1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* net/atm/pppoatm.c - RFC2364 PPP over ATM/AAL5 */
3
4 /* Copyright 1999-2000 by Mitchell Blank Jr */
5 /* Based on clip.c; 1995-1999 by Werner Almesberger, EPFL LRC/ICA */
6 /* And on ppp_async.c; Copyright 1999 Paul Mackerras */
7 /* And help from Jens Axboe */
8
9 /*
10 *
11 * This driver provides the encapsulation and framing for sending
12 * and receiving PPP frames in ATM AAL5 PDUs.
13 */
14
15 /*
16 * One shortcoming of this driver is that it does not comply with
17 * section 8 of RFC2364 - we are supposed to detect a change
18 * in encapsulation and immediately abort the connection (in order
19 * to avoid a black-hole being created if our peer loses state
20 * and changes encapsulation unilaterally. However, since the
21 * ppp_generic layer actually does the decapsulation, we need
22 * a way of notifying it when we _think_ there might be a problem)
23 * There's two cases:
24 * 1. LLC-encapsulation was missing when it was enabled. In
25 * this case, we should tell the upper layer "tear down
26 * this session if this skb looks ok to you"
27 * 2. LLC-encapsulation was present when it was disabled. Then
28 * we need to tell the upper layer "this packet may be
29 * ok, but if its in error tear down the session"
30 * These hooks are not yet available in ppp_generic
31 */
32
33 #define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__
34
35 #include <linux/module.h>
36 #include <linux/init.h>
37 #include <linux/interrupt.h>
38 #include <linux/skbuff.h>
39 #include <linux/slab.h>
40 #include <linux/atm.h>
41 #include <linux/atmdev.h>
42 #include <linux/capability.h>
43 #include <linux/ppp_defs.h>
44 #include <linux/ppp-ioctl.h>
45 #include <linux/ppp_channel.h>
46 #include <linux/atmppp.h>
47
48 #include "common.h"
49
50 enum pppoatm_encaps {
51 e_autodetect = PPPOATM_ENCAPS_AUTODETECT,
52 e_vc = PPPOATM_ENCAPS_VC,
53 e_llc = PPPOATM_ENCAPS_LLC,
54 };
55
56 struct pppoatm_vcc {
57 struct atm_vcc *atmvcc; /* VCC descriptor */
58 void (*old_push)(struct atm_vcc *, struct sk_buff *);
59 void (*old_pop)(struct atm_vcc *, struct sk_buff *);
60 void (*old_release_cb)(struct atm_vcc *);
61 struct module *old_owner;
62 /* keep old push/pop for detaching */
63 enum pppoatm_encaps encaps;
64 atomic_t inflight;
65 unsigned long blocked;
66 int flags; /* SC_COMP_PROT - compress protocol */
67 struct ppp_channel chan; /* interface to generic ppp layer */
68 struct tasklet_struct wakeup_tasklet;
69 };
70
71 /*
72 * We want to allow two packets in the queue. The one that's currently in
73 * flight, and *one* queued up ready for the ATM device to send immediately
74 * from its TX done IRQ. We want to be able to use atomic_inc_not_zero(), so
75 * inflight == -2 represents an empty queue, -1 one packet, and zero means
76 * there are two packets in the queue.
