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 *buf, size_t count,
263		  void **cookie, unsigned long offset)
264{
265	return -EAGAIN;
266}
267
268/*
269 * Write on the tty does nothing, the packets all come in
270 * from the ppp generic stuff.
271 */
272static ssize_t
273ppp_asynctty_write(struct tty_struct *tty, struct file *file,
274		   const unsigned char *buf, size_t count)
275{
276	return -EAGAIN;
277}
278
279/*
280 * Called in process context only. May be re-entered by multiple
281 * ioctl calling threads.
282 */
283
284static int
285ppp_asynctty_ioctl(struct tty_struct *tty, struct file *file,
286		   unsigned int cmd, unsigned long arg)
287{
288	struct asyncppp *ap = ap_get(tty);
289	int err, val;
290	int __user *p = (int __user *)arg;
291
292	if (!ap)
293		return -ENXIO;
294	err = -EFAULT;
295	switch (cmd) {
296	case PPPIOCGCHAN:
297		err = -EFAULT;
298		if (put_user(ppp_channel_index(&ap->chan), p))
299			break;
300		err = 0;
301		break;
302
303	case PPPIOCGUNIT:
304		err = -EFAULT;
305		if (put_user(ppp_unit_number(&ap->chan), p))
306			break;
307		err = 0;
308		break;
309
310	case TCFLSH:
311		/* flush our buffers and the serial port's buffer */
312		if (arg == TCIOFLUSH || arg == TCOFLUSH)
313			ppp_async_flush_output(ap);
314		err = n_tty_ioctl_helper(tty, file, cmd, arg);
315		break;
316
317	case FIONREAD:
318		val = 0;
319		if (put_user(val, p))
320			break;
321		err = 0;
322		break;
323
324	default:
325		/* Try the various mode ioctls */
326		err = tty_mode_ioctl(tty, file, cmd, arg);
327	}
328
329	ap_put(ap);
330	return err;
331}
332
333/* No kernel lock - fine */
334static __poll_t
335ppp_asynctty_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
336{
337	return 0;
338}
339
340/* May sleep, don't call from interrupt level or with interrupts disabled */
341static void
342ppp_asynctty_receive(struct tty_struct *tty, const unsigned char *buf,
343		  char *cflags, int count)
344{
345	struct asyncppp *ap = ap_get(tty);
346	unsigned long flags;
347
348	if (!ap)
349		return;
350	spin_lock_irqsave(&ap->recv_lock, flags);
351	ppp_async_input(ap, buf, cflags, count);
352	spin_unlock_irqrestore(&ap->recv_lock, flags);
353	if (!skb_queue_empty(&ap->rqueue))
354		tasklet_schedule(&ap->tsk);
355	ap_put(ap);
356	tty_unthrottle(tty);
357}
358
359static void
360ppp_asynctty_wakeup(struct tty_struct *tty)
361{
362	struct asyncppp *ap = ap_get(tty);
363
364	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
365	if (!ap)
366		return;
367	set_bit(XMIT_WAKEUP, &ap->xmit_flags);
368	tasklet_schedule(&ap->tsk);
369	ap_put(ap);
370}
371
372
373static struct tty_ldisc_ops ppp_ldisc = {
374	.owner  = THIS_MODULE,
375	.magic	= TTY_LDISC_MAGIC,
376	.name	= "ppp",
377	.open	= ppp_asynctty_open,
378	.close	= ppp_asynctty_close,
379	.hangup	= ppp_asynctty_hangup,
380	.read	= ppp_asynctty_read,
381	.write	= ppp_asynctty_write,
382	.ioctl	= ppp_asynctty_ioctl,
383	.poll	= ppp_asynctty_poll,
384	.receive_buf = ppp_asynctty_receive,
385	.write_wakeup = ppp_asynctty_wakeup,
386};
387
388static int __init
389ppp_async_init(void)
390{
391	int err;
392
393	err = tty_register_ldisc(N_PPP, &ppp_ldisc);
394	if (err != 0)
395		printk(KERN_ERR "PPP_async: error %d registering line disc.\n",
396		       err);
397	return err;
398}
399
400/*
401 * The following routines provide the PPP channel interface.
