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(struct tasklet_struct *t)
105 {
106 struct pppoatm_vcc *pvcc = from_tasklet(pvcc, t, wakeup_tasklet);
107
108 ppp_output_wakeup(&pvcc->chan);
109 }
110
111 static void pppoatm_release_cb(struct atm_vcc *atmvcc)
112 {
113 struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
114
115 /*
116 * As in pppoatm_pop(), it's safe to clear the BLOCKED bit here because
117 * the wakeup *can't* race with pppoatm_send(). They both hold the PPP
118 * channel's ->downl lock. And the potential race with *setting* it,
119 * which leads to the double-check dance in pppoatm_may_send(), doesn't
120 * exist here. In the sock_owned_by_user() case in pppoatm_send(), we
121 * set the BLOCKED bit while the socket is still locked. We know that
122 * ->release_cb() can't be called until that's done.
123 */
124 if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
125 tasklet_schedule(&pvcc->wakeup_tasklet);
126 if (pvcc->old_release_cb)
127 pvcc->old_release_cb(atmvcc);
128 }
129 /*
130 * This gets called every time the ATM card has finished sending our
131 * skb. The ->old_pop will take care up normal atm flow control,
132 * but we also need to wake up the device if we blocked it
133 */
134 static void pppoatm_pop(struct atm_vcc *atmvcc, struct sk_buff *skb)
135 {
136 struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
137
138 pvcc->old_pop(atmvcc, skb);
139 atomic_dec(&pvcc->inflight);
140
141 /*
142 * We always used to run the wakeup tasklet unconditionally here, for
143 * fear of race conditions where we clear the BLOCKED flag just as we
144 * refuse another packet in pppoatm_send(). This was quite inefficient.
145 *
146 * In fact it's OK. The PPP core will only ever call pppoatm_send()
147 * while holding the channel->downl lock. And ppp_output_wakeup() as
148 * called by the tasklet will *also* grab that lock. So even if another
149 * CPU is in pppoatm_send() right now, the tasklet isn't going to race
150 * with it. The wakeup *will* happen after the other CPU is safely out
151 * of pppoatm_send() again.
152 *
153 * So if the CPU in pppoatm_send() has already set the BLOCKED bit and
154 * it about to return, that's fine. We trigger a wakeup which will
155 * happen later. And if the CPU in pppoatm_send() *hasn't* set the
156 * BLOCKED bit yet, that's fine too because of the double check in
157 * pppoatm_may_send() which is commented there.
158 */
159 if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
160 tasklet_schedule(&pvcc->wakeup_tasklet);
161 }
162
163 /*
164 * Unbind from PPP - currently we only do this when closing the socket,
165 * but we could put this into an ioctl if need be
166 */
167 static void pppoatm_unassign_vcc(struct atm_vcc *atmvcc)
168 {
169 struct pppoatm_vcc *pvcc;
170 pvcc = atmvcc_to_pvcc(atmvcc);
171 atmvcc->push = pvcc->old_push;
172 atmvcc->pop = pvcc->old_pop;
173 atmvcc->release_cb = pvcc->old_release_cb;
174 tasklet_kill(&pvcc->wakeup_tasklet);
175 ppp_unregister_channel(&pvcc->chan);
176 atmvcc->user_back = NULL;
177 kfree(pvcc);
178 }
179
180 /* Called when an AAL5 PDU comes in */
181 static void pppoatm_push(struct atm_vcc *atmvcc, struct sk_buff *skb)
182 {
183 struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
184 pr_debug("\n");
185 if (skb == NULL) { /* VCC was closed */
186 struct module *module;
187
188 pr_debug("removing ATMPPP VCC %p\n", pvcc);
189 module = pvcc->old_owner;
190 pppoatm_unassign_vcc(atmvcc);