77 */
78 #define NONE_INFLIGHT -2
79
80 #define BLOCKED 0
81
82 /*
83 * Header used for LLC Encapsulated PPP (4 bytes) followed by the LCP protocol
84 * ID (0xC021) used in autodetection
85 */
86 static const unsigned char pppllc[6] = { 0xFE, 0xFE, 0x03, 0xCF, 0xC0, 0x21 };
87 #define LLC_LEN (4)
88
89 static inline struct pppoatm_vcc *atmvcc_to_pvcc(const struct atm_vcc *atmvcc)
90 {
91 return (struct pppoatm_vcc *) (atmvcc->user_back);
92 }
93
94 static inline struct pppoatm_vcc *chan_to_pvcc(const struct ppp_channel *chan)
95 {
96 return (struct pppoatm_vcc *) (chan->private);
97 }
98
99 /*
100 * We can't do this directly from our _pop handler, since the ppp code
101 * doesn't want to be called in interrupt context, so we do it from
102 * a tasklet
103 */
104 static void pppoatm_wakeup_sender(unsigned long arg)
105 {
106 ppp_output_wakeup((struct ppp_channel *) arg);
107 }
108
109 static void pppoatm_release_cb(struct atm_vcc *atmvcc)
110 {
111 struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
112
113 /*
114 * As in pppoatm_pop(), it's safe to clear the BLOCKED bit here because
115 * the wakeup *can't* race with pppoatm_send(). They both hold the PPP
116 * channel's ->downl lock. And the potential race with *setting* it,
117 * which leads to the double-check dance in pppoatm_may_send(), doesn't
118 * exist here. In the sock_owned_by_user() case in pppoatm_send(), we
119 * set the BLOCKED bit while the socket is still locked. We know that
120 * ->release_cb() can't be called until that's done.
121 */
122 if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
123 tasklet_schedule(&pvcc->wakeup_tasklet);
124 if (pvcc->old_release_cb)
125 pvcc->old_release_cb(atmvcc);
126 }
127 /*
128 * This gets called every time the ATM card has finished sending our
129 * skb. The ->old_pop will take care up normal atm flow control,
130 * but we also need to wake up the device if we blocked it
131 */
132 static void pppoatm_pop(struct atm_vcc *atmvcc, struct sk_buff *skb)
133 {
134 struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
135
136 pvcc->old_pop(atmvcc, skb);
137 atomic_dec(&pvcc->inflight);
138
139 /*
140 * We always used to run the wakeup tasklet unconditionally here, for
141 * fear of race conditions where we clear the BLOCKED flag just as we
142 * refuse another packet in pppoatm_send(). This was quite inefficient.
143 *
144 * In fact it's OK. The PPP core will only ever call pppoatm_send()
145 * while holding the channel->downl lock. And ppp_output_wakeup() as
146 * called by the tasklet will *also* grab that lock. So even if another
147 * CPU is in pppoatm_send() right now, the tasklet isn't going to race
148 * with it. The wakeup *will* happen after the other CPU is safely out
149 * of pppoatm_send() again.
150 *
151 * So if the CPU in pppoatm_send() has already set the BLOCKED bit and
152 * it about to return, that's fine. We trigger a wakeup which will
153 * happen later. And if the CPU in pppoatm_send() *hasn't* set the
154 * BLOCKED bit yet, that's fine too because of the double check in
155 * pppoatm_may_send() which is commented there.
156 */
157 if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
158 tasklet_schedule(&pvcc->wakeup_tasklet);
159 }
160
161 /*
162 * Unbind from PPP - currently we only do this when closing the socket,
163 * but we could put this into an ioctl if need be
164 */
165 static void pppoatm_unassign_vcc(struct atm_vcc *atmvcc)
166 {
167 struct pppoatm_vcc *pvcc;
168 pvcc = atmvcc_to_pvcc(atmvcc);
169 atmvcc->push = pvcc->old_push;
170 atmvcc->pop = pvcc->old_pop;
171 atmvcc->release_cb = pvcc->old_release_cb;
172 tasklet_kill(&pvcc->wakeup_tasklet);
173 ppp_unregister_channel(&pvcc->chan);
174 atmvcc->user_back = NULL;
175 kfree(pvcc);
176 }
177
178 /* Called when an AAL5 PDU comes in */
