net/atm/pppoatm.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* net/atm/pppoatm.c - RFC2364 PPP over ATM/AAL5 */
   3
   4 /* Copyright 1999-2000 by Mitchell Blank Jr */
   5 /* Based on clip.c; 1995-1999 by Werner Almesberger, EPFL LRC/ICA */
   6 /* And on ppp_async.c; Copyright 1999 Paul Mackerras */
   7 /* And help from Jens Axboe */
   8
   9 /*
  10  *
  11  * This driver provides the encapsulation and framing for sending
  12  * and receiving PPP frames in ATM AAL5 PDUs.
  13  */
  14
  15 /*
  16  * One shortcoming of this driver is that it does not comply with
  17  * section 8 of RFC2364 - we are supposed to detect a change
  18  * in encapsulation and immediately abort the connection (in order
  19  * to avoid a black-hole being created if our peer loses state
  20  * and changes encapsulation unilaterally.  However, since the
  21  * ppp_generic layer actually does the decapsulation, we need
  22  * a way of notifying it when we _think_ there might be a problem)
  23  * There's two cases:
  24  *   1. LLC-encapsulation was missing when it was enabled.  In
  25  *      this case, we should tell the upper layer "tear down
  26  *      this session if this skb looks ok to you"
  27  *   2. LLC-encapsulation was present when it was disabled.  Then
  28  *      we need to tell the upper layer "this packet may be
  29  *      ok, but if its in error tear down the session"
  30  * These hooks are not yet available in ppp_generic
  31  */
  32
  33 #define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__
  34
  35 #include <linux/module.h>
  36 #include <linux/init.h>
  37 #include <linux/interrupt.h>
  38 #include <linux/skbuff.h>
  39 #include <linux/slab.h>
  40 #include <linux/atm.h>
  41 #include <linux/atmdev.h>
  42 #include <linux/capability.h>
  43 #include <linux/ppp_defs.h>
  44 #include <linux/ppp-ioctl.h>
  45 #include <linux/ppp_channel.h>
  46 #include <linux/atmppp.h>
  47
  48 #include "common.h"
  49
  50 enum pppoatm_encaps {
  51         e_autodetect = PPPOATM_ENCAPS_AUTODETECT,
  52         e_vc = PPPOATM_ENCAPS_VC,
  53         e_llc = PPPOATM_ENCAPS_LLC,
  54 };
  55
  56 struct pppoatm_vcc {
  57         struct atm_vcc  *atmvcc;        /* VCC descriptor */
  58         void (*old_push)(struct atm_vcc *, struct sk_buff *);
  59         void (*old_pop)(struct atm_vcc *, struct sk_buff *);
  60         void (*old_release_cb)(struct atm_vcc *);
  61         struct module *old_owner;
  62                                         /* keep old push/pop for detaching */
  63         enum pppoatm_encaps encaps;
  64         atomic_t inflight;
  65         unsigned long blocked;
  66         int flags;                      /* SC_COMP_PROT - compress protocol */
  67         struct ppp_channel chan;        /* interface to generic ppp layer */
  68         struct tasklet_struct wakeup_tasklet;
  69 };
  70
  71 /*
  72  * We want to allow two packets in the queue. The one that's currently in
  73  * flight, and *one* queued up ready for the ATM device to send immediately
  74  * from its TX done IRQ. We want to be able to use atomic_inc_not_zero(), so
  75  * inflight == -2 represents an empty queue, -1 one packet, and zero means
  76  * there are two packets in the queue.
