// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Generic PPP layer for Linux.
 *
 * Copyright 1999-2002 Paul Mackerras.
 *
 * The generic PPP layer handles the PPP network interfaces, the
 * /dev/ppp device, packet and VJ compression, and multilink.
 * It talks to PPP `channels' via the interface defined in
 * include/linux/ppp_channel.h.  Channels provide the basic means for
 * sending and receiving PPP frames on some kind of communications
 * channel.
 *
 * Part of the code in this driver was inspired by the old async-only
 * PPP driver, written by Michael Callahan and Al Longyear, and
 * subsequently hacked by Paul Mackerras.
 *
 * ==FILEVERSION 20041108==
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/sched/signal.h>
#include <linux/kmod.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/idr.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/ppp_defs.h>
#include <linux/filter.h>
#include <linux/ppp-ioctl.h>
#include <linux/ppp_channel.h>
#include <linux/ppp-comp.h>
#include <linux/skbuff.h>
#include <linux/rculist.h>
#include <linux/rtnetlink.h>
#include <linux/if_arp.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/spinlock.h>
#include <linux/rwsem.h>
#include <linux/stddef.h>
#include <linux/device.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/unaligned.h>
#include <net/netdev_lock.h>
#include <net/slhc_vj.h>
#include <linux/atomic.h>
#include <linux/refcount.h>

#include <linux/nsproxy.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>

#define PPP_VERSION	"2.4.2"

/*
 * Network protocols we support.
 */
#define NP_IP	0		/* Internet Protocol V4 */
#define NP_IPV6	1		/* Internet Protocol V6 */
#define NP_IPX	2		/* IPX protocol */
#define NP_AT	3		/* Appletalk protocol */
#define NP_MPLS_UC 4		/* MPLS unicast */
#define NP_MPLS_MC 5		/* MPLS multicast */
#define NUM_NP	6		/* Number of NPs. */

#define MPHDRLEN	6	/* multilink protocol header length */
#define MPHDRLEN_SSN	4	/* ditto with short sequence numbers */

#define PPP_PROTO_LEN	2
#define PPP_LCP_HDRLEN	4

/* The filter instructions generated by libpcap are constructed
 * assuming a four-byte PPP header on each packet, where the last
 * 2 bytes are the protocol field defined in the RFC and the first
 * byte of the first 2 bytes indicates the direction.
 * The second byte is currently unused, but we still need to initialize
 * it to prevent crafted BPF programs from reading them which would
 * cause reading of uninitialized data.
 */
#define PPP_FILTER_OUTBOUND_TAG 0x0100
#define PPP_FILTER_INBOUND_TAG  0x0000

/*
 * An instance of /dev/ppp can be associated with either a ppp
 * interface unit or a ppp channel.  In both cases, file->private_data
 * points to one of these.
 */
struct ppp_file {
	enum {
		INTERFACE=1, CHANNEL
	}		kind;
	struct sk_buff_head xq;		/* pppd transmit queue */
	struct sk_buff_head rq;		/* receive queue for pppd */
	wait_queue_head_t rwait;	/* for poll on reading /dev/ppp */
	refcount_t	refcnt;		/* # refs (incl /dev/ppp attached) */
	int		hdrlen;		/* space to leave for headers */
	int		index;		/* interface unit / channel number */
	int		dead;		/* unit/channel has been shut down */
};

#define PF_TO_X(pf, X)		container_of(pf, X, file)

#define PF_TO_PPP(pf)		PF_TO_X(pf, struct ppp)
#define PF_TO_CHANNEL(pf)	PF_TO_X(pf, struct channel)

struct ppp_xmit_recursion {
	struct task_struct *owner;
	local_lock_t bh_lock;
};

/*
 * Data structure describing one ppp unit.
 * A ppp unit corresponds to a ppp network interface device
 * and represents a multilink bundle.
 * It can have 0 or more ppp channels connected to it.
 */
struct ppp {
	struct ppp_file	file;		/* stuff for read/write/poll 0 */
	struct file	*owner;		/* file that owns this unit 48 */
	struct list_head channels;	/* list of attached channels 4c */
	int		n_channels;	/* how many channels are attached 54 */
	spinlock_t	rlock;		/* lock for receive side 58 */
	spinlock_t	wlock;		/* lock for transmit side 5c */
	struct ppp_xmit_recursion __percpu *xmit_recursion; /* xmit recursion detect */
	int		mru;		/* max receive unit 60 */
	unsigned int	flags;		/* control bits 64 */
	unsigned int	xstate;		/* transmit state bits 68 */
	unsigned int	rstate;		/* receive state bits 6c */
	int		debug;		/* debug flags 70 */
	struct slcompress *vj;		/* state for VJ header compression */
	enum NPmode	npmode[NUM_NP];	/* what to do with each net proto 78 */
	struct compressor *xcomp;	/* transmit packet compressor 8c */
	void		*xc_state;	/* its internal state 90 */
	struct compressor *rcomp;	/* receive decompressor 94 */
	void		*rc_state;	/* its internal state 98 */
	unsigned long	last_xmit;	/* jiffies when last pkt sent 9c */
	unsigned long	last_recv;	/* jiffies when last pkt rcvd a0 */
	struct net_device *dev;		/* network interface device a4 */
	int		closing;	/* is device closing down? a8 */
#ifdef CONFIG_PPP_MULTILINK
	int		nxchan;		/* next channel to send something on */
	u32		nxseq;		/* next sequence number to send */
	int		mrru;		/* MP: max reconst. receive unit */
	u32		nextseq;	/* MP: seq no of next packet */
	u32		minseq;		/* MP: min of most recent seqnos */
	struct sk_buff_head mrq;	/* MP: receive reconstruction queue */
#endif /* CONFIG_PPP_MULTILINK */
#ifdef CONFIG_PPP_FILTER
	struct bpf_prog *pass_filter;	/* filter for packets to pass */
	struct bpf_prog *active_filter; /* filter for pkts to reset idle */
#endif /* CONFIG_PPP_FILTER */
	struct net	*ppp_net;	/* the net we belong to */
};

/*
 * Bits in flags: SC_NO_TCP_CCID, SC_CCP_OPEN, SC_CCP_UP, SC_LOOP_TRAFFIC,
 * SC_MULTILINK, SC_MP_SHORTSEQ, SC_MP_XSHORTSEQ, SC_COMP_TCP, SC_REJ_COMP_TCP,
 * SC_MUST_COMP
 * Bits in rstate: SC_DECOMP_RUN, SC_DC_ERROR, SC_DC_FERROR.
 * Bits in xstate: SC_COMP_RUN
 */
#define SC_FLAG_BITS	(SC_NO_TCP_CCID|SC_CCP_OPEN|SC_CCP_UP|SC_LOOP_TRAFFIC \
			 |SC_MULTILINK|SC_MP_SHORTSEQ|SC_MP_XSHORTSEQ \
			 |SC_COMP_TCP|SC_REJ_COMP_TCP|SC_MUST_COMP)

/*
 * Private data structure for each channel.
 * This includes the data structure used for multilink.
 */
struct channel {
	struct ppp_file	file;		/* stuff for read/write/poll */
	struct list_head list;		/* link in all/new_channels list */
	struct ppp_channel *chan;	/* public channel data structure */
	struct rw_semaphore chan_sem;	/* protects `chan' during chan ioctl */
	spinlock_t	downl;		/* protects `chan', file.xq dequeue */
	struct ppp __rcu *ppp;		/* ppp unit we're connected to */
	struct net	*chan_net;	/* the net channel belongs to */
	netns_tracker	ns_tracker;
	struct list_head clist;		/* link in list of channels per unit */
	spinlock_t	upl;		/* protects `ppp' and 'bridge' */
	struct channel __rcu *bridge;	/* "bridged" ppp channel */
	struct rcu_head rcu;		/* for RCU-deferred free of the channel */
#ifdef CONFIG_PPP_MULTILINK
	u8		avail;		/* flag used in multilink stuff */
	u8		had_frag;	/* >= 1 fragments have been sent */
	u32		lastseq;	/* MP: last sequence # received */
	int		speed;		/* speed of the corresponding ppp channel*/
#endif /* CONFIG_PPP_MULTILINK */
};

struct ppp_config {
	struct file *file;
	s32 unit;
	bool ifname_is_set;
};

/*
 * SMP locking issues:
 * Both the ppp.rlock and ppp.wlock locks protect the ppp.channels
 * list and the ppp.n_channels field, you need to take both locks
 * before you modify them.
 * The lock ordering is: channel.upl -> ppp.wlock -> ppp.rlock ->
 * channel.downl.
 */

static DEFINE_MUTEX(ppp_mutex);
static atomic_t ppp_unit_count = ATOMIC_INIT(0);
static atomic_t channel_count = ATOMIC_INIT(0);