402 */
403static int
404ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
405{
406	struct asyncppp *ap = chan->private;
407	void __user *argp = (void __user *)arg;
408	int __user *p = argp;
409	int err, val;
410	u32 accm[8];
411
412	err = -EFAULT;
413	switch (cmd) {
414	case PPPIOCGFLAGS:
415		val = ap->flags | ap->rbits;
416		if (put_user(val, p))
417			break;
418		err = 0;
419		break;
420	case PPPIOCSFLAGS:
421		if (get_user(val, p))
422			break;
423		ap->flags = val & ~SC_RCV_BITS;
424		spin_lock_irq(&ap->recv_lock);
425		ap->rbits = val & SC_RCV_BITS;
426		spin_unlock_irq(&ap->recv_lock);
427		err = 0;
428		break;
429
430	case PPPIOCGASYNCMAP:
431		if (put_user(ap->xaccm[0], (u32 __user *)argp))
432			break;
433		err = 0;
434		break;
435	case PPPIOCSASYNCMAP:
436		if (get_user(ap->xaccm[0], (u32 __user *)argp))
437			break;
438		err = 0;
439		break;
440
441	case PPPIOCGRASYNCMAP:
442		if (put_user(ap->raccm, (u32 __user *)argp))
443			break;
444		err = 0;
445		break;
446	case PPPIOCSRASYNCMAP:
447		if (get_user(ap->raccm, (u32 __user *)argp))
448			break;
449		err = 0;
450		break;
451
452	case PPPIOCGXASYNCMAP:
453		if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
454			break;
455		err = 0;
456		break;
457	case PPPIOCSXASYNCMAP:
458		if (copy_from_user(accm, argp, sizeof(accm)))
459			break;
460		accm[2] &= ~0x40000000U;	/* can't escape 0x5e */
461		accm[3] |= 0x60000000U;		/* must escape 0x7d, 0x7e */
462		memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
463		err = 0;
464		break;
465
466	case PPPIOCGMRU:
467		if (put_user(ap->mru, p))
468			break;
469		err = 0;
470		break;
471	case PPPIOCSMRU:
472		if (get_user(val, p))
473			break;
474		if (val > U16_MAX) {
475			err = -EINVAL;
476			break;
477		}
478		if (val < PPP_MRU)
479			val = PPP_MRU;
480		ap->mru = val;
481		err = 0;
482		break;
483
484	default:
485		err = -ENOTTY;
486	}
487
488	return err;
489}
490
491/*
492 * This is called at softirq level to deliver received packets
493 * to the ppp_generic code, and to tell the ppp_generic code
494 * if we can accept more output now.
495 */
496static void ppp_async_process(unsigned long arg)
497{
498	struct asyncppp *ap = (struct asyncppp *) arg;
499	struct sk_buff *skb;
500
501	/* process received packets */
502	while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
503		if (skb->cb[0])
504			ppp_input_error(&ap->chan, 0);
505		ppp_input(&ap->chan, skb);
506	}
507
508	/* try to push more stuff out */
509	if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_async_push(ap))
510		ppp_output_wakeup(&ap->chan);
511}
512
513/*
514 * Procedures for encapsulation and framing.
515 */
516
517/*
518 * Procedure to encode the data for async serial transmission.
519 * Does octet stuffing (escaping), puts the address/control bytes
520 * on if A/C compression is disabled, and does protocol compression.
521 * Assumes ap->tpkt != 0 on entry.
522 * Returns 1 if we finished the current frame, 0 otherwise.
