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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 
 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         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;
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");
501 

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