = buf;
 606
 607	consume_skb(ap->tpkt);
 608	ap->tpkt = NULL;
 609	return 1;
 610}
 611
 612/*
 613 * Transmit-side routines.
 614 */
 615
 616/*
 617 * Send a packet to the peer over an async tty line.
 618 * Returns 1 iff the packet was accepted.
 619 * If the packet was not accepted, we will call ppp_output_wakeup
 620 * at some later time.
 621 */
 622static int
 623ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb)
 624{
 625	struct asyncppp *ap = chan->private;
 626
 627	ppp_async_push(ap);
 628
 629	if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
 630		return 0;	/* already full */
 631	ap->tpkt = skb;
 632	ap->tpkt_pos = 0;
 633
 634	ppp_async_push(ap);
 635	return 1;
 636}
 637
 638/*
 639 * Push as much data as possible out to the tty.
 640 */
 641static int
 642ppp_async_push(struct asyncppp *ap)
 643{
 644	int avail, sent, done = 0;
 645	struct tty_struct *tty = ap->tty;
 646	int tty_stuffed = 0;
 647
 648	/*
 649	 * We can get called recursively here if the tty write
 650	 * function calls our wakeup function.  This can happen
 651	 * for example on a pty with both the master and slave
 652	 * set to PPP line discipline.
 653	 * We use the XMIT_BUSY bit to detect this and get out,
 654	 * leaving the XMIT_WAKEUP bit set to tell the other
 655	 * instance that it may now be able to write more now.
 656	 */
 657	if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
 658		return 0;
 659	spin_lock_bh(&ap->xmit_lock);
 660	for (;;) {
 661		if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
 662			tty_stuffed = 0;
 663		if (!tty_stuffed && ap->optr < ap->olim) {
 664			avail = ap->olim - ap->optr;
 665			set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 666			sent = tty->ops->write(tty, ap->optr, avail);
 667			if (sent < 0)
 668				goto flush;	/* error, e.g. loss of CD */
 669			ap->optr += sent;
 670			if (sent < avail)
 671				tty_stuffed = 1;
 672			continue;
 673		}
 674		if (ap->optr >= ap->olim && ap->tpkt) {
 675			if (ppp_async_encode(ap)) {
 676				/* finished processing ap->tpkt */
 677				clear_bit(XMIT_FULL, &ap->xmit_flags);
 678				done = 1;
 679			}
 680			continue;
 681		}
 682		/*
 683		 * We haven't made any progress this time around.
 684		 * Clear XMIT_BUSY to let other callers in, but
 685		 * after doing so we have to check if anyone set
 686		 * XMIT_WAKEUP since we last checked it.  If they
 687		 * did, we should try again to set XMIT_BUSY and go
 688		 * around again in case XMIT_BUSY was still set when
 689		 * the other caller tried.
 690		 */
 691		clear_bit(XMIT_BUSY, &ap->xmit_flags);
 692		/* any more work to do? if not, exit the loop */
 693		if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) ||
 694		      (!tty_stuffed && ap->tpkt)))
 695			break;
 696		/* more work to do, see if we can do it now */
 697		if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
 698			break;
 699	}
 700	spin_unlock_bh(&ap->xmit_lock);
 701	return done;
 702
 703flush:
 704	clear_bit(XMIT_BUSY, &ap->xmit_flags);
 705	if (ap->tpkt) {
 706		kfree_skb(ap->tpkt);
 707		ap->tpkt = NULL;
 708		clear_bit(XMIT_FULL, &ap->xmit_flags);
 709		done = 1;
 710	}
 711	ap->optr = ap->olim;
 712	spin_unlock_bh(&ap->xmit_lock);
 713	return done;
 714}
 715
 716/*
 717 * Flush output from our internal buffers.
 718 * Called for the TCFLSH ioctl. Can be entered in parallel
 719 * but this is covered by the xmit_lock.
 720 */
 721static void
 722ppp_async_flush_output(struct asyncppp *ap)
 723{
 724	int done = 0;
 725
 726	spin_lock_bh(&ap->xmit_lock);
 727	ap->optr = ap->olim;
 728	if (ap->tpkt != NULL) {
 729		kfree_skb(ap->tpkt);
 730		ap->tpkt = NULL;
 731		clear_bit(XMIT_FULL, &ap->xmit_flags);
 732		done = 1;
 733	}
 734	spin_unlock_bh(&ap->xmit_lock);
 735	if (done)
 736		ppp_output_wakeup(&ap->chan);
 737}
 738
 739/*
 740 * Receive-side routines.
