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                                        /* keep old push/pop for detaching */
  64        enum pppoatm_encaps encaps;
  65        atomic_t inflight;
  66        unsigned long blocked;
  67        int flags;                      /* SC_COMP_PROT - compress protocol */
  68        struct ppp_channel chan;        /* interface to generic ppp layer */
  69        struct tasklet_struct wakeup_tasklet;
  70};
  71
  72/*
  73 * We want to allow two packets in the queue. The one that's currently in
  74 * flight, and *one* queued up ready for the ATM device to send immediately
  75 * from its TX done IRQ. We want to be able to use atomic_inc_not_zero(), so
  76 * inflight == -2 represents an empty queue, -1 one packet, and zero means
  77 * there are two packets in the queue.
  78 */
  79#define NONE_INFLIGHT -2
  80
  81#define BLOCKED 0
  82
  83/*
  84 * Header used for LLC Encapsulated PPP (4 bytes) followed by the LCP protocol
  85 * ID (0xC021) used in autodetection
  86 */
  87static const unsigned char pppllc[6] = { 0xFE, 0xFE, 0x03, 0xCF, 0xC0, 0x21 };
  88#define LLC_LEN         (4)
  89
  90static inline struct pppoatm_vcc *atmvcc_to_pvcc(const struct atm_vcc *atmvcc)
  91{
  92        return (struct pppoatm_vcc *) (atmvcc->user_back);
  93}
  94
  95static inline struct pppoatm_vcc *chan_to_pvcc(const struct ppp_channel *chan)
  96{
  97        return (struct pppoatm_vcc *) (chan->private);
  98}
  99
 100/*
 101 * We can't do this directly from our _pop handler, since the ppp code
 102 * doesn't want to be called in interrupt context, so we do it from
 103 * a tasklet
 104 */
 105static void pppoatm_wakeup_sender(unsigned long arg)
 106{
 107        ppp_output_wakeup((struct ppp_channel *) arg);
 108}
 109
 110/*
 111 * This gets called every time the ATM card has finished sending our
 112 * skb.  The ->old_pop will take care up normal atm flow control,
 113 * but we also need to wake up the device if we blocked it
 114 */
 115static void pppoatm_pop(struct atm_vcc *atmvcc, struct sk_buff *skb)
 116{
 117        struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
 118
 119        pvcc->old_pop(atmvcc, skb);
 120        atomic_dec(&pvcc->inflight);
 121
 122        /*
 123         * We always used to run the wakeup tasklet unconditionally here, for
 124         * fear of race conditions where we clear the BLOCKED flag just as we
 125         * refuse another packet in pppoatm_send(). This was quite inefficient.
 126         *
 127         * In fact it's OK. The PPP core will only ever call pppoatm_send()
 128         * while holding the channel->downl lock. And ppp_output_wakeup() as
 129         * called by the tasklet will *also* grab that lock. So even if another
 130         * CPU is in pppoatm_send() right now, the tasklet isn't going to race
 131         * with it. The wakeup *will* happen after the other CPU is safely out
 132         * of pppoatm_send() again.
 133         *
 134         * So if the CPU in pppoatm_send() has already set the BLOCKED bit and
 135         * it about to return, that's fine. We trigger a wakeup which will
 136         * happen later. And if the CPU in pppoatm_send() *hasn't* set the
 137         * BLOCKED bit yet, that's fine too because of the double check in
 138         * pppoatm_may_send() which is commented there.
