1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * PPP synchronous tty channel driver for Linux. 4 * 5 * This is a ppp channel driver that can be used with tty device drivers 6 * that are frame oriented, such as synchronous HDLC devices. 7 * 8 * Complete PPP frames without encoding/decoding are exchanged between 9 * the channel driver and the device driver. 10 * 11 * The async map IOCTL codes are implemented to keep the user mode 12 * applications happy if they call them. Synchronous PPP does not use 13 * the async maps. 14 * 15 * Copyright 1999 Paul Mackerras. 16 * 17 * Also touched by the grubby hands of Paul Fulghum paulkf@microgate.com 18 * 19 * This driver provides the encapsulation and framing for sending 20 * and receiving PPP frames over sync serial lines. It relies on 21 * the generic PPP layer to give it frames to send and to process 22 * received frames. It implements the PPP line discipline. 23 * 24 * Part of the code in this driver was inspired by the old async-only 25 * PPP driver, written by Michael Callahan and Al Longyear, and 26 * subsequently hacked by Paul Mackerras. 27 * 28 * ==FILEVERSION 20040616== 29 */ 30 31 #include <linux/module.h> 32 #include <linux/kernel.h> 33 #include <linux/skbuff.h> 34 #include <linux/tty.h> 35 #include <linux/netdevice.h> 36 #include <linux/poll.h> 37 #include <linux/ppp_defs.h> 38 #include <linux/ppp-ioctl.h> 39 #include <linux/ppp_channel.h> 40 #include <linux/spinlock.h> 41 #include <linux/completion.h> 42 #include <linux/init.h> 43 #include <linux/interrupt.h> 44 #include <linux/slab.h> 45 #include <linux/refcount.h> 46 #include <asm/unaligned.h> 47 #include <linux/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 refcount_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(struct tasklet_struct *t); 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 const char *flags, int count); 98 99 static const struct ppp_channel_ops sync_ops = { 100 .start_xmit = ppp_sync_send, 101 .ioctl = ppp_sync_ioctl, 102 }; 103 104 /* 105 * Utility procedure to print a buffer in hex/ascii 106 */ 107 static void 108 ppp_print_buffer (const char *name, const __u8 *buf, int count) 109 { 110 if (name != NULL) 111 printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count); 112 113 print_hex_dump_bytes("", DUMP_PREFIX_NONE, buf, count); 114 } 115 116 117 /* 118 * Routines implementing the synchronous PPP line discipline. 119 */ 120 121 /* 122 * We have a potential race on dereferencing tty->disc_data, 123 * because the tty layer provides no locking at all - thus one 124 * cpu could be running ppp_synctty_receive while another 125 * calls ppp_synctty_close, which zeroes tty->disc_data and 126 * frees the memory that ppp_synctty_receive is using. The best 127 * way to fix this is to use a rwlock in the tty struct, but for now 128 * we use a single global rwlock for all ttys in ppp line discipline. 129 * 130 * FIXME: Fixed in tty_io nowadays. 131 */ 132 static DEFINE_RWLOCK(disc_data_lock); 133 134 static struct syncppp *sp_get(struct tty_struct *tty) 135 { 136 struct syncppp *ap; 137 138 read_lock(&disc_data_lock); 139 ap = tty->disc_data; 140 if (ap != NULL) 141 refcount_inc(&ap->refcnt); 142 read_unlock(&disc_data_lock); 143 return ap; 144 } 145 146 static void sp_put(struct syncppp *ap) 147 { 148 if (refcount_dec_and_test(&ap->refcnt)) 149 complete(&ap->dead_cmp); 150 } 151 152 /* 153 * Called when a tty is put into sync-PPP line discipline. 