net/atm/pppoatm.c

   1 /* net/atm/pppoatm.c - RFC2364 PPP over ATM/AAL5 */
   2
   3 /* Copyright 1999-2000 by Mitchell Blank Jr */
   4 /* Based on clip.c; 1995-1999 by Werner Almesberger, EPFL LRC/ICA */
   5 /* And on ppp_async.c; Copyright 1999 Paul Mackerras */
   6 /* And help from Jens Axboe */
   7
   8 /*
   9  *  This program is free software; you can redistribute it and/or
  10  *  modify it under the terms of the GNU General Public License
  11  *  as published by the Free Software Foundation; either version
  12  *  2 of the License, or (at your option) any later version.
  13  *
  14  * This driver provides the encapsulation and framing for sending
  15  * and receiving PPP frames in ATM AAL5 PDUs.
  16  */
  17
  18 /*
  19  * One shortcoming of this driver is that it does not comply with
  20  * section 8 of RFC2364 - we are supposed to detect a change
  21  * in encapsulation and immediately abort the connection (in order
  22  * to avoid a black-hole being created if our peer loses state
  23  * and changes encapsulation unilaterally.  However, since the
  24  * ppp_generic layer actually does the decapsulation, we need
  25  * a way of notifying it when we _think_ there might be a problem)
  26  * There's two cases:
  27  *   1. LLC-encapsulation was missing when it was enabled.  In
  28  *      this case, we should tell the upper layer "tear down
  29  *      this session if this skb looks ok to you"
  30  *   2. LLC-encapsulation was present when it was disabled.  Then
  31  *      we need to tell the upper layer "this packet may be
  32  *      ok, but if its in error tear down the session"
  33  * These hooks are not yet available in ppp_generic
  34  */
  35
  36 #define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__
  37
  38 #include <linux/module.h>
  39 #include <linux/init.h>
  40 #include <linux/interrupt.h>
  41 #include <linux/skbuff.h>
  42 #include <linux/slab.h>
  43 #include <linux/atm.h>
  44 #include <linux/atmdev.h>
  45 #include <linux/capability.h>
  46 #include <linux/ppp_defs.h>
  47 #include <linux/ppp-ioctl.h>
  48 #include <linux/ppp_channel.h>
  49 #include <linux/atmppp.h>
  50
  51 #include "common.h"
  52
  53 enum pppoatm_encaps {
  54         e_autodetect = PPPOATM_ENCAPS_AUTODETECT,
  55         e_vc = PPPOATM_ENCAPS_VC,
  56         e_llc = PPPOATM_ENCAPS_LLC,
  57 };
  58
  59 struct pppoatm_vcc {
  60         struct atm_vcc  *atmvcc;        /* VCC descriptor */
  61         void (*old_push)(struct atm_vcc *, struct sk_buff *);
  62         void (*old_pop)(struct atm_vcc *, struct sk_buff *);
  63         void (*old_release_cb)(struct atm_vcc *);
  64         struct module *old_owner;
  65                                         /* keep old push/pop for detaching */
  66         enum pppoatm_encaps encaps;
  67         atomic_t inflight;
  68         unsigned long blocked;
  69         int flags;                      /* SC_COMP_PROT - compress protocol */
  70         struct ppp_channel chan;        /* interface to generic ppp layer */
  71         struct tasklet_struct wakeup_tasklet;
  72 };
  73
  74 /*
  75  * We want to allow two packets in the queue. The one that's currently in
  76  * flight, and *one* queued up ready for the ATM device to send immediately
  77  * from its TX done IRQ. We want to be able to use atomic_inc_not_zero(), so
  78  * inflight == -2 represents an empty queue, -1 one packet, and zero means
  79  * there are two packets in the queue.