 139         */
 140        if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
 141                tasklet_schedule(&pvcc->wakeup_tasklet);
 142}
 143
 144/*
 145 * Unbind from PPP - currently we only do this when closing the socket,
 146 * but we could put this into an ioctl if need be
 147 */
 148static void pppoatm_unassign_vcc(struct atm_vcc *atmvcc)
 149{
 150        struct pppoatm_vcc *pvcc;
 151        pvcc = atmvcc_to_pvcc(atmvcc);
 152        atmvcc->push = pvcc->old_push;
 153        atmvcc->pop = pvcc->old_pop;
 154        tasklet_kill(&pvcc->wakeup_tasklet);
 155        ppp_unregister_channel(&pvcc->chan);
 156        atmvcc->user_back = NULL;
 157        kfree(pvcc);
 158        /* Gee, I hope we have the big kernel lock here... */
 159        module_put(THIS_MODULE);
 160}
 161
 162/* Called when an AAL5 PDU comes in */
 163static void pppoatm_push(struct atm_vcc *atmvcc, struct sk_buff *skb)
 164{
 165        struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
 166        pr_debug("\n");
 167        if (skb == NULL) {                      /* VCC was closed */
 168                pr_debug("removing ATMPPP VCC %p\n", pvcc);
 169                pppoatm_unassign_vcc(atmvcc);
 170                atmvcc->push(atmvcc, NULL);     /* Pass along bad news */
 171                return;
 172        }
 173        atm_return(atmvcc, skb->truesize);
 174        switch (pvcc->encaps) {
 175        case e_llc:
 176                if (skb->len < LLC_LEN ||
 177                    memcmp(skb->data, pppllc, LLC_LEN))
 178                        goto error;
 179                skb_pull(skb, LLC_LEN);
 180                break;
 181        case e_autodetect:
 182                if (pvcc->chan.ppp == NULL) {   /* Not bound yet! */
 183                        kfree_skb(skb);
 184                        return;
 185                }
 186                if (skb->len >= sizeof(pppllc) &&
 187                    !memcmp(skb->data, pppllc, sizeof(pppllc))) {
 188                        pvcc->encaps = e_llc;
 189                        skb_pull(skb, LLC_LEN);
 190                        break;
 191                }
 192                if (skb->len >= (sizeof(pppllc) - LLC_LEN) &&
 193                    !memcmp(skb->data, &pppllc[LLC_LEN],
 194                    sizeof(pppllc) - LLC_LEN)) {
 195                        pvcc->encaps = e_vc;
 196                        pvcc->chan.mtu += LLC_LEN;
 197                        break;
 198                }
 199                pr_debug("Couldn't autodetect yet (skb: %02X %02X %02X %02X %02X %02X)\n",
 200                         skb->data[0], skb->data[1], skb->data[2],
 201                         skb->data[3], skb->data[4], skb->data[5]);
 202                goto error;
 203        case e_vc:
 204                break;
 205        }
 206        ppp_input(&pvcc->chan, skb);
 207        return;
 208
 209error:
 210        kfree_skb(skb);
 211        ppp_input_error(&pvcc->chan, 0);
 212}
 213
 214static inline int pppoatm_may_send(struct pppoatm_vcc *pvcc, int size)
 215{
 216        /*
 217         * It's not clear that we need to bother with using atm_may_send()
 218         * to check we don't exceed sk->sk_sndbuf. If userspace sets a
 219         * value of sk_sndbuf which is lower than the MTU, we're going to
 220         * block for ever. But the code always did that before we introduced
 221         * the packet count limit, so...
 222         */
 223        if (atm_may_send(pvcc->atmvcc, size) &&
 224            atomic_inc_not_zero_hint(&pvcc->inflight, NONE_INFLIGHT))
 225                return 1;
 226
 227        /*
 228         * We use test_and_set_bit() rather than set_bit() here because
 229         * we need to ensure there's a memory barrier after it. The bit
 230         * *must* be set before we do the atomic_inc() on pvcc->inflight.
 231         * There's no smp_mb__after_set_bit(), so it's this or abuse
 232         * smp_mb__after_clear_bit().
 233         */
 234        test_and_set_bit(BLOCKED, &pvcc->blocked);
 235
 236        /*
 237         * We may have raced with pppoatm_pop(). If it ran for the
 238         * last packet in the queue, *just* before we set the BLOCKED
 239         * bit, then it might never run again and the channel could
 240         * remain permanently blocked. Cope with that race by checking
 241         * *again*. If it did run in that window, we'll have space on
 242         * the queue now and can return success. It's harmless to leave
 243         * the BLOCKED flag set, since it's only used as a trigger to
 244         * run the wakeup tasklet. Another wakeup will never hurt.
 245         * If pppoatm_pop() is running but hasn't got as far as making
 246         * space on the queue yet, then it hasn't checked the BLOCKED
 247         * flag yet either, so we're safe in that case too. It'll issue
 248         * an "immediate" wakeup... where "immediate" actually involves
 249         * taking the PPP channel's ->downl lock, which is held by the
 250         * code path that calls pppoatm_send(), and is thus going to
 251         * wait for us to finish.