523 */
524
525#define PUT_BYTE(ap, buf, c, islcp)	do {		\
526	if ((islcp && c < 0x20) || (ap->xaccm[c >> 5] & (1 << (c & 0x1f)))) {\
527		*buf++ = PPP_ESCAPE;			\
528		*buf++ = c ^ PPP_TRANS;			\
529	} else						\
530		*buf++ = c;				\
531} while (0)
532
533static int
534ppp_async_encode(struct asyncppp *ap)
535{
536	int fcs, i, count, c, proto;
537	unsigned char *buf, *buflim;
538	unsigned char *data;
539	int islcp;
540
541	buf = ap->obuf;
542	ap->olim = buf;
543	ap->optr = buf;
544	i = ap->tpkt_pos;
545	data = ap->tpkt->data;
546	count = ap->tpkt->len;
547	fcs = ap->tfcs;
548	proto = get_unaligned_be16(data);
549
550	/*
551	 * LCP packets with code values between 1 (configure-reqest)
552	 * and 7 (code-reject) must be sent as though no options
553	 * had been negotiated.
554	 */
555	islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
556
557	if (i == 0) {
558		if (islcp)
559			async_lcp_peek(ap, data, count, 0);
560
561		/*
562		 * Start of a new packet - insert the leading FLAG
563		 * character if necessary.
564		 */
565		if (islcp || flag_time == 0 ||
566		    time_after_eq(jiffies, ap->last_xmit + flag_time))
567			*buf++ = PPP_FLAG;
568		ap->last_xmit = jiffies;
569		fcs = PPP_INITFCS;
570
571		/*
572		 * Put in the address/control bytes if necessary
573		 */
574		if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
575			PUT_BYTE(ap, buf, 0xff, islcp);
576			fcs = PPP_FCS(fcs, 0xff);
577			PUT_BYTE(ap, buf, 0x03, islcp);
578			fcs = PPP_FCS(fcs, 0x03);
579		}
580	}
581
582	/*
583	 * Once we put in the last byte, we need to put in the FCS
584	 * and closing flag, so make sure there is at least 7 bytes
585	 * of free space in the output buffer.
586	 */
587	buflim = ap->obuf + OBUFSIZE - 6;
588	while (i < count && buf < buflim) {
589		c = data[i++];
590		if (i == 1 && c == 0 && (ap->flags & SC_COMP_PROT))
591			continue;	/* compress protocol field */
592		fcs = PPP_FCS(fcs, c);
593		PUT_BYTE(ap, buf, c, islcp);
594	}
595
596	if (i < count) {
597		/*
598		 * Remember where we are up to in this packet.
599		 */
600		ap->olim = buf;
601		ap->tpkt_pos = i;
602		ap->tfcs = fcs;
603		return 0;
604	}
605
606	/*
607	 * We have finished the packet.  Add the FCS and flag.
608	 */
609	fcs = ~fcs;
610	c = fcs & 0xff;
611	PUT_BYTE(ap, buf, c, islcp);
612	c = (fcs >> 8) & 0xff;
613	PUT_BYTE(ap, buf, c, islcp);
614	*buf++ = PPP_FLAG;
615	ap->olim = buf;
616
617	consume_skb(ap->tpkt);
618	ap->tpkt = NULL;
619	return 1;
620}
621
622/*
623 * Transmit-side routines.
624 */
625
626/*
627 * Send a packet to the peer over an async tty line.
628 * Returns 1 iff the packet was accepted.
629 * If the packet was not accepted, we will call ppp_output_wakeup
630 * at some later time.
631 */
632static int
633ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb)
634{
635	struct asyncppp *ap = chan->private;
636
637	ppp_async_push(ap);
638
639	if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
640		return 0;	/* already full */
641	ap->tpkt = skb;
642	ap->tpkt_pos = 0;
643
644	ppp_async_push(ap);
645	return 1;
646}
647
648/*
649 * Push as much data as possible out to the tty.
650 */
651static int
652ppp_async_push(struct asyncppp *ap)
653{
654	int avail, sent, done = 0;
655	struct tty_struct *tty = ap->tty;
656	int tty_stuffed = 0;
657
658	/*
659	 * We can get called recursively here if the tty write
660	 * function calls our wakeup function.  This can happen
661	 * for example on a pty with both the master and slave
662	 * set to PPP line discipline.
663	 * We use the XMIT_BUSY bit to detect this and get out,
664	 * leaving the XMIT_WAKEUP bit set to tell the other
665	 * instance that it may now be able to write more now.
