pppoatm.c

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/* 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 program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 *
 * 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 *);
                    /* 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(unsigned long arg)
{
    ppp_output_wakeup((struct ppp_channel *) arg);
}

/*
 * 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;
    tasklet_kill(&pvcc->wakeup_tasklet);
    ppp_unregister_channel(&pvcc->chan);
    atmvcc->user_back = NULL;
    kfree(pvcc);
    /* Gee, I hope we have the big kernel lock here... */
    module_put(THIS_MODULE);
}

/* 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 */
        pr_debug("removing ATMPPP VCC %p\n", pvcc);
        pppoatm_unassign_vcc(atmvcc);
        atmvcc->push(atmvcc, NULL); /* Pass along bad news */
        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: %02X %02X %02X %02X %02X %02X)\n",
             skb->data[0], skb->data[1], skb->data[2],
             skb->data[3], skb->data[4], skb->data[5]);
        goto error;
    case e_vc:
        break;
    }
    ppp_input(&pvcc->chan, skb);
    return;

error:
    kfree_skb(skb);
    ppp_input_error(&pvcc->chan, 0);
}

static inline 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_hint(&pvcc->inflight, NONE_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_clear_bit().
     */
    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);
    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);
    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)
                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:
        pr_debug("Trying to send without setting encaps!\n");
        kfree_skb(skb);
        return 1;
    }

    atomic_add(skb->truesize, &sk_atm(ATM_SKB(skb)->vcc)->sk_wmem_alloc);
    ATM_SKB(skb)->atm_options = ATM_SKB(skb)->vcc->atm_options;
    pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n",
         skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
    return ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
        ? DROP_PACKET : 1;
nospace:
    /*
     * 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;
    /*
     * Each PPPoATM instance has its own tasklet - this is just a
     * prototypical one used to initialize them
     */
    static const DECLARE_TASKLET(tasklet_proto, pppoatm_wakeup_sender, 0);
    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->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);
    pvcc->wakeup_tasklet = tasklet_proto;
    pvcc->wakeup_tasklet.data = (unsigned long) &pvcc->chan;
    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;
    __module_get(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;
        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");