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			    const u8 *flags, int count);
102static int ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd,
103			   unsigned long arg);
104static void ppp_async_process(struct tasklet_struct *t);
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_setup(&ap->tsk, ppp_async_process);
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 void ppp_asynctty_hangup(struct tty_struct *tty)
251{
252	ppp_asynctty_close(tty);
253}
254
255/*
256 * Read does nothing - no data is ever available this way.
257 * Pppd reads and writes packets via /dev/ppp instead.
258 */
259static ssize_t
260ppp_asynctty_read(struct tty_struct *tty, struct file *file, u8 *buf,
261		  size_t count, void **cookie, unsigned long offset)
262{
263	return -EAGAIN;
264}
265
266/*
267 * Write on the tty does nothing, the packets all come in
268 * from the ppp generic stuff.
269 */
270static ssize_t
271ppp_asynctty_write(struct tty_struct *tty, struct file *file, const u8 *buf,
272		   size_t count)
273{
274	return -EAGAIN;
275}
276
277/*
278 * Called in process context only. May be re-entered by multiple
279 * ioctl calling threads.
280 */
281
282static int
283ppp_asynctty_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
284{
285	struct asyncppp *ap = ap_get(tty);
286	int err, val;
287	int __user *p = (int __user *)arg;
288
289	if (!ap)
290		return -ENXIO;
291	err = -EFAULT;
292	switch (cmd) {
293	case PPPIOCGCHAN:
294		err = -EFAULT;
295		if (put_user(ppp_channel_index(&ap->chan), p))
296			break;
297		err = 0;
298		break;
299
300	case PPPIOCGUNIT:
301		err = -EFAULT;
302		if (put_user(ppp_unit_number(&ap->chan), p))
303			break;
304		err = 0;
305		break;
306
307	case TCFLSH:
308		/* flush our buffers and the serial port's buffer */
309		if (arg == TCIOFLUSH || arg == TCOFLUSH)
310			ppp_async_flush_output(ap);
311		err = n_tty_ioctl_helper(tty, cmd, arg);
312		break;
313
314	case FIONREAD:
315		val = 0;
316		if (put_user(val, p))
317			break;
318		err = 0;
319		break;
320
321	default:
322		/* Try the various mode ioctls */
323		err = tty_mode_ioctl(tty, cmd, arg);
324	}
325
326	ap_put(ap);
327	return err;
328}
329
330/* May sleep, don't call from interrupt level or with interrupts disabled */
331static void
332ppp_asynctty_receive(struct tty_struct *tty, const u8 *buf, const u8 *cflags,
333		     size_t count)
334{
335	struct asyncppp *ap = ap_get(tty);
336	unsigned long flags;
337
338	if (!ap)
339		return;
340	spin_lock_irqsave(&ap->recv_lock, flags);
341	ppp_async_input(ap, buf, cflags, count);
342	spin_unlock_irqrestore(&ap->recv_lock, flags);
343	if (!skb_queue_empty(&ap->rqueue))
344		tasklet_schedule(&ap->tsk);
345	ap_put(ap);
346	tty_unthrottle(tty);
347}
348
349static void
350ppp_asynctty_wakeup(struct tty_struct *tty)
351{
352	struct asyncppp *ap = ap_get(tty);
353
354	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
355	if (!ap)
356		return;
357	set_bit(XMIT_WAKEUP, &ap->xmit_flags);
358	tasklet_schedule(&ap->tsk);
359	ap_put(ap);
360}
361
362
363static struct tty_ldisc_ops ppp_ldisc = {
364	.owner  = THIS_MODULE,
365	.num	= N_PPP,
366	.name	= "ppp",
367	.open	= ppp_asynctty_open,
368	.close	= ppp_asynctty_close,
369	.hangup	= ppp_asynctty_hangup,
370	.read	= ppp_asynctty_read,
371	.write	= ppp_asynctty_write,
372	.ioctl	= ppp_asynctty_ioctl,
373	.receive_buf = ppp_asynctty_receive,
374	.write_wakeup = ppp_asynctty_wakeup,
375};
376
377static int __init
378ppp_async_init(void)
379{
380	int err;
381
382	err = tty_register_ldisc(&ppp_ldisc);
383	if (err != 0)
384		printk(KERN_ERR "PPP_async: error %d registering line disc.\n",
385		       err);
386	return err;
387}
388
389/*
390 * The following routines provide the PPP channel interface.