154 */ 155 static int 156 ppp_sync_open(struct tty_struct *tty) 157 { 158 struct syncppp *ap; 159 int err; 160 int speed; 161 162 if (tty->ops->write == NULL) 163 return -EOPNOTSUPP; 164 165 ap = kzalloc(sizeof(*ap), GFP_KERNEL); 166 err = -ENOMEM; 167 if (!ap) 168 goto out; 169 170 /* initialize the syncppp structure */ 171 ap->tty = tty; 172 ap->mru = PPP_MRU; 173 spin_lock_init(&ap->xmit_lock); 174 spin_lock_init(&ap->recv_lock); 175 ap->xaccm[0] = ~0U; 176 ap->xaccm[3] = 0x60000000U; 177 ap->raccm = ~0U; 178 179 skb_queue_head_init(&ap->rqueue); 180 tasklet_setup(&ap->tsk, ppp_sync_process); 181 182 refcount_set(&ap->refcnt, 1); 183 init_completion(&ap->dead_cmp); 184 185 ap->chan.private = ap; 186 ap->chan.ops = &sync_ops; 187 ap->chan.mtu = PPP_MRU; 188 ap->chan.hdrlen = 2; /* for A/C bytes */ 189 speed = tty_get_baud_rate(tty); 190 ap->chan.speed = speed; 191 err = ppp_register_channel(&ap->chan); 192 if (err) 193 goto out_free; 194 195 tty->disc_data = ap; 196 tty->receive_room = 65536; 197 return 0; 198 199 out_free: 200 kfree(ap); 201 out: 202 return err; 203 } 204 205 /* 206 * Called when the tty is put into another line discipline 207 * or it hangs up. We have to wait for any cpu currently 208 * executing in any of the other ppp_synctty_* routines to 209 * finish before we can call ppp_unregister_channel and free 210 * the syncppp struct. This routine must be called from 211 * process context, not interrupt or softirq context. 212 */ 213 static void 214 ppp_sync_close(struct tty_struct *tty) 215 { 216 struct syncppp *ap; 217 218 write_lock_irq(&disc_data_lock); 219 ap = tty->disc_data; 220 tty->disc_data = NULL; 221 write_unlock_irq(&disc_data_lock); 222 if (!ap) 223 return; 224 225 /* 226 * We have now ensured that nobody can start using ap from now 227 * on, but we have to wait for all existing users to finish. 228 * Note that ppp_unregister_channel ensures that no calls to 229 * our channel ops (i.e. ppp_sync_send/ioctl) are in progress 230 * by the time it returns. 231 */ 232 if (!refcount_dec_and_test(&ap->refcnt)) 233 wait_for_completion(&ap->dead_cmp); 234 tasklet_kill(&ap->tsk); 235 236 ppp_unregister_channel(&ap->chan); 237 skb_queue_purge(&ap->rqueue); 238 kfree_skb(ap->tpkt); 239 kfree(ap); 240 } 241 242 /* 243 * Called on tty hangup in process context. 244 * 245 * Wait for I/O to driver to complete and unregister PPP channel. 246 * This is already done by the close routine, so just call that. 247 */ 248 static void ppp_sync_hangup(struct tty_struct *tty) 249 { 250 ppp_sync_close(tty); 251 } 252 253 /* 254 * Read does nothing - no data is ever available this way. 255 * Pppd reads and writes packets via /dev/ppp instead. 256 */ 257 static ssize_t 258 ppp_sync_read(struct tty_struct *tty, struct file *file, 259 unsigned char *buf, size_t count, 260 void **cookie, unsigned long offset) 261 { 262 return -EAGAIN; 263 } 264 265 /* 266 * Write on the tty does nothing, the packets all come in 267 * from the ppp generic stuff. 268 */ 269 static ssize_t 270 ppp_sync_write(struct tty_struct *tty, struct file *file, 271 const unsigned char *buf, size_t count) 272 { 273 return -EAGAIN; 274 } 275 276 static int 277 ppp_synctty_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg) 278 { 279 struct syncppp *ap = sp_get(tty); 280 int __user *p = (int __user *)arg; 281 int err, val; 282 283 if (!ap) 284 return -ENXIO; 285 err = -EFAULT; 286 switch (cmd) { 287 case PPPIOCGCHAN: 288 err = -EFAULT; 289 if (put_user(ppp_channel_index(&ap->chan), p)) 290 break; 291 err = 0; 292 break; 293 294 case PPPIOCGUNIT: 295 