 741 */
 742
 743/* see how many ordinary chars there are at the start of buf */
 744static inline int
 745scan_ordinary(struct asyncppp *ap, const unsigned char *buf, int count)
 746{
 747	int i, c;
 748
 749	for (i = 0; i < count; ++i) {
 750		c = buf[i];
 751		if (c == PPP_ESCAPE || c == PPP_FLAG ||
 752		    (c < 0x20 && (ap->raccm & (1 << c)) != 0))
 753			break;
 754	}
 755	return i;
 756}
 757
 758/* called when a flag is seen - do end-of-packet processing */
 759static void
 760process_input_packet(struct asyncppp *ap)
 761{
 762	struct sk_buff *skb;
 763	unsigned char *p;
 764	unsigned int len, fcs;
 765
 766	skb = ap->rpkt;
 767	if (ap->state & (SC_TOSS | SC_ESCAPE))
 768		goto err;
 769
 770	if (skb == NULL)
 771		return;		/* 0-length packet */
 772
 773	/* check the FCS */
 774	p = skb->data;
 775	len = skb->len;
 776	if (len < 3)
 777		goto err;	/* too short */
 778	fcs = PPP_INITFCS;
 779	for (; len > 0; --len)
 780		fcs = PPP_FCS(fcs, *p++);
 781	if (fcs != PPP_GOODFCS)
 782		goto err;	/* bad FCS */
 783	skb_trim(skb, skb->len - 2);
 784
 785	/* check for address/control and protocol compression */
 786	p = skb->data;
 787	if (p[0] == PPP_ALLSTATIONS) {
 788		/* chop off address/control */
 789		if (p[1] != PPP_UI || skb->len < 3)
 790			goto err;
 791		p = skb_pull(skb, 2);
 792	}
 793
 794	/* If protocol field is not compressed, it can be LCP packet */
 795	if (!(p[0] & 0x01)) {
 796		unsigned int proto;
 797
 798		if (skb->len < 2)
 799			goto err;
 800		proto = (p[0] << 8) + p[1];
 801		if (proto == PPP_LCP)
 802			async_lcp_peek(ap, p, skb->len, 1);
 803	}
 804
 805	/* queue the frame to be processed */
 806	skb->cb[0] = ap->state;
 807	skb_queue_tail(&ap->rqueue, skb);
 808	ap->rpkt = NULL;
 809	ap->state = 0;
 810	return;
 811
 812 err:
 813	/* frame had an error, remember that, reset SC_TOSS & SC_ESCAPE */
 814	ap->state = SC_PREV_ERROR;
 815	if (skb) {
 816		/* make skb appear as freshly allocated */
 817		skb_trim(skb, 0);
 818		skb_reserve(skb, - skb_headroom(skb));
 819	}
 820}
 821
 822/* Called when the tty driver has data for us. Runs parallel with the
 823   other ldisc functions but will not be re-entered */
 824
 825static void
 826ppp_async_input(struct asyncppp *ap, const u8 *buf, const u8 *flags, int count)
 
 827{
 828	struct sk_buff *skb;
 829	int c, i, j, n, s, f;
 830	unsigned char *sp;
 831
 832	/* update bits used for 8-bit cleanness detection */
 833	if (~ap->rbits & SC_RCV_BITS) {
 834		s = 0;
 835		for (i = 0; i < count; ++i) {
 836			c = buf[i];
 837			if (flags && flags[i] != 0)
 838				continue;
 839			s |= (c & 0x80)? SC_RCV_B7_1: SC_RCV_B7_0;
 840			c = ((c >> 4) ^ c) & 0xf;
 841			s |= (0x6996 & (1 << c))? SC_RCV_ODDP: SC_RCV_EVNP;
 842		}
 843		ap->rbits |= s;
 844	}
 845
 846	while (count > 0) {
 847		/* scan through and see how many chars we can do in bulk */
 848		if ((ap->state & SC_ESCAPE) && buf[0] == PPP_ESCAPE)
 849			n = 1;
 850		else
 851			n = scan_ordinary(ap, buf, count);
 852
 853		f = 0;
 854		if (flags && (ap->state & SC_TOSS) == 0) {
 855			/* check the flags to see if any char had an error */
 856			for (j = 0; j < n; ++j)
 857				if ((f = flags[j]) != 0)
 858					break;
 859		}
 860		if (f != 0) {
 861			/* start tossing */
 862			ap->state |= SC_TOSS;
 863
 864		} else if (n > 0 && (ap->state & SC_TOSS) == 0) {
 865			/* stuff the chars in the skb */
 866			skb = ap->rpkt;
 867			if (!skb) {
 868				skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
 869				if (!skb)
 870					goto nomem;
 871				ap->rpkt = skb;
 872			}
 873			if (skb->len == 0) {
 874				/* Try to get the payload 4-byte aligned.
 875				 * This should match the
 876				 * PPP_ALLSTATIONS/PPP_UI/compressed tests in
 877				 * process_input_packet, but we do not have
 878				 * enough chars here to test buf[1] and buf[2].
