1 /*
2 * PPP synchronous tty channel driver for Linux.
3 *
4 * This is a ppp channel driver that can be used with tty device drivers
5 * that are frame oriented, such as synchronous HDLC devices.
6 *
7 * Complete PPP frames without encoding/decoding are exchanged between
8 * the channel driver and the device driver.
9 *
10 * The async map IOCTL codes are implemented to keep the user mode
11 * applications happy if they call them. Synchronous PPP does not use
12 * the async maps.
13 *
14 * Copyright 1999 Paul Mackerras.
15 *
16 * Also touched by the grubby hands of Paul Fulghum paulkf@microgate.com
17 *
18 * This program is free software; you can redistribute it and/or
19 * modify it under the terms of the GNU General Public License
20 * as published by the Free Software Foundation; either version
21 * 2 of the License, or (at your option) any later version.
22 *
23 * This driver provides the encapsulation and framing for sending
24 * and receiving PPP frames over sync serial lines. It relies on
25 * the generic PPP layer to give it frames to send and to process
26 * received frames. It implements the PPP line discipline.
27 *
28 * Part of the code in this driver was inspired by the old async-only
29 * PPP driver, written by Michael Callahan and Al Longyear, and
30 * subsequently hacked by Paul Mackerras.
31 *
32 * ==FILEVERSION 20040616==
33 */
34
35 #include <linux/module.h>
36 #include <linux/kernel.h>
37 #include <linux/skbuff.h>
38 #include <linux/tty.h>
39 #include <linux/netdevice.h>
40 #include <linux/poll.h>
41 #include <linux/ppp_defs.h>
42 #include <linux/if_ppp.h>
43 #include <linux/ppp_channel.h>
44 #include <linux/spinlock.h>
45 #include <linux/completion.h>
46 #include <linux/init.h>
47 #include <asm/uaccess.h>
48
49 #define PPP_VERSION "2.4.2"
50
51 /* Structure for storing local state. */
52 struct syncppp {
53 struct tty_struct *tty;
54 unsigned int flags;
55 unsigned int rbits;
56 int mru;
57 spinlock_t xmit_lock;
58 spinlock_t recv_lock;
59 unsigned long xmit_flags;
60 u32 xaccm[8];
61 u32 raccm;
62 unsigned int bytes_sent;
63 unsigned int bytes_rcvd;
64
65 struct sk_buff *tpkt;
66 unsigned long last_xmit;
67
68 struct sk_buff_head rqueue;
69
70 struct tasklet_struct tsk;
71
72 atomic_t refcnt;
73 struct completion dead_cmp;
74 struct ppp_channel chan; /* interface to generic ppp layer */
75 };
76
77 /* Bit numbers in xmit_flags */
78 #define XMIT_WAKEUP 0
79 #define XMIT_FULL 1
80
81 /* Bits in rbits */
82 #define SC_RCV_BITS (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
83
84 #define PPPSYNC_MAX_RQLEN 32 /* arbitrary */
85
86 /*
87 * Prototypes.
