1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * PPP async serial channel driver for Linux.
5 * Copyright 1999 Paul Mackerras.
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.
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.
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>
36 #define PPP_VERSION "2.4.2"
40 /* Structure for storing local state. */
42 struct tty_struct *tty;
49 unsigned long xmit_flags;
52 unsigned int bytes_sent;
53 unsigned int bytes_rcvd;
60 unsigned long last_xmit;
64 struct sk_buff_head rqueue;
66 struct tasklet_struct tsk;
69 struct completion dead;
70 struct ppp_channel chan; /* interface to generic ppp layer */
71 unsigned char obuf[OBUFSIZE];
74 /* Bit numbers in xmit_flags */
82 #define SC_PREV_ERROR 4
85 #define SC_RCV_BITS (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
87 static int flag_time = HZ;
88 module_param(flag_time, int, 0);
89 MODULE_PARM_DESC(flag_time, "ppp_async: interval between flagged packets (in clock ticks)");
90 MODULE_LICENSE("GPL");
91 MODULE_ALIAS_LDISC(N_PPP);
96 static int ppp_async_encode(struct asyncppp *ap);
97 static int ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb);
98 static int ppp_async_push(struct asyncppp *ap);
99 static void ppp_async_flush_output(struct asyncppp *ap);
100 static void ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
101 const u8 *flags, int count);
102 static int ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd,
104 static void ppp_async_process(struct tasklet_struct *t);
106 static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
107 int len, int inbound);
109 static const struct ppp_channel_ops async_ops = {
110 .start_xmit = ppp_async_send,
111 .ioctl = ppp_async_ioctl,
115 * Routines implementing the PPP line discipline.
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.
127 * FIXME: this is no longer true. The _close path for the ldisc is
128 * now guaranteed to be sane.
130 static DEFINE_RWLOCK(disc_data_lock);
132 static struct asyncppp *ap_get(struct tty_struct *tty)
136 read_lock(&disc_data_lock);
139 refcount_inc(&ap->refcnt);
140 read_unlock(&disc_data_lock);
144 static void ap_put(struct asyncppp *ap)
146 if (refcount_dec_and_test(&ap->refcnt))
151 * Called when a tty is put into PPP line discipline. Called in process
155 ppp_asynctty_open(struct tty_struct *tty)
161 if (tty->ops->write == NULL)
165 ap = kzalloc(sizeof(*ap), GFP_KERNEL);
169 /* initialize the asyncppp structure */
172 spin_lock_init(&ap->xmit_lock);
173 spin_lock_init(&ap->recv_lock);
175 ap->xaccm[3] = 0x60000000U;
181 skb_queue_head_init(&ap->rqueue);
182 tasklet_setup(&ap->tsk, ppp_async_process);
184 refcount_set(&ap->refcnt, 1);
185 init_completion(&ap->dead);
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);
197 tty->receive_room = 65536;
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.
215 ppp_asynctty_close(struct tty_struct *tty)
219 write_lock_irq(&disc_data_lock);
221 tty->disc_data = NULL;
222 write_unlock_irq(&disc_data_lock);
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.
233 if (!refcount_dec_and_test(&ap->refcnt))
234 wait_for_completion(&ap->dead);
235 tasklet_kill(&ap->tsk);
237 ppp_unregister_channel(&ap->chan);
239 skb_queue_purge(&ap->rqueue);
245 * Called on tty hangup in process context.
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.
250 static void ppp_asynctty_hangup(struct tty_struct *tty)
252 ppp_asynctty_close(tty);
256 * Read does nothing - no data is ever available this way.
257 * Pppd reads and writes packets via /dev/ppp instead.
260 ppp_asynctty_read(struct tty_struct *tty, struct file *file, u8 *buf,
261 size_t count, void **cookie, unsigned long offset)
267 * Write on the tty does nothing, the packets all come in
268 * from the ppp generic stuff.
271 ppp_asynctty_write(struct tty_struct *tty, struct file *file, const u8 *buf,
278 * Called in process context only. May be re-entered by multiple
279 * ioctl calling threads.