/* per-net private data for this module */
static unsigned int ppp_net_id __read_mostly;
struct ppp_net {
	/* units to ppp mapping */
	struct idr units_idr;

	/*
	 * all_ppp_mutex protects the units_idr mapping.
	 * It also ensures that finding a ppp unit in the units_idr
	 * map and updating its file.refcnt field is atomic.
	 */
	struct mutex all_ppp_mutex;

	/* channels */
	struct list_head all_channels;
	struct list_head new_channels;
	int last_channel_index;

	/*
	 * all_channels_lock protects all_channels and
	 * last_channel_index, and the atomicity of find
	 * a channel and updating its file.refcnt field.
	 */
	spinlock_t all_channels_lock;
};

/* Get the PPP protocol number from a skb */
#define PPP_PROTO(skb)	get_unaligned_be16((skb)->data)

/* We limit the length of ppp->file.rq to this (arbitrary) value */
#define PPP_MAX_RQLEN	32

/*
 * Maximum number of multilink fragments queued up.
 * This has to be large enough to cope with the maximum latency of
 * the slowest channel relative to the others.  Strictly it should
 * depend on the number of channels and their characteristics.
 */
#define PPP_MP_MAX_QLEN	128

/* Multilink header bits. */
#define B	0x80		/* this fragment begins a packet */
#define E	0x40		/* this fragment ends a packet */

/* Compare multilink sequence numbers (assumed to be 32 bits wide) */
#define seq_before(a, b)	((s32)((a) - (b)) < 0)
#define seq_after(a, b)		((s32)((a) - (b)) > 0)

/* Prototypes. */
static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
			struct file *file, unsigned int cmd, unsigned long arg);
static void ppp_xmit_process(struct ppp *ppp, struct sk_buff *skb);
static int ppp_prepare_tx_skb(struct ppp *ppp, struct sk_buff **pskb);
static int ppp_push(struct ppp *ppp, struct sk_buff *skb);
static void ppp_channel_push(struct channel *pch);
static void ppp_receive_frame(struct ppp *ppp, struct sk_buff *skb,
			      struct channel *pch);
static void ppp_receive_error(struct ppp *ppp);
static void ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb);
static struct sk_buff *ppp_decompress_frame(struct ppp *ppp,
					    struct sk_buff *skb);
#ifdef CONFIG_PPP_MULTILINK
static void ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb,
				struct channel *pch);
static void ppp_mp_insert(struct ppp *ppp, struct sk_buff *skb);
static struct sk_buff *ppp_mp_reconstruct(struct ppp *ppp);
static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb);
#endif /* CONFIG_PPP_MULTILINK */
static int ppp_set_compress(struct ppp *ppp, struct ppp_option_data *data);
static void ppp_ccp_peek(struct ppp *ppp, struct sk_buff *skb, int inbound);
static void ppp_ccp_closed(struct ppp *ppp);
static struct compressor *find_compressor(int type);
static void ppp_get_stats(struct ppp *ppp, struct ppp_stats *st);
static int ppp_create_interface(struct net *net, struct file *file, int *unit);
static void init_ppp_file(struct ppp_file *pf, int kind);
static void ppp_release_interface(struct ppp *ppp);
static struct ppp *ppp_find_unit(struct ppp_net *pn, int unit);
static struct channel *ppp_find_channel(struct ppp_net *pn, int unit);
static int ppp_connect_channel(struct channel *pch, int unit);
static int ppp_disconnect_channel(struct channel *pch);
static void ppp_release_channel(struct channel *pch);
static int unit_get(struct idr *p, void *ptr, int min);
static int unit_set(struct idr *p, void *ptr, int n);
static void unit_put(struct idr *p, int n);
static void *unit_find(struct idr *p, int n);
static void ppp_setup(struct net_device *dev);

static const struct net_device_ops ppp_netdev_ops;

static const struct class ppp_class = {
	.name = "ppp",
};

/* per net-namespace data */
static inline struct ppp_net *ppp_pernet(struct net *net)
{
	return net_generic(net, ppp_net_id);
}

/* Translates a PPP protocol number to a NP index (NP == network protocol) */
static inline int proto_to_npindex(int proto)
{
	switch (proto) {
	case PPP_IP:
		return NP_IP;
	case PPP_IPV6:
		return NP_IPV6;
	case PPP_IPX:
		return NP_IPX;
	case PPP_AT:
		return NP_AT;
	case PPP_MPLS_UC:
		return NP_MPLS_UC;
	case PPP_MPLS_MC:
		return NP_MPLS_MC;
	}
	return -EINVAL;
}

/* Translates an NP index into a PPP protocol number */
static const int npindex_to_proto[NUM_NP] = {
	PPP_IP,
	PPP_IPV6,
	PPP_IPX,
	PPP_AT,
	PPP_MPLS_UC,
	PPP_MPLS_MC,
};

/* Translates an ethertype into an NP index */
static inline int ethertype_to_npindex(int ethertype)
{
	switch (ethertype) {
	case ETH_P_IP:
		return NP_IP;
	case ETH_P_IPV6:
		return NP_IPV6;
	case ETH_P_IPX:
		return NP_IPX;
	case ETH_P_PPPTALK:
	case ETH_P_ATALK:
		return NP_AT;
	case ETH_P_MPLS_UC:
		return NP_MPLS_UC;
	case ETH_P_MPLS_MC:
		return NP_MPLS_MC;
	}
	return -1;
}

/* Translates an NP index into an ethertype */
static const int npindex_to_ethertype[NUM_NP] = {
	ETH_P_IP,
	ETH_P_IPV6,
	ETH_P_IPX,
	ETH_P_PPPTALK,
	ETH_P_MPLS_UC,
	ETH_P_MPLS_MC,
};

/*
 * Locking shorthand.
 */
#define ppp_xmit_lock(ppp)	spin_lock_bh(&(ppp)->wlock)
#define ppp_xmit_unlock(ppp)	spin_unlock_bh(&(ppp)->wlock)
#define ppp_recv_lock(ppp)	spin_lock_bh(&(ppp)->rlock)
#define ppp_recv_unlock(ppp)	spin_unlock_bh(&(ppp)->rlock)
#define ppp_lock(ppp)		do { ppp_xmit_lock(ppp); \
				     ppp_recv_lock(ppp); } while (0)
#define ppp_unlock(ppp)		do { ppp_recv_unlock(ppp); \
				     ppp_xmit_unlock(ppp); } while (0)

/*
 * /dev/ppp device routines.
 * The /dev/ppp device is used by pppd to control the ppp unit.
 * It supports the read, write, ioctl and poll functions.
 * Open instances of /dev/ppp can be in one of three states:
 * unattached, attached to a ppp unit, or attached to a ppp channel.
 */
static int ppp_open(struct inode *inode, struct file *file)
{
	/*
	 * This could (should?) be enforced by the permissions on /dev/ppp.
	 */
	if (!ns_capable(file->f_cred->user_ns, CAP_NET_ADMIN))
		return -EPERM;
	return 0;
}

static int ppp_release(struct inode *unused, struct file *file)
{
	struct ppp_file *pf = file->private_data;
	struct ppp *ppp;

	if (pf) {
		file->private_data = NULL;
		switch (pf->kind) {
		case INTERFACE:
			ppp = PF_TO_PPP(pf);
			rtnl_lock();
			if (file == ppp->owner)
				unregister_netdevice(ppp->dev);
			rtnl_unlock();
			ppp_release_interface(ppp);
			break;
		case CHANNEL:
			ppp_release_channel(PF_TO_CHANNEL(pf));
			break;
		}
	}
	return 0;
}

static ssize_t ppp_read(struct file *file, char __user *buf,
			size_t count, loff_t *ppos)
{
	struct ppp_file *pf = file->private_data;
	DECLARE_WAITQUEUE(wait, current);
	ssize_t ret;
	struct sk_buff *skb = NULL;
	struct iovec iov;
	struct iov_iter to;

	ret = count;

	if (!pf)
		return -ENXIO;
	add_wait_queue(&pf->rwait, &wait);
	for (;;) {
		set_current_state(TASK_INTERRUPTIBLE);
		skb = skb_dequeue(&pf->rq);
		if (skb)
			break;
		ret = 0;
		if (pf->dead)
			break;
		if (pf->kind == INTERFACE) {
			/*
			 * Return 0 (EOF) on an interface that has no
			 * channels connected, unless it is looping
			 * network traffic (demand mode).
			 */
			struct ppp *ppp = PF_TO_PPP(pf);