  77  */
  78 #define NONE_INFLIGHT -2
  79
  80 #define BLOCKED 0
  81
  82 /*
  83  * Header used for LLC Encapsulated PPP (4 bytes) followed by the LCP protocol
  84  * ID (0xC021) used in autodetection
  85  */
  86 static const unsigned char pppllc[6] = { 0xFE, 0xFE, 0x03, 0xCF, 0xC0, 0x21 };
  87 #define LLC_LEN         (4)
  88
  89 static inline struct pppoatm_vcc *atmvcc_to_pvcc(const struct atm_vcc *atmvcc)
  90 {
  91         return (struct pppoatm_vcc *) (atmvcc->user_back);
  92 }
  93
  94 static inline struct pppoatm_vcc *chan_to_pvcc(const struct ppp_channel *chan)
  95 {
  96         return (struct pppoatm_vcc *) (chan->private);
  97 }
  98
  99 /*
 100  * We can't do this directly from our _pop handler, since the ppp code
 101  * doesn't want to be called in interrupt context, so we do it from
 102  * a tasklet
 103  */
 104 static void pppoatm_wakeup_sender(unsigned long arg)
 105 {
 106         ppp_output_wakeup((struct ppp_channel *) arg);
 107 }
 108
 109 static void pppoatm_release_cb(struct atm_vcc *atmvcc)
 110 {
 111         struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
 112
 113         /*
 114          * As in pppoatm_pop(), it's safe to clear the BLOCKED bit here because
 115          * the wakeup *can't* race with pppoatm_send(). They both hold the PPP
 116          * channel's ->downl lock. And the potential race with *setting* it,
 117          * which leads to the double-check dance in pppoatm_may_send(), doesn't
 118          * exist here. In the sock_owned_by_user() case in pppoatm_send(), we
 119          * set the BLOCKED bit while the socket is still locked. We know that
 120          * ->release_cb() can't be called until that's done.
 121          */
 122         if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
 123                 tasklet_schedule(&pvcc->wakeup_tasklet);
 124         if (pvcc->old_release_cb)
 125                 pvcc->old_release_cb(atmvcc);
 126 }
 127 /*
 128  * This gets called every time the ATM card has finished sending our
 129  * skb.  The ->old_pop will take care up normal atm flow control,
 130  * but we also need to wake up the device if we blocked it
 131  */
 132 static void pppoatm_pop(struct atm_vcc *atmvcc, struct sk_buff *skb)
 133 {
 134         struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
 135
 136         pvcc->old_pop(atmvcc, skb);
 137         atomic_dec(&pvcc->inflight);
 138
 139         /*
 140          * We always used to run the wakeup tasklet unconditionally here, for
 141          * fear of race conditions where we clear the BLOCKED flag just as we
 142          * refuse another packet in pppoatm_send(). This was quite inefficient.
 143          *
 144          * In fact it's OK. The PPP core will only ever call pppoatm_send()
 145          * while holding the channel->downl lock. And ppp_output_wakeup() as
 146          * called by the tasklet will *also* grab that lock. So even if another
 147          * CPU is in pppoatm_send() right now, the tasklet isn't going to race
 148          * with it. The wakeup *will* happen after the other CPU is safely out
 149          * of pppoatm_send() again.
 150          *
 151          * So if the CPU in pppoatm_send() has already set the BLOCKED bit and
 152          * it about to return, that's fine. We trigger a wakeup which will
 153          * happen later. And if the CPU in pppoatm_send() *hasn't* set the
 154          * BLOCKED bit yet, that's fine too because of the double check in
 155          * pppoatm_may_send() which is commented there.
 156          */
 157         if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
 158                 tasklet_schedule(&pvcc->wakeup_tasklet);
 159 }
 160
 161 /*
 162  * Unbind from PPP - currently we only do this when closing the socket,
 163  * but we could put this into an ioctl if need be
 164  */
 165 static void pppoatm_unassign_vcc(struct atm_vcc *atmvcc)
 166 {
 167         struct pppoatm_vcc *pvcc;
 168         pvcc = atmvcc_to_pvcc(atmvcc);
 169         atmvcc->push = pvcc->old_push;
 170         atmvcc->pop = pvcc->old_pop;
 171         atmvcc->release_cb = pvcc->old_release_cb;
 172         tasklet_kill(&pvcc->wakeup_tasklet);
 173         ppp_unregister_channel(&pvcc->chan);
 174         atmvcc->user_back = NULL;
 175         kfree(pvcc);
 176 }
 177
 178 /* Called when an AAL5 PDU comes in */
 179 static void pppoatm_push(struct atm_vcc *atmvcc, struct sk_buff *skb)
 180 {
 181         struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
 182         pr_debug("\n");
 183         if (skb == NULL) {                      /* VCC was closed */
 184                 struct module *module;
 185