391 */
392static int
393ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
394{
395	struct asyncppp *ap = chan->private;
396	void __user *argp = (void __user *)arg;
397	int __user *p = argp;
398	int err, val;
399	u32 accm[8];
400
401	err = -EFAULT;
402	switch (cmd) {
403	case PPPIOCGFLAGS:
404		val = ap->flags | ap->rbits;
405		if (put_user(val, p))
406			break;
407		err = 0;
408		break;
409	case PPPIOCSFLAGS:
410		if (get_user(val, p))
411			break;
412		ap->flags = val & ~SC_RCV_BITS;
413		spin_lock_irq(&ap->recv_lock);
414		ap->rbits = val & SC_RCV_BITS;
415		spin_unlock_irq(&ap->recv_lock);
416		err = 0;
417		break;
418
419	case PPPIOCGASYNCMAP:
420		if (put_user(ap->xaccm[0], (u32 __user *)argp))
421			break;
422		err = 0;
423		break;
424	case PPPIOCSASYNCMAP:
425		if (get_user(ap->xaccm[0], (u32 __user *)argp))
426			break;
427		err = 0;
428		break;
429
430	case PPPIOCGRASYNCMAP:
431		if (put_user(ap->raccm, (u32 __user *)argp))
432			break;
433		err = 0;
434		break;
435	case PPPIOCSRASYNCMAP:
436		if (get_user(ap->raccm, (u32 __user *)argp))
437			break;
438		err = 0;
439		break;
440
441	case PPPIOCGXASYNCMAP:
442		if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
443			break;
444		err = 0;
445		break;
446	case PPPIOCSXASYNCMAP:
447		if (copy_from_user(accm, argp, sizeof(accm)))
448			break;
449		accm[2] &= ~0x40000000U;	/* can't escape 0x5e */
450		accm[3] |= 0x60000000U;		/* must escape 0x7d, 0x7e */
451		memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
452		err = 0;
453		break;
454
455	case PPPIOCGMRU:
456		if (put_user(ap->mru, p))
457			break;
458		err = 0;
459		break;
460	case PPPIOCSMRU:
461		if (get_user(val, p))
462			break;
463		if (val > U16_MAX) {
464			err = -EINVAL;
465			break;
466		}
467		if (val < PPP_MRU)
468			val = PPP_MRU;
469		ap->mru = val;
470		err = 0;
471		break;
472
473	default:
474		err = -ENOTTY;
475	}
476
477	return err;
478}
479
480/*
481 * This is called at softirq level to deliver received packets
482 * to the ppp_generic code, and to tell the ppp_generic code
483 * if we can accept more output now.
484 */
485static void ppp_async_process(struct tasklet_struct *t)
486{
487	struct asyncppp *ap = from_tasklet(ap, t, tsk);
488	struct sk_buff *skb;
489
490	/* process received packets */
491	while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
492		if (skb->cb[0])
493			ppp_input_error(&ap->chan, 0);
494		ppp_input(&ap->chan, skb);
495	}
496
497	/* try to push more stuff out */
498	if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_async_push(ap))
499		ppp_output_wakeup(&ap->chan);
500}
501
502/*
503 * Procedures for encapsulation and framing.
504 */
505
506/*
507 * Procedure to encode the data for async serial transmission.
508 * Does octet stuffing (escaping), puts the address/control bytes
509 * on if A/C compression is disabled, and does protocol compression.
510 * Assumes ap->tpkt != 0 on entry.
511 * Returns 1 if we finished the current frame, 0 otherwise.
