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