88 */
89 static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
90 static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
91 static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
92 unsigned long arg);
93 static void ppp_sync_process(unsigned long arg);
94 static int ppp_sync_push(struct syncppp *ap);
95 static void ppp_sync_flush_output(struct syncppp *ap);
96 static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
97 char *flags, int count);
98
99 static struct ppp_channel_ops sync_ops = {
100 ppp_sync_send,
101 ppp_sync_ioctl
102 };
103
104 /*
105 * Utility procedures to print a buffer in hex/ascii
106 */
107 static void
ppp_print_hex(register __u8 * out,const __u8 * in,int count)108 ppp_print_hex (register __u8 * out, const __u8 * in, int count)
109 {
110 register __u8 next_ch;
111 static const char hex[] = "0123456789ABCDEF";
112
113 while (count-- > 0) {
114 next_ch = *in++;
115 *out++ = hex[(next_ch >> 4) & 0x0F];
116 *out++ = hex[next_ch & 0x0F];
117 ++out;
118 }
119 }
120
121 static void
ppp_print_char(register __u8 * out,const __u8 * in,int count)122 ppp_print_char (register __u8 * out, const __u8 * in, int count)
123 {
124 register __u8 next_ch;
125
126 while (count-- > 0) {
127 next_ch = *in++;
128
129 if (next_ch < 0x20 || next_ch > 0x7e)
130 *out++ = '.';
131 else {
132 *out++ = next_ch;
133 if (next_ch == '%') /* printk/syslogd has a bug !! */
134 *out++ = '%';
135 }
136 }
137 *out = '\0';
138 }
139
140 static void
ppp_print_buffer(const char * name,const __u8 * buf,int count)141 ppp_print_buffer (const char *name, const __u8 *buf, int count)
142 {
143 __u8 line[44];
144
145 if (name != NULL)
146 printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);
147
148 while (count > 8) {
149 memset (line, 32, 44);
150 ppp_print_hex (line, buf, 8);
151 ppp_print_char (&line[8 * 3], buf, 8);
152 printk(KERN_DEBUG "%s\n", line);
153 count -= 8;
154 buf += 8;
155 }
156
157 if (count > 0) {
158 memset (line, 32, 44);
159 ppp_print_hex (line, buf, count);
160 ppp_print_char (&line[8 * 3], buf, count);
161 printk(KERN_DEBUG "%s\n", line);
162 }
163 }
164
165
166 /*
167 * Routines implementing the synchronous PPP line discipline.
168 */
169
170 /*
171 * We have a potential race on dereferencing tty->disc_data,
172 * because the tty layer provides no locking at all - thus one
173 * cpu could be running ppp_synctty_receive while another
174 * calls ppp_synctty_close, which zeroes tty->disc_data and
175 * frees the memory that ppp_synctty_receive is using. The best
176 * way to fix this is to use a rwlock in the tty struct, but for now
177 * we use a single global rwlock for all ttys in ppp line discipline.
178 *
179 * FIXME: Fixed in tty_io nowdays.
180 */
181 static DEFINE_RWLOCK(disc_data_lock);
182
sp_get(struct tty_struct * tty)183 static struct syncppp *sp_get(struct tty_struct *tty)
184 {
185 struct syncppp *ap;
186
187 read_lock(&disc_data_lock);
188 ap = tty->disc_data;
189 if (ap != NULL)
190 atomic_inc(&ap->refcnt);
191 read_unlock(&disc_data_lock);
192 return ap;
193 }
194
sp_put(struct syncppp * ap)195 static void sp_put(struct syncppp *ap)
196 {
197 if (atomic_dec_and_test(&ap->refcnt))
198 complete(&ap->dead_cmp);
199 }
200
201 /*
202 * Called when a tty is put into sync-PPP line discipline.
203 */
204 static int
ppp_sync_open(struct tty_struct * tty)205 ppp_sync_open(struct tty_struct *tty)
206 {
207 struct syncppp *ap;
208 int err;
209
210 if (tty->ops->write == NULL)
211 return -EOPNOTSUPP;
212
213 ap = kzalloc(sizeof(*ap), GFP_KERNEL);
214 err = -ENOMEM;
215 if (!ap)
216 goto out;
217
218 /* initialize the syncppp structure */
219 ap->tty = tty;
220 ap->mru = PPP_MRU;
221 spin_lock_init(&ap->xmit_lock);
222 spin_lock_init(&ap->recv_lock);
223 ap->xaccm[0] = ~0U;
224 ap->xaccm[3] = 0x60000000U;
225 ap->raccm = ~0U;
226
227 skb_queue_head_init(&ap->rqueue);
228 tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);
229
230 atomic_set(&ap->refcnt, 1);
231 init_completion(&ap->dead_cmp);
232
233 ap->chan.private = ap;
234 ap->chan.ops = &sync_ops;
235 ap->chan.mtu = PPP_MRU;
236 ap->chan.hdrlen = 2; /* for A/C bytes */
237 err = ppp_register_channel(&ap->chan);
238 if (err)
239 goto out_free;
240
241 tty->disc_data = ap;
242 tty->receive_room = 65536;
243 return 0;
244
245 out_free:
246 kfree(ap);
247 out:
248 return err;
249 }
250
251 /*
252 * Called when the tty is put into another line discipline
253 * or it hangs up. We have to wait for any cpu currently
254 * executing in any of the other ppp_synctty_* routines to
255 * finish before we can call ppp_unregister_channel and free
256 * the syncppp struct. This routine must be called from
257 * process context, not interrupt or softirq context.