 186                 pr_debug("removing ATMPPP VCC %p\n", pvcc);
 187                 module = pvcc->old_owner;
 188                 pppoatm_unassign_vcc(atmvcc);
 189                 atmvcc->push(atmvcc, NULL);     /* Pass along bad news */
 190                 module_put(module);
 191                 return;
 192         }
 193         atm_return(atmvcc, skb->truesize);
 194         switch (pvcc->encaps) {
 195         case e_llc:
 196                 if (skb->len < LLC_LEN ||
 197                     memcmp(skb->data, pppllc, LLC_LEN))
 198                         goto error;
 199                 skb_pull(skb, LLC_LEN);
 200                 break;
 201         case e_autodetect:
 202                 if (pvcc->chan.ppp == NULL) {   /* Not bound yet! */
 203                         kfree_skb(skb);
 204                         return;
 205                 }
 206                 if (skb->len >= sizeof(pppllc) &&
 207                     !memcmp(skb->data, pppllc, sizeof(pppllc))) {
 208                         pvcc->encaps = e_llc;
 209                         skb_pull(skb, LLC_LEN);
 210                         break;
 211                 }
 212                 if (skb->len >= (sizeof(pppllc) - LLC_LEN) &&
 213                     !memcmp(skb->data, &pppllc[LLC_LEN],
 214                     sizeof(pppllc) - LLC_LEN)) {
 215                         pvcc->encaps = e_vc;
 216                         pvcc->chan.mtu += LLC_LEN;
 217                         break;
 218                 }
 219                 pr_debug("Couldn't autodetect yet (skb: %6ph)\n", skb->data);
 220                 goto error;
 221         case e_vc:
 222                 break;
 223         }
 224         ppp_input(&pvcc->chan, skb);
 225         return;
 226
 227 error:
 228         kfree_skb(skb);
 229         ppp_input_error(&pvcc->chan, 0);
 230 }
 231
 232 static int pppoatm_may_send(struct pppoatm_vcc *pvcc, int size)
 233 {
 234         /*
 235          * It's not clear that we need to bother with using atm_may_send()
 236          * to check we don't exceed sk->sk_sndbuf. If userspace sets a
 237          * value of sk_sndbuf which is lower than the MTU, we're going to
 238          * block for ever. But the code always did that before we introduced
 239          * the packet count limit, so...
 240          */
 241         if (atm_may_send(pvcc->atmvcc, size) &&
 242             atomic_inc_not_zero(&pvcc->inflight))
 243                 return 1;
 244
 245         /*
 246          * We use test_and_set_bit() rather than set_bit() here because
 247          * we need to ensure there's a memory barrier after it. The bit
 248          * *must* be set before we do the atomic_inc() on pvcc->inflight.
 249          * There's no smp_mb__after_set_bit(), so it's this or abuse
 250          * smp_mb__after_atomic().
 251          */
 252         test_and_set_bit(BLOCKED, &pvcc->blocked);
 253
 254         /*
 255          * We may have raced with pppoatm_pop(). If it ran for the
 256          * last packet in the queue, *just* before we set the BLOCKED
 257          * bit, then it might never run again and the channel could
 258          * remain permanently blocked. Cope with that race by checking
 259          * *again*. If it did run in that window, we'll have space on
 260          * the queue now and can return success. It's harmless to leave
 261          * the BLOCKED flag set, since it's only used as a trigger to
 262          * run the wakeup tasklet. Another wakeup will never hurt.
 263          * If pppoatm_pop() is running but hasn't got as far as making
 264          * space on the queue yet, then it hasn't checked the BLOCKED
 265          * flag yet either, so we're safe in that case too. It'll issue
 266          * an "immediate" wakeup... where "immediate" actually involves
 267          * taking the PPP channel's ->downl lock, which is held by the
 268          * code path that calls pppoatm_send(), and is thus going to
 269          * wait for us to finish.
 270          */
 271         if (atm_may_send(pvcc->atmvcc, size) &&
 272             atomic_inc_not_zero(&pvcc->inflight))
 273                 return 1;
 274
 275         return 0;
 276 }
 277 /*
 278  * Called by the ppp_generic.c to send a packet - returns true if packet
 279  * was accepted.  If we return false, then it's our job to call
 280  * ppp_output_wakeup(chan) when we're feeling more up to it.
 281  * Note that in the ENOMEM case (as opposed to the !atm_may_send case)
 282  * we should really drop the packet, but the generic layer doesn't
 283  * support this yet.  We just return 'DROP_PACKET' which we actually define
 284  * as success, just to be clear what we're really doing.