283 ppp_asynctty_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
285 struct asyncppp *ap = ap_get(tty);
287 int __user *p = (int __user *)arg;
295 if (put_user(ppp_channel_index(&ap->chan), p))
302 if (put_user(ppp_unit_number(&ap->chan), p))
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);
316 if (put_user(val, p))
322 /* Try the various mode ioctls */
323 err = tty_mode_ioctl(tty, cmd, arg);
330 /* May sleep, don't call from interrupt level or with interrupts disabled */
332 ppp_asynctty_receive(struct tty_struct *tty, const u8 *buf, const u8 *cflags,
335 struct asyncppp *ap = ap_get(tty);
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);
350 ppp_asynctty_wakeup(struct tty_struct *tty)
352 struct asyncppp *ap = ap_get(tty);
354 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
357 set_bit(XMIT_WAKEUP, &ap->xmit_flags);
358 tasklet_schedule(&ap->tsk);
363 static struct tty_ldisc_ops ppp_ldisc = {
364 .owner = THIS_MODULE,
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,
382 err = tty_register_ldisc(&ppp_ldisc);
384 printk(KERN_ERR "PPP_async: error %d registering line disc.\n",
390 * The following routines provide the PPP channel interface.
393 ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
395 struct asyncppp *ap = chan->private;
396 void __user *argp = (void __user *)arg;
397 int __user *p = argp;
404 val = ap->flags | ap->rbits;
405 if (put_user(val, p))
410 if (get_user(val, p))
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);
419 case PPPIOCGASYNCMAP:
420 if (put_user(ap->xaccm[0], (u32 __user *)argp))
424 case PPPIOCSASYNCMAP:
425 if (get_user(ap->xaccm[0], (u32 __user *)argp))
430 case PPPIOCGRASYNCMAP:
431 if (put_user(ap->raccm, (u32 __user *)argp))
435 case PPPIOCSRASYNCMAP:
436 if (get_user(ap->raccm, (u32 __user *)argp))
441 case PPPIOCGXASYNCMAP:
442 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
446 case PPPIOCSXASYNCMAP:
447 if (copy_from_user(accm, argp, sizeof(accm)))
449 accm[2] &= ~0x40000000U; /* can't escape 0x5e */
450 accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */
451 memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
456 if (put_user(ap->mru, p))
461 if (get_user(val, p))
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.
485 static void ppp_async_process(struct tasklet_struct *t)
487 struct asyncppp *ap = from_tasklet(ap, t, tsk);
490 /* process received packets */
491 while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
493 ppp_input_error(&ap->chan, 0);
494 ppp_input(&ap->chan, skb);
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);
503 * Procedures for encapsulation and framing.
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.
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; \
523 ppp_async_encode(struct asyncppp *ap)
525 int fcs, i, count, c, proto;
526 unsigned char *buf, *buflim;
534 data = ap->tpkt->data;
535 count = ap->tpkt->len;
537 proto = get_unaligned_be16(data);
540 * LCP packets with code values between 1 (configure-request)
541 * and 7 (code-reject) must be sent as though no options
542 * had been negotiated.
544 islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
548 async_lcp_peek(ap, data, count, 0);
551 * Start of a new packet - insert the leading FLAG
552 * character if necessary.
554 if (islcp || flag_time == 0 ||
555 time_after_eq(jiffies, ap->last_xmit + flag_time))
557 ap->last_xmit = jiffies;
561 * Put in the address/control bytes if necessary
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);
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.
576 buflim = ap->obuf + OBUFSIZE - 6;
577 while (i < count && buf < buflim) {
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);
587 * Remember where we are up to in this packet.
596 * We have finished the packet. Add the FCS and flag.
600 PUT_BYTE(ap, buf, c, islcp);
601 c = (fcs >> 8) & 0xff;
602 PUT_BYTE(ap, buf, c, islcp);
606 consume_skb(ap->tpkt);
612 * Transmit-side routines.
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.
622 ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb)
624 struct asyncppp *ap = chan->private;
628 if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
629 return 0; /* already full */
638 * Push as much data as possible out to the tty.
641 ppp_async_push(struct asyncppp *ap)
643 int avail, sent, done = 0;
644 struct tty_struct *tty = ap->tty;
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.
656 if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
658 spin_lock_bh(&ap->xmit_lock);
660 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
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);
667 goto flush; /* error, e.g. loss of CD */
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);
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.
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)))
695 /* more work to do, see if we can do it now */
696 if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
699 spin_unlock_bh(&ap->xmit_lock);
703 clear_bit(XMIT_BUSY, &ap->xmit_flags);
707 clear_bit(XMIT_FULL, &ap->xmit_flags);
711 spin_unlock_bh(&ap->xmit_lock);
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.
721 ppp_async_flush_output(struct asyncppp *ap)
725 spin_lock_bh(&ap->xmit_lock);
727 if (ap->tpkt != NULL) {
730 clear_bit(XMIT_FULL, &ap->xmit_flags);
733 spin_unlock_bh(&ap->xmit_lock);
735 ppp_output_wakeup(&ap->chan);
739 * Receive-side routines.