191 atmvcc->push(atmvcc, NULL); /* Pass along bad news */
192 module_put(module);
193 return;
194 }
195 atm_return(atmvcc, skb->truesize);
196 switch (pvcc->encaps) {
197 case e_llc:
198 if (skb->len < LLC_LEN ||
199 memcmp(skb->data, pppllc, LLC_LEN))
200 goto error;
201 skb_pull(skb, LLC_LEN);
202 break;
203 case e_autodetect:
204 if (pvcc->chan.ppp == NULL) { /* Not bound yet! */
205 kfree_skb(skb);
206 return;
207 }
208 if (skb->len >= sizeof(pppllc) &&
209 !memcmp(skb->data, pppllc, sizeof(pppllc))) {
210 pvcc->encaps = e_llc;
211 skb_pull(skb, LLC_LEN);
212 break;
213 }
214 if (skb->len >= (sizeof(pppllc) - LLC_LEN) &&
215 !memcmp(skb->data, &pppllc[LLC_LEN],
216 sizeof(pppllc) - LLC_LEN)) {
217 pvcc->encaps = e_vc;
218 pvcc->chan.mtu += LLC_LEN;
219 break;
220 }
221 pr_debug("Couldn't autodetect yet (skb: %6ph)\n", skb->data);
222 goto error;
223 case e_vc:
224 break;
225 }
226 ppp_input(&pvcc->chan, skb);
227 return;
228
229 error:
230 kfree_skb(skb);
231 ppp_input_error(&pvcc->chan, 0);
232 }
233
234 static int pppoatm_may_send(struct pppoatm_vcc *pvcc, int size)
235 {
236 /*
237 * It's not clear that we need to bother with using atm_may_send()
238 * to check we don't exceed sk->sk_sndbuf. If userspace sets a
239 * value of sk_sndbuf which is lower than the MTU, we're going to
240 * block for ever. But the code always did that before we introduced
241 * the packet count limit, so...
242 */
243 if (atm_may_send(pvcc->atmvcc, size) &&
244 atomic_inc_not_zero(&pvcc->inflight))
245 return 1;
246
247 /*
248 * We use test_and_set_bit() rather than set_bit() here because
249 * we need to ensure there's a memory barrier after it. The bit
250 * *must* be set before we do the atomic_inc() on pvcc->inflight.
251 * There's no smp_mb__after_set_bit(), so it's this or abuse
252 * smp_mb__after_atomic().
253 */
254 test_and_set_bit(BLOCKED, &pvcc->blocked);
255
256 /*
257 * We may have raced with pppoatm_pop(). If it ran for the
258 * last packet in the queue, *just* before we set the BLOCKED
259 * bit, then it might never run again and the channel could
260 * remain permanently blocked. Cope with that race by checking
261 * *again*. If it did run in that window, we'll have space on
262 * the queue now and can return success. It's harmless to leave
263 * the BLOCKED flag set, since it's only used as a trigger to
264 * run the wakeup tasklet. Another wakeup will never hurt.
265 * If pppoatm_pop() is running but hasn't got as far as making
266 * space on the queue yet, then it hasn't checked the BLOCKED
267 * flag yet either, so we're safe in that case too. It'll issue
268 * an "immediate" wakeup... where "immediate" actually involves
269 * taking the PPP channel's ->downl lock, which is held by the
270 * code path that calls pppoatm_send(), and is thus going to
271 * wait for us to finish.
272 */
273 if (atm_may_send(pvcc->atmvcc, size) &&
274 atomic_inc_not_zero(&pvcc->inflight))
275 return 1;
276
277 return 0;
278 }
279 /*
280 * Called by the ppp_generic.c to send a packet - returns true if packet
281 * was accepted. If we return false, then it's our job to call
282 * ppp_output_wakeup(chan) when we're feeling more up to it.
283 * Note that in the ENOMEM case (as opposed to the !atm_may_send case)
284 * we should really drop the packet, but the generic layer doesn't
285 * support this yet. We just return 'DROP_PACKET' which we actually define
286 * as success, just to be clear what we're really doing.