258 */
259 static void
ppp_sync_close(struct tty_struct * tty)260 ppp_sync_close(struct tty_struct *tty)
261 {
262 struct syncppp *ap;
263
264 write_lock_irq(&disc_data_lock);
265 ap = tty->disc_data;
266 tty->disc_data = NULL;
267 write_unlock_irq(&disc_data_lock);
268 if (!ap)
269 return;
270
271 /*
272 * We have now ensured that nobody can start using ap from now
273 * on, but we have to wait for all existing users to finish.
274 * Note that ppp_unregister_channel ensures that no calls to
275 * our channel ops (i.e. ppp_sync_send/ioctl) are in progress
276 * by the time it returns.
277 */
278 if (!atomic_dec_and_test(&ap->refcnt))
279 wait_for_completion(&ap->dead_cmp);
280 tasklet_kill(&ap->tsk);
281
282 ppp_unregister_channel(&ap->chan);
283 skb_queue_purge(&ap->rqueue);
284 if (ap->tpkt)
285 kfree_skb(ap->tpkt);
286 kfree(ap);
287 }
288
289 /*
290 * Called on tty hangup in process context.
291 *
292 * Wait for I/O to driver to complete and unregister PPP channel.
293 * This is already done by the close routine, so just call that.
294 */
ppp_sync_hangup(struct tty_struct * tty)295 static int ppp_sync_hangup(struct tty_struct *tty)
296 {
297 ppp_sync_close(tty);
298 return 0;
299 }
300
301 /*
302 * Read does nothing - no data is ever available this way.
303 * Pppd reads and writes packets via /dev/ppp instead.
304 */
305 static ssize_t
ppp_sync_read(struct tty_struct * tty,struct file * file,unsigned char __user * buf,size_t count)306 ppp_sync_read(struct tty_struct *tty, struct file *file,
307 unsigned char __user *buf, size_t count)
308 {
309 return -EAGAIN;
310 }
311
312 /*
313 * Write on the tty does nothing, the packets all come in
314 * from the ppp generic stuff.
315 */
316 static ssize_t
ppp_sync_write(struct tty_struct * tty,struct file * file,const unsigned char * buf,size_t count)317 ppp_sync_write(struct tty_struct *tty, struct file *file,
318 const unsigned char *buf, size_t count)
319 {
320 return -EAGAIN;
321 }
322
323 static int
ppp_synctty_ioctl(struct tty_struct * tty,struct file * file,unsigned int cmd,unsigned long arg)324 ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
325 unsigned int cmd, unsigned long arg)
326 {
327 struct syncppp *ap = sp_get(tty);
328 int __user *p = (int __user *)arg;
329 int err, val;
330
331 if (!ap)
332 return -ENXIO;
333 err = -EFAULT;
334 switch (cmd) {
335 case PPPIOCGCHAN:
336 err = -EFAULT;
337 if (put_user(ppp_channel_index(&ap->chan), p))
338 break;
339 err = 0;
340 break;
341
342 case PPPIOCGUNIT:
343 err = -EFAULT;
344 if (put_user(ppp_unit_number(&ap->chan), p))
345 break;
346 err = 0;
347 break;
348
349 case TCFLSH:
350 /* flush our buffers and the serial port's buffer */
351 if (arg == TCIOFLUSH || arg == TCOFLUSH)
352 ppp_sync_flush_output(ap);
353 err = tty_perform_flush(tty, arg);
354 break;
355
356 case FIONREAD:
357 val = 0;
358 if (put_user(val, p))
359 break;
360 err = 0;
361 break;
362
363 default:
364 err = tty_mode_ioctl(tty, file, cmd, arg);
365 break;
366 }
367
368 sp_put(ap);
369 return err;
370 }
371
372 /* No kernel lock - fine */
373 static unsigned int
ppp_sync_poll(struct tty_struct * tty,struct file * file,poll_table * wait)374 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
375 {
376 return 0;
377 }
378
379 /*
380 * This can now be called from hard interrupt level as well
381 * as soft interrupt level or mainline.