666	 */
667	if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
668		return 0;
669	spin_lock_bh(&ap->xmit_lock);
670	for (;;) {
671		if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
672			tty_stuffed = 0;
673		if (!tty_stuffed && ap->optr < ap->olim) {
674			avail = ap->olim - ap->optr;
675			set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
676			sent = tty->ops->write(tty, ap->optr, avail);
677			if (sent < 0)
678				goto flush;	/* error, e.g. loss of CD */
679			ap->optr += sent;
680			if (sent < avail)
681				tty_stuffed = 1;
682			continue;
683		}
684		if (ap->optr >= ap->olim && ap->tpkt) {
685			if (ppp_async_encode(ap)) {
686				/* finished processing ap->tpkt */
687				clear_bit(XMIT_FULL, &ap->xmit_flags);
688				done = 1;
689			}
690			continue;
691		}
692		/*
693		 * We haven't made any progress this time around.
694		 * Clear XMIT_BUSY to let other callers in, but
695		 * after doing so we have to check if anyone set
696		 * XMIT_WAKEUP since we last checked it.  If they
697		 * did, we should try again to set XMIT_BUSY and go
698		 * around again in case XMIT_BUSY was still set when
699		 * the other caller tried.
700		 */
701		clear_bit(XMIT_BUSY, &ap->xmit_flags);
702		/* any more work to do? if not, exit the loop */
703		if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) ||
704		      (!tty_stuffed && ap->tpkt)))
705			break;
706		/* more work to do, see if we can do it now */
707		if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
708			break;
709	}
710	spin_unlock_bh(&ap->xmit_lock);
711	return done;
712
713flush:
714	clear_bit(XMIT_BUSY, &ap->xmit_flags);
715	if (ap->tpkt) {
716		kfree_skb(ap->tpkt);
717		ap->tpkt = NULL;
718		clear_bit(XMIT_FULL, &ap->xmit_flags);
719		done = 1;
720	}
721	ap->optr = ap->olim;
722	spin_unlock_bh(&ap->xmit_lock);
723	return done;
724}
725
726/*
727 * Flush output from our internal buffers.
728 * Called for the TCFLSH ioctl. Can be entered in parallel
729 * but this is covered by the xmit_lock.
730 */
731static void
732ppp_async_flush_output(struct asyncppp *ap)
733{
734	int done = 0;
735
736	spin_lock_bh(&ap->xmit_lock);
737	ap->optr = ap->olim;
738	if (ap->tpkt != NULL) {
739		kfree_skb(ap->tpkt);
740		ap->tpkt = NULL;
741		clear_bit(XMIT_FULL, &ap->xmit_flags);
742		done = 1;
743	}
744	spin_unlock_bh(&ap->xmit_lock);
745	if (done)
746		ppp_output_wakeup(&ap->chan);
747}
748
749/*
750 * Receive-side routines.