err = -EFAULT; 296 if (put_user(ppp_unit_number(&ap->chan), p)) 297 break; 298 err = 0; 299 break; 300 301 case TCFLSH: 302 /* flush our buffers and the serial port's buffer */ 303 if (arg == TCIOFLUSH || arg == TCOFLUSH) 304 ppp_sync_flush_output(ap); 305 err = n_tty_ioctl_helper(tty, cmd, arg); 306 break; 307 308 case FIONREAD: 309 val = 0; 310 if (put_user(val, p)) 311 break; 312 err = 0; 313 break; 314 315 default: 316 err = tty_mode_ioctl(tty, cmd, arg); 317 break; 318 } 319 320 sp_put(ap); 321 return err; 322 } 323 324 /* No kernel lock - fine */ 325 static __poll_t 326 ppp_sync_poll(struct tty_struct *tty, struct file *file, poll_table *wait) 327 { 328 return 0; 329 } 330 331 /* May sleep, don't call from interrupt level or with interrupts disabled */ 332 static void 333 ppp_sync_receive(struct tty_struct *tty, const unsigned char *buf, 334 const char *cflags, int count) 335 { 336 struct syncppp *ap = sp_get(tty); 337 unsigned long flags; 338 339 if (!ap) 340 return; 341 spin_lock_irqsave(&ap->recv_lock, flags); 342 ppp_sync_input(ap, buf, cflags, count); 343 spin_unlock_irqrestore(&ap->recv_lock, flags); 344 if (!skb_queue_empty(&ap->rqueue)) 345 tasklet_schedule(&ap->tsk); 346 sp_put(ap); 347 tty_unthrottle(tty); 348 } 349 350 static void 351 ppp_sync_wakeup(struct tty_struct *tty) 352 { 353 struct syncppp *ap = sp_get(tty); 354 355 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); 356 if (!ap) 357 return; 358 set_bit(XMIT_WAKEUP, &ap->xmit_flags); 359 tasklet_schedule(&ap->tsk); 360 sp_put(ap); 361 } 362 363 364 static struct tty_ldisc_ops ppp_sync_ldisc = { 365 .owner = THIS_MODULE, 366 .num = N_SYNC_PPP, 367 .name = "pppsync", 368 .open = ppp_sync_open, 369 .close = ppp_sync_close, 370 .hangup = ppp_sync_hangup, 371 .read = ppp_sync_read, 372 .write = ppp_sync_write, 373 .ioctl = ppp_synctty_ioctl, 374 .poll = ppp_sync_poll, 375 .receive_buf = ppp_sync_receive, 376 .write_wakeup = ppp_sync_wakeup, 377 }; 378 379 static int __init 380 ppp_sync_init(void) 381 { 382 int err; 383 384 err = tty_register_ldisc(&ppp_sync_ldisc); 385 if (err != 0) 386 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n", 387 err); 388 return err; 389 } 390 391 /* 392 * The following routines provide the PPP channel interface. 393 */ 394 static int 395 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg) 396 { 397 struct syncppp *ap = chan->private; 398 int err, val; 399 u32 accm[8]; 400 void __user *argp = (void __user *)arg; 401 u32 __user *p = argp; 402 403 err = -EFAULT; 404 switch (cmd) { 405 case PPPIOCGFLAGS: 406 val = ap->flags | ap->rbits; 407 if (put_user(val, (int __user *) argp)) 408 break; 409 err = 0; 410 break; 411 case PPPIOCSFLAGS: 412 if (get_user(val, (int __user *) argp)) 413 break; 414 ap->flags = val & ~SC_RCV_BITS; 415 spin_lock_irq(&ap->recv_lock); 416 ap->rbits = val & SC_RCV_BITS; 417 spin_unlock_irq(&ap->recv_lock); 418 err = 0; 419 break; 420 421 case PPPIOCGASYNCMAP: 422 if (put_user(ap->xaccm[0], p)) 423 break; 424 err = 0; 425 break; 426 case PPPIOCSASYNCMAP: 427 if (get_user(ap->xaccm[0], p)) 428 break; 429 err = 0; 430 break; 431 432 case PPPIOCGRASYNCMAP: 433 if (put_user(ap->raccm, p)) 434 break; 435 err = 0; 436 break; 437 case PPPIOCSRASYNCMAP: 438 if (get_user(ap->raccm, p)) 439 break; 440 err = 0; 441 break; 442 443 case PPPIOCGXASYNCMAP: 444 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm))) 445 break; 446 err = 0; 447 break; 448 case PPPIOCSXASYNCMAP: 449 if (copy_from_user(accm, argp, sizeof(accm))) 450 