// SPDX-License-Identifier: GPL-2.0-or-later
/* net/atm/pppoatm.c - RFC2364 PPP over ATM/AAL5 */
/* Copyright 1999-2000 by Mitchell Blank Jr */
/* Based on clip.c; 1995-1999 by Werner Almesberger, EPFL LRC/ICA */
/* And on ppp_async.c; Copyright 1999 Paul Mackerras */
/* And help from Jens Axboe */
/*
*
* This driver provides the encapsulation and framing for sending
* and receiving PPP frames in ATM AAL5 PDUs.
*/
/*
* One shortcoming of this driver is that it does not comply with
* section 8 of RFC2364 - we are supposed to detect a change
* in encapsulation and immediately abort the connection (in order
* to avoid a black-hole being created if our peer loses state
* and changes encapsulation unilaterally. However, since the
* ppp_generic layer actually does the decapsulation, we need
* a way of notifying it when we _think_ there might be a problem)
* There's two cases:
* 1. LLC-encapsulation was missing when it was enabled. In
* this case, we should tell the upper layer "tear down
* this session if this skb looks ok to you"
* 2. LLC-encapsulation was present when it was disabled. Then
* we need to tell the upper layer "this packet may be
* ok, but if its in error tear down the session"
* These hooks are not yet available in ppp_generic
*/
#define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__
#include <linux/module.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/atm.h>
#include <linux/atmdev.h>
#include <linux/capability.h>
#include <linux/ppp_defs.h>
#include <linux/ppp-ioctl.h>
#include <linux/ppp_channel.h>
#include <linux/atmppp.h>
#include "common.h"
enum pppoatm_encaps {
e_autodetect = PPPOATM_ENCAPS_AUTODETECT,
e_vc = PPPOATM_ENCAPS_VC,
e_llc = PPPOATM_ENCAPS_LLC,
};
struct pppoatm_vcc {
struct atm_vcc *atmvcc; /* VCC descriptor */
void (*old_push)(struct atm_vcc *, struct sk_buff *);
void (*old_pop)(struct atm_vcc *, struct sk_buff *);
void (*old_release_cb)(struct atm_vcc *);
struct module *old_owner;
/* keep old push/pop for detaching */
enum pppoatm_encaps encaps;
atomic_t inflight;
unsigned long blocked;
int flags; /* SC_COMP_PROT - compress protocol */
struct ppp_channel chan; /* interface to generic ppp layer */
struct tasklet_struct wakeup_tasklet;
};
/*
* We want to allow two packets in the queue. The one that's currently in
* flight, and *one* queued up ready for the ATM device to send immediately
* from its TX done IRQ. We want to be able to use atomic_inc_not_zero(), so
* inflight == -2 represents an empty queue, -1 one packet, and zero means
* there are two packets in the queue.
*/
#define NONE_INFLIGHT -2
#define BLOCKED 0
/*
* Header used for LLC Encapsulated PPP (4 bytes) followed by the LCP protocol
* ID (0xC021) used in autodetection
*/
static const unsigned char pppllc[6] = { 0xFE, 0xFE, 0x03, 0xCF, 0xC0, 0x21 };
#define LLC_LEN (4)
static inline struct pppoatm_vcc *atmvcc_to_pvcc(const struct atm_vcc *atmvcc)
{
return (struct pppoatm_vcc *) (atmvcc->user_back);
}
static inline struct pppoatm_vcc *chan_to_pvcc(const struct ppp_channel *chan)
{
return (struct pppoatm_vcc *) (chan->private);
}
/*
* We can't do this directly from our _pop handler, since the ppp code
* doesn't want to be called in interrupt context, so we do it from
* a tasklet
*/
static void pppoatm_wakeup_sender(struct tasklet_struct *t)
{
struct pppoatm_vcc *pvcc = from_tasklet(pvcc, t, wakeup_tasklet);
ppp_output_wakeup(&pvcc->chan);
}
static void pppoatm_release_cb(struct atm_vcc *atmvcc)
{
struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
/*
* As in pppoatm_pop(), it's safe to clear the BLOCKED bit here because
* the wakeup *can't* race with pppoatm_send(). They both hold the PPP
* channel's ->downl lock. And the potential race with *setting* it,
* which leads to the double-check dance in pppoatm_may_send(), doesn't
* exist here. In the sock_owned_by_user() case in pppoatm_send(), we
* set the BLOCKED bit while the socket is still locked. We know that
* ->release_cb() can't be called until that's done.
