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 u8 *buf, const u8 *flags, 97 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, u8 *buf, size_t count, 259 void **cookie, unsigned long offset) 260 { 261 return -EAGAIN; 262 } 263 264 /* 265 * Write on the tty does nothing, the packets all come in 266 * from the ppp generic stuff. 267 */ 268 static ssize_t 269 ppp_sync_write(struct tty_struct *tty, struct file *file, const u8 *buf, 270 size_t count) 271 { 272 return -EAGAIN; 273 } 274 275 static int 276 ppp_synctty_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg) 277 { 278 struct syncppp *ap = sp_get(tty); 279 int __user *p = (int __user *)arg; 280 int err, val; 281 282 if (!ap) 283 return -ENXIO; 284 err = -EFAULT; 285 switch (cmd) { 286 case PPPIOCGCHAN: 287 err = -EFAULT; 288 if (put_user(ppp_channel_index(&ap->chan), p)) 289 break; 290 err = 0; 291 break; 292 293 case PPPIOCGUNIT: 294 err = -EFAULT; 295 if (put_user(ppp_unit_number(&ap->chan), p)) 296 break; 297 err = 0; 298 break; 299 300 case TCFLSH: 301 /* flush our buffers and the serial port's buffer */ 302 if (arg == TCIOFLUSH || arg == TCOFLUSH) 303 ppp_sync_flush_output(ap); 304 err = n_tty_ioctl_helper(tty, cmd, arg); 305 break; 306 307 case FIONREAD: 308 val = 0; 309 if (put_user(val, p)) 310 break; 311 err = 0; 312 break; 313 314 default: 315 err = tty_mode_ioctl(tty, cmd, arg); 316 break; 317 } 318 319 sp_put(ap); 320 return err; 321 } 322 323 /* May sleep, don't call from interrupt level or with interrupts disabled */ 324 static void 325 ppp_sync_receive(struct tty_struct *tty, const u8 *buf, const u8 *cflags, 326 size_t count) 327 { 328 struct syncppp *ap = sp_get(tty); 329 unsigned long flags; 330 331 if (!ap) 332 return; 333 spin_lock_irqsave(&ap->recv_lock, flags); 334 ppp_sync_input(ap, buf, cflags, count); 335 spin_unlock_irqrestore(&ap->recv_lock, flags); 336 if (!skb_queue_empty(&ap->rqueue)) 337 tasklet_schedule(&ap->tsk); 338 sp_put(ap); 339 tty_unthrottle(tty); 340 } 341 342 static void 343 ppp_sync_wakeup(struct tty_struct *tty) 344 { 345 struct syncppp *ap = sp_get(tty); 346 347 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); 348 if (!ap) 349 return; 350 set_bit(XMIT_WAKEUP, &ap->xmit_flags); 351 tasklet_schedule(&ap->tsk); 352 sp_put(ap); 353 } 354 355 356 static struct tty_ldisc_ops ppp_sync_ldisc = { 357 .owner = THIS_MODULE, 358 .num = N_SYNC_PPP, 359 .name = "pppsync", 360 .open = ppp_sync_open, 361 .close = ppp_sync_close, 362 .hangup = ppp_sync_hangup, 363 .read = ppp_sync_read, 364 .write = ppp_sync_write, 365 .ioctl = ppp_synctty_ioctl, 366 .receive_buf = ppp_sync_receive, 367 .write_wakeup = ppp_sync_wakeup, 368 }; 369 370 static int __init 371 ppp_sync_init(void) 372 { 373 int err; 374 375 err = tty_register_ldisc(&ppp_sync_ldisc); 376 if (err != 0) 377 printk(KERN_ERR "PPP_sync: error %d registering line disc.\n", 378 err); 379 return err; 380 } 381 382 /* 383 * The following routines provide the PPP channel interface. 384 */ 385 static int 386 ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg) 387 { 388 struct syncppp *ap = chan->private; 389 int err, val; 390 u32 accm[8]; 391 void __user *argp = (void __user *)arg; 392 u32 __user *p = argp; 393 394 err = -EFAULT; 395 switch (cmd) { 396 case PPPIOCGFLAGS: 397 val = ap->flags | ap->rbits; 398 if (put_user(val, (int __user *) argp)) 399 break; 400 err = 0; 401 break; 402 case PPPIOCSFLAGS: 403 if (get_user(val, (int __user *) argp)) 404 break; 405 ap->flags = val & ~SC_RCV_BITS; 406 spin_lock_irq(&ap->recv_lock); 407 ap->rbits = val & SC_RCV_BITS; 408 spin_unlock_irq(&ap->recv_lock); 409 err = 0; 410 break; 411 412 case PPPIOCGASYNCMAP: 413 if (put_user(ap->xaccm[0], p)) 414 break; 415 err = 0; 416 break; 417 case