			ppp_recv_lock(ppp);
			if (ppp->n_channels == 0 &&
			    (ppp->flags & SC_LOOP_TRAFFIC) == 0) {
				ppp_recv_unlock(ppp);
				break;
			}
			ppp_recv_unlock(ppp);
		}
		ret = -EAGAIN;
		if (file->f_flags & O_NONBLOCK)
			break;
		ret = -ERESTARTSYS;
		if (signal_pending(current))
			break;
		schedule();
	}
	set_current_state(TASK_RUNNING);
	remove_wait_queue(&pf->rwait, &wait);

	if (!skb)
		goto out;

	ret = -EOVERFLOW;
	if (skb->len > count)
		goto outf;
	ret = -EFAULT;
	iov.iov_base = buf;
	iov.iov_len = count;
	iov_iter_init(&to, ITER_DEST, &iov, 1, count);
	if (skb_copy_datagram_iter(skb, 0, &to, skb->len))
		goto outf;
	ret = skb->len;

 outf:
	kfree_skb(skb);
 out:
	return ret;
}

static bool ppp_check_packet(struct sk_buff *skb, size_t count)
{
	/* LCP packets must include LCP header which 4 bytes long:
	 * 1-byte code, 1-byte identifier, and 2-byte length.
	 */
	return get_unaligned_be16(skb->data) != PPP_LCP ||
		count >= PPP_PROTO_LEN + PPP_LCP_HDRLEN;
}

static ssize_t ppp_write(struct file *file, const char __user *buf,
			 size_t count, loff_t *ppos)
{
	struct ppp_file *pf = file->private_data;
	struct sk_buff *skb;
	ssize_t ret;

	if (!pf)
		return -ENXIO;
	/* All PPP packets should start with the 2-byte protocol */
	if (count < PPP_PROTO_LEN)
		return -EINVAL;
	ret = -ENOMEM;
	skb = alloc_skb(count + pf->hdrlen, GFP_KERNEL);
	if (!skb)
		goto out;
	skb_reserve(skb, pf->hdrlen);
	ret = -EFAULT;
	if (copy_from_user(skb_put(skb, count), buf, count)) {
		kfree_skb(skb);
		goto out;
	}
	ret = -EINVAL;
	if (unlikely(!ppp_check_packet(skb, count))) {
		kfree_skb(skb);
		goto out;
	}

	switch (pf->kind) {
	case INTERFACE:
		ppp_xmit_process(PF_TO_PPP(pf), skb);
		break;
	case CHANNEL:
		skb_queue_tail(&pf->xq, skb);
		ppp_channel_push(PF_TO_CHANNEL(pf));
		break;
	}

	ret = count;

 out:
	return ret;
}

/* No kernel lock - fine */
static __poll_t ppp_poll(struct file *file, poll_table *wait)
{
	struct ppp_file *pf = file->private_data;
	__poll_t mask;

	if (!pf)
		return 0;
	poll_wait(file, &pf->rwait, wait);
	mask = EPOLLOUT | EPOLLWRNORM;
	if (skb_peek(&pf->rq))
		mask |= EPOLLIN | EPOLLRDNORM;
	if (pf->dead)
		mask |= EPOLLHUP;
	else if (pf->kind == INTERFACE) {
		/* see comment in ppp_read */
		struct ppp *ppp = PF_TO_PPP(pf);

		ppp_recv_lock(ppp);
		if (ppp->n_channels == 0 &&
		    (ppp->flags & SC_LOOP_TRAFFIC) == 0)
			mask |= EPOLLIN | EPOLLRDNORM;
		ppp_recv_unlock(ppp);
	}

	return mask;
}

#ifdef CONFIG_PPP_FILTER
static struct bpf_prog *get_filter(struct sock_fprog *uprog)
{
	struct sock_fprog_kern fprog;
	struct bpf_prog *res = NULL;
	int err;

	if (!uprog->len)
		return NULL;

	/* uprog->len is unsigned short, so no overflow here */
	fprog.len = uprog->len;
	fprog.filter = memdup_array_user(uprog->filter,
					 uprog->len, sizeof(struct sock_filter));
	if (IS_ERR(fprog.filter))
		return ERR_CAST(fprog.filter);

	err = bpf_prog_create(&res, &fprog);
	kfree(fprog.filter);

	return err ? ERR_PTR(err) : res;
}

static struct bpf_prog *ppp_get_filter(struct sock_fprog __user *p)
{
	struct sock_fprog uprog;

	if (copy_from_user(&uprog, p, sizeof(struct sock_fprog)))
		return ERR_PTR(-EFAULT);
	return get_filter(&uprog);
}

#ifdef CONFIG_COMPAT
struct sock_fprog32 {
	unsigned short len;
	compat_caddr_t filter;
};

#define PPPIOCSPASS32		_IOW('t', 71, struct sock_fprog32)
#define PPPIOCSACTIVE32		_IOW('t', 70, struct sock_fprog32)

static struct bpf_prog *compat_ppp_get_filter(struct sock_fprog32 __user *p)
{
	struct sock_fprog32 uprog32;
	struct sock_fprog uprog;

	if (copy_from_user(&uprog32, p, sizeof(struct sock_fprog32)))
		return ERR_PTR(-EFAULT);
	uprog.len = uprog32.len;
	uprog.filter = compat_ptr(uprog32.filter);
	return get_filter(&uprog);
}
#endif
#endif

/* Bridge one PPP channel to another.
 * When two channels are bridged, ppp_input on one channel is redirected to
 * the other's ops->start_xmit handler.
 * In order to safely bridge channels we must reject channels which are already
 * part of a bridge instance, or which form part of an existing unit.
 * Once successfully bridged, each channel holds a reference on the other
 * to prevent it being freed while the bridge is extant.
 */
static int ppp_bridge_channels(struct channel *pch, struct channel *pchb)
{
	spin_lock(&pch->upl);
	if (rcu_dereference_protected(pch->ppp, lockdep_is_held(&pch->upl)) ||
	    rcu_dereference_protected(pch->bridge, lockdep_is_held(&pch->upl))) {
		spin_unlock(&pch->upl);
		return -EALREADY;
	}
	refcount_inc(&pchb->file.refcnt);
	rcu_assign_pointer(pch->bridge, pchb);
	spin_unlock(&pch->upl);

	spin_lock(&pchb->upl);
	if (rcu_dereference_protected(pchb->ppp, lockdep_is_held(&pchb->upl)) ||
	    rcu_dereference_protected(pchb->bridge, lockdep_is_held(&pchb->upl))) {
		spin_unlock(&pchb->upl);
		goto err_unset;
	}
	refcount_inc(&pch->file.refcnt);
	rcu_assign_pointer(pchb->bridge, pch);
	spin_unlock(&pchb->upl);

	return 0;

err_unset:
	spin_lock(&pch->upl);
	/* Re-read pch->bridge with upl held in case it was modified concurrently */
	pchb = rcu_dereference_protected(pch->bridge, lockdep_is_held(&pch->upl));
	RCU_INIT_POINTER(pch->bridge, NULL);
	spin_unlock(&pch->upl);
	synchronize_rcu();

	if (pchb)
		ppp_release_channel(pchb);

	return -EALREADY;
}

static int ppp_unbridge_channels(struct channel *pch)
{
	struct channel *pchb, *pchbb;

	spin_lock(&pch->upl);
	pchb = rcu_dereference_protected(pch->bridge, lockdep_is_held(&pch->upl));
	if (!pchb) {
		spin_unlock(&pch->upl);
		return -EINVAL;
	}
	RCU_INIT_POINTER(pch->bridge, NULL);
	spin_unlock(&pch->upl);