179 static void pppoatm_push(struct atm_vcc *atmvcc, struct sk_buff *skb)
180 {
181 struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
182 pr_debug("\n");
183 if (skb == NULL) { /* VCC was closed */
184 struct module *module;
185
186 pr_debug("removing ATMPPP VCC %p\n", pvcc);
187 module = pvcc->old_owner;
188 pppoatm_unassign_vcc(atmvcc);
189 atmvcc->push(atmvcc, NULL); /* Pass along bad news */
190 module_put(module);
191 return;
192 }
193 atm_return(atmvcc, skb->truesize);
194 switch (pvcc->encaps) {
195 case e_llc:
196 if (skb->len < LLC_LEN ||
197 memcmp(skb->data, pppllc, LLC_LEN))
198 goto error;
199 skb_pull(skb, LLC_LEN);
200 break;
201 case e_autodetect:
202 if (pvcc->chan.ppp == NULL) { /* Not bound yet! */
203 kfree_skb(skb);
204 return;
205 }
206 if (skb->len >= sizeof(pppllc) &&
207 !memcmp(skb->data, pppllc, sizeof(pppllc))) {
208 pvcc->encaps = e_llc;
209 skb_pull(skb, LLC_LEN);
210 break;
211 }
212 if (skb->len >= (sizeof(pppllc) - LLC_LEN) &&
213 !memcmp(skb->data, &pppllc[LLC_LEN],
214 sizeof(pppllc) - LLC_LEN)) {
215 pvcc->encaps = e_vc;
216 pvcc->chan.mtu += LLC_LEN;
217 break;
218 }
219 pr_debug("Couldn't autodetect yet (skb: %6ph)\n", skb->data);
220 goto error;
221 case e_vc:
222 break;
223 }
224 ppp_input(&pvcc->chan, skb);
225 return;
226
227 error:
228 kfree_skb(skb);
229 ppp_input_error(&pvcc->chan, 0);
230 }
231
232 static int pppoatm_may_send(struct pppoatm_vcc *pvcc, int size)
233 {
234 /*
235 * It's not clear that we need to bother with using atm_may_send()
236 * to check we don't exceed sk->sk_sndbuf. If userspace sets a
237 * value of sk_sndbuf which is lower than the MTU, we're going to
238 * block for ever. But the code always did that before we introduced
239 * the packet count limit, so...
240 */
241 if (atm_may_send(pvcc->atmvcc, size) &&
242 atomic_inc_not_zero(&pvcc->inflight))
243 return 1;
244
245 /*
246 * We use test_and_set_bit() rather than set_bit() here because
247 * we need to ensure there's a memory barrier after it. The bit
248 * *must* be set before we do the atomic_inc() on pvcc->inflight.
249 * There's no smp_mb__after_set_bit(), so it's this or abuse
250 * smp_mb__after_atomic().
251 */
252 test_and_set_bit(BLOCKED, &pvcc->blocked);
253
254 /*
255 * We may have raced with pppoatm_pop(). If it ran for the
256 * last packet in the queue, *just* before we set the BLOCKED
257 * bit, then it might never run again and the channel could
258 * remain permanently blocked. Cope with that race by checking
259 * *again*. If it did run in that window, we'll have space on
260 * the queue now and can return success. It's harmless to leave
261 * the BLOCKED flag set, since it's only used as a trigger to
262 * run the wakeup tasklet. Another wakeup will never hurt.
263 * If pppoatm_pop() is running but hasn't got as far as making
264 * space on the queue yet, then it hasn't checked the BLOCKED
265 * flag yet either, so we're safe in that case too. It'll issue
266 * an "immediate" wakeup... where "immediate" actually involves
267 * taking the PPP channel's ->downl lock, which is held by the
268 * code path that calls pppoatm_send(), and is thus going to
269 * wait for us to finish.
270 */
271 if (atm_may_send(pvcc->atmvcc, size) &&
272 atomic_inc_not_zero(&pvcc->inflight))
273 return 1;
274
275 return 0;
276 }
277 /*
278 * Called by the ppp_generic.c to send a packet - returns true if packet
279 * was accepted. If we return false, then it's our job to call
280 * ppp_output_wakeup(chan) when we're feeling more up to it.
281 * Note that in the ENOMEM case (as opposed to the !atm_may_send case)
282 * we should really drop the packet, but the generic layer doesn't
283 * support this yet. We just return 'DROP_PACKET' which we actually define
284 * as success, just to be clear what we're really doing.