*/
if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
tasklet_schedule(&pvcc->wakeup_tasklet);
if (pvcc->old_release_cb)
pvcc->old_release_cb(atmvcc);
}
/*
* This gets called every time the ATM card has finished sending our
* skb. The ->old_pop will take care up normal atm flow control,
* but we also need to wake up the device if we blocked it
*/
static void pppoatm_pop(struct atm_vcc *atmvcc, struct sk_buff *skb)
{
struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
pvcc->old_pop(atmvcc, skb);
atomic_dec(&pvcc->inflight);
/*
* We always used to run the wakeup tasklet unconditionally here, for
* fear of race conditions where we clear the BLOCKED flag just as we
* refuse another packet in pppoatm_send(). This was quite inefficient.
*
* In fact it's OK. The PPP core will only ever call pppoatm_send()
* while holding the channel->downl lock. And ppp_output_wakeup() as
* called by the tasklet will *also* grab that lock. So even if another
* CPU is in pppoatm_send() right now, the tasklet isn't going to race
* with it. The wakeup *will* happen after the other CPU is safely out
* of pppoatm_send() again.
*
* So if the CPU in pppoatm_send() has already set the BLOCKED bit and
* it about to return, that's fine. We trigger a wakeup which will
* happen later. And if the CPU in pppoatm_send() *hasn't* set the
* BLOCKED bit yet, that's fine too because of the double check in
* pppoatm_may_send() which is commented there.
*/
if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
tasklet_schedule(&pvcc->wakeup_tasklet);
}
/*
* Unbind from PPP - currently we only do this when closing the socket,
* but we could put this into an ioctl if need be
*/
static void pppoatm_unassign_vcc(struct atm_vcc *atmvcc)
{
struct pppoatm_vcc *pvcc;
pvcc = atmvcc_to_pvcc(atmvcc);
atmvcc->push = pvcc->old_push;
atmvcc->pop = pvcc->old_pop;
atmvcc->release_cb = pvcc->old_release_cb;
tasklet_kill(&pvcc->wakeup_tasklet);
ppp_unregister_channel(&pvcc->chan);
atmvcc->user_back = NULL;
kfree(pvcc);
}
/* Called when an AAL5 PDU comes in */
static void pppoatm_push(struct atm_vcc *atmvcc, struct sk_buff *skb)
{
struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
pr_debug("\n");
if (skb == NULL) { /* VCC was closed */
struct module *module;
pr_debug("removing ATMPPP VCC %p\n", pvcc);
module = pvcc->old_owner;
pppoatm_unassign_vcc(atmvcc);
atmvcc->push(atmvcc, NULL); /* Pass along bad news */
module_put(module);
return;
}
atm_return(atmvcc, skb->truesize);
switch (pvcc->encaps) {
case e_llc:
if (skb->len < LLC_LEN ||
memcmp(skb->data, pppllc, LLC_LEN))
goto error;
skb_pull(skb, LLC_LEN);
break;
case e_autodetect:
if (pvcc->chan.ppp == NULL) { /* Not bound yet! */
kfree_skb(skb);
return;
}
if (skb->len >= sizeof(pppllc) &&
!memcmp(skb->data, pppllc, sizeof(pppllc))) {
pvcc->encaps = e_llc;
skb_pull(skb, LLC_LEN);
break;
}
if (skb->len >= (sizeof(pppllc) - LLC_LEN) &&
!memcmp(skb->data, &pppllc[LLC_LEN],
sizeof(pppllc) - LLC_LEN)) {
pvcc->encaps = e_vc;
pvcc->chan.mtu += LLC_LEN;
break;
}
pr_debug("Couldn't autodetect yet (skb: %6ph)\n", skb->data);
goto error;
case e_vc:
break;
}
ppp_input(&pvcc->chan, skb);
return;
error:
kfree_skb(skb);
ppp_input_error(&pvcc->chan, 0);
}
static int pppoatm_may_send(struct pppoatm_vcc *pvcc, int size)
{
/*
* It's not clear that we need to bother with using atm_may_send()
* to check we don't exceed sk->sk_sndbuf. If userspace sets a
* value of sk_sndbuf which is lower than the MTU, we're going to
* block for ever. But the code always did that before we introduced
* the packet count limit, so...
*/
if (atm_may_send(pvcc->atmvcc, size) &&
atomic_inc_not_zero(&pvcc->inflight))
return 1;
/*
* We use test_and_set_bit() rather than set_bit() here because
* we need to ensure there's a memory barrier after it. The bit
* *must* be set before we do the atomic_inc() on pvcc->inflight.