742 /* see how many ordinary chars there are at the start of buf */
744 scan_ordinary(struct asyncppp *ap, const unsigned char *buf, int count)
748 for (i = 0; i < count; ++i) {
750 if (c == PPP_ESCAPE || c == PPP_FLAG ||
751 (c < 0x20 && (ap->raccm & (1 << c)) != 0))
757 /* called when a flag is seen - do end-of-packet processing */
759 process_input_packet(struct asyncppp *ap)
763 unsigned int len, fcs;
766 if (ap->state & (SC_TOSS | SC_ESCAPE))
770 return; /* 0-length packet */
776 goto err; /* too short */
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);
784 /* check for address/control and protocol compression */
786 if (p[0] == PPP_ALLSTATIONS) {
787 /* chop off address/control */
788 if (p[1] != PPP_UI || skb->len < 3)
790 p = skb_pull(skb, 2);
793 /* If protocol field is not compressed, it can be LCP packet */
794 if (!(p[0] & 0x01)) {
799 proto = (p[0] << 8) + p[1];
800 if (proto == PPP_LCP)
801 async_lcp_peek(ap, p, skb->len, 1);
804 /* queue the frame to be processed */
805 skb->cb[0] = ap->state;
806 skb_queue_tail(&ap->rqueue, skb);
812 /* frame had an error, remember that, reset SC_TOSS & SC_ESCAPE */
813 ap->state = SC_PREV_ERROR;
815 /* make skb appear as freshly allocated */
817 skb_reserve(skb, - skb_headroom(skb));
821 /* Called when the tty driver has data for us. Runs parallel with the
822 other ldisc functions but will not be re-entered */
825 ppp_async_input(struct asyncppp *ap, const u8 *buf, const u8 *flags, int count)
828 int c, i, j, n, s, f;
831 /* update bits used for 8-bit cleanness detection */
832 if (~ap->rbits & SC_RCV_BITS) {
834 for (i = 0; i < count; ++i) {
836 if (flags && flags[i] != 0)
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;
846 /* scan through and see how many chars we can do in bulk */
847 if ((ap->state & SC_ESCAPE) && buf[0] == PPP_ESCAPE)
850 n = scan_ordinary(ap, buf, count);
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)
861 ap->state |= SC_TOSS;
863 } else if (n > 0 && (ap->state & SC_TOSS) == 0) {
864 /* stuff the chars in the skb */
867 skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
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].
879 if (buf[0] != PPP_ALLSTATIONS)
880 skb_reserve(skb, 2 + (buf[0] & 1));
882 if (n > skb_tailroom(skb)) {
883 /* packet overflowed MRU */
884 ap->state |= SC_TOSS;
886 sp = skb_put_data(skb, buf, n);
887 if (ap->state & SC_ESCAPE) {
889 ap->state &= ~SC_ESCAPE;
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))
907 else if (c == STOP_CHAR(ap->tty))
910 /* otherwise it's a char in the recv ACCM */
921 printk(KERN_ERR "PPPasync: no memory (input pkt)\n");
922 ap->state |= SC_TOSS;
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.
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).
938 #define CONFREQ 1 /* LCP code field values */
940 #define LCP_MRU 1 /* LCP option numbers */
941 #define LCP_ASYNCMAP 2
943 static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
944 int len, int inbound)
946 int dlen, fcs, i, code;
949 data += 2; /* skip protocol bytes */
951 if (len < 4) /* 4 = code, ID, length */
954 if (code != CONFACK && code != CONFREQ)
956 dlen = get_unaligned_be16(data + 2);
958 return; /* packet got truncated or length is bogus */
960 if (code == (inbound? CONFACK: CONFREQ)) {
962 * sent confreq or received confack:
963 * calculate the crc of the data from the ID field on.
966 for (i = 1; i < dlen; ++i)
967 fcs = PPP_FCS(fcs, data[i]);
970 /* outbound confreq - remember the crc for later */
975 /* received confack, check the crc */
981 return; /* not interested in received confreq */
983 /* process the options in the confack */
986 /* data[0] is code, data[1] is length */
987 while (dlen >= 2 && dlen >= data[1] && data[1] >= 2) {
990 val = get_unaligned_be16(data + 2);
997 val = get_unaligned_be32(data + 2);
1009 static void __exit ppp_async_cleanup(void)
1011 tty_unregister_ldisc(&ppp_ldisc);
1014 module_init(ppp_async_init);
1015 module_exit(ppp_async_cleanup);