	/* Only modify pchb if phcb->bridge points back to pch.
	 * If not, it implies that there has been a race unbridging (and possibly
	 * even rebridging) pchb.  We should leave pchb alone to avoid either a
	 * refcount underflow, or breaking another established bridge instance.
	 */
	spin_lock(&pchb->upl);
	pchbb = rcu_dereference_protected(pchb->bridge, lockdep_is_held(&pchb->upl));
	if (pchbb == pch)
		RCU_INIT_POINTER(pchb->bridge, NULL);
	spin_unlock(&pchb->upl);

	synchronize_rcu();

	if (pchbb == pch)
		ppp_release_channel(pch);

	ppp_release_channel(pchb);

	return 0;
}

static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	struct ppp_file *pf;
	struct ppp *ppp;
	int err = -EFAULT, val, val2, i;
	struct ppp_idle32 idle32;
	struct ppp_idle64 idle64;
	struct npioctl npi;
	int unit, cflags;
	struct slcompress *vj;
	void __user *argp = (void __user *)arg;
	int __user *p = argp;

	mutex_lock(&ppp_mutex);

	pf = file->private_data;
	if (!pf) {
		err = ppp_unattached_ioctl(current->nsproxy->net_ns,
					   pf, file, cmd, arg);
		goto out;
	}

	if (cmd == PPPIOCDETACH) {
		/*
		 * PPPIOCDETACH is no longer supported as it was heavily broken,
		 * and is only known to have been used by pppd older than
		 * ppp-2.4.2 (released November 2003).
		 */
		pr_warn_once("%s (%d) used obsolete PPPIOCDETACH ioctl\n",
			     current->comm, current->pid);
		err = -EINVAL;
		goto out;
	}

	if (pf->kind == CHANNEL) {
		struct channel *pch, *pchb;
		struct ppp_channel *chan;
		struct ppp_net *pn;

		pch = PF_TO_CHANNEL(pf);

		switch (cmd) {
		case PPPIOCCONNECT:
			if (get_user(unit, p))
				break;
			err = ppp_connect_channel(pch, unit);
			break;

		case PPPIOCDISCONN:
			err = ppp_disconnect_channel(pch);
			break;

		case PPPIOCBRIDGECHAN:
			if (get_user(unit, p))
				break;
			err = -ENXIO;
			pn = ppp_pernet(current->nsproxy->net_ns);
			spin_lock_bh(&pn->all_channels_lock);
			pchb = ppp_find_channel(pn, unit);
			/* Hold a reference to prevent pchb being freed while
			 * we establish the bridge.
			 */
			if (pchb)
				refcount_inc(&pchb->file.refcnt);
			spin_unlock_bh(&pn->all_channels_lock);
			if (!pchb)
				break;
			err = ppp_bridge_channels(pch, pchb);
			/* Drop earlier refcount now bridge establishment is complete */
			ppp_release_channel(pchb);
			break;

		case PPPIOCUNBRIDGECHAN:
			err = ppp_unbridge_channels(pch);
			break;

		default:
			down_read(&pch->chan_sem);
			chan = pch->chan;
			err = -ENOTTY;
			if (chan && chan->ops->ioctl)
				err = chan->ops->ioctl(chan, cmd, arg);
			up_read(&pch->chan_sem);
		}
		goto out;
	}

	if (pf->kind != INTERFACE) {
		/* can't happen */
		pr_err("PPP: not interface or channel??\n");
		err = -EINVAL;
		goto out;
	}

	ppp = PF_TO_PPP(pf);
	switch (cmd) {
	case PPPIOCSMRU:
		if (get_user(val, p))
			break;
		ppp_recv_lock(ppp);
		ppp->mru = val;
		ppp_recv_unlock(ppp);
		err = 0;
		break;

	case PPPIOCSFLAGS:
		if (get_user(val, p))
			break;
		ppp_lock(ppp);
		cflags = ppp->flags & ~val;
#ifdef CONFIG_PPP_MULTILINK
		if (!(ppp->flags & SC_MULTILINK) && (val & SC_MULTILINK))
			ppp->nextseq = 0;
#endif
		ppp->flags = val & SC_FLAG_BITS;
		ppp_unlock(ppp);
		if (cflags & SC_CCP_OPEN)
			ppp_ccp_closed(ppp);
		err = 0;
		break;

	case PPPIOCGFLAGS:
		ppp_lock(ppp);
		val = ppp->flags | ppp->xstate | ppp->rstate;
		ppp_unlock(ppp);
		if (put_user(val, p))
			break;
		err = 0;
		break;

	case PPPIOCSCOMPRESS:
	{
		struct ppp_option_data data;
		if (copy_from_user(&data, argp, sizeof(data)))
			err = -EFAULT;
		else
			err = ppp_set_compress(ppp, &data);
		break;
	}
	case PPPIOCGUNIT:
		if (put_user(ppp->file.index, p))
			break;
		err = 0;
		break;

	case PPPIOCSDEBUG:
		if (get_user(val, p))
			break;
		WRITE_ONCE(ppp->debug, val);
		err = 0;
		break;

	case PPPIOCGDEBUG:
		if (put_user(ppp->debug, p))
			break;
		err = 0;
		break;

	case PPPIOCGIDLE32:
		idle32.xmit_idle = max(0L, (long)(jiffies - READ_ONCE(ppp->last_xmit))) / HZ;
		idle32.recv_idle = max(0L, (long)(jiffies - READ_ONCE(ppp->last_recv))) / HZ;
		if (copy_to_user(argp, &idle32, sizeof(idle32)))
			break;
		err = 0;
		break;

	case PPPIOCGIDLE64:
		idle64.xmit_idle = max(0L, (long)(jiffies - READ_ONCE(ppp->last_xmit))) / HZ;
		idle64.recv_idle = max(0L, (long)(jiffies - READ_ONCE(ppp->last_recv))) / HZ;
		if (copy_to_user(argp, &idle64, sizeof(idle64)))
			break;
		err = 0;
		break;

	case PPPIOCSMAXCID:
		if (get_user(val, p))
			break;
		val2 = 15;
		if ((val >> 16) != 0) {
			val2 = val >> 16;
			val &= 0xffff;
		}
		vj = slhc_init(val2+1, val+1);
		if (IS_ERR(vj)) {
			err = PTR_ERR(vj);
			break;
		}
		ppp_lock(ppp);
		if (ppp->vj)
			slhc_free(ppp->vj);
		ppp->vj = vj;
		ppp_unlock(ppp);
		err = 0;
		break;

	case PPPIOCGNPMODE:
	case PPPIOCSNPMODE:
		if (copy_from_user(&npi, argp, sizeof(npi)))
			break;
		err = proto_to_npindex(npi.protocol);
		if (err < 0)
			break;
		i = err;
		if (cmd == PPPIOCGNPMODE) {
			err = -EFAULT;
			npi.mode = ppp->npmode[i];
			if (copy_to_user(argp, &npi, sizeof(npi)))
				break;
		} else {
			WRITE_ONCE(ppp->npmode[i], npi.mode);
			/* we may be able to transmit more packets now (??) */
			netif_wake_queue(ppp->dev);
		}
		err = 0;
		break;

#ifdef CONFIG_PPP_FILTER
	case PPPIOCSPASS:
	case PPPIOCSACTIVE:
	{
		struct bpf_prog *filter = ppp_get_filter(argp);
		struct bpf_prog **which;

		if (IS_ERR(filter)) {
			err = PTR_ERR(filter);
			break;
		}
		if (cmd == PPPIOCSPASS)
			which = &ppp->pass_filter;
		else
			which = &ppp->active_filter;
		ppp_lock(ppp);
		if (*which)
			bpf_prog_destroy(*which);
		*which = filter;
		ppp_unlock(ppp);
		err = 0;
		break;
	}
#endif /* CONFIG_PPP_FILTER */

#ifdef CONFIG_PPP_MULTILINK
	case PPPIOCSMRRU:
		if (get_user(val, p))
			break;
		ppp_recv_lock(ppp);
		ppp->mrru = val;
		ppp_recv_unlock(ppp);
		err = 0;
		break;
#endif /* CONFIG_PPP_MULTILINK */

	default:
		err = -ENOTTY;
	}

out:
	mutex_unlock(&ppp_mutex);

	return err;
}

#ifdef CONFIG_COMPAT
struct ppp_option_data32 {
	compat_uptr_t		ptr;
	u32			length;
	compat_int_t		transmit;
};
#define PPPIOCSCOMPRESS32	_IOW('t', 77, struct ppp_option_data32)

static long ppp_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	struct ppp_file *pf;
	int err = -ENOIOCTLCMD;
	void __user *argp = (void __user *)arg;

	mutex_lock(&ppp_mutex);

	pf = file->private_data;
	if (pf && pf->kind == INTERFACE) {
		struct ppp *ppp = PF_TO_PPP(pf);
		switch (cmd) {
#ifdef CONFIG_PPP_FILTER
		case PPPIOCSPASS32:
		case PPPIOCSACTIVE32:
		{
			struct bpf_prog *filter = compat_ppp_get_filter(argp);
			struct bpf_prog **which;

			if (IS_ERR(filter)) {
				err = PTR_ERR(filter);
				break;
			}
			if (cmd == PPPIOCSPASS32)
				which = &ppp->pass_filter;
			else
				which = &ppp->active_filter;
			ppp_lock(ppp);
			if (*which)
				bpf_prog_destroy(*which);
			*which = filter;
			ppp_unlock(ppp);
			err = 0;
			break;
		}
#endif /* CONFIG_PPP_FILTER */
		case PPPIOCSCOMPRESS32:
		{
			struct ppp_option_data32 data32;
			if (copy_from_user(&data32, argp, sizeof(data32))) {
				err = -EFAULT;
			} else {
				struct ppp_option_data data = {
					.ptr = compat_ptr(data32.ptr),
					.length = data32.length,
					.transmit = data32.transmit
				};
				err = ppp_set_compress(ppp, &data);
			}
			break;
		}
		}
	}
	mutex_unlock(&ppp_mutex);