PPPIOCSASYNCMAP: 418 if (get_user(ap->xaccm[0], p)) 419 break; 420 err = 0; 421 break; 422 423 case PPPIOCGRASYNCMAP: 424 if (put_user(ap->raccm, p)) 425 break; 426 err = 0; 427 break; 428 case PPPIOCSRASYNCMAP: 429 if (get_user(ap->raccm, p)) 430 break; 431 err = 0; 432 break; 433 434 case PPPIOCGXASYNCMAP: 435 if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm))) 436 break; 437 err = 0; 438 break; 439 case PPPIOCSXASYNCMAP: 440 if (copy_from_user(accm, argp, sizeof(accm))) 441 break; 442 accm[2] &= ~0x40000000U; /* can't escape 0x5e */ 443 accm[3] |= 0x60000000U; /* must escape 0x7d, 0x7e */ 444 memcpy(ap->xaccm, accm, sizeof(ap->xaccm)); 445 err = 0; 446 break; 447 448 case PPPIOCGMRU: 449 if (put_user(ap->mru, (int __user *) argp)) 450 break; 451 err = 0; 452 break; 453 case PPPIOCSMRU: 454 if (get_user(val, (int __user *) argp)) 455 break; 456 if (val < PPP_MRU) 457 val = PPP_MRU; 458 ap->mru = val; 459 err = 0; 460 break; 461 462 default: 463 err = -ENOTTY; 464 } 465 return err; 466 } 467 468 /* 469 * This is called at softirq level to deliver received packets 470 * to the ppp_generic code, and to tell the ppp_generic code 471 * if we can accept more output now. 472 */ 473 static void ppp_sync_process(struct tasklet_struct *t) 474 { 475 struct syncppp *ap = from_tasklet(ap, t, tsk); 476 struct sk_buff *skb; 477 478 /* process received packets */ 479 while ((skb = skb_dequeue(&ap->rqueue)) != NULL) { 480 if (skb->len == 0) { 481 /* zero length buffers indicate error */ 482 ppp_input_error(&ap->chan, 0); 483 kfree_skb(skb); 484 } 485 else 486 ppp_input(&ap->chan, skb); 487 } 488 489 /* try to push more stuff out */ 490 if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap)) 491 ppp_output_wakeup(&ap->chan); 492 } 493 494 /* 495 * Procedures for encapsulation and framing. 496 */ 497 498 static struct sk_buff* 499 ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb) 500 { 501 int proto; 502 unsigned char *data; 503 int islcp; 504 505 data = skb->data; 506 proto = get_unaligned_be16(data); 507 508 /* LCP packets with codes between 1 (configure-request) 509 * and 7 (code-reject) must be sent as though no options 510 * have been negotiated. 511 */ 512 islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7; 513 514 /* compress protocol field if option enabled */ 515 if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp) 516 skb_pull(skb,1); 517 518 /* prepend address/control fields if necessary */ 519 if ((ap->flags & SC_COMP_AC) == 0 || islcp) { 520 if (skb_headroom(skb) < 2) { 521 struct sk_buff *npkt = dev_alloc_skb(skb->len + 2); 522 if (npkt == NULL) { 523 kfree_skb(skb); 524 return NULL; 525 } 526 skb_reserve(npkt,2); 527 skb_copy_from_linear_data(skb, 528 skb_put(npkt, skb->len), skb->len); 529 consume_skb(skb); 530 skb = npkt; 531 } 532 skb_push(skb,2); 533 skb->data[0] = PPP_ALLSTATIONS; 534 skb->data[1] = PPP_UI; 535 } 536 537 ap->last_xmit = jiffies; 538 539 if (skb && ap->flags & SC_LOG_OUTPKT) 540 ppp_print_buffer ("send buffer", skb->data, skb->len); 541 542 return skb; 543 } 544 545 /* 546 * Transmit-side routines. 547 */ 548 549 /* 550 * Send a packet to the peer over an sync tty line. 551 * Returns 1 iff the packet was accepted. 