512 */
513
514#define PUT_BYTE(ap, buf, c, islcp)	do {		\
515	if ((islcp && c < 0x20) || (ap->xaccm[c >> 5] & (1 << (c & 0x1f)))) {\
516		*buf++ = PPP_ESCAPE;			\
517		*buf++ = c ^ PPP_TRANS;			\
518	} else						\
519		*buf++ = c;				\
520} while (0)
521
522static int
523ppp_async_encode(struct asyncppp *ap)
524{
525	int fcs, i, count, c, proto;
526	unsigned char *buf, *buflim;
527	unsigned char *data;
528	int islcp;
529
530	buf = ap->obuf;
531	ap->olim = buf;
532	ap->optr = buf;
533	i = ap->tpkt_pos;
534	data = ap->tpkt->data;
535	count = ap->tpkt->len;
536	fcs = ap->tfcs;
537	proto = get_unaligned_be16(data);
538
539	/*
540	 * LCP packets with code values between 1 (configure-reqest)
541	 * and 7 (code-reject) must be sent as though no options
542	 * had been negotiated.
543	 */
544	islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
545
546	if (i == 0) {
547		if (islcp)
548			async_lcp_peek(ap, data, count, 0);
549
550		/*
551		 * Start of a new packet - insert the leading FLAG
552		 * character if necessary.
553		 */
554		if (islcp || flag_time == 0 ||
555		    time_after_eq(jiffies, ap->last_xmit + flag_time))
556			*buf++ = PPP_FLAG;
557		ap->last_xmit = jiffies;
558		fcs = PPP_INITFCS;
559
560		/*
561		 * Put in the address/control bytes if necessary
562		 */
563		if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
564			PUT_BYTE(ap, buf, 0xff, islcp);
565			fcs = PPP_FCS(fcs, 0xff);
566			PUT_BYTE(ap, buf, 0x03, islcp);
567			fcs = PPP_FCS(fcs, 0x03);
568		}
569	}
570
571	/*
572	 * Once we put in the last byte, we need to put in the FCS
573	 * and closing flag, so make sure there is at least 7 bytes
574	 * of free space in the output buffer.
575	 */
576	buflim = ap->obuf + OBUFSIZE - 6;
577	while (i < count && buf < buflim) {
578		c = data[i++];
579		if (i == 1 && c == 0 && (ap->flags & SC_COMP_PROT))
580			continue;	/* compress protocol field */
581		fcs = PPP_FCS(fcs, c);
582		PUT_BYTE(ap, buf, c, islcp);
583	}
584
585	if (i < count) {
586		/*
587		 * Remember where we are up to in this packet.
588		 */
589		ap->olim = buf;
590		ap->tpkt_pos = i;
591		ap->tfcs = fcs;
592		return 0;
593	}
594
595	/*
596	 * We have finished the packet.  Add the FCS and flag.
597	 */
598	fcs = ~fcs;
599	c = fcs & 0xff;
600	PUT_BYTE(ap, buf, c, islcp);
601	c = (fcs >> 8) & 0xff;
602	PUT_BYTE(ap, buf, c, islcp);
603	*buf++ = PPP_FLAG;
604	ap->olim = buf;
605
606	consume_skb(ap->tpkt);
607	ap->tpkt = NULL;
608	return 1;
609}
610
611/*
612 * Transmit-side routines.
613 */
614
615/*
616 * Send a packet to the peer over an async tty line.
617 * Returns 1 iff the packet was accepted.
618 * If the packet was not accepted, we will call ppp_output_wakeup
619 * at some later time.
620 */
621static int
622ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb)
623{
624	struct asyncppp *ap = chan->private;
625
626	ppp_async_push(ap);
627
628	if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
629		return 0;	/* already full */
630	ap->tpkt = skb;
631	ap->tpkt_pos = 0;
632
633	ppp_async_push(ap);
634	return 1;
635}
636
637/*
638 * Push as much data as possible out to the tty.
639 */
640static int
641ppp_async_push(struct asyncppp *ap)
642{
643	int avail, sent, done = 0;
644	struct tty_struct *tty = ap->tty;
645	int tty_stuffed = 0;
646
647	/*
648	 * We can get called recursively here if the tty write
649	 * function calls our wakeup function.  This can happen
650	 * for example on a pty with both the master and slave
651	 * set to PPP line discipline.