break; 451 accm[2] &= ~0x40000000U; /* can't escape 0x5e */ 452 accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */ 453 memcpy(ap->xaccm, accm, sizeof(ap->xaccm)); 454 err = 0; 455 break; 456 457 case PPPIOCGMRU: 458 if (put_user(ap->mru, (int __user *) argp)) 459 break; 460 err = 0; 461 break; 462 case PPPIOCSMRU: 463 if (get_user(val, (int __user *) argp)) 464 break; 465 if (val < PPP_MRU) 466 val = PPP_MRU; 467 ap->mru = val; 468 err = 0; 469 break; 470 471 default: 472 err = -ENOTTY; 473 } 474 return err; 475 } 476 477 /* 478 * This is called at softirq level to deliver received packets 479 * to the ppp_generic code, and to tell the ppp_generic code 480 * if we can accept more output now. 481 */ 482 static void ppp_sync_process(struct tasklet_struct *t) 483 { 484 struct syncppp *ap = from_tasklet(ap, t, tsk); 485 struct sk_buff *skb; 486 487 /* process received packets */ 488 while ((skb = skb_dequeue(&ap->rqueue)) != NULL) { 489 if (skb->len == 0) { 490 /* zero length buffers indicate error */ 491 ppp_input_error(&ap->chan, 0); 492 kfree_skb(skb); 493 } 494 else 495 ppp_input(&ap->chan, skb); 496 } 497 498 /* try to push more stuff out */ 499 if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap)) 500 ppp_output_wakeup(&ap->chan); 501 } 502 503 /* 504 * Procedures for encapsulation and framing. 505 */ 506 507 static struct sk_buff* 508 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb) 509 { 510 int proto; 511 unsigned char *data; 512 int islcp; 513 514 data = skb->data; 515 proto = get_unaligned_be16(data); 516 517 /* LCP packets with codes between 1 (configure-request) 518 * and 7 (code-reject) must be sent as though no options 519 * have been negotiated. 520 */ 521 islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7; 522 523 /* compress protocol field if option enabled */ 524 if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp) 525 skb_pull(skb,1); 526 527 /* prepend address/control fields if necessary */ 528 if ((ap->flags & SC_COMP_AC) == 0 || islcp) { 529 if (skb_headroom(skb) < 2) { 530 struct sk_buff *npkt = dev_alloc_skb(skb->len + 2); 531 if (npkt == NULL) { 532 kfree_skb(skb); 533 return NULL; 534 } 535 skb_reserve(npkt,2); 536 skb_copy_from_linear_data(skb, 537 skb_put(npkt, skb->len), skb->len); 538 consume_skb(skb); 539 skb = npkt; 540 } 541 skb_push(skb,2); 542 skb->data[0] = PPP_ALLSTATIONS; 543 skb->data[1] = PPP_UI; 544 } 545 546 ap->last_xmit = jiffies; 547 548 if (skb && ap->flags & SC_LOG_OUTPKT) 549 ppp_print_buffer ("send buffer", skb->data, skb->len); 550 551 return skb; 552 } 553 554 /* 555 * Transmit-side routines. 556 */ 557 558 /* 559 * Send a packet to the peer over an sync tty line. 560 * Returns 1 iff the packet was accepted. 561 * If the packet was not accepted, we will call ppp_output_wakeup 562 * at some later time. 563 */ 564 static int 565 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb) 566 { 567 struct syncppp *ap = chan->private; 568 569 ppp_sync_push(ap); 570 571 if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags)) 572 return 0; /* already full */ 573 skb = ppp_sync_txmunge(ap, skb); 574 if (skb != NULL) 575 ap->tpkt = skb; 576 else 577 clear_bit(XMIT_FULL, &ap->xmit_flags); 578 579 ppp_sync_push(ap); 580 return 1; 581 } 582 583 /* 584 * Push as much data as possible out to the tty. 585 */ 586 static int 587 ppp_sync_push(struct syncppp *ap) 588 { 589 int sent, done = 0; 590 struct tty_struct *tty = ap->tty; 591 int tty_stuffed = 0; 592 593 if (!spin_trylock_bh(&ap->xmit_lock)) 