285 */
286 #define DROP_PACKET 1
287 static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
288 {
289 struct pppoatm_vcc *pvcc = chan_to_pvcc(chan);
290 struct atm_vcc *vcc;
291 int ret;
292
293 ATM_SKB(skb)->vcc = pvcc->atmvcc;
294 pr_debug("(skb=0x%p, vcc=0x%p)\n", skb, pvcc->atmvcc);
295 if (skb->data[0] == '\0' && (pvcc->flags & SC_COMP_PROT))
296 (void) skb_pull(skb, 1);
297
298 vcc = ATM_SKB(skb)->vcc;
299 bh_lock_sock(sk_atm(vcc));
300 if (sock_owned_by_user(sk_atm(vcc))) {
301 /*
302 * Needs to happen (and be flushed, hence test_and_) before we unlock
303 * the socket. It needs to be seen by the time our ->release_cb gets
304 * called.
305 */
306 test_and_set_bit(BLOCKED, &pvcc->blocked);
307 goto nospace;
308 }
309 if (test_bit(ATM_VF_RELEASED, &vcc->flags) ||
310 test_bit(ATM_VF_CLOSE, &vcc->flags) ||
311 !test_bit(ATM_VF_READY, &vcc->flags)) {
312 bh_unlock_sock(sk_atm(vcc));
313 kfree_skb(skb);
314 return DROP_PACKET;
315 }
316
317 switch (pvcc->encaps) { /* LLC encapsulation needed */
318 case e_llc:
319 if (skb_headroom(skb) < LLC_LEN) {
320 struct sk_buff *n;
321 n = skb_realloc_headroom(skb, LLC_LEN);
322 if (n != NULL &&
323 !pppoatm_may_send(pvcc, n->truesize)) {
324 kfree_skb(n);
325 goto nospace;
326 }
327 consume_skb(skb);
328 skb = n;
329 if (skb == NULL) {
330 bh_unlock_sock(sk_atm(vcc));
331 return DROP_PACKET;
332 }
333 } else if (!pppoatm_may_send(pvcc, skb->truesize))
334 goto nospace;
335 memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN);
336 break;
337 case e_vc:
338 if (!pppoatm_may_send(pvcc, skb->truesize))
339 goto nospace;
340 break;
341 case e_autodetect:
342 bh_unlock_sock(sk_atm(vcc));
343 pr_debug("Trying to send without setting encaps!\n");
344 kfree_skb(skb);
345 return 1;
346 }
347
348 atm_account_tx(vcc, skb);
349 pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n",
350 skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
351 ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
352 ? DROP_PACKET : 1;
353 bh_unlock_sock(sk_atm(vcc));
354 return ret;
355 nospace:
356 bh_unlock_sock(sk_atm(vcc));
357 /*
358 * We don't have space to send this SKB now, but we might have
359 * already applied SC_COMP_PROT compression, so may need to undo
360 */
361 if ((pvcc->flags & SC_COMP_PROT) && skb_headroom(skb) > 0 &&
362 skb->data[-1] == '\0')
363 (void) skb_push(skb, 1);
364 return 0;
365 }
366
367 /* This handles ioctls sent to the /dev/ppp interface */
368 static int pppoatm_devppp_ioctl(struct ppp_channel *chan, unsigned int cmd,
369 unsigned long arg)
370 {
371 switch (cmd) {
372 case PPPIOCGFLAGS:
373 return put_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
374 ? -EFAULT : 0;
375 case PPPIOCSFLAGS:
376 return get_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
377 ? -EFAULT : 0;
378 }
379 return -ENOTTY;
380 }
381
382 static const struct ppp_channel_ops pppoatm_ops = {
383 .start_xmit = pppoatm_send,
384 .ioctl = pppoatm_devppp_ioctl,
385 };
386
387 static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
388 {
389 struct atm_backend_ppp be;
390 struct pppoatm_vcc *pvcc;
391 int err;
392 /*