	/* all other commands have compatible arguments */
	if (err == -ENOIOCTLCMD)
		err = ppp_ioctl(file, cmd, (unsigned long)compat_ptr(arg));

	return err;
}
#endif

static int ppp_unattached_ioctl(struct net *net, struct ppp_file *pf,
			struct file *file, unsigned int cmd, unsigned long arg)
{
	int unit, err = -EFAULT;
	struct ppp *ppp;
	struct channel *chan;
	struct ppp_net *pn;
	int __user *p = (int __user *)arg;

	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
		return -EPERM;

	switch (cmd) {
	case PPPIOCNEWUNIT:
		/* Create a new ppp unit */
		if (get_user(unit, p))
			break;
		err = ppp_create_interface(net, file, &unit);
		if (err < 0)
			break;

		err = -EFAULT;
		if (put_user(unit, p))
			break;
		err = 0;
		break;

	case PPPIOCATTACH:
		/* Attach to an existing ppp unit */
		if (get_user(unit, p))
			break;
		err = -ENXIO;
		pn = ppp_pernet(net);
		mutex_lock(&pn->all_ppp_mutex);
		ppp = ppp_find_unit(pn, unit);
		if (ppp) {
			refcount_inc(&ppp->file.refcnt);
			file->private_data = &ppp->file;
			err = 0;
		}
		mutex_unlock(&pn->all_ppp_mutex);
		break;

	case PPPIOCATTCHAN:
		if (get_user(unit, p))
			break;
		err = -ENXIO;
		pn = ppp_pernet(net);
		spin_lock_bh(&pn->all_channels_lock);
		chan = ppp_find_channel(pn, unit);
		if (chan) {
			refcount_inc(&chan->file.refcnt);
			file->private_data = &chan->file;
			err = 0;
		}
		spin_unlock_bh(&pn->all_channels_lock);
		break;

	default:
		err = -ENOTTY;
	}

	return err;
}

static const struct file_operations ppp_device_fops = {
	.owner		= THIS_MODULE,
	.read		= ppp_read,
	.write		= ppp_write,
	.poll		= ppp_poll,
	.unlocked_ioctl	= ppp_ioctl,
#ifdef CONFIG_COMPAT
	.compat_ioctl	= ppp_compat_ioctl,
#endif
	.open		= ppp_open,
	.release	= ppp_release,
	.llseek		= noop_llseek,
};

static void ppp_nl_dellink(struct net_device *dev, struct list_head *head);

static __net_init int ppp_init_net(struct net *net)
{
	struct ppp_net *pn = net_generic(net, ppp_net_id);

	idr_init(&pn->units_idr);
	mutex_init(&pn->all_ppp_mutex);

	INIT_LIST_HEAD(&pn->all_channels);
	INIT_LIST_HEAD(&pn->new_channels);

	spin_lock_init(&pn->all_channels_lock);

	return 0;
}

static __net_exit void ppp_exit_rtnl_net(struct net *net,
					 struct list_head *dev_to_kill)
{
	struct ppp_net *pn = net_generic(net, ppp_net_id);
	struct ppp *ppp;
	int id;

	idr_for_each_entry(&pn->units_idr, ppp, id)
		ppp_nl_dellink(ppp->dev, dev_to_kill);
}

static __net_exit void ppp_exit_net(struct net *net)
{
	struct ppp_net *pn = net_generic(net, ppp_net_id);

	mutex_destroy(&pn->all_ppp_mutex);
	idr_destroy(&pn->units_idr);
	WARN_ON_ONCE(!list_empty(&pn->all_channels));
	WARN_ON_ONCE(!list_empty(&pn->new_channels));
}

static struct pernet_operations ppp_net_ops = {
	.init = ppp_init_net,
	.exit_rtnl = ppp_exit_rtnl_net,
	.exit = ppp_exit_net,
	.id   = &ppp_net_id,
	.size = sizeof(struct ppp_net),
};

static int ppp_unit_register(struct ppp *ppp, int unit, bool ifname_is_set)
{
	struct ppp_net *pn = ppp_pernet(ppp->ppp_net);
	int ret;

	mutex_lock(&pn->all_ppp_mutex);

	if (unit < 0) {
		ret = unit_get(&pn->units_idr, ppp, 0);
		if (ret < 0)
			goto err;
		if (!ifname_is_set) {
			while (1) {
				snprintf(ppp->dev->name, IFNAMSIZ, "ppp%i", ret);
				if (!netdev_name_in_use(ppp->ppp_net, ppp->dev->name))
					break;
				unit_put(&pn->units_idr, ret);
				ret = unit_get(&pn->units_idr, ppp, ret + 1);
				if (ret < 0)
					goto err;
			}
		}
	} else {
		/* Caller asked for a specific unit number. Fail with -EEXIST
		 * if unavailable. For backward compatibility, return -EEXIST
		 * too if idr allocation fails; this makes pppd retry without
		 * requesting a specific unit number.
		 */
		if (unit_find(&pn->units_idr, unit)) {
			ret = -EEXIST;
			goto err;
		}
		ret = unit_set(&pn->units_idr, ppp, unit);
		if (ret < 0) {
			/* Rewrite error for backward compatibility */
			ret = -EEXIST;
			goto err;
		}
	}
	ppp->file.index = ret;

	if (!ifname_is_set)
		snprintf(ppp->dev->name, IFNAMSIZ, "ppp%i", ppp->file.index);

	mutex_unlock(&pn->all_ppp_mutex);

	ret = register_netdevice(ppp->dev);
	if (ret < 0)
		goto err_unit;

	atomic_inc(&ppp_unit_count);

	return 0;

err_unit:
	mutex_lock(&pn->all_ppp_mutex);
	unit_put(&pn->units_idr, ppp->file.index);
err:
	mutex_unlock(&pn->all_ppp_mutex);

	return ret;
}

static int ppp_dev_configure(struct net *src_net, struct net_device *dev,
			     const struct ppp_config *conf)
{
	struct ppp *ppp = netdev_priv(dev);
	int indx;
	int err;
	int cpu;

	ppp->dev = dev;
	ppp->ppp_net = src_net;
	ppp->mru = PPP_MRU;
	ppp->owner = conf->file;

	init_ppp_file(&ppp->file, INTERFACE);
	ppp->file.hdrlen = PPP_HDRLEN - 2; /* don't count proto bytes */

	for (indx = 0; indx < NUM_NP; ++indx)
		ppp->npmode[indx] = NPMODE_PASS;
	INIT_LIST_HEAD(&ppp->channels);
	spin_lock_init(&ppp->rlock);
	spin_lock_init(&ppp->wlock);

	ppp->xmit_recursion = alloc_percpu(struct ppp_xmit_recursion);
	if (!ppp->xmit_recursion) {
		err = -ENOMEM;
		goto err1;
	}
	for_each_possible_cpu(cpu) {
		struct ppp_xmit_recursion *xmit_recursion;

		xmit_recursion = per_cpu_ptr(ppp->xmit_recursion, cpu);
		xmit_recursion->owner = NULL;
		local_lock_init(&xmit_recursion->bh_lock);
	}

#ifdef CONFIG_PPP_MULTILINK
	ppp->minseq = -1;
	skb_queue_head_init(&ppp->mrq);
#endif /* CONFIG_PPP_MULTILINK */
#ifdef CONFIG_PPP_FILTER
	ppp->pass_filter = NULL;
	ppp->active_filter = NULL;
#endif /* CONFIG_PPP_FILTER */

	err = ppp_unit_register(ppp, conf->unit, conf->ifname_is_set);
	if (err < 0)
		goto err2;

	conf->file->private_data = &ppp->file;

	return 0;
err2:
	free_percpu(ppp->xmit_recursion);
err1:
	return err;
}

static const struct nla_policy ppp_nl_policy[IFLA_PPP_MAX + 1] = {
	[IFLA_PPP_DEV_FD]	= { .type = NLA_S32 },
};

static int ppp_nl_validate(struct nlattr *tb[], struct nlattr *data[],
			   struct netlink_ext_ack *extack)
{
	if (!data)
		return -EINVAL;

	if (!data[IFLA_PPP_DEV_FD])
		return -EINVAL;
	if (nla_get_s32(data[IFLA_PPP_DEV_FD]) < 0)
		return -EBADF;

	return 0;
}

static int ppp_nl_newlink(struct net_device *dev,
			  struct rtnl_newlink_params *params,
			  struct netlink_ext_ack *extack)
{
	struct net *link_net = rtnl_newlink_link_net(params);
	struct nlattr **data = params->data;
	struct nlattr **tb = params->tb;
	struct ppp_config conf = {
		.unit = -1,
		.ifname_is_set = true,
	};
	struct file *file;
	int err;

	file = fget(nla_get_s32(data[IFLA_PPP_DEV_FD]));
	if (!file)
		return -EBADF;