382 */
383 static void
ppp_sync_receive(struct tty_struct * tty,const unsigned char * buf,char * cflags,int count)384 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf,
385 char *cflags, int count)
386 {
387 struct syncppp *ap = sp_get(tty);
388 unsigned long flags;
389
390 if (!ap)
391 return;
392 spin_lock_irqsave(&ap->recv_lock, flags);
393 ppp_sync_input(ap, buf, cflags, count);
394 spin_unlock_irqrestore(&ap->recv_lock, flags);
395 if (!skb_queue_empty(&ap->rqueue))
396 tasklet_schedule(&ap->tsk);
397 sp_put(ap);
398 tty_unthrottle(tty);
399 }
400
401 static void
ppp_sync_wakeup(struct tty_struct * tty)402 ppp_sync_wakeup(struct tty_struct *tty)
403 {
404 struct syncppp *ap = sp_get(tty);
405
406 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
407 if (!ap)
408 return;
409 set_bit(XMIT_WAKEUP, &ap->xmit_flags);
410 tasklet_schedule(&ap->tsk);
411 sp_put(ap);
412 }
413
414
415 static struct tty_ldisc_ops ppp_sync_ldisc = {
416 .owner = THIS_MODULE,
417 .magic = TTY_LDISC_MAGIC,
418 .name = "pppsync",
419 .open = ppp_sync_open,
420 .close = ppp_sync_close,
421 .hangup = ppp_sync_hangup,
422 .read = ppp_sync_read,
423 .write = ppp_sync_write,
424 .ioctl = ppp_synctty_ioctl,
425 .poll = ppp_sync_poll,
426 .receive_buf = ppp_sync_receive,
427 .write_wakeup = ppp_sync_wakeup,
428 };
429
430 static int __init
ppp_sync_init(void)431 ppp_sync_init(void)
432 {
433 int err;
434
435 err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
436 if (err != 0)
437 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
438 err);
439 return err;
440 }
441
442 /*
443 * The following routines provide the PPP channel interface.
444 */
445 static int
ppp_sync_ioctl(struct ppp_channel * chan,unsigned int cmd,unsigned long arg)446 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
447 {
448 struct syncppp *ap = chan->private;
449 int err, val;
450 u32 accm[8];
451 void __user *argp = (void __user *)arg;
452 u32 __user *p = argp;
453
454 err = -EFAULT;
455 switch (cmd) {
456 case PPPIOCGFLAGS:
457 val = ap->flags | ap->rbits;
458 if (put_user(val, (int __user *) argp))
459 break;
460 err = 0;
461 break;
462 case PPPIOCSFLAGS:
463 if (get_user(val, (int __user *) argp))
464 break;
465 ap->flags = val & ~SC_RCV_BITS;
466 spin_lock_irq(&ap->recv_lock);
467 ap->rbits = val & SC_RCV_BITS;
468 spin_unlock_irq(&ap->recv_lock);
469 err = 0;
470 break;
471
472 case PPPIOCGASYNCMAP:
473 if (put_user(ap->xaccm[0], p))
474 break;
475 err = 0;
476 break;
477 case PPPIOCSASYNCMAP:
478 if (get_user(ap->xaccm[0], p))
479 break;
480 err = 0;
481 break;
482
483 case PPPIOCGRASYNCMAP:
484 if (put_user(ap->raccm, p))
485 break;
486 err = 0;
487 break;
488 case PPPIOCSRASYNCMAP:
489 if (get_user(ap->raccm, p))
490 break;
491 err = 0;
492 break;
493
494 case PPPIOCGXASYNCMAP:
495 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
496 break;
497 err = 0;
498 break;
499 case PPPIOCSXASYNCMAP:
500 if (copy_from_user(accm, argp, sizeof(accm)))
501 break;
502 accm[2] &= ~0x40000000U; /* can't escape 0x5e */
503 accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */
504 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
505 err = 0;
506 break;
507
508 case PPPIOCGMRU:
509 if (put_user(ap->mru, (int __user *) argp))
510 break;
511 err = 0;
512 break;
513 case PPPIOCSMRU:
514 if (get_user(val, (int __user *) argp))
515 break;
516 if (val < PPP_MRU)
517 val = PPP_MRU;
518 ap->mru = val;
519 err = 0;
520 break;
521
522 default:
523 err = -ENOTTY;
524 }
525 return err;
526 }
527
528 /*
529 * This is called at softirq level to deliver received packets
530 * to the ppp_generic code, and to tell the ppp_generic code
531 * if we can accept more output now.