393 * Each PPPoATM instance has its own tasklet - this is just a
394 * prototypical one used to initialize them
395 */
396 static const DECLARE_TASKLET(tasklet_proto, pppoatm_wakeup_sender, 0);
397 if (copy_from_user(&be, arg, sizeof be))
398 return -EFAULT;
399 if (be.encaps != PPPOATM_ENCAPS_AUTODETECT &&
400 be.encaps != PPPOATM_ENCAPS_VC && be.encaps != PPPOATM_ENCAPS_LLC)
401 return -EINVAL;
402 pvcc = kzalloc(sizeof(*pvcc), GFP_KERNEL);
403 if (pvcc == NULL)
404 return -ENOMEM;
405 pvcc->atmvcc = atmvcc;
406
407 /* Maximum is zero, so that we can use atomic_inc_not_zero() */
408 atomic_set(&pvcc->inflight, NONE_INFLIGHT);
409 pvcc->old_push = atmvcc->push;
410 pvcc->old_pop = atmvcc->pop;
411 pvcc->old_owner = atmvcc->owner;
412 pvcc->old_release_cb = atmvcc->release_cb;
413 pvcc->encaps = (enum pppoatm_encaps) be.encaps;
414 pvcc->chan.private = pvcc;
415 pvcc->chan.ops = &pppoatm_ops;
416 pvcc->chan.mtu = atmvcc->qos.txtp.max_sdu - PPP_HDRLEN -
417 (be.encaps == e_vc ? 0 : LLC_LEN);
418 pvcc->wakeup_tasklet = tasklet_proto;
419 pvcc->wakeup_tasklet.data = (unsigned long) &pvcc->chan;
420 err = ppp_register_channel(&pvcc->chan);
421 if (err != 0) {
422 kfree(pvcc);
423 return err;
424 }
425 atmvcc->user_back = pvcc;
426 atmvcc->push = pppoatm_push;
427 atmvcc->pop = pppoatm_pop;
428 atmvcc->release_cb = pppoatm_release_cb;
429 __module_get(THIS_MODULE);
430 atmvcc->owner = THIS_MODULE;
431
432 /* re-process everything received between connection setup and
433 backend setup */
434 vcc_process_recv_queue(atmvcc);
435 return 0;
436 }
437
438 /*
439 * This handles ioctls actually performed on our vcc - we must return
440 * -ENOIOCTLCMD for any unrecognized ioctl
441 */
442 static int pppoatm_ioctl(struct socket *sock, unsigned int cmd,
443 unsigned long arg)
444 {
445 struct atm_vcc *atmvcc = ATM_SD(sock);
446 void __user *argp = (void __user *)arg;
447
448 if (cmd != ATM_SETBACKEND && atmvcc->push != pppoatm_push)
449 return -ENOIOCTLCMD;
450 switch (cmd) {
451 case ATM_SETBACKEND: {
452 atm_backend_t b;
453 if (get_user(b, (atm_backend_t __user *) argp))
454 return -EFAULT;
455 if (b != ATM_BACKEND_PPP)
456 return -ENOIOCTLCMD;
457 if (!capable(CAP_NET_ADMIN))
458 return -EPERM;
459 if (sock->state != SS_CONNECTED)
460 return -EINVAL;
461 return pppoatm_assign_vcc(atmvcc, argp);
462 }
463 case PPPIOCGCHAN:
464 return put_user(ppp_channel_index(&atmvcc_to_pvcc(atmvcc)->
465 chan), (int __user *) argp) ? -EFAULT : 0;
466 case PPPIOCGUNIT:
467 return put_user(ppp_unit_number(&atmvcc_to_pvcc(atmvcc)->
468 chan), (int __user *) argp) ? -EFAULT : 0;
469 }
470 return -ENOIOCTLCMD;
471 }
472
473 static struct atm_ioctl pppoatm_ioctl_ops = {
474 .owner = THIS_MODULE,
475 .ioctl = pppoatm_ioctl,
476 };
477
478 static int __init pppoatm_init(void)
479 {
480 register_atm_ioctl(&pppoatm_ioctl_ops);
481 return 0;
482 }
483
484 static void __exit pppoatm_exit(void)
485 {
486 deregister_atm_ioctl(&pppoatm_ioctl_ops);
487 }
488
489 module_init(pppoatm_init);
490 module_exit(pppoatm_exit);
491
492 MODULE_AUTHOR("Mitchell Blank Jr <mitch@sfgoth.com>");
493 MODULE_DESCRIPTION("RFC2364 PPP over ATM/AAL5");
494 MODULE_LICENSE("GPL");