  80  */
  81 #define NONE_INFLIGHT -2
  82
  83 #define BLOCKED 0
  84
  85 /*
  86  * Header used for LLC Encapsulated PPP (4 bytes) followed by the LCP protocol
  87  * ID (0xC021) used in autodetection
  88  */
  89 static const unsigned char pppllc[6] = { 0xFE, 0xFE, 0x03, 0xCF, 0xC0, 0x21 };
  90 #define LLC_LEN         (4)
  91
  92 static inline struct pppoatm_vcc *atmvcc_to_pvcc(const struct atm_vcc *atmvcc)
  93 {
  94         return (struct pppoatm_vcc *) (atmvcc->user_back);
  95 }
  96
  97 static inline struct pppoatm_vcc *chan_to_pvcc(const struct ppp_channel *chan)
  98 {
  99         return (struct pppoatm_vcc *) (chan->private);
 100 }
 101
 102 /*
 103  * We can't do this directly from our _pop handler, since the ppp code
 104  * doesn't want to be called in interrupt context, so we do it from
 105  * a tasklet
 106  */
 107 static void pppoatm_wakeup_sender(unsigned long arg)
 108 {
 109         ppp_output_wakeup((struct ppp_channel *) arg);
 110 }
 111
 112 static void pppoatm_release_cb(struct atm_vcc *atmvcc)
 113 {
 114         struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
 115
 116         /*
 117          * As in pppoatm_pop(), it's safe to clear the BLOCKED bit here because
 118          * the wakeup *can't* race with pppoatm_send(). They both hold the PPP
 119          * channel's ->downl lock. And the potential race with *setting* it,
 120          * which leads to the double-check dance in pppoatm_may_send(), doesn't
 121          * exist here. In the sock_owned_by_user() case in pppoatm_send(), we
 122          * set the BLOCKED bit while the socket is still locked. We know that
 123          * ->release_cb() can't be called until that's done.
 124          */
 125         if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
 126                 tasklet_schedule(&pvcc->wakeup_tasklet);
 127         if (pvcc->old_release_cb)
 128                 pvcc->old_release_cb(atmvcc);
 129 }
 130 /*
 131  * This gets called every time the ATM card has finished sending our
 132  * skb.  The ->old_pop will take care up normal atm flow control,
 133  * but we also need to wake up the device if we blocked it
 134  */
 135 static void pppoatm_pop(struct atm_vcc *atmvcc, struct sk_buff *skb)
 136 {
 137         struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
 138
 139         pvcc->old_pop(atmvcc, skb);
 140         atomic_dec(&pvcc->inflight);
 141
 142         /*
 143          * We always used to run the wakeup tasklet unconditionally here, for
 144          * fear of race conditions where we clear the BLOCKED flag just as we
 145          * refuse another packet in pppoatm_send(). This was quite inefficient.
 146          *
 147          * In fact it's OK. The PPP core will only ever call pppoatm_send()
 148          * while holding the channel->downl lock. And ppp_output_wakeup() as
 149          * called by the tasklet will *also* grab that lock. So even if another
 150          * CPU is in pppoatm_send() right now, the tasklet isn't going to race
 151          * with it. The wakeup *will* happen after the other CPU is safely out
 152          * of pppoatm_send() again.
 153          *
 154          * So if the CPU in pppoatm_send() has already set the BLOCKED bit and
 155          * it about to return, that's fine. We trigger a wakeup which will
 156          * happen later. And if the CPU in pppoatm_send() *hasn't* set the
 157          * BLOCKED bit yet, that's fine too because of the double check in
 158          * pppoatm_may_send() which is commented there.
 159          */
 160         if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
 161                 tasklet_schedule(&pvcc->wakeup_tasklet);
 162 }
 163
 164 /*
 165  * Unbind from PPP - currently we only do this when closing the socket,
 166  * but we could put this into an ioctl if need be
 167  */
 168 static void pppoatm_unassign_vcc(struct atm_vcc *atmvcc)
 169 {
 170         struct pppoatm_vcc *pvcc;
 171         pvcc = atmvcc_to_pvcc(atmvcc);
 172         atmvcc->push = pvcc->old_push;
 173         atmvcc->pop = pvcc->old_pop;
 174         atmvcc->release_cb = pvcc->old_release_cb;
 175         tasklet_kill(&pvcc->wakeup_tasklet);
 176         ppp_unregister_channel(&pvcc->chan);
 177         atmvcc->user_back = NULL;
 178         kfree(pvcc);
 179 }
 180
 181 /* Called when an AAL5 PDU comes in */
 182 static void pppoatm_push(struct atm_vcc *atmvcc, struct sk_buff *skb)
 183 {
 184         struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
 185         pr_debug("\n");
 186         if (skb == NULL) {                      /* VCC was closed */
 187                 struct module *module;
 188
 189                 pr_debug("removing ATMPPP VCC %p\n", pvcc);
 190                 module = pvcc->old_owner;