751 */
752
753/* see how many ordinary chars there are at the start of buf */
754static inline int
755scan_ordinary(struct asyncppp *ap, const unsigned char *buf, int count)
756{
757	int i, c;
758
759	for (i = 0; i < count; ++i) {
760		c = buf[i];
761		if (c == PPP_ESCAPE || c == PPP_FLAG ||
762		    (c < 0x20 && (ap->raccm & (1 << c)) != 0))
763			break;
764	}
765	return i;
766}
767
768/* called when a flag is seen - do end-of-packet processing */
769static void
770process_input_packet(struct asyncppp *ap)
771{
772	struct sk_buff *skb;
773	unsigned char *p;
774	unsigned int len, fcs;
775
776	skb = ap->rpkt;
777	if (ap->state & (SC_TOSS | SC_ESCAPE))
778		goto err;
779
780	if (skb == NULL)
781		return;		/* 0-length packet */
782
783	/* check the FCS */
784	p = skb->data;
785	len = skb->len;
786	if (len < 3)
787		goto err;	/* too short */
788	fcs = PPP_INITFCS;
789	for (; len > 0; --len)
790		fcs = PPP_FCS(fcs, *p++);
791	if (fcs != PPP_GOODFCS)
792		goto err;	/* bad FCS */
793	skb_trim(skb, skb->len - 2);
794
795	/* check for address/control and protocol compression */
796	p = skb->data;
797	if (p[0] == PPP_ALLSTATIONS) {
798		/* chop off address/control */
799		if (p[1] != PPP_UI || skb->len < 3)
800			goto err;
801		p = skb_pull(skb, 2);
802	}
803
804	/* If protocol field is not compressed, it can be LCP packet */
805	if (!(p[0] & 0x01)) {
806		unsigned int proto;
807
808		if (skb->len < 2)
809			goto err;
810		proto = (p[0] << 8) + p[1];
811		if (proto == PPP_LCP)
812			async_lcp_peek(ap, p, skb->len, 1);
813	}
814
815	/* queue the frame to be processed */
816	skb->cb[0] = ap->state;
817	skb_queue_tail(&ap->rqueue, skb);
818	ap->rpkt = NULL;
819	ap->state = 0;
820	return;
821
822 err:
823	/* frame had an error, remember that, reset SC_TOSS & SC_ESCAPE */
824	ap->state = SC_PREV_ERROR;
825	if (skb) {
826		/* make skb appear as freshly allocated */
827		skb_trim(skb, 0);
828		skb_reserve(skb, - skb_headroom(skb));
829	}
830}
831
832/* Called when the tty driver has data for us. Runs parallel with the
833   other ldisc functions but will not be re-entered */
834
835static void
836ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
837		char *flags, int count)
838{
839	struct sk_buff *skb;
840	int c, i, j, n, s, f;
841	unsigned char *sp;
842
843	/* update bits used for 8-bit cleanness detection */
844	if (~ap->rbits & SC_RCV_BITS) {
845		s = 0;
846		for (i = 0; i < count; ++i) {
847			c = buf[i];
848			if (flags && flags[i] != 0)
849				continue;
850			s |= (c & 0x80)? SC_RCV_B7_1: SC_RCV_B7_0;
851			c = ((c >> 4) ^ c) & 0xf;
852			s |= (0x6996 & (1 << c))? SC_RCV_ODDP: SC_RCV_EVNP;
853		}
854		ap->rbits |= s;
855	}
856
857	while (count > 0) {
858		/* scan through and see how many chars we can do in bulk */
859		if ((ap->state & SC_ESCAPE) && buf[0] == PPP_ESCAPE)
860			n = 1;
861		else
862			n = scan_ordinary(ap, buf, count);
863
864		f = 0;
865		if (flags && (ap->state & SC_TOSS) == 0) {
866			/* check the flags to see if any char had an error */
867			for (j = 0; j < n; ++j)
868				if ((f = flags[j]) != 0)
869					break;
870		}
871		if (f != 0) {
872			/* start tossing */
873			ap->state |= SC_TOSS;
874
875		} else if (n > 0 && (ap->state & SC_TOSS) == 0) {
876			/* stuff the chars in the skb */
877			skb = ap->rpkt;
878			if (!skb) {
879				skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
880				if (!skb)
881					goto nomem;
882				ap->rpkt = skb;
883			}
884			if (skb->len == 0) {
885				/* Try to get the payload 4-byte aligned.
886				 * This should match the
887				 * PPP_ALLSTATIONS/PPP_UI/compressed tests in
888				 * process_input_packet, but we do not have
889				 * enough chars here to test buf[1] and buf[2].