 879				 */
 880				if (buf[0] != PPP_ALLSTATIONS)
 881					skb_reserve(skb, 2 + (buf[0] & 1));
 882			}
 883			if (n > skb_tailroom(skb)) {
 884				/* packet overflowed MRU */
 885				ap->state |= SC_TOSS;
 886			} else {
 887				sp = skb_put_data(skb, buf, n);
 888				if (ap->state & SC_ESCAPE) {
 889					sp[0] ^= PPP_TRANS;
 890					ap->state &= ~SC_ESCAPE;
 891				}
 892			}
 893		}
 894
 895		if (n >= count)
 896			break;
 897
 898		c = buf[n];
 899		if (flags != NULL && flags[n] != 0) {
 900			ap->state |= SC_TOSS;
 901		} else if (c == PPP_FLAG) {
 902			process_input_packet(ap);
 903		} else if (c == PPP_ESCAPE) {
 904			ap->state |= SC_ESCAPE;
 905		} else if (I_IXON(ap->tty)) {
 906			if (c == START_CHAR(ap->tty))
 907				start_tty(ap->tty);
 908			else if (c == STOP_CHAR(ap->tty))
 909				stop_tty(ap->tty);
 910		}
 911		/* otherwise it's a char in the recv ACCM */
 912		++n;
 913
 914		buf += n;
 915		if (flags)
 916			flags += n;
 917		count -= n;
 918	}
 919	return;
 920
 921 nomem:
 922	printk(KERN_ERR "PPPasync: no memory (input pkt)\n");
 923	ap->state |= SC_TOSS;
 924}
 925
 926/*
 927 * We look at LCP frames going past so that we can notice
 928 * and react to the LCP configure-ack from the peer.
 929 * In the situation where the peer has been sent a configure-ack
 930 * already, LCP is up once it has sent its configure-ack
 931 * so the immediately following packet can be sent with the
 932 * configured LCP options.  This allows us to process the following
 933 * packet correctly without pppd needing to respond quickly.
 934 *
 935 * We only respond to the received configure-ack if we have just
 936 * sent a configure-request, and the configure-ack contains the
 937 * same data (this is checked using a 16-bit crc of the data).
 938 */
 939#define CONFREQ		1	/* LCP code field values */
 940#define CONFACK		2
 941#define LCP_MRU		1	/* LCP option numbers */
 942#define LCP_ASYNCMAP	2
 943
 944static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
 945			   int len, int inbound)
 946{
 947	int dlen, fcs, i, code;
 948	u32 val;
 949
 950	data += 2;		/* skip protocol bytes */
 951	len -= 2;
 952	if (len < 4)		/* 4 = code, ID, length */
 953		return;
 954	code = data[0];
 955	if (code != CONFACK && code != CONFREQ)
 956		return;
 957	dlen = get_unaligned_be16(data + 2);
 958	if (len < dlen)
 959		return;		/* packet got truncated or length is bogus */
 960
 961	if (code == (inbound? CONFACK: CONFREQ)) {
 962		/*
 963		 * sent confreq or received confack:
 964		 * calculate the crc of the data from the ID field on.
 965		 */
 966		fcs = PPP_INITFCS;
 967		for (i = 1; i < dlen; ++i)
 968			fcs = PPP_FCS(fcs, data[i]);
 969
 970		if (!inbound) {
 971			/* outbound confreq - remember the crc for later */
 972			ap->lcp_fcs = fcs;
 973			return;
 974		}
 975
 976		/* received confack, check the crc */
 977		fcs ^= ap->lcp_fcs;
 978		ap->lcp_fcs = -1;
 979		if (fcs != 0)
 980			return;
 981	} else if (inbound)
 982		return;	/* not interested in received confreq */
 983
 984	/* process the options in the confack */
 985	data += 4;
 986	dlen -= 4;
 987	/* data[0] is code, data[1] is length */
 988	while (dlen >= 2 && dlen >= data[1] && data[1] >= 2) {
 989		switch (data[0]) {
 990		case LCP_MRU:
 991			val = get_unaligned_be16(data + 2);
 992			if (inbound)
 993				ap->mru = val;
 994			else
 995				ap->chan.mtu = val;
 996			break;
 997		case LCP_ASYNCMAP:
 998			val = get_unaligned_be32(data + 2);
 999			if (inbound)
1000				ap->raccm = val;
1001			else
1002				ap->xaccm[0] = val;
1003			break;
1004		}
1005		dlen -= data[1];
1006		data += data[1];
1007	}
1008}
1009
1010static void __exit ppp_async_cleanup(void)
1011{
1012	tty_unregister_ldisc(&ppp_ldisc);
1013}
1014
1015module_init(ppp_async_init);
1016module_exit(ppp_async_cleanup);