* There's no smp_mb__after_set_bit(), so it's this or abuse
* smp_mb__after_atomic().
*/
test_and_set_bit(BLOCKED, &pvcc->blocked);
/*
* We may have raced with pppoatm_pop(). If it ran for the
* last packet in the queue, *just* before we set the BLOCKED
* bit, then it might never run again and the channel could
* remain permanently blocked. Cope with that race by checking
* *again*. If it did run in that window, we'll have space on
* the queue now and can return success. It's harmless to leave
* the BLOCKED flag set, since it's only used as a trigger to
* run the wakeup tasklet. Another wakeup will never hurt.
* If pppoatm_pop() is running but hasn't got as far as making
* space on the queue yet, then it hasn't checked the BLOCKED
* flag yet either, so we're safe in that case too. It'll issue
* an "immediate" wakeup... where "immediate" actually involves
* taking the PPP channel's ->downl lock, which is held by the
* code path that calls pppoatm_send(), and is thus going to
* wait for us to finish.
*/
if (atm_may_send(pvcc->atmvcc, size) &&
atomic_inc_not_zero(&pvcc->inflight))
return 1;
return 0;
}
/*
* Called by the ppp_generic.c to send a packet - returns true if packet
* was accepted. If we return false, then it's our job to call
* ppp_output_wakeup(chan) when we're feeling more up to it.
* Note that in the ENOMEM case (as opposed to the !atm_may_send case)
* we should really drop the packet, but the generic layer doesn't
* support this yet. We just return 'DROP_PACKET' which we actually define
* as success, just to be clear what we're really doing.
*/
#define DROP_PACKET 1
static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
{
struct pppoatm_vcc *pvcc = chan_to_pvcc(chan);
struct atm_vcc *vcc;
int ret;
ATM_SKB(skb)->vcc = pvcc->atmvcc;
pr_debug("(skb=0x%p, vcc=0x%p)\n", skb, pvcc->atmvcc);
if (skb->data[0] == '\0' && (pvcc->flags & SC_COMP_PROT))
(void) skb_pull(skb, 1);
vcc = ATM_SKB(skb)->vcc;
bh_lock_sock(sk_atm(vcc));
if (sock_owned_by_user(sk_atm(vcc))) {
/*
* Needs to happen (and be flushed, hence test_and_) before we unlock
* the socket. It needs to be seen by the time our ->release_cb gets
* called.
*/
test_and_set_bit(BLOCKED, &pvcc->blocked);
goto nospace;
}
if (test_bit(ATM_VF_RELEASED, &vcc->flags) ||
test_bit(ATM_VF_CLOSE, &vcc->flags) ||
!test_bit(ATM_VF_READY, &vcc->flags)) {
bh_unlock_sock(sk_atm(vcc));
kfree_skb(skb);
return DROP_PACKET;
}
switch (pvcc->encaps) { /* LLC encapsulation needed */
case e_llc:
if (skb_headroom(skb) < LLC_LEN) {
struct sk_buff *n;
n = skb_realloc_headroom(skb, LLC_LEN);
if (n != NULL &&
!pppoatm_may_send(pvcc, n->truesize)) {
kfree_skb(n);
goto nospace;
}
consume_skb(skb);
skb = n;
if (skb == NULL) {
bh_unlock_sock(sk_atm(vcc));
return DROP_PACKET;
}
} else if (!pppoatm_may_send(pvcc, skb->truesize))
goto nospace;
memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN);
break;
case e_vc:
if (!pppoatm_may_send(pvcc, skb->truesize))
goto nospace;
break;
case e_autodetect:
bh_unlock_sock(sk_atm(vcc));
pr_debug("Trying to send without setting encaps!\n");
kfree_skb(skb);
return 1;
}
atm_account_tx(vcc, skb);
pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n",
skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
? DROP_PACKET : 1;
bh_unlock_sock(sk_atm(vcc));
return ret;
nospace:
bh_unlock_sock(sk_atm(vcc));
/*
* We don't have space to send this SKB now, but we might have