652	 * We use the XMIT_BUSY bit to detect this and get out,
653	 * leaving the XMIT_WAKEUP bit set to tell the other
654	 * instance that it may now be able to write more now.
655	 */
656	if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
657		return 0;
658	spin_lock_bh(&ap->xmit_lock);
659	for (;;) {
660		if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
661			tty_stuffed = 0;
662		if (!tty_stuffed && ap->optr < ap->olim) {
663			avail = ap->olim - ap->optr;
664			set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
665			sent = tty->ops->write(tty, ap->optr, avail);
666			if (sent < 0)
667				goto flush;	/* error, e.g. loss of CD */
668			ap->optr += sent;
669			if (sent < avail)
670				tty_stuffed = 1;
671			continue;
672		}
673		if (ap->optr >= ap->olim && ap->tpkt) {
674			if (ppp_async_encode(ap)) {
675				/* finished processing ap->tpkt */
676				clear_bit(XMIT_FULL, &ap->xmit_flags);
677				done = 1;
678			}
679			continue;
680		}
681		/*
682		 * We haven't made any progress this time around.
683		 * Clear XMIT_BUSY to let other callers in, but
684		 * after doing so we have to check if anyone set
685		 * XMIT_WAKEUP since we last checked it.  If they
686		 * did, we should try again to set XMIT_BUSY and go
687		 * around again in case XMIT_BUSY was still set when
688		 * the other caller tried.
689		 */
690		clear_bit(XMIT_BUSY, &ap->xmit_flags);
691		/* any more work to do? if not, exit the loop */
692		if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) ||
693		      (!tty_stuffed && ap->tpkt)))
694			break;
695		/* more work to do, see if we can do it now */
696		if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
697			break;
698	}
699	spin_unlock_bh(&ap->xmit_lock);
700	return done;
701
702flush:
703	clear_bit(XMIT_BUSY, &ap->xmit_flags);
704	if (ap->tpkt) {
705		kfree_skb(ap->tpkt);
706		ap->tpkt = NULL;
707		clear_bit(XMIT_FULL, &ap->xmit_flags);
708		done = 1;
709	}
710	ap->optr = ap->olim;
711	spin_unlock_bh(&ap->xmit_lock);
712	return done;
713}
714
715/*
716 * Flush output from our internal buffers.
717 * Called for the TCFLSH ioctl. Can be entered in parallel
718 * but this is covered by the xmit_lock.
719 */
720static void
721ppp_async_flush_output(struct asyncppp *ap)
722{
723	int done = 0;
724
725	spin_lock_bh(&ap->xmit_lock);
726	ap->optr = ap->olim;
727	if (ap->tpkt != NULL) {
728		kfree_skb(ap->tpkt);
729		ap->tpkt = NULL;
730		clear_bit(XMIT_FULL, &ap->xmit_flags);
731		done = 1;
732	}
733	spin_unlock_bh(&ap->xmit_lock);
734	if (done)
735		ppp_output_wakeup(&ap->chan);
736}
737
738/*
739 * Receive-side routines.
