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 /* 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 */ 87 static const unsigned char pppllc[6] = { 0xFE, 0xFE, 0x03, 0xCF, 0xC0, 0x21 }; 88 #define LLC_LEN (4) 89 90 static inline struct pppoatm_vcc *atmvcc_to_pvcc(const struct atm_vcc *atmvcc) 91 { 92 return (struct pppoatm_vcc *) (atmvcc->user_back); 93 } 94 95 static 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 */ 105 static 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 */ 115 static 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 */ 148 static 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 */ 163 static 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; 208 209 error: 210 kfree_skb(skb); 211 ppp_input_error(&pvcc->chan, 0); 212 } 213 214 static 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 1 269 static 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; 310 nospace: 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 */ 322 static 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 } 335 336 static const struct ppp_channel_ops pppoatm_ops = { 337 .start_xmit = pppoatm_send, 338 .ioctl = pppoatm_devppp_ioctl, 339 }; 340 341 static 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 */ 392 static 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 } 420 421 static struct atm_ioctl pppoatm_ioctl_ops = { 422 .owner = THIS_MODULE, 423 .ioctl = pppoatm_ioctl, 424 }; 425 426 static int __init pppoatm_init(void) 427 { 428 register_atm_ioctl(&pppoatm_ioctl_ops); 429 return 0; 430 } 431 432 static void __exit pppoatm_exit(void) 433 { 434 deregister_atm_ioctl(&pppoatm_ioctl_ops); 435 } 436 437 module_init(pppoatm_init); 438 module_exit(pppoatm_exit); 439 440 MODULE_AUTHOR("Mitchell Blank Jr <mitch@sfgoth.com>"); 441 MODULE_DESCRIPTION("RFC2364 PPP over ATM/AAL5"); 442 MODULE_LICENSE("GPL"); 443