594 return 0; 595 for (;;) { 596 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags)) 597 tty_stuffed = 0; 598 if (!tty_stuffed && ap->tpkt) { 599 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); 600 sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len); 601 if (sent < 0) 602 goto flush; /* error, e.g. loss of CD */ 603 if (sent < ap->tpkt->len) { 604 tty_stuffed = 1; 605 } else { 606 consume_skb(ap->tpkt); 607 ap->tpkt = NULL; 608 clear_bit(XMIT_FULL, &ap->xmit_flags); 609 done = 1; 610 } 611 continue; 612 } 613 /* haven't made any progress */ 614 spin_unlock_bh(&ap->xmit_lock); 615 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) || 616 (!tty_stuffed && ap->tpkt))) 617 break; 618 if (!spin_trylock_bh(&ap->xmit_lock)) 619 break; 620 } 621 return done; 622 623 flush: 624 if (ap->tpkt) { 625 kfree_skb(ap->tpkt); 626 ap->tpkt = NULL; 627 clear_bit(XMIT_FULL, &ap->xmit_flags); 628 done = 1; 629 } 630 spin_unlock_bh(&ap->xmit_lock); 631 return done; 632 } 633 634 /* 635 * Flush output from our internal buffers. 636 * Called for the TCFLSH ioctl. 637 */ 638 static void 639 ppp_sync_flush_output(struct syncppp *ap) 640 { 641 int done = 0; 642 643 spin_lock_bh(&ap->xmit_lock); 644 if (ap->tpkt != NULL) { 645 kfree_skb(ap->tpkt); 646 ap->tpkt = NULL; 647 clear_bit(XMIT_FULL, &ap->xmit_flags); 648 done = 1; 649 } 650 spin_unlock_bh(&ap->xmit_lock); 651 if (done) 652 ppp_output_wakeup(&ap->chan); 653 } 654 655 /* 656 * Receive-side routines. 657 */ 658 659 /* called when the tty driver has data for us. 660 * 661 * Data is frame oriented: each call to ppp_sync_input is considered 662 * a whole frame. If the 1st flag byte is non-zero then the whole 663 * frame is considered to be in error and is tossed. 664 */ 665 static void 666 ppp_sync_input(struct syncppp *ap, const unsigned char *buf, 667 const char *flags, int count) 668 { 669 struct sk_buff *skb; 670 unsigned char *p; 671 672 if (count == 0) 673 return; 674 675 if (ap->flags & SC_LOG_INPKT) 676 ppp_print_buffer ("receive buffer", buf, count); 677 678 /* stuff the chars in the skb */ 679 skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2); 680 if (!skb) { 681 printk(KERN_ERR "PPPsync: no memory (input pkt)\n"); 682 goto err; 683 } 684 /* Try to get the payload 4-byte aligned */ 685 if (buf[0] != PPP_ALLSTATIONS) 686 skb_reserve(skb, 2 + (buf[0] & 1)); 687 688 if (flags && *flags) { 689 /* error flag set, ignore frame */ 690 goto err; 691 } else if (count > skb_tailroom(skb)) { 692 /* packet overflowed MRU */ 693 goto err; 694 } 695 696 skb_put_data(skb, buf, count); 697 698 /* strip address/control field if present */ 699 p = skb->data; 700 if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) { 701 /* chop off address/control */ 702 if (skb->len < 3) 703 goto err; 704 p = skb_pull(skb, 2); 705 } 706 707 /* PPP packet length should be >= 2 bytes when protocol field is not 708 * compressed. 709 */ 710 if (!(p[0] & 0x01) && skb->len < 2) 711 goto err; 712 713 /* queue the frame to be processed */ 714 skb_queue_tail(&ap->rqueue, skb); 715 return; 716 717 err: 718 /* queue zero length packet as error indication */ 719 if (skb || (skb = dev_alloc_skb(0))) { 720 skb_trim(skb, 0); 721 skb_queue_tail(&ap->rqueue, skb); 722 } 723 } 724 725 static void __exit 726 ppp_sync_cleanup(void) 727 { 728 tty_unregister_ldisc(&ppp_sync_ldisc); 729 } 730 731 module_init(ppp_sync_init); 732 module_exit(ppp_sync_cleanup); 733 MODULE_LICENSE("GPL"); 734 MODULE_ALIAS_LDISC(N_SYNC_PPP); 735