 252         */
 253        if (atm_may_send(pvcc->atmvcc, size) &&
 254            atomic_inc_not_zero(&pvcc->inflight))
 255                return 1;
 256
 257        return 0;
 258}
 259/*
 260 * Called by the ppp_generic.c to send a packet - returns true if packet
 261 * was accepted.  If we return false, then it's our job to call
 262 * ppp_output_wakeup(chan) when we're feeling more up to it.
 263 * Note that in the ENOMEM case (as opposed to the !atm_may_send case)
 264 * we should really drop the packet, but the generic layer doesn't
 265 * support this yet.  We just return 'DROP_PACKET' which we actually define
 266 * as success, just to be clear what we're really doing.
 267 */
 268#define DROP_PACKET 1
 269static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
 270{
 271        struct pppoatm_vcc *pvcc = chan_to_pvcc(chan);
 272        ATM_SKB(skb)->vcc = pvcc->atmvcc;
 273        pr_debug("(skb=0x%p, vcc=0x%p)\n", skb, pvcc->atmvcc);
 274        if (skb->data[0] == '\0' && (pvcc->flags & SC_COMP_PROT))
 275                (void) skb_pull(skb, 1);
 276        switch (pvcc->encaps) {         /* LLC encapsulation needed */
 277        case e_llc:
 278                if (skb_headroom(skb) < LLC_LEN) {
 279                        struct sk_buff *n;
 280                        n = skb_realloc_headroom(skb, LLC_LEN);
 281                        if (n != NULL &&
 282                            !pppoatm_may_send(pvcc, n->truesize)) {
 283                                kfree_skb(n);
 284                                goto nospace;
 285                        }
 286                        consume_skb(skb);
 287                        skb = n;
 288                        if (skb == NULL)
 289                                return DROP_PACKET;
 290                } else if (!pppoatm_may_send(pvcc, skb->truesize))
 291                        goto nospace;
 292                memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN);
 293                break;
 294        case e_vc:
 295                if (!pppoatm_may_send(pvcc, skb->truesize))
 296                        goto nospace;
 297                break;
 298        case e_autodetect:
 299                pr_debug("Trying to send without setting encaps!\n");
 300                kfree_skb(skb);
 301                return 1;
 302        }
 303
 304        atomic_add(skb->truesize, &sk_atm(ATM_SKB(skb)->vcc)->sk_wmem_alloc);
 305        ATM_SKB(skb)->atm_options = ATM_SKB(skb)->vcc->atm_options;
 306        pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n",
 307                 skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
 308        return ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
 309            ? DROP_PACKET : 1;
 310nospace:
 311        /*
 312         * We don't have space to send this SKB now, but we might have
 313         * already applied SC_COMP_PROT compression, so may need to undo
 314         */
 315        if ((pvcc->flags & SC_COMP_PROT) && skb_headroom(skb) > 0 &&
 316            skb->data[-1] == '\0')
 317                (void) skb_push(skb, 1);
 318        return 0;
 319}
 320
 321/* This handles ioctls sent to the /dev/ppp interface */
 322static int pppoatm_devppp_ioctl(struct ppp_channel *chan, unsigned int cmd,
 323        unsigned long arg)
 324{
 325        switch (cmd) {
 326        case PPPIOCGFLAGS:
 327                return put_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
 328                    ? -EFAULT : 0;
 329        case PPPIOCSFLAGS:
 330                return get_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
 331                    ? -EFAULT : 0;
 332        }
 333        return -ENOTTY;
 334}
 335
 336static const struct ppp_channel_ops pppoatm_ops = {
 337        .start_xmit = pppoatm_send,
 338        .ioctl = pppoatm_devppp_ioctl,
 339};
 340
 341static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