552 * If the packet was not accepted, we will call ppp_output_wakeup 553 * at some later time. 554 */ 555 static int 556 ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb) 557 { 558 struct syncppp *ap = chan->private; 559 560 ppp_sync_push(ap); 561 562 if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags)) 563 return 0; /* already full */ 564 skb = ppp_sync_txmunge(ap, skb); 565 if (skb != NULL) 566 ap->tpkt = skb; 567 else 568 clear_bit(XMIT_FULL, &ap->xmit_flags); 569 570 ppp_sync_push(ap); 571 return 1; 572 } 573 574 /* 575 * Push as much data as possible out to the tty. 576 */ 577 static int 578 ppp_sync_push(struct syncppp *ap) 579 { 580 int sent, done = 0; 581 struct tty_struct *tty = ap->tty; 582 int tty_stuffed = 0; 583 584 if (!spin_trylock_bh(&ap->xmit_lock)) 585 return 0; 586 for (;;) { 587 if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags)) 588 tty_stuffed = 0; 589 if (!tty_stuffed && ap->tpkt) { 590 set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); 591 sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len); 592 if (sent < 0) 593 goto flush; /* error, e.g. loss of CD */ 594 if (sent < ap->tpkt->len) { 595 tty_stuffed = 1; 596 } else { 597 consume_skb(ap->tpkt); 598 ap->tpkt = NULL; 599 clear_bit(XMIT_FULL, &ap->xmit_flags); 600 done = 1; 601 } 602 continue; 603 } 604 /* haven't made any progress */ 605 spin_unlock_bh(&ap->xmit_lock); 606 if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) || 607 (!tty_stuffed && ap->tpkt))) 608 break; 609 if (!spin_trylock_bh(&ap->xmit_lock)) 610 break; 611 } 612 return done; 613 614 flush: 615 if (ap->tpkt) { 616 kfree_skb(ap->tpkt); 617 ap->tpkt = NULL; 618 clear_bit(XMIT_FULL, &ap->xmit_flags); 619 done = 1; 620 } 621 spin_unlock_bh(&ap->xmit_lock); 622 return done; 623 } 624 625 /* 626 * Flush output from our internal buffers. 627 * Called for the TCFLSH ioctl. 628 */ 629 static void 630 ppp_sync_flush_output(struct syncppp *ap) 631 { 632 int done = 0; 633 634 spin_lock_bh(&ap->xmit_lock); 635 if (ap->tpkt != NULL) { 636 kfree_skb(ap->tpkt); 637 ap->tpkt = NULL; 638 clear_bit(XMIT_FULL, &ap->xmit_flags); 639 done = 1; 640 } 641 spin_unlock_bh(&ap->xmit_lock); 642 if (done) 643 ppp_output_wakeup(&ap->chan); 644 } 645 646 /* 647 * Receive-side routines. 648 */ 649 650 /* called when the tty driver has data for us. 651 * 652 * Data is frame oriented: each call to ppp_sync_input is considered 653 * a whole frame. If the 1st flag byte is non-zero then the whole 654 * frame is considered to be in error and is tossed. 655 */ 656 static void 657 ppp_sync_input(struct syncppp *ap, const u8 *buf, const u8 *flags, int count) 658 { 659 struct sk_buff *skb; 660 unsigned char *p; 661 662 if (count == 0) 663 return; 664 665 if (ap->flags & SC_LOG_INPKT) 666 ppp_print_buffer ("receive buffer", buf, count); 667 668 /* stuff the chars in the skb */ 669 skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2); 670 if (!skb) { 671 printk(KERN_ERR "PPPsync: no memory (input pkt)\n"); 672 goto err; 673 } 674 /* Try to get the payload 4-byte aligned */ 675 if (buf[0] != PPP_ALLSTATIONS) 676 skb_reserve(skb, 2 + (buf[0] & 1)); 677 678 if (flags && *flags) { 679 /* error flag set, ignore frame */ 680 goto err; 681 } else if (count > skb_tailroom(skb)) { 682 /* packet overflowed MRU */ 683 goto err; 684 } 685 686 skb_put_data(skb, buf, count); 687 688 /* strip address/control field if present */ 689 p = skb->data; 690 if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) { 691 /* chop off address/control */ 692 if (skb->len < 3) 693 goto err; 694 p = skb_pull(skb, 2); 695 } 696 697 /* PPP packet length should be >= 2 bytes when protocol field is not 698 * compressed. 699 */ 700 if (!(p[0] & 0x01) && skb->len < 2) 701 goto err; 702 703 /* queue the frame to be processed */ 704 skb_queue_tail(&ap->rqueue, skb); 705 return; 706 707 err: 708 /* queue zero length packet as error indication */ 709 if (skb || (skb = dev_alloc_skb(0))) { 710 skb_trim(skb, 0); 711 skb_queue_tail(&ap->rqueue, skb); 712 } 713 } 714 715 static void __exit 716 ppp_sync_cleanup(void) 717 { 718 tty_unregister_ldisc(&ppp_sync_ldisc); 719 } 720 721 module_init(ppp_sync_init); 722 module_exit(ppp_sync_cleanup); 723 MODULE_LICENSE("GPL"); 724 MODULE_ALIAS_LDISC(N_SYNC_PPP); 725