 285  */
 286 #define DROP_PACKET 1
 287 static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
 288 {
 289         struct pppoatm_vcc *pvcc = chan_to_pvcc(chan);
 290         struct atm_vcc *vcc;
 291         int ret;
 292
 293         ATM_SKB(skb)->vcc = pvcc->atmvcc;
 294         pr_debug("(skb=0x%p, vcc=0x%p)\n", skb, pvcc->atmvcc);
 295         if (skb->data[0] == '\0' && (pvcc->flags & SC_COMP_PROT))
 296                 (void) skb_pull(skb, 1);
 297
 298         vcc = ATM_SKB(skb)->vcc;
 299         bh_lock_sock(sk_atm(vcc));
 300         if (sock_owned_by_user(sk_atm(vcc))) {
 301                 /*
 302                  * Needs to happen (and be flushed, hence test_and_) before we unlock
 303                  * the socket. It needs to be seen by the time our ->release_cb gets
 304                  * called.
 305                  */
 306                 test_and_set_bit(BLOCKED, &pvcc->blocked);
 307                 goto nospace;
 308         }
 309         if (test_bit(ATM_VF_RELEASED, &vcc->flags) ||
 310             test_bit(ATM_VF_CLOSE, &vcc->flags) ||
 311             !test_bit(ATM_VF_READY, &vcc->flags)) {
 312                 bh_unlock_sock(sk_atm(vcc));
 313                 kfree_skb(skb);
 314                 return DROP_PACKET;
 315         }
 316
 317         switch (pvcc->encaps) {         /* LLC encapsulation needed */
 318         case e_llc:
 319                 if (skb_headroom(skb) < LLC_LEN) {
 320                         struct sk_buff *n;
 321                         n = skb_realloc_headroom(skb, LLC_LEN);
 322                         if (n != NULL &&
 323                             !pppoatm_may_send(pvcc, n->truesize)) {
 324                                 kfree_skb(n);
 325                                 goto nospace;
 326                         }
 327                         consume_skb(skb);
 328                         skb = n;
 329                         if (skb == NULL) {
 330                                 bh_unlock_sock(sk_atm(vcc));
 331                                 return DROP_PACKET;
 332                         }
 333                 } else if (!pppoatm_may_send(pvcc, skb->truesize))
 334                         goto nospace;
 335                 memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN);
 336                 break;
 337         case e_vc:
 338                 if (!pppoatm_may_send(pvcc, skb->truesize))
 339                         goto nospace;
 340                 break;
 341         case e_autodetect:
 342                 bh_unlock_sock(sk_atm(vcc));
 343                 pr_debug("Trying to send without setting encaps!\n");
 344                 kfree_skb(skb);
 345                 return 1;
 346         }
 347
 348         atm_account_tx(vcc, skb);
 349         pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n",
 350                  skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
 351         ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
 352             ? DROP_PACKET : 1;
 353         bh_unlock_sock(sk_atm(vcc));
 354         return ret;
 355 nospace:
 356         bh_unlock_sock(sk_atm(vcc));
 357         /*
 358          * We don't have space to send this SKB now, but we might have
 359          * already applied SC_COMP_PROT compression, so may need to undo
 360          */
 361         if ((pvcc->flags & SC_COMP_PROT) && skb_headroom(skb) > 0 &&
 362             skb->data[-1] == '\0')
 363                 (void) skb_push(skb, 1);
 364         return 0;
 365 }
 366
 367 /* This handles ioctls sent to the /dev/ppp interface */
 368 static int pppoatm_devppp_ioctl(struct ppp_channel *chan, unsigned int cmd,
 369         unsigned long arg)
 370 {
 371         switch (cmd) {
 372         case PPPIOCGFLAGS:
 373                 return put_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
 374                     ? -EFAULT : 0;
 375         case PPPIOCSFLAGS:
 376                 return get_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
 377                     ? -EFAULT : 0;
 378         }
 379         return -ENOTTY;
 380 }
 381
 382 static const struct ppp_channel_ops pppoatm_ops = {
 383         .start_xmit = pppoatm_send,
 384         .ioctl = pppoatm_devppp_ioctl,
 385 };
 386