740 */
741
742/* see how many ordinary chars there are at the start of buf */
743static inline int
744scan_ordinary(struct asyncppp *ap, const unsigned char *buf, int count)
745{
746	int i, c;
747
748	for (i = 0; i < count; ++i) {
749		c = buf[i];
750		if (c == PPP_ESCAPE || c == PPP_FLAG ||
751		    (c < 0x20 && (ap->raccm & (1 << c)) != 0))
752			break;
753	}
754	return i;
755}
756
757/* called when a flag is seen - do end-of-packet processing */
758static void
759process_input_packet(struct asyncppp *ap)
760{
761	struct sk_buff *skb;
762	unsigned char *p;
763	unsigned int len, fcs;
764
765	skb = ap->rpkt;
766	if (ap->state & (SC_TOSS | SC_ESCAPE))
767		goto err;
768
769	if (skb == NULL)
770		return;		/* 0-length packet */
771
772	/* check the FCS */
773	p = skb->data;
774	len = skb->len;
775	if (len < 3)
776		goto err;	/* too short */
777	fcs = PPP_INITFCS;
778	for (; len > 0; --len)
779		fcs = PPP_FCS(fcs, *p++);
780	if (fcs != PPP_GOODFCS)
781		goto err;	/* bad FCS */
782	skb_trim(skb, skb->len - 2);
783
784	/* check for address/control and protocol compression */
785	p = skb->data;
786	if (p[0] == PPP_ALLSTATIONS) {
787		/* chop off address/control */
788		if (p[1] != PPP_UI || skb->len < 3)
789			goto err;
790		p = skb_pull(skb, 2);
791	}
792
793	/* If protocol field is not compressed, it can be LCP packet */
794	if (!(p[0] & 0x01)) {
795		unsigned int proto;
796
797		if (skb->len < 2)
798			goto err;
799		proto = (p[0] << 8) + p[1];
800		if (proto == PPP_LCP)
801			async_lcp_peek(ap, p, skb->len, 1);
802	}
803
804	/* queue the frame to be processed */
805	skb->cb[0] = ap->state;
806	skb_queue_tail(&ap->rqueue, skb);
807	ap->rpkt = NULL;
808	ap->state = 0;
809	return;
810
811 err:
812	/* frame had an error, remember that, reset SC_TOSS & SC_ESCAPE */
813	ap->state = SC_PREV_ERROR;
814	if (skb) {
815		/* make skb appear as freshly allocated */
816		skb_trim(skb, 0);
817		skb_reserve(skb, - skb_headroom(skb));
818	}
819}
820
821/* Called when the tty driver has data for us. Runs parallel with the
822   other ldisc functions but will not be re-entered */
823
824static void
825ppp_async_input(struct asyncppp *ap, const u8 *buf, const u8 *flags, int count)
826{
827	struct sk_buff *skb;
828	int c, i, j, n, s, f;
829	unsigned char *sp;
830
831	/* update bits used for 8-bit cleanness detection */
832	if (~ap->rbits & SC_RCV_BITS) {
833		s = 0;
834		for (i = 0; i < count; ++i) {
835			c = buf[i];
836			if (flags && flags[i] != 0)
837				continue;
838			s |= (c & 0x80)? SC_RCV_B7_1: SC_RCV_B7_0;
839			c = ((c >> 4) ^ c) & 0xf;
840			s |= (0x6996 & (1 << c))? SC_RCV_ODDP: SC_RCV_EVNP;
841		}
842		ap->rbits |= s;
843	}
844
845	while (count > 0) {
846		/* scan through and see how many chars we can do in bulk */
847		if ((ap->state & SC_ESCAPE) && buf[0] == PPP_ESCAPE)
848			n = 1;
849		else
850			n = scan_ordinary(ap, buf, count);
851
852		f = 0;
853		if (flags && (ap->state & SC_TOSS) == 0) {
854			/* check the flags to see if any char had an error */
855			for (j = 0; j < n; ++j)
856				if ((f = flags[j]) != 0)
857					break;
858		}
859		if (f != 0) {
860			/* start tossing */
861			ap->state |= SC_TOSS;
862
863		} else if (n > 0 && (ap->state & SC_TOSS) == 0) {
864			/* stuff the chars in the skb */
865			skb = ap->rpkt;
866			if (!skb) {
867				skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
868				if (!skb)
869					goto nomem;
870				ap->rpkt = skb;
871			}
872			if (skb->len == 0) {
873				/* Try to get the payload 4-byte aligned.
874				 * This should match the
875				 * PPP_ALLSTATIONS/PPP_UI/compressed tests in
876				 * process_input_packet, but we do not have
877				 * enough chars here to test buf[1] and buf[2].
