linux/net/atm/pppoatm.c
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   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
  53enum pppoatm_encaps {
  54        e_autodetect = PPPOATM_ENCAPS_AUTODETECT,
  55        e_vc = PPPOATM_ENCAPS_VC,
  56        e_llc = PPPOATM_ENCAPS_LLC,
  57};
  58
  59struct 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 */
  89static const unsigned char pppllc[6] = { 0xFE, 0xFE, 0x03, 0xCF, 0xC0, 0x21 };
  90#define LLC_LEN         (4)
  91
  92static inline struct pppoatm_vcc *atmvcc_to_pvcc(const struct atm_vcc *atmvcc)
  93{
  94        return (struct pppoatm_vcc *) (atmvcc->user_back);
  95}
  96
  97static 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 */
 107static void pppoatm_wakeup_sender(unsigned long arg)
 108{
 109        ppp_output_wakeup((struct ppp_channel *) arg);
 110}
 111
 112static 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 */
 135static 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 */
 168static 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 */
 182static 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
 232error:
 233        kfree_skb(skb);
 234        ppp_input_error(&pvcc->chan, 0);
 235}
 236
 237static 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_clear_bit().
 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
 292static 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        atomic_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;
 361nospace:
 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 */
 374static 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
 388static const struct ppp_channel_ops pppoatm_ops = {
 389        .start_xmit = pppoatm_send,
 390        .ioctl = pppoatm_devppp_ioctl,
 391};
 392
 393static 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 */
 448static 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
 479static struct atm_ioctl pppoatm_ioctl_ops = {
 480        .owner  = THIS_MODULE,
 481        .ioctl  = pppoatm_ioctl,
 482};
 483
 484static int __init pppoatm_init(void)
 485{
 486        register_atm_ioctl(&pppoatm_ioctl_ops);
 487        return 0;
 488}
 489
 490static void __exit pppoatm_exit(void)
 491{
 492        deregister_atm_ioctl(&pppoatm_ioctl_ops);
 493}
 494
 495module_init(pppoatm_init);
 496module_exit(pppoatm_exit);
 497
 498MODULE_AUTHOR("Mitchell Blank Jr <mitch@sfgoth.com>");
 499MODULE_DESCRIPTION("RFC2364 PPP over ATM/AAL5");
 500MODULE_LICENSE("GPL");
 501