287 */
288 #define DROP_PACKET 1
289 static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
290 {
291 struct pppoatm_vcc *pvcc = chan_to_pvcc(chan);
292 struct atm_vcc *vcc;
293 int ret;
294
295 ATM_SKB(skb)->vcc = pvcc->atmvcc;
296 pr_debug("(skb=0x%p, vcc=0x%p)\n", skb, pvcc->atmvcc);
297 if (skb->data[0] == '\0' && (pvcc->flags & SC_COMP_PROT))
298 (void) skb_pull(skb, 1);
299
300 vcc = ATM_SKB(skb)->vcc;
301 bh_lock_sock(sk_atm(vcc));
302 if (sock_owned_by_user(sk_atm(vcc))) {
303 /*
304 * Needs to happen (and be flushed, hence test_and_) before we unlock
305 * the socket. It needs to be seen by the time our ->release_cb gets
306 * called.
307 */
308 test_and_set_bit(BLOCKED, &pvcc->blocked);
309 goto nospace;
310 }
311 if (test_bit(ATM_VF_RELEASED, &vcc->flags) ||
312 test_bit(ATM_VF_CLOSE, &vcc->flags) ||
313 !test_bit(ATM_VF_READY, &vcc->flags)) {
314 bh_unlock_sock(sk_atm(vcc));
315 kfree_skb(skb);
316 return DROP_PACKET;
317 }
318
319 switch (pvcc->encaps) { /* LLC encapsulation needed */
320 case e_llc:
321 if (skb_headroom(skb) < LLC_LEN) {
322 struct sk_buff *n;
323 n = skb_realloc_headroom(skb, LLC_LEN);
324 if (n != NULL &&
325 !pppoatm_may_send(pvcc, n->truesize)) {
326 kfree_skb(n);
327 goto nospace;
328 }
329 consume_skb(skb);
330 skb = n;
331 if (skb == NULL) {
332 bh_unlock_sock(sk_atm(vcc));
333 return DROP_PACKET;
334 }
335 } else if (!pppoatm_may_send(pvcc, skb->truesize))
336 goto nospace;
337 memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN);
338 break;
339 case e_vc:
340 if (!pppoatm_may_send(pvcc, skb->truesize))
341 goto nospace;
342 break;
343 case e_autodetect:
344 bh_unlock_sock(sk_atm(vcc));
345 pr_debug("Trying to send without setting encaps!\n");
346 kfree_skb(skb);
347 return 1;
348 }
349
350 atm_account_tx(vcc, skb);
351 pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n",
352 skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
353 ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
354 ? DROP_PACKET : 1;
355 bh_unlock_sock(sk_atm(vcc));
356 return ret;
357 nospace:
358 bh_unlock_sock(sk_atm(vcc));
359 /*
360 * We don't have space to send this SKB now, but we might have
361 * already applied SC_COMP_PROT compression, so may need to undo
362 */
363 if ((pvcc->flags & SC_COMP_PROT) && skb_headroom(skb) > 0 &&
364 skb->data[-1] == '\0')
365 (void) skb_push(skb, 1);
366 return 0;
367 }
368
369 /* This handles ioctls sent to the /dev/ppp interface */
370 static int pppoatm_devppp_ioctl(struct ppp_channel *chan, unsigned int cmd,
371 unsigned long arg)
372 {
373 switch (cmd) {
374 case PPPIOCGFLAGS:
375 return put_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
376 ? -EFAULT : 0;
377 case PPPIOCSFLAGS:
378 return get_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
379 ? -EFAULT : 0;
380 }
381 return -ENOTTY;
382 }
383
384 static const struct ppp_channel_ops pppoatm_ops = {
385 .start_xmit = pppoatm_send,
386 .ioctl = pppoatm_devppp_ioctl,
387 };
388
389 static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
390 {
391 struct atm_backend_ppp be;