878				 */
879				if (buf[0] != PPP_ALLSTATIONS)
880					skb_reserve(skb, 2 + (buf[0] & 1));
881			}
882			if (n > skb_tailroom(skb)) {
883				/* packet overflowed MRU */
884				ap->state |= SC_TOSS;
885			} else {
886				sp = skb_put_data(skb, buf, n);
887				if (ap->state & SC_ESCAPE) {
888					sp[0] ^= PPP_TRANS;
889					ap->state &= ~SC_ESCAPE;
890				}
891			}
892		}
893
894		if (n >= count)
895			break;
896
897		c = buf[n];
898		if (flags != NULL && flags[n] != 0) {
899			ap->state |= SC_TOSS;
900		} else if (c == PPP_FLAG) {
901			process_input_packet(ap);
902		} else if (c == PPP_ESCAPE) {
903			ap->state |= SC_ESCAPE;
904		} else if (I_IXON(ap->tty)) {
905			if (c == START_CHAR(ap->tty))
906				start_tty(ap->tty);
907			else if (c == STOP_CHAR(ap->tty))
908				stop_tty(ap->tty);
909		}
910		/* otherwise it's a char in the recv ACCM */
911		++n;
912
913		buf += n;
914		if (flags)
915			flags += n;
916		count -= n;
917	}
918	return;
919
920 nomem:
921	printk(KERN_ERR "PPPasync: no memory (input pkt)\n");
922	ap->state |= SC_TOSS;
923}
924
925/*
926 * We look at LCP frames going past so that we can notice
927 * and react to the LCP configure-ack from the peer.
928 * In the situation where the peer has been sent a configure-ack
929 * already, LCP is up once it has sent its configure-ack
930 * so the immediately following packet can be sent with the
931 * configured LCP options.  This allows us to process the following
932 * packet correctly without pppd needing to respond quickly.
933 *
934 * We only respond to the received configure-ack if we have just
935 * sent a configure-request, and the configure-ack contains the
936 * same data (this is checked using a 16-bit crc of the data).
937 */
938#define CONFREQ		1	/* LCP code field values */
939#define CONFACK		2
940#define LCP_MRU		1	/* LCP option numbers */
941#define LCP_ASYNCMAP	2
942
943static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
944			   int len, int inbound)
945{
946	int dlen, fcs, i, code;
947	u32 val;
948
949	data += 2;		/* skip protocol bytes */
950	len -= 2;
951	if (len < 4)		/* 4 = code, ID, length */
952		return;
953	code = data[0];
954	if (code != CONFACK && code != CONFREQ)
955		return;
956	dlen = get_unaligned_be16(data + 2);
957	if (len < dlen)
958		return;		/* packet got truncated or length is bogus */
959
960	if (code == (inbound? CONFACK: CONFREQ)) {
961		/*
962		 * sent confreq or received confack:
963		 * calculate the crc of the data from the ID field on.
964		 */
965		fcs = PPP_INITFCS;
966		for (i = 1; i < dlen; ++i)
967			fcs = PPP_FCS(fcs, data[i]);
968
969		if (!inbound) {
970			/* outbound confreq - remember the crc for later */
971			ap->lcp_fcs = fcs;
972			return;
973		}
974
975		/* received confack, check the crc */
976		fcs ^= ap->lcp_fcs;
977		ap->lcp_fcs = -1;
978		if (fcs != 0)
979			return;
980	} else if (inbound)
981		return;	/* not interested in received confreq */
982
983	/* process the options in the confack */
984	data += 4;
985	dlen -= 4;
986	/* data[0] is code, data[1] is length */
987	while (dlen >= 2 && dlen >= data[1] && data[1] >= 2) {
988		switch (data[0]) {
989		case LCP_MRU:
990			val = get_unaligned_be16(data + 2);
991			if (inbound)
992				ap->mru = val;
993			else
994				ap->chan.mtu = val;
995			break;
996		case LCP_ASYNCMAP:
997			val = get_unaligned_be32(data + 2);
998			if (inbound)
999				ap->raccm = val;
1000			else
1001				ap->xaccm[0] = val;
1002			break;
1003		}
1004		dlen -= data[1];
1005		data += data[1];
1006	}
1007}
1008
1009static void __exit ppp_async_cleanup(void)
1010{
1011	tty_unregister_ldisc(&ppp_ldisc);
1012}
1013
1014module_init(ppp_async_init);
1015module_exit(ppp_async_cleanup);
1016