532 */
ppp_sync_process(unsigned long arg)533 static void ppp_sync_process(unsigned long arg)
534 {
535 struct syncppp *ap = (struct syncppp *) arg;
536 struct sk_buff *skb;
537
538 /* process received packets */
539 while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
540 if (skb->len == 0) {
541 /* zero length buffers indicate error */
542 ppp_input_error(&ap->chan, 0);
543 kfree_skb(skb);
544 }
545 else
546 ppp_input(&ap->chan, skb);
547 }
548
549 /* try to push more stuff out */
550 if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
551 ppp_output_wakeup(&ap->chan);
552 }
553
554 /*
555 * Procedures for encapsulation and framing.
556 */
557
558 static struct sk_buff*
ppp_sync_txmunge(struct syncppp * ap,struct sk_buff * skb)559 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
560 {
561 int proto;
562 unsigned char *data;
563 int islcp;
564
565 data = skb->data;
566 proto = (data[0] << 8) + data[1];
567
568 /* LCP packets with codes between 1 (configure-request)
569 * and 7 (code-reject) must be sent as though no options
570 * have been negotiated.
571 */
572 islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
573
574 /* compress protocol field if option enabled */
575 if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
576 skb_pull(skb,1);
577
578 /* prepend address/control fields if necessary */
579 if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
580 if (skb_headroom(skb) < 2) {
581 struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
582 if (npkt == NULL) {
583 kfree_skb(skb);
584 return NULL;
585 }
586 skb_reserve(npkt,2);
587 skb_copy_from_linear_data(skb,
588 skb_put(npkt, skb->len), skb->len);
589 kfree_skb(skb);
590 skb = npkt;
591 }
592 skb_push(skb,2);
593 skb->data[0] = PPP_ALLSTATIONS;
594 skb->data[1] = PPP_UI;
595 }
596
597 ap->last_xmit = jiffies;
598
599 if (skb && ap->flags & SC_LOG_OUTPKT)
600 ppp_print_buffer ("send buffer", skb->data, skb->len);
601
602 return skb;
603 }
604
605 /*
606 * Transmit-side routines.
607 */
608
609 /*
610 * Send a packet to the peer over an sync tty line.
611 * Returns 1 iff the packet was accepted.
612 * If the packet was not accepted, we will call ppp_output_wakeup
613 * at some later time.
614 */
615 static int
ppp_sync_send(struct ppp_channel * chan,struct sk_buff * skb)616 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
617 {
618 struct syncppp *ap = chan->private;
619
620 ppp_sync_push(ap);
621
622 if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
623 return 0; /* already full */
624 skb = ppp_sync_txmunge(ap, skb);
625 if (skb != NULL)
626 ap->tpkt = skb;
627 else
628 clear_bit(XMIT_FULL, &ap->xmit_flags);
629
630 ppp_sync_push(ap);
631 return 1;
632 }
633
634 /*
635 * Push as much data as possible out to the tty.