	/* rtnl_lock is already held here, but ppp_create_interface() locks
	 * ppp_mutex before holding rtnl_lock. Using mutex_trylock() avoids
	 * possible deadlock due to lock order inversion, at the cost of
	 * pushing the problem back to userspace.
	 */
	if (!mutex_trylock(&ppp_mutex)) {
		err = -EBUSY;
		goto out;
	}

	if (file->f_op != &ppp_device_fops || file->private_data) {
		err = -EBADF;
		goto out_unlock;
	}

	conf.file = file;

	/* Don't use device name generated by the rtnetlink layer when ifname
	 * isn't specified. Let ppp_dev_configure() set the device name using
	 * the PPP unit identifer as suffix (i.e. ppp<unit_id>). This allows
	 * userspace to infer the device name using to the PPPIOCGUNIT ioctl.
	 */
	if (!tb[IFLA_IFNAME] || !nla_len(tb[IFLA_IFNAME]) || !*(char *)nla_data(tb[IFLA_IFNAME]))
		conf.ifname_is_set = false;

	err = ppp_dev_configure(link_net, dev, &conf);

out_unlock:
	mutex_unlock(&ppp_mutex);
out:
	fput(file);

	return err;
}

static void ppp_nl_dellink(struct net_device *dev, struct list_head *head)
{
	unregister_netdevice_queue(dev, head);
}

static size_t ppp_nl_get_size(const struct net_device *dev)
{
	return 0;
}

static int ppp_nl_fill_info(struct sk_buff *skb, const struct net_device *dev)
{
	return 0;
}

static struct net *ppp_nl_get_link_net(const struct net_device *dev)
{
	struct ppp *ppp = netdev_priv(dev);

	return READ_ONCE(ppp->ppp_net);
}

static struct rtnl_link_ops ppp_link_ops __read_mostly = {
	.kind		= "ppp",
	.maxtype	= IFLA_PPP_MAX,
	.policy		= ppp_nl_policy,
	.priv_size	= sizeof(struct ppp),
	.setup		= ppp_setup,
	.validate	= ppp_nl_validate,
	.newlink	= ppp_nl_newlink,
	.dellink	= ppp_nl_dellink,
	.get_size	= ppp_nl_get_size,
	.fill_info	= ppp_nl_fill_info,
	.get_link_net	= ppp_nl_get_link_net,
};

#define PPP_MAJOR	108

/* Called at boot time if ppp is compiled into the kernel,
   or at module load time (from init_module) if compiled as a module. */
static int __init ppp_init(void)
{
	int err;

	pr_info("PPP generic driver version " PPP_VERSION "\n");

	err = register_pernet_device(&ppp_net_ops);
	if (err) {
		pr_err("failed to register PPP pernet device (%d)\n", err);
		goto out;
	}

	err = register_chrdev(PPP_MAJOR, "ppp", &ppp_device_fops);
	if (err) {
		pr_err("failed to register PPP device (%d)\n", err);
		goto out_net;
	}

	err = class_register(&ppp_class);
	if (err)
		goto out_chrdev;

	err = rtnl_link_register(&ppp_link_ops);
	if (err) {
		pr_err("failed to register rtnetlink PPP handler\n");
		goto out_class;
	}

	/* not a big deal if we fail here :-) */
	device_create(&ppp_class, NULL, MKDEV(PPP_MAJOR, 0), NULL, "ppp");

	return 0;

out_class:
	class_unregister(&ppp_class);
out_chrdev:
	unregister_chrdev(PPP_MAJOR, "ppp");
out_net:
	unregister_pernet_device(&ppp_net_ops);
out:
	return err;
}

/*
 * Network interface unit routines.
 */
static netdev_tx_t
ppp_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct ppp *ppp = netdev_priv(dev);
	int npi, proto;
	unsigned char *pp;

	npi = ethertype_to_npindex(ntohs(skb->protocol));
	if (npi < 0)
		goto outf;

	/* Drop, accept or reject the packet */
	switch (READ_ONCE(ppp->npmode[npi])) {
	case NPMODE_PASS:
		break;
	case NPMODE_QUEUE:
		/* it would be nice to have a way to tell the network
		   system to queue this one up for later. */
		goto outf;
	case NPMODE_DROP:
	case NPMODE_ERROR:
		goto outf;
	}

	/* Put the 2-byte PPP protocol number on the front,
	   making sure there is room for the address and control fields. */
	if (skb_cow_head(skb, PPP_HDRLEN))
		goto outf;

	pp = skb_push(skb, 2);
	proto = npindex_to_proto[npi];
	put_unaligned_be16(proto, pp);

	skb_scrub_packet(skb, !net_eq(ppp->ppp_net, dev_net(dev)));
	ppp_xmit_process(ppp, skb);

	return NETDEV_TX_OK;

 outf:
	kfree_skb(skb);
	DEV_STATS_INC(dev, tx_dropped);
	return NETDEV_TX_OK;
}

static int
ppp_net_siocdevprivate(struct net_device *dev, struct ifreq *ifr,
		       void __user *addr, int cmd)
{
	struct ppp *ppp = netdev_priv(dev);
	int err = -EFAULT;
	struct ppp_stats stats;
	struct ppp_comp_stats cstats;
	char *vers;

	switch (cmd) {
	case SIOCGPPPSTATS:
		ppp_get_stats(ppp, &stats);
		if (copy_to_user(addr, &stats, sizeof(stats)))
			break;
		err = 0;
		break;

	case SIOCGPPPCSTATS:
		memset(&cstats, 0, sizeof(cstats));
		if (ppp->xc_state)
			ppp->xcomp->comp_stat(ppp->xc_state, &cstats.c);
		if (ppp->rc_state)
			ppp->rcomp->decomp_stat(ppp->rc_state, &cstats.d);
		if (copy_to_user(addr, &cstats, sizeof(cstats)))
			break;
		err = 0;
		break;

	case SIOCGPPPVER:
		vers = PPP_VERSION;
		if (copy_to_user(addr, vers, strlen(vers) + 1))
			break;
		err = 0;
		break;

	default:
		err = -EINVAL;
	}

	return err;
}

static void
ppp_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats64)
{
	stats64->rx_errors        = DEV_STATS_READ(dev, rx_errors);
	stats64->tx_errors        = DEV_STATS_READ(dev, tx_errors);
	stats64->rx_dropped       = DEV_STATS_READ(dev, rx_dropped);
	stats64->tx_dropped       = DEV_STATS_READ(dev, tx_dropped);
	stats64->rx_length_errors = DEV_STATS_READ(dev, rx_length_errors);
	dev_fetch_sw_netstats(stats64, dev->tstats);
}

static int ppp_dev_init(struct net_device *dev)
{
	struct ppp *ppp;

	netdev_lockdep_set_classes(dev);

	ppp = netdev_priv(dev);
	/* Let the netdevice take a reference on the ppp file. This ensures
	 * that ppp_destroy_interface() won't run before the device gets
	 * unregistered.
	 */
	refcount_inc(&ppp->file.refcnt);

	return 0;
}

static void ppp_dev_uninit(struct net_device *dev)
{
	struct ppp *ppp = netdev_priv(dev);
	struct ppp_net *pn = ppp_pernet(ppp->ppp_net);

	ppp_lock(ppp);
	ppp->closing = 1;
	ppp_unlock(ppp);

	mutex_lock(&pn->all_ppp_mutex);
	unit_put(&pn->units_idr, ppp->file.index);
	mutex_unlock(&pn->all_ppp_mutex);

	ppp->owner = NULL;

	ppp->file.dead = 1;
	wake_up_interruptible(&ppp->file.rwait);
}

static void ppp_dev_priv_destructor(struct net_device *dev)
{
	struct ppp *ppp;

	ppp = netdev_priv(dev);
	ppp_release_interface(ppp);
}

static int ppp_fill_forward_path(struct net_device_path_ctx *ctx,
				 struct net_device_path *path)
{
	struct ppp *ppp = netdev_priv(ctx->dev);
	struct ppp_channel *chan;
	struct channel *pch;

	if (ppp->flags & SC_MULTILINK)
		return -EOPNOTSUPP;

	pch = list_first_or_null_rcu(&ppp->channels, struct channel, clist);
	if (!pch)
		return -ENODEV;

	chan = pch->chan;
	if (!chan->ops->fill_forward_path)
		return -EOPNOTSUPP;

	return chan->ops->fill_forward_path(ctx, path, chan);
}

static const struct net_device_ops ppp_netdev_ops = {
	.ndo_init	 = ppp_dev_init,
	.ndo_uninit      = ppp_dev_uninit,
	.ndo_start_xmit  = ppp_start_xmit,
	.ndo_siocdevprivate = ppp_net_siocdevprivate,
	.ndo_get_stats64 = ppp_get_stats64,
	.ndo_fill_forward_path = ppp_fill_forward_path,
};

static const struct device_type ppp_type = {
	.name = "ppp",
};

static void ppp_setup(struct net_device *dev)
{
	dev->netdev_ops = &ppp_netdev_ops;
	SET_NETDEV_DEVTYPE(dev, &ppp_type);

	dev->lltx = true;

	dev->hard_header_len = PPP_HDRLEN;
	dev->mtu = PPP_MRU;
	dev->addr_len = 0;
	dev->tx_queue_len = 3;
	dev->type = ARPHRD_PPP;
	dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
	dev->priv_destructor = ppp_dev_priv_destructor;
	dev->pcpu_stat_type = NETDEV_PCPU_STAT_TSTATS;
	dev->features = NETIF_F_SG | NETIF_F_FRAGLIST;
	dev->hw_features = dev->features;
	netif_keep_dst(dev);
}