* already applied SC_COMP_PROT compression, so may need to undo
*/
if ((pvcc->flags & SC_COMP_PROT) && skb_headroom(skb) > 0 &&
skb->data[-1] == '\0')
(void) skb_push(skb, 1);
return 0;
}
/* This handles ioctls sent to the /dev/ppp interface */
static int pppoatm_devppp_ioctl(struct ppp_channel *chan, unsigned int cmd,
unsigned long arg)
{
switch (cmd) {
case PPPIOCGFLAGS:
return put_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
? -EFAULT : 0;
case PPPIOCSFLAGS:
return get_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
? -EFAULT : 0;
}
return -ENOTTY;
}
static const struct ppp_channel_ops pppoatm_ops = {
.start_xmit = pppoatm_send,
.ioctl = pppoatm_devppp_ioctl,
};
static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
{
struct atm_backend_ppp be;
struct pppoatm_vcc *pvcc;
int err;
if (copy_from_user(&be, arg, sizeof be))
return -EFAULT;
if (be.encaps != PPPOATM_ENCAPS_AUTODETECT &&
be.encaps != PPPOATM_ENCAPS_VC && be.encaps != PPPOATM_ENCAPS_LLC)
return -EINVAL;
pvcc = kzalloc(sizeof(*pvcc), GFP_KERNEL);
if (pvcc == NULL)
return -ENOMEM;
pvcc->atmvcc = atmvcc;
/* Maximum is zero, so that we can use atomic_inc_not_zero() */
atomic_set(&pvcc->inflight, NONE_INFLIGHT);
pvcc->old_push = atmvcc->push;
pvcc->old_pop = atmvcc->pop;
pvcc->old_owner = atmvcc->owner;
pvcc->old_release_cb = atmvcc->release_cb;
pvcc->encaps = (enum pppoatm_encaps) be.encaps;
pvcc->chan.private = pvcc;
pvcc->chan.ops = &pppoatm_ops;
pvcc->chan.mtu = atmvcc->qos.txtp.max_sdu - PPP_HDRLEN -
(be.encaps == e_vc ? 0 : LLC_LEN);
tasklet_setup(&pvcc->wakeup_tasklet, pppoatm_wakeup_sender);
err = ppp_register_channel(&pvcc->chan);
if (err != 0) {
kfree(pvcc);
return err;
}
atmvcc->user_back = pvcc;
atmvcc->push = pppoatm_push;
atmvcc->pop = pppoatm_pop;
atmvcc->release_cb = pppoatm_release_cb;
__module_get(THIS_MODULE);
atmvcc->owner = THIS_MODULE;
/* re-process everything received between connection setup and
backend setup */
vcc_process_recv_queue(atmvcc);
return 0;
}
/*
* This handles ioctls actually performed on our vcc - we must return
* -ENOIOCTLCMD for any unrecognized ioctl
*/
static int pppoatm_ioctl(struct socket *sock, unsigned int cmd,
unsigned long arg)
{
struct atm_vcc *atmvcc = ATM_SD(sock);
void __user *argp = (void __user *)arg;
if (cmd != ATM_SETBACKEND && atmvcc->push != pppoatm_push)
return -ENOIOCTLCMD;
switch (cmd) {
case ATM_SETBACKEND: {
atm_backend_t b;
if (get_user(b, (atm_backend_t __user *) argp))
return -EFAULT;
if (b != ATM_BACKEND_PPP)
return -ENOIOCTLCMD;
if (!capable(CAP_NET_ADMIN))
return -EPERM;
if (sock->state != SS_CONNECTED)
return -EINVAL;
return pppoatm_assign_vcc(atmvcc, argp);
}
case PPPIOCGCHAN:
return put_user(ppp_channel_index(&atmvcc_to_pvcc(atmvcc)->
chan), (int __user *) argp) ? -EFAULT : 0;
case PPPIOCGUNIT:
return put_user(ppp_unit_number(&atmvcc_to_pvcc(atmvcc)->
chan), (int __user *) argp) ? -EFAULT : 0;
}
return -ENOIOCTLCMD;
}
static struct atm_ioctl pppoatm_ioctl_ops = {
.owner = THIS_MODULE,
.ioctl = pppoatm_ioctl,
};
static int __init pppoatm_init(void)
{
register_atm_ioctl(&pppoatm_ioctl_ops);
return 0;
}
static void __exit pppoatm_exit(void)
{
deregister_atm_ioctl(&pppoatm_ioctl_ops);
}
module_init(pppoatm_init);
module_exit(pppoatm_exit);
MODULE_AUTHOR("Mitchell Blank Jr <[email protected]>");
MODULE_DESCRIPTION("RFC2364 PPP over ATM/AAL5");
MODULE_LICENSE("GPL");
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