 387 static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
 388 {
 389         struct atm_backend_ppp be;
 390         struct pppoatm_vcc *pvcc;
 391         int err;
 392         /*
 393          * Each PPPoATM instance has its own tasklet - this is just a
 394          * prototypical one used to initialize them
 395          */
 396         static const DECLARE_TASKLET(tasklet_proto, pppoatm_wakeup_sender, 0);
 397         if (copy_from_user(&be, arg, sizeof be))
 398                 return -EFAULT;
 399         if (be.encaps != PPPOATM_ENCAPS_AUTODETECT &&
 400             be.encaps != PPPOATM_ENCAPS_VC && be.encaps != PPPOATM_ENCAPS_LLC)
 401                 return -EINVAL;
 402         pvcc = kzalloc(sizeof(*pvcc), GFP_KERNEL);
 403         if (pvcc == NULL)
 404                 return -ENOMEM;
 405         pvcc->atmvcc = atmvcc;
 406
 407         /* Maximum is zero, so that we can use atomic_inc_not_zero() */
 408         atomic_set(&pvcc->inflight, NONE_INFLIGHT);
 409         pvcc->old_push = atmvcc->push;
 410         pvcc->old_pop = atmvcc->pop;
 411         pvcc->old_owner = atmvcc->owner;
 412         pvcc->old_release_cb = atmvcc->release_cb;
 413         pvcc->encaps = (enum pppoatm_encaps) be.encaps;
 414         pvcc->chan.private = pvcc;
 415         pvcc->chan.ops = &pppoatm_ops;
 416         pvcc->chan.mtu = atmvcc->qos.txtp.max_sdu - PPP_HDRLEN -
 417             (be.encaps == e_vc ? 0 : LLC_LEN);
 418         pvcc->wakeup_tasklet = tasklet_proto;
 419         pvcc->wakeup_tasklet.data = (unsigned long) &pvcc->chan;
 420         err = ppp_register_channel(&pvcc->chan);
 421         if (err != 0) {
 422                 kfree(pvcc);
 423                 return err;
 424         }
 425         atmvcc->user_back = pvcc;
 426         atmvcc->push = pppoatm_push;
 427         atmvcc->pop = pppoatm_pop;
 428         atmvcc->release_cb = pppoatm_release_cb;
 429         __module_get(THIS_MODULE);
 430         atmvcc->owner = THIS_MODULE;
 431
 432         /* re-process everything received between connection setup and
 433            backend setup */
 434         vcc_process_recv_queue(atmvcc);
 435         return 0;
 436 }
 437
 438 /*
 439  * This handles ioctls actually performed on our vcc - we must return
 440  * -ENOIOCTLCMD for any unrecognized ioctl
 441  */
 442 static int pppoatm_ioctl(struct socket *sock, unsigned int cmd,
 443         unsigned long arg)
 444 {
 445         struct atm_vcc *atmvcc = ATM_SD(sock);
 446         void __user *argp = (void __user *)arg;
 447
 448         if (cmd != ATM_SETBACKEND && atmvcc->push != pppoatm_push)
 449                 return -ENOIOCTLCMD;
 450         switch (cmd) {
 451         case ATM_SETBACKEND: {
 452                 atm_backend_t b;
 453                 if (get_user(b, (atm_backend_t __user *) argp))
 454                         return -EFAULT;
 455                 if (b != ATM_BACKEND_PPP)
 456                         return -ENOIOCTLCMD;
 457                 if (!capable(CAP_NET_ADMIN))
 458                         return -EPERM;
 459                 if (sock->state != SS_CONNECTED)
 460                         return -EINVAL;
 461                 return pppoatm_assign_vcc(atmvcc, argp);
 462                 }
 463         case PPPIOCGCHAN:
 464                 return put_user(ppp_channel_index(&atmvcc_to_pvcc(atmvcc)->
 465                     chan), (int __user *) argp) ? -EFAULT : 0;
 466         case PPPIOCGUNIT:
 467                 return put_user(ppp_unit_number(&atmvcc_to_pvcc(atmvcc)->
 468                     chan), (int __user *) argp) ? -EFAULT : 0;
 469         }
 470         return -ENOIOCTLCMD;
 471 }
 472
 473 static struct atm_ioctl pppoatm_ioctl_ops = {
 474         .owner  = THIS_MODULE,
 475         .ioctl  = pppoatm_ioctl,
 476 };
 477
 478 static int __init pppoatm_init(void)
 479 {
 480         register_atm_ioctl(&pppoatm_ioctl_ops);
 481         return 0;
 482 }
 483
 484 static void __exit pppoatm_exit(void)
 485 {
 486         deregister_atm_ioctl(&pppoatm_ioctl_ops);
 487 }
 488
 489 module_init(pppoatm_init);
 490 module_exit(pppoatm_exit);
 491
 492 MODULE_AUTHOR("Mitchell Blank Jr <mitch@sfgoth.com>");
 493 MODULE_DESCRIPTION("RFC2364 PPP over ATM/AAL5");
 494 MODULE_LICENSE("GPL");