890				 */
891				if (buf[0] != PPP_ALLSTATIONS)
892					skb_reserve(skb, 2 + (buf[0] & 1));
893			}
894			if (n > skb_tailroom(skb)) {
895				/* packet overflowed MRU */
896				ap->state |= SC_TOSS;
897			} else {
898				sp = skb_put_data(skb, buf, n);
899				if (ap->state & SC_ESCAPE) {
900					sp[0] ^= PPP_TRANS;
901					ap->state &= ~SC_ESCAPE;
902				}
903			}
904		}
905
906		if (n >= count)
907			break;
908
909		c = buf[n];
910		if (flags != NULL && flags[n] != 0) {
911			ap->state |= SC_TOSS;
912		} else if (c == PPP_FLAG) {
913			process_input_packet(ap);
914		} else if (c == PPP_ESCAPE) {
915			ap->state |= SC_ESCAPE;
916		} else if (I_IXON(ap->tty)) {
917			if (c == START_CHAR(ap->tty))
918				start_tty(ap->tty);
919			else if (c == STOP_CHAR(ap->tty))
920				stop_tty(ap->tty);
921		}
922		/* otherwise it's a char in the recv ACCM */
923		++n;
924
925		buf += n;
926		if (flags)
927			flags += n;
928		count -= n;
929	}
930	return;
931
932 nomem:
933	printk(KERN_ERR "PPPasync: no memory (input pkt)\n");
934	ap->state |= SC_TOSS;
935}
936
937/*
938 * We look at LCP frames going past so that we can notice
939 * and react to the LCP configure-ack from the peer.
940 * In the situation where the peer has been sent a configure-ack
941 * already, LCP is up once it has sent its configure-ack
942 * so the immediately following packet can be sent with the
943 * configured LCP options.  This allows us to process the following
944 * packet correctly without pppd needing to respond quickly.
945 *
946 * We only respond to the received configure-ack if we have just
947 * sent a configure-request, and the configure-ack contains the
948 * same data (this is checked using a 16-bit crc of the data).
949 */
950#define CONFREQ		1	/* LCP code field values */
951#define CONFACK		2
952#define LCP_MRU		1	/* LCP option numbers */
953#define LCP_ASYNCMAP	2
954
955static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
956			   int len, int inbound)
957{
958	int dlen, fcs, i, code;
959	u32 val;
960
961	data += 2;		/* skip protocol bytes */
962	len -= 2;
963	if (len < 4)		/* 4 = code, ID, length */
964		return;
965	code = data[0];
966	if (code != CONFACK && code != CONFREQ)
967		return;
968	dlen = get_unaligned_be16(data + 2);
969	if (len < dlen)
970		return;		/* packet got truncated or length is bogus */
971
972	if (code == (inbound? CONFACK: CONFREQ)) {
973		/*
974		 * sent confreq or received confack:
975		 * calculate the crc of the data from the ID field on.
976		 */
977		fcs = PPP_INITFCS;
978		for (i = 1; i < dlen; ++i)
979			fcs = PPP_FCS(fcs, data[i]);
980
981		if (!inbound) {
982			/* outbound confreq - remember the crc for later */
983			ap->lcp_fcs = fcs;
984			return;
985		}
986
987		/* received confack, check the crc */
988		fcs ^= ap->lcp_fcs;
989		ap->lcp_fcs = -1;
990		if (fcs != 0)
991			return;
992	} else if (inbound)
993		return;	/* not interested in received confreq */
994
995	/* process the options in the confack */
996	data += 4;
997	dlen -= 4;
998	/* data[0] is code, data[1] is length */
999	while (dlen >= 2 && dlen >= data[1] && data[1] >= 2) {
1000		switch (data[0]) {
1001		case LCP_MRU:
1002			val = get_unaligned_be16(data + 2);
1003			if (inbound)
1004				ap->mru = val;
1005			else
1006				ap->chan.mtu = val;
1007			break;
1008		case LCP_ASYNCMAP:
1009			val = get_unaligned_be32(data + 2);
1010			if (inbound)
1011				ap->raccm = val;
1012			else
1013				ap->xaccm[0] = val;
1014			break;
1015		}
1016		dlen -= data[1];
1017		data += data[1];
1018	}
1019}
1020
1021static void __exit ppp_async_cleanup(void)
1022{
1023	if (tty_unregister_ldisc(N_PPP) != 0)
1024		printk(KERN_ERR "failed to unregister PPP line discipline\n");
1025}
1026
1027module_init(ppp_async_init);
1028module_exit(ppp_async_cleanup);
1029