/*
 * Transmit-side routines.
 */

/* Called to do any work queued up on the transmit side that can now be done */
static void ppp_xmit_flush(struct ppp *ppp)
{
	struct sk_buff *skb;

	while ((skb = skb_dequeue(&ppp->file.xq))) {
		if (unlikely(!ppp_push(ppp, skb))) {
			skb_queue_head(&ppp->file.xq, skb);
			return;
		}
	}
	/* If there's no work left to do, tell the core net code that we can
	 * accept some more.
	 */
	netif_wake_queue(ppp->dev);
}

static void __ppp_xmit_process(struct ppp *ppp, struct sk_buff *skb)
{
	ppp_xmit_lock(ppp);
	if (unlikely(ppp->closing)) {
		kfree_skb(skb);
		goto out;
	}
	if (unlikely(ppp_prepare_tx_skb(ppp, &skb)))
		goto out;
	/* Fastpath: No backlog, just send the new skb. */
	if (likely(skb_queue_empty(&ppp->file.xq))) {
		if (unlikely(!ppp_push(ppp, skb))) {
			skb_queue_tail(&ppp->file.xq, skb);
			netif_stop_queue(ppp->dev);
		}
		goto out;
	}

	/* Slowpath: Enqueue the new skb and process backlog */
	skb_queue_tail(&ppp->file.xq, skb);
	ppp_xmit_flush(ppp);
out:
	ppp_xmit_unlock(ppp);
}

static void ppp_xmit_process(struct ppp *ppp, struct sk_buff *skb)
{
	struct ppp_xmit_recursion *xmit_recursion;

	local_bh_disable();

	xmit_recursion = this_cpu_ptr(ppp->xmit_recursion);
	if (xmit_recursion->owner == current)
		goto err;
	local_lock_nested_bh(&ppp->xmit_recursion->bh_lock);
	xmit_recursion->owner = current;

	__ppp_xmit_process(ppp, skb);

	xmit_recursion->owner = NULL;
	local_unlock_nested_bh(&ppp->xmit_recursion->bh_lock);
	local_bh_enable();

	return;

err:
	local_bh_enable();

	kfree_skb(skb);

	if (net_ratelimit())
		netdev_err(ppp->dev, "recursion detected\n");
}

static inline struct sk_buff *
pad_compress_skb(struct ppp *ppp, struct sk_buff *skb)
{
	struct sk_buff *new_skb;
	int len;
	int new_skb_size = ppp->dev->mtu +
		ppp->xcomp->comp_extra + ppp->dev->hard_header_len;
	int compressor_skb_size = ppp->dev->mtu +
		ppp->xcomp->comp_extra + PPP_HDRLEN;

	if (skb_linearize(skb))
		return NULL;

	new_skb = alloc_skb(new_skb_size, GFP_ATOMIC);
	if (!new_skb) {
		if (net_ratelimit())
			netdev_err(ppp->dev, "PPP: no memory (comp pkt)\n");
		return NULL;
	}
	if (ppp->dev->hard_header_len > PPP_HDRLEN)
		skb_reserve(new_skb,
			    ppp->dev->hard_header_len - PPP_HDRLEN);

	/* compressor still expects A/C bytes in hdr */
	len = ppp->xcomp->compress(ppp->xc_state, skb->data - 2,
				   new_skb->data, skb->len + 2,
				   compressor_skb_size);
	if (len > 0 && (ppp->flags & SC_CCP_UP)) {
		consume_skb(skb);
		skb = new_skb;
		skb_put(skb, len);
		skb_pull(skb, 2);	/* pull off A/C bytes */
	} else if (len == 0) {
		/* didn't compress, or CCP not up yet */
		consume_skb(new_skb);
		new_skb = skb;
	} else {
		/*
		 * (len < 0)
		 * MPPE requires that we do not send unencrypted
		 * frames.  The compressor will return -1 if we
		 * should drop the frame.  We cannot simply test
		 * the compress_proto because MPPE and MPPC share
		 * the same number.
		 */
		if (net_ratelimit())
			netdev_err(ppp->dev, "ppp: compressor dropped pkt\n");
		consume_skb(new_skb);
		new_skb = NULL;
	}
	return new_skb;
}

/*
 * Compress and prepare to send a frame.
 * The caller should have locked the xmit path.
 * Returns 1 if the skb was consumed, 0 if it can be passed to ppp_push().
 * @pskb is updated if a compressor is in use.
 */
static int
ppp_prepare_tx_skb(struct ppp *ppp, struct sk_buff **pskb)
{
	struct sk_buff *skb = *pskb;
	int proto = PPP_PROTO(skb);
	struct sk_buff *new_skb;
	int len;
	unsigned char *cp;

	skb->dev = ppp->dev;

	if (proto < 0x8000) {
#ifdef CONFIG_PPP_FILTER
		/* check if the packet passes the pass and active filters.
		 * See comment for PPP_FILTER_OUTBOUND_TAG above.
		 */
		*(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_OUTBOUND_TAG);
		if (ppp->pass_filter &&
		    bpf_prog_run(ppp->pass_filter, skb) == 0) {
			if (READ_ONCE(ppp->debug) & 1)
				netdev_printk(KERN_DEBUG, ppp->dev,
					      "PPP: outbound frame "
					      "not passed\n");
			kfree_skb(skb);
			return 1;
		}
		/* if this packet passes the active filter, record the time */
		if (!(ppp->active_filter &&
		      bpf_prog_run(ppp->active_filter, skb) == 0))
			WRITE_ONCE(ppp->last_xmit, jiffies);
		skb_pull(skb, 2);
#else
		/* for data packets, record the time */
		WRITE_ONCE(ppp->last_xmit, jiffies);
#endif /* CONFIG_PPP_FILTER */
	}

	dev_sw_netstats_tx_add(ppp->dev, 1, skb->len - PPP_PROTO_LEN);

	switch (proto) {
	case PPP_IP:
		if (!ppp->vj || (ppp->flags & SC_COMP_TCP) == 0)
			break;

		if (skb_linearize(skb))
			goto drop;

		/* try to do VJ TCP header compression */
		new_skb = alloc_skb(skb->len + ppp->dev->hard_header_len - 2,
				    GFP_ATOMIC);
		if (!new_skb) {
			netdev_err(ppp->dev, "PPP: no memory (VJ comp pkt)\n");
			goto drop;
		}
		skb_reserve(new_skb, ppp->dev->hard_header_len - 2);
		cp = skb->data + 2;
		len = slhc_compress(ppp->vj, cp, skb->len - 2,
				    new_skb->data + 2, &cp,
				    !(ppp->flags & SC_NO_TCP_CCID));
		if (cp == skb->data + 2) {
			/* didn't compress */
			consume_skb(new_skb);
		} else {
			if (cp[0] & SL_TYPE_COMPRESSED_TCP) {
				proto = PPP_VJC_COMP;
				cp[0] &= ~SL_TYPE_COMPRESSED_TCP;
			} else {
				proto = PPP_VJC_UNCOMP;
				cp[0] = skb->data[2];
			}
			consume_skb(skb);
			skb = new_skb;
			*pskb = skb;
			cp = skb_put(skb, len + 2);
			cp[0] = 0;
			cp[1] = proto;
		}
		break;

	case PPP_CCP:
		/* peek at outbound CCP frames */
		ppp_ccp_peek(ppp, skb, 0);
		break;
	}