 342{
 343        struct atm_backend_ppp be;
 344        struct pppoatm_vcc *pvcc;
 345        int err;
 346        /*
 347         * Each PPPoATM instance has its own tasklet - this is just a
 348         * prototypical one used to initialize them
 349         */
 350        static const DECLARE_TASKLET(tasklet_proto, pppoatm_wakeup_sender, 0);
 351        if (copy_from_user(&be, arg, sizeof be))
 352                return -EFAULT;
 353        if (be.encaps != PPPOATM_ENCAPS_AUTODETECT &&
 354            be.encaps != PPPOATM_ENCAPS_VC && be.encaps != PPPOATM_ENCAPS_LLC)
 355                return -EINVAL;
 356        pvcc = kzalloc(sizeof(*pvcc), GFP_KERNEL);
 357        if (pvcc == NULL)
 358                return -ENOMEM;
 359        pvcc->atmvcc = atmvcc;
 360
 361        /* Maximum is zero, so that we can use atomic_inc_not_zero() */
 362        atomic_set(&pvcc->inflight, NONE_INFLIGHT);
 363        pvcc->old_push = atmvcc->push;
 364        pvcc->old_pop = atmvcc->pop;
 365        pvcc->encaps = (enum pppoatm_encaps) be.encaps;
 366        pvcc->chan.private = pvcc;
 367        pvcc->chan.ops = &pppoatm_ops;
 368        pvcc->chan.mtu = atmvcc->qos.txtp.max_sdu - PPP_HDRLEN -
 369            (be.encaps == e_vc ? 0 : LLC_LEN);
 370        pvcc->wakeup_tasklet = tasklet_proto;
 371        pvcc->wakeup_tasklet.data = (unsigned long) &pvcc->chan;
 372        err = ppp_register_channel(&pvcc->chan);
 373        if (err != 0) {
 374                kfree(pvcc);
 375                return err;
 376        }
 377        atmvcc->user_back = pvcc;
 378        atmvcc->push = pppoatm_push;
 379        atmvcc->pop = pppoatm_pop;
 380        __module_get(THIS_MODULE);
 381
 382        /* re-process everything received between connection setup and
 383           backend setup */
 384        vcc_process_recv_queue(atmvcc);
 385        return 0;
 386}
 387
 388/*
 389 * This handles ioctls actually performed on our vcc - we must return
 390 * -ENOIOCTLCMD for any unrecognized ioctl
 391 */
 392static int pppoatm_ioctl(struct socket *sock, unsigned int cmd,
 393        unsigned long arg)
 394{
 395        struct atm_vcc *atmvcc = ATM_SD(sock);
 396        void __user *argp = (void __user *)arg;
 397
 398        if (cmd != ATM_SETBACKEND && atmvcc->push != pppoatm_push)
 399                return -ENOIOCTLCMD;
 400        switch (cmd) {
 401        case ATM_SETBACKEND: {
 402                atm_backend_t b;
 403                if (get_user(b, (atm_backend_t __user *) argp))
 404                        return -EFAULT;
 405                if (b != ATM_BACKEND_PPP)
 406                        return -ENOIOCTLCMD;
 407                if (!capable(CAP_NET_ADMIN))
 408                        return -EPERM;
 409                return pppoatm_assign_vcc(atmvcc, argp);
 410                }
 411        case PPPIOCGCHAN:
 412                return put_user(ppp_channel_index(&atmvcc_to_pvcc(atmvcc)->
 413                    chan), (int __user *) argp) ? -EFAULT : 0;
 414        case PPPIOCGUNIT:
 415                return put_user(ppp_unit_number(&atmvcc_to_pvcc(atmvcc)->
 416                    chan), (int __user *) argp) ? -EFAULT : 0;
 417        }
 418        return -ENOIOCTLCMD;
 419}
 420
 421static struct atm_ioctl pppoatm_ioctl_ops = {
 422        .owner  = THIS_MODULE,
 423        .ioctl  = pppoatm_ioctl,
 424};
 425
 426static int __init pppoatm_init(void)
 427{
 428        register_atm_ioctl(&pppoatm_ioctl_ops);
 429        return 0;
 430}
 431
 432static void __exit pppoatm_exit(void)
 433{
 434        deregister_atm_ioctl(&pppoatm_ioctl_ops);
 435}
 436
 437module_init(pppoatm_init);
 438module_exit(pppoatm_exit);
 439
 440MODULE_AUTHOR("Mitchell Blank Jr <mitch@sfgoth.com>");
 441MODULE_DESCRIPTION("RFC2364 PPP over ATM/AAL5");
 442MODULE_LICENSE("GPL");
 443
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