 191                 pppoatm_unassign_vcc(atmvcc);
 192                 atmvcc->push(atmvcc, NULL);     /* Pass along bad news */
 193                 module_put(module);
 194                 return;
 195         }
 196         atm_return(atmvcc, skb->truesize);
 197         switch (pvcc->encaps) {
 198         case e_llc:
 199                 if (skb->len < LLC_LEN ||
 200                     memcmp(skb->data, pppllc, LLC_LEN))
 201                         goto error;
 202                 skb_pull(skb, LLC_LEN);
 203                 break;
 204         case e_autodetect:
 205                 if (pvcc->chan.ppp == NULL) {   /* Not bound yet! */
 206                         kfree_skb(skb);
 207                         return;
 208                 }
 209                 if (skb->len >= sizeof(pppllc) &&
 210                     !memcmp(skb->data, pppllc, sizeof(pppllc))) {
 211                         pvcc->encaps = e_llc;
 212                         skb_pull(skb, LLC_LEN);
 213                         break;
 214                 }
 215                 if (skb->len >= (sizeof(pppllc) - LLC_LEN) &&
 216                     !memcmp(skb->data, &pppllc[LLC_LEN],
 217                     sizeof(pppllc) - LLC_LEN)) {
 218                         pvcc->encaps = e_vc;
 219                         pvcc->chan.mtu += LLC_LEN;
 220                         break;
 221                 }
 222                 pr_debug("Couldn't autodetect yet (skb: %02X %02X %02X %02X %02X %02X)\n",
 223                          skb->data[0], skb->data[1], skb->data[2],
 224                          skb->data[3], skb->data[4], skb->data[5]);
 225                 goto error;
 226         case e_vc:
 227                 break;
 228         }
 229         ppp_input(&pvcc->chan, skb);
 230         return;
 231
 232 error:
 233         kfree_skb(skb);
 234         ppp_input_error(&pvcc->chan, 0);
 235 }
 236
 237 static int pppoatm_may_send(struct pppoatm_vcc *pvcc, int size)
 238 {
 239         /*
 240          * It's not clear that we need to bother with using atm_may_send()
 241          * to check we don't exceed sk->sk_sndbuf. If userspace sets a
 242          * value of sk_sndbuf which is lower than the MTU, we're going to
 243          * block for ever. But the code always did that before we introduced
 244          * the packet count limit, so...
 245          */
 246         if (atm_may_send(pvcc->atmvcc, size) &&
 247             atomic_inc_not_zero_hint(&pvcc->inflight, NONE_INFLIGHT))
 248                 return 1;
 249
 250         /*
 251          * We use test_and_set_bit() rather than set_bit() here because
 252          * we need to ensure there's a memory barrier after it. The bit
 253          * *must* be set before we do the atomic_inc() on pvcc->inflight.
 254          * There's no smp_mb__after_set_bit(), so it's this or abuse
 255          * smp_mb__after_atomic().
 256          */
 257         test_and_set_bit(BLOCKED, &pvcc->blocked);
 258
 259         /*
 260          * We may have raced with pppoatm_pop(). If it ran for the
 261          * last packet in the queue, *just* before we set the BLOCKED
 262          * bit, then it might never run again and the channel could
 263          * remain permanently blocked. Cope with that race by checking
 264          * *again*. If it did run in that window, we'll have space on
 265          * the queue now and can return success. It's harmless to leave
 266          * the BLOCKED flag set, since it's only used as a trigger to
 267          * run the wakeup tasklet. Another wakeup will never hurt.
 268          * If pppoatm_pop() is running but hasn't got as far as making
 269          * space on the queue yet, then it hasn't checked the BLOCKED
 270          * flag yet either, so we're safe in that case too. It'll issue
 271          * an "immediate" wakeup... where "immediate" actually involves
 272          * taking the PPP channel's ->downl lock, which is held by the
 273          * code path that calls pppoatm_send(), and is thus going to
 274          * wait for us to finish.
 275          */
 276         if (atm_may_send(pvcc->atmvcc, size) &&
 277             atomic_inc_not_zero(&pvcc->inflight))
 278                 return 1;
 279
 280         return 0;
 281 }
 282 /*
 283  * Called by the ppp_generic.c to send a packet - returns true if packet
 284  * was accepted.  If we return false, then it's our job to call
 285  * ppp_output_wakeup(chan) when we're feeling more up to it.
 286  * Note that in the ENOMEM case (as opposed to the !atm_may_send case)
 287  * we should really drop the packet, but the generic layer doesn't
 288  * support this yet.  We just return 'DROP_PACKET' which we actually define
 289  * as success, just to be clear what we're really doing.