636 */
637 static int
ppp_sync_push(struct syncppp * ap)638 ppp_sync_push(struct syncppp *ap)
639 {
640 int sent, done = 0;
641 struct tty_struct *tty = ap->tty;
642 int tty_stuffed = 0;
643
644 if (!spin_trylock_bh(&ap->xmit_lock))
645 return 0;
646 for (;;) {
647 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
648 tty_stuffed = 0;
649 if (!tty_stuffed && ap->tpkt) {
650 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
651 sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len);
652 if (sent < 0)
653 goto flush; /* error, e.g. loss of CD */
654 if (sent < ap->tpkt->len) {
655 tty_stuffed = 1;
656 } else {
657 kfree_skb(ap->tpkt);
658 ap->tpkt = NULL;
659 clear_bit(XMIT_FULL, &ap->xmit_flags);
660 done = 1;
661 }
662 continue;
663 }
664 /* haven't made any progress */
665 spin_unlock_bh(&ap->xmit_lock);
666 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
667 || (!tty_stuffed && ap->tpkt)))
668 break;
669 if (!spin_trylock_bh(&ap->xmit_lock))
670 break;
671 }
672 return done;
673
674 flush:
675 if (ap->tpkt) {
676 kfree_skb(ap->tpkt);
677 ap->tpkt = NULL;
678 clear_bit(XMIT_FULL, &ap->xmit_flags);
679 done = 1;
680 }
681 spin_unlock_bh(&ap->xmit_lock);
682 return done;
683 }
684
685 /*
686 * Flush output from our internal buffers.
687 * Called for the TCFLSH ioctl.
688 */
689 static void
ppp_sync_flush_output(struct syncppp * ap)690 ppp_sync_flush_output(struct syncppp *ap)
691 {
692 int done = 0;
693
694 spin_lock_bh(&ap->xmit_lock);
695 if (ap->tpkt != NULL) {
696 kfree_skb(ap->tpkt);
697 ap->tpkt = NULL;
698 clear_bit(XMIT_FULL, &ap->xmit_flags);
699 done = 1;
700 }
701 spin_unlock_bh(&ap->xmit_lock);
702 if (done)
703 ppp_output_wakeup(&ap->chan);
704 }
705
706 /*
707 * Receive-side routines.
708 */
709
710 /* called when the tty driver has data for us.
711 *
712 * Data is frame oriented: each call to ppp_sync_input is considered
713 * a whole frame. If the 1st flag byte is non-zero then the whole
714 * frame is considered to be in error and is tossed.
715 */
716 static void
ppp_sync_input(struct syncppp * ap,const unsigned char * buf,char * flags,int count)717 ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
718 char *flags, int count)
719 {
720 struct sk_buff *skb;
721 unsigned char *p;
722
723 if (count == 0)
724 return;
725
726 if (ap->flags & SC_LOG_INPKT)
727 ppp_print_buffer ("receive buffer", buf, count);
728
729 /* stuff the chars in the skb */
730 skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
731 if (!skb) {
732 printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
733 goto err;
734 }
735 /* Try to get the payload 4-byte aligned */
736 if (buf[0] != PPP_ALLSTATIONS)
737 skb_reserve(skb, 2 + (buf[0] & 1));
738
739 if (flags && *flags) {
740 /* error flag set, ignore frame */
741 goto err;
742 } else if (count > skb_tailroom(skb)) {
743 /* packet overflowed MRU */
744 goto err;
745 }
746
747 p = skb_put(skb, count);
748 memcpy(p, buf, count);
749
750 /* strip address/control field if present */
751 p = skb->data;
752 if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
753 /* chop off address/control */
754 if (skb->len < 3)
755 goto err;
756 p = skb_pull(skb, 2);
757 }
758
759 /* decompress protocol field if compressed */
760 if (p[0] & 1) {
761 /* protocol is compressed */
762 skb_push(skb, 1)[0] = 0;
763 } else if (skb->len < 2)
764 goto err;
765
766 /* queue the frame to be processed */
767 skb_queue_tail(&ap->rqueue, skb);
768 return;
769
770 err:
771 /* queue zero length packet as error indication */
772 if (skb || (skb = dev_alloc_skb(0))) {
773 skb_trim(skb, 0);
774 skb_queue_tail(&ap->rqueue, skb);
775 }
776 }
777
778 static void __exit
ppp_sync_cleanup(void)779 ppp_sync_cleanup(void)
780 {
781 if (tty_unregister_ldisc(N_SYNC_PPP) != 0)
782 printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
783 }
784
785 module_init(ppp_sync_init);
786 module_exit(ppp_sync_cleanup);
787 MODULE_LICENSE("GPL");
788 MODULE_ALIAS_LDISC(N_SYNC_PPP);
789