392 struct pppoatm_vcc *pvcc;
393 int err;
394
395 if (copy_from_user(&be, arg, sizeof be))
396 return -EFAULT;
397 if (be.encaps != PPPOATM_ENCAPS_AUTODETECT &&
398 be.encaps != PPPOATM_ENCAPS_VC && be.encaps != PPPOATM_ENCAPS_LLC)
399 return -EINVAL;
400 pvcc = kzalloc(sizeof(*pvcc), GFP_KERNEL);
401 if (pvcc == NULL)
402 return -ENOMEM;
403 pvcc->atmvcc = atmvcc;
404
405 /* Maximum is zero, so that we can use atomic_inc_not_zero() */
406 atomic_set(&pvcc->inflight, NONE_INFLIGHT);
407 pvcc->old_push = atmvcc->push;
408 pvcc->old_pop = atmvcc->pop;
409 pvcc->old_owner = atmvcc->owner;
410 pvcc->old_release_cb = atmvcc->release_cb;
411 pvcc->encaps = (enum pppoatm_encaps) be.encaps;
412 pvcc->chan.private = pvcc;
413 pvcc->chan.ops = &pppoatm_ops;
414 pvcc->chan.mtu = atmvcc->qos.txtp.max_sdu - PPP_HDRLEN -
415 (be.encaps == e_vc ? 0 : LLC_LEN);
416 tasklet_setup(&pvcc->wakeup_tasklet, pppoatm_wakeup_sender);
417 err = ppp_register_channel(&pvcc->chan);
418 if (err != 0) {
419 kfree(pvcc);
420 return err;
421 }
422 atmvcc->user_back = pvcc;
423 atmvcc->push = pppoatm_push;
424 atmvcc->pop = pppoatm_pop;
425 atmvcc->release_cb = pppoatm_release_cb;
426 __module_get(THIS_MODULE);
427 atmvcc->owner = THIS_MODULE;
428
429 /* re-process everything received between connection setup and
430 backend setup */
431 vcc_process_recv_queue(atmvcc);
432 return 0;
433 }
434
435 /*
436 * This handles ioctls actually performed on our vcc - we must return
437 * -ENOIOCTLCMD for any unrecognized ioctl
438 */
439 static int pppoatm_ioctl(struct socket *sock, unsigned int cmd,
440 unsigned long arg)
441 {
442 struct atm_vcc *atmvcc = ATM_SD(sock);
443 void __user *argp = (void __user *)arg;
444
445 if (cmd != ATM_SETBACKEND && atmvcc->push != pppoatm_push)
446 return -ENOIOCTLCMD;
447 switch (cmd) {
448 case ATM_SETBACKEND: {
449 atm_backend_t b;
450 if (get_user(b, (atm_backend_t __user *) argp))
451 return -EFAULT;
452 if (b != ATM_BACKEND_PPP)
453 return -ENOIOCTLCMD;
454 if (!capable(CAP_NET_ADMIN))
455 return -EPERM;
456 if (sock->state != SS_CONNECTED)
457 return -EINVAL;
458 return pppoatm_assign_vcc(atmvcc, argp);
459 }
460 case PPPIOCGCHAN:
461 return put_user(ppp_channel_index(&atmvcc_to_pvcc(atmvcc)->
462 chan), (int __user *) argp) ? -EFAULT : 0;
463 case PPPIOCGUNIT:
464 return put_user(ppp_unit_number(&atmvcc_to_pvcc(atmvcc)->
465 chan), (int __user *) argp) ? -EFAULT : 0;
466 }
467 return -ENOIOCTLCMD;
468 }
469
470 static struct atm_ioctl pppoatm_ioctl_ops = {
471 .owner = THIS_MODULE,
472 .ioctl = pppoatm_ioctl,
473 };
474
475 static int __init pppoatm_init(void)
476 {
477 register_atm_ioctl(&pppoatm_ioctl_ops);
478 return 0;
479 }
480
481 static void __exit pppoatm_exit(void)
482 {
483 deregister_atm_ioctl(&pppoatm_ioctl_ops);
484 }
485
486 module_init(pppoatm_init);
487 module_exit(pppoatm_exit);
488
489 MODULE_AUTHOR("Mitchell Blank Jr <mitch@sfgoth.com>");
490 MODULE_DESCRIPTION("RFC2364 PPP over ATM/AAL5");
491 MODULE_LICENSE("GPL");
492
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