 290  */
 291 #define DROP_PACKET 1
 292 static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
 293 {
 294         struct pppoatm_vcc *pvcc = chan_to_pvcc(chan);
 295         struct atm_vcc *vcc;
 296         int ret;
 297
 298         ATM_SKB(skb)->vcc = pvcc->atmvcc;
 299         pr_debug("(skb=0x%p, vcc=0x%p)\n", skb, pvcc->atmvcc);
 300         if (skb->data[0] == '\0' && (pvcc->flags & SC_COMP_PROT))
 301                 (void) skb_pull(skb, 1);
 302
 303         vcc = ATM_SKB(skb)->vcc;
 304         bh_lock_sock(sk_atm(vcc));
 305         if (sock_owned_by_user(sk_atm(vcc))) {
 306                 /*
 307                  * Needs to happen (and be flushed, hence test_and_) before we unlock
 308                  * the socket. It needs to be seen by the time our ->release_cb gets
 309                  * called.
 310                  */
 311                 test_and_set_bit(BLOCKED, &pvcc->blocked);
 312                 goto nospace;
 313         }
 314         if (test_bit(ATM_VF_RELEASED, &vcc->flags) ||
 315             test_bit(ATM_VF_CLOSE, &vcc->flags) ||
 316             !test_bit(ATM_VF_READY, &vcc->flags)) {
 317                 bh_unlock_sock(sk_atm(vcc));
 318                 kfree_skb(skb);
 319                 return DROP_PACKET;
 320         }
 321
 322         switch (pvcc->encaps) {         /* LLC encapsulation needed */
 323         case e_llc:
 324                 if (skb_headroom(skb) < LLC_LEN) {
 325                         struct sk_buff *n;
 326                         n = skb_realloc_headroom(skb, LLC_LEN);
 327                         if (n != NULL &&
 328                             !pppoatm_may_send(pvcc, n->truesize)) {
 329                                 kfree_skb(n);
 330                                 goto nospace;
 331                         }
 332                         consume_skb(skb);
 333                         skb = n;
 334                         if (skb == NULL) {
 335                                 bh_unlock_sock(sk_atm(vcc));
 336                                 return DROP_PACKET;
 337                         }
 338                 } else if (!pppoatm_may_send(pvcc, skb->truesize))
 339                         goto nospace;
 340                 memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN);
 341                 break;
 342         case e_vc:
 343                 if (!pppoatm_may_send(pvcc, skb->truesize))
 344                         goto nospace;
 345                 break;
 346         case e_autodetect:
 347                 bh_unlock_sock(sk_atm(vcc));
 348                 pr_debug("Trying to send without setting encaps!\n");
 349                 kfree_skb(skb);
 350                 return 1;
 351         }
 352
 353         refcount_add(skb->truesize, &sk_atm(ATM_SKB(skb)->vcc)->sk_wmem_alloc);
 354         ATM_SKB(skb)->atm_options = ATM_SKB(skb)->vcc->atm_options;
 355         pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n",
 356                  skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
 357         ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
 358             ? DROP_PACKET : 1;
 359         bh_unlock_sock(sk_atm(vcc));
 360         return ret;
 361 nospace:
 362         bh_unlock_sock(sk_atm(vcc));
 363         /*
 364          * We don't have space to send this SKB now, but we might have
 365          * already applied SC_COMP_PROT compression, so may need to undo
 366          */
 367         if ((pvcc->flags & SC_COMP_PROT) && skb_headroom(skb) > 0 &&
 368             skb->data[-1] == '\0')
 369                 (void) skb_push(skb, 1);
 370         return 0;
 371 }
 372
 373 /* This handles ioctls sent to the /dev/ppp interface */
 374 static int pppoatm_devppp_ioctl(struct ppp_channel *chan, unsigned int cmd,
 375         unsigned long arg)
 376 {
 377         switch (cmd) {
 378         case PPPIOCGFLAGS:
 379                 return put_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
 380                     ? -EFAULT : 0;
 381         case PPPIOCSFLAGS:
 382                 return get_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
 383                     ? -EFAULT : 0;
 384         }
 385         return -ENOTTY;
 386 }
 387
 388 static const struct ppp_channel_ops pppoatm_ops = {
 389         .start_xmit = pppoatm_send,
 390         .ioctl = pppoatm_devppp_ioctl,
 391 };
 392
 393 static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
 394 {
 395         struct atm_backend_ppp be;
 396         struct pppoatm_vcc *pvcc;
 397         int err;
 398         /*
 399          * Each PPPoATM instance has its own tasklet - this is just a
 400          * prototypical one used to initialize them
 401          */
 402         static const DECLARE_TASKLET(tasklet_proto, pppoatm_wakeup_sender, 0);
 403         if (copy_from_user(&be, arg, sizeof be))
 404                 return -EFAULT;
 405         if (be.encaps != PPPOATM_ENCAPS_AUTODETECT &&
 406             be.encaps != PPPOATM_ENCAPS_VC && be.encaps != PPPOATM_ENCAPS_LLC)
 407                 return -EINVAL;
 408         pvcc = kzalloc(sizeof(*pvcc), GFP_KERNEL);
 409         if (pvcc == NULL)
 410                 return -ENOMEM;
 411         pvcc->atmvcc = atmvcc;
 412
 413         /* Maximum is zero, so that we can use atomic_inc_not_zero() */
 414         atomic_set(&pvcc->inflight, NONE_INFLIGHT);
 415         pvcc->old_push = atmvcc->push;
 416         pvcc->old_pop = atmvcc->pop;
 417         pvcc->old_owner = atmvcc->owner;
 418         pvcc->old_release_cb = atmvcc->release_cb;
 419         pvcc->encaps = (enum pppoatm_encaps) be.encaps;
 420         pvcc->chan.private = pvcc;
 421         pvcc->chan.ops = &pppoatm_ops;
 422         pvcc->chan.mtu = atmvcc->qos.txtp.max_sdu - PPP_HDRLEN -
 423             (be.encaps == e_vc ? 0 : LLC_LEN);
 424         pvcc->wakeup_tasklet = tasklet_proto;
 425         pvcc->wakeup_tasklet.data = (unsigned long) &pvcc->chan;
 426         err = ppp_register_channel(&pvcc->chan);
 427         if (err != 0) {
 428                 kfree(pvcc);
 429                 return err;
 430         }
 431         atmvcc->user_back = pvcc;
 432         atmvcc->push = pppoatm_push;
 433         atmvcc->pop = pppoatm_pop;
 434         atmvcc->release_cb = pppoatm_release_cb;
 435         __module_get(THIS_MODULE);
 436         atmvcc->owner = THIS_MODULE;
 437
 438         /* re-process everything received between connection setup and
 439            backend setup */
 440         vcc_process_recv_queue(atmvcc);
 441         return 0;
 442 }
 443
 444 /*
 445  * This handles ioctls actually performed on our vcc - we must return
 446  * -ENOIOCTLCMD for any unrecognized ioctl
 447  */
 448 static int pppoatm_ioctl(struct socket *sock, unsigned int cmd,
 449         unsigned long arg)
 450 {
 451         struct atm_vcc *atmvcc = ATM_SD(sock);
 452         void __user *argp = (void __user *)arg;
 453
 454         if (cmd != ATM_SETBACKEND && atmvcc->push != pppoatm_push)
 455                 return -ENOIOCTLCMD;
 456         switch (cmd) {
 457         case ATM_SETBACKEND: {
 458                 atm_backend_t b;
 459                 if (get_user(b, (atm_backend_t __user *) argp))
 460                         return -EFAULT;
 461                 if (b != ATM_BACKEND_PPP)
 462                         return -ENOIOCTLCMD;
 463                 if (!capable(CAP_NET_ADMIN))
 464                         return -EPERM;
 465                 if (sock->state != SS_CONNECTED)
 466                         return -EINVAL;
 467                 return pppoatm_assign_vcc(atmvcc, argp);
 468                 }
 469         case PPPIOCGCHAN:
 470                 return put_user(ppp_channel_index(&atmvcc_to_pvcc(atmvcc)->
 471                     chan), (int __user *) argp) ? -EFAULT : 0;
 472         case PPPIOCGUNIT:
 473                 return put_user(ppp_unit_number(&atmvcc_to_pvcc(atmvcc)->
 474                     chan), (int __user *) argp) ? -EFAULT : 0;
 475         }
 476         return -ENOIOCTLCMD;
 477 }
 478
 479 static struct atm_ioctl pppoatm_ioctl_ops = {
 480         .owner  = THIS_MODULE,
 481         .ioctl  = pppoatm_ioctl,
 482 };
 483
 484 static int __init pppoatm_init(void)
 485 {
 486         register_atm_ioctl(&pppoatm_ioctl_ops);
 487         return 0;
 488 }
 489
 490 static void __exit pppoatm_exit(void)
 491 {
 492         deregister_atm_ioctl(&pppoatm_ioctl_ops);
 493 }
 494
 495 module_init(pppoatm_init);
 496 module_exit(pppoatm_exit);
 497
 498 MODULE_AUTHOR("Mitchell Blank Jr <mitch@sfgoth.com>");
 499 MODULE_DESCRIPTION("RFC2364 PPP over ATM/AAL5");
 500 MODULE_LICENSE("GPL");