	/* try to do packet compression */
	if ((ppp->xstate & SC_COMP_RUN) && ppp->xc_state &&
	    proto != PPP_LCP && proto != PPP_CCP) {
		if (!(ppp->flags & SC_CCP_UP) && (ppp->flags & SC_MUST_COMP)) {
			if (net_ratelimit())
				netdev_err(ppp->dev,
					   "ppp: compression required but "
					   "down - pkt dropped.\n");
			goto drop;
		}
		new_skb = pad_compress_skb(ppp, skb);
		if (!new_skb)
			goto drop;
		skb = new_skb;
		*pskb = skb;
	}

	/*
	 * If we are waiting for traffic (demand dialling),
	 * queue it up for pppd to receive.
	 */
	if (ppp->flags & SC_LOOP_TRAFFIC) {
		if (ppp->file.rq.qlen > PPP_MAX_RQLEN)
			goto drop;
		skb_queue_tail(&ppp->file.rq, skb);
		wake_up_interruptible(&ppp->file.rwait);
		return 1;
	}

	return 0;

 drop:
	kfree_skb(skb);
	DEV_STATS_INC(ppp->dev, tx_errors);
	return 1;
}

/*
 * Try to send the frame.
 * The caller should have the xmit path locked.
 * Returns 1 if the skb was consumed, 0 if not.
 */
static int
ppp_push(struct ppp *ppp, struct sk_buff *skb)
{
	struct list_head *list;
	struct channel *pch;

	list = &ppp->channels;
	if (list_empty(list)) {
		/* nowhere to send the packet, just drop it */
		kfree_skb(skb);
		return 1;
	}

	if ((ppp->flags & SC_MULTILINK) == 0) {
		struct ppp_channel *chan;
		int ret;
		/* not doing multilink: send it down the first channel */
		list = list->next;
		pch = list_entry(list, struct channel, clist);

		spin_lock(&pch->downl);
		chan = pch->chan;
		if (unlikely(!chan->direct_xmit && skb_linearize(skb))) {
			/* channel requires a linear skb but linearization
			 * failed
			 */
			kfree_skb(skb);
			ret = 1;
			goto out;
		}

		ret = chan->ops->start_xmit(chan, skb);

out:
		spin_unlock(&pch->downl);
		return ret;
	}

#ifdef CONFIG_PPP_MULTILINK
	/* Multilink: fragment the packet over as many links
	   as can take the packet at the moment. */
	if (!ppp_mp_explode(ppp, skb))
		return 0;
#endif /* CONFIG_PPP_MULTILINK */

	kfree_skb(skb);
	return 1;
}

#ifdef CONFIG_PPP_MULTILINK
static bool mp_protocol_compress __read_mostly = true;
module_param(mp_protocol_compress, bool, 0644);
MODULE_PARM_DESC(mp_protocol_compress,
		 "compress protocol id in multilink fragments");

/*
 * Divide a packet to be transmitted into fragments and
 * send them out the individual links.
 */
static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb)
{
	int len, totlen;
	int i, bits, hdrlen, mtu;
	int flen;
	int navail, nfree, nzero;
	int nbigger;
	int totspeed;
	int totfree;
	unsigned char *p, *q;
	struct list_head *list;
	struct channel *pch;
	struct sk_buff *frag;
	struct ppp_channel *chan;

	totspeed = 0; /*total bitrate of the bundle*/
	nfree = 0; /* # channels which have no packet already queued */
	navail = 0; /* total # of usable channels (not deregistered) */
	nzero = 0; /* number of channels with zero speed associated*/
	totfree = 0; /*total # of channels available and
				  *having no queued packets before
				  *starting the fragmentation*/

	hdrlen = (ppp->flags & SC_MP_XSHORTSEQ)? MPHDRLEN_SSN: MPHDRLEN;
	i = 0;
	list_for_each_entry(pch, &ppp->channels, clist) {
		pch->avail = 1;
		navail++;
		pch->speed = pch->chan->speed;

		if (skb_queue_empty(&pch->file.xq) || !pch->had_frag) {
			if (pch->speed == 0)
				nzero++;
			else
				totspeed += pch->speed;

			pch->avail = 2;
			++nfree;
			++totfree;
		}
		if (!pch->had_frag && i < ppp->nxchan)
			ppp->nxchan = i;

		++i;
	}
	/*
	 * Don't start sending this packet unless at least half of
	 * the channels are free.  This gives much better TCP
	 * performance if we have a lot of channels.
	 */
	if (nfree == 0 || nfree < navail / 2)
		return 0; /* can't take now, leave it in transmit queue */

	/* Do protocol field compression */
	if (skb_linearize(skb))
		goto err_linearize;
	p = skb->data;
	len = skb->len;
	if (*p == 0 && mp_protocol_compress) {
		++p;
		--len;
	}

	totlen = len;
	nbigger = len % nfree;

	/* skip to the channel after the one we last used
	   and start at that one */
	list = &ppp->channels;
	for (i = 0; i < ppp->nxchan; ++i) {
		list = list->next;
		if (list == &ppp->channels) {
			i = 0;
			break;
		}
	}

	/* create a fragment for each channel */
	bits = B;
	while (len > 0) {
		list = list->next;
		if (list == &ppp->channels) {
			i = 0;
			continue;
		}
		pch = list_entry(list, struct channel, clist);
		++i;
		if (!pch->avail)
			continue;

		/*
		 * Skip this channel if it has a fragment pending already and
		 * we haven't given a fragment to all of the free channels.
		 */
		if (pch->avail == 1) {
			if (nfree > 0)
				continue;
		} else {
			pch->avail = 1;
		}

		spin_lock(&pch->downl);
		/*
		*if the channel speed is not set divide
		*the packet evenly among the free channels;
		*otherwise divide it according to the speed
		*of the channel we are going to transmit on
		*/
		flen = len;
		if (nfree > 0) {
			if (pch->speed == 0) {
				flen = len/nfree;
				if (nbigger > 0) {
					flen++;
					nbigger--;
				}
			} else {
				flen = (((totfree - nzero)*(totlen + hdrlen*totfree)) /
					((totspeed*totfree)/pch->speed)) - hdrlen;
				if (nbigger > 0) {
					flen += ((totfree - nzero)*pch->speed)/totspeed;
					nbigger -= ((totfree - nzero)*pch->speed)/
							totspeed;
				}
			}
			nfree--;
		}

		/*
		 *check if we are on the last channel or
		 *we exceded the length of the data to
		 *fragment
		 */
		if ((nfree <= 0) || (flen > len))
			flen = len;
		/*
		 *it is not worth to tx on slow channels:
		 *in that case from the resulting flen according to the
		 *above formula will be equal or less than zero.
		 *Skip the channel in this case
		 */
		if (flen <= 0) {
			pch->avail = 2;
			spin_unlock(&pch->downl);
			continue;
		}

		/*
		 * hdrlen includes the 2-byte PPP protocol field, but the
		 * MTU counts only the payload excluding the protocol field.
		 * (RFC1661 Section 2)
		 */
		mtu = pch->chan->mtu - (hdrlen - 2);
		if (mtu < 4)
			mtu = 4;
		if (flen > mtu)
			flen = mtu;
		if (flen == len)
			bits |= E;
		frag = alloc_skb(flen + hdrlen + (flen == 0), GFP_ATOMIC);
		if (!frag)
			goto noskb;
		q = skb_put(frag, flen + hdrlen);

		/* make the MP header */
		put_unaligned_be16(PPP_MP, q);
		if (ppp->flags & SC_MP_XSHORTSEQ) {
			q[2] = bits + ((ppp->nxseq >> 8) & 0xf);
			q[3] = ppp->nxseq;
		} else {
			q[2] = bits;
			q[3] = ppp->nxseq >> 16;
			q[4] = ppp->nxseq >> 8;
			q[5] = ppp->nxseq;
		}

		memcpy(q + hdrlen, p, flen);

		/* try to send it down the channel */
		chan = pch->chan;
		if (!skb_queue_empty(&pch->file.xq) ||
			!chan->ops->start_xmit(chan, frag))
			skb_queue_tail(&pch->file.xq, frag);
		pch->had_frag = 1;
		p += flen;
		len -= flen;
		++ppp->nxseq;
		bits = 0;
		spin_unlock(&pch->downl);
	}
	ppp->nxchan = i;

	return 1;

 noskb:
	spin_unlock(&pch->downl);
 err_linearize:
	if (READ_ONCE(ppp->debug) & 1)
		netdev_err(ppp->dev, "PPP: no memory (fragment)\n");
	DEV_STATS_INC(ppp->dev, tx_errors);
	++ppp->nxseq;
	return 1;	/* abandon the frame */
}
#endif /* CONFIG_PPP_MULTILINK */

/* Try to send data out on a channel */
static void __ppp_channel_push(struct channel *pch, struct ppp *ppp)
{
	struct sk_buff *skb;

	spin_lock(&pch->downl);
	if (pch->chan) {
		while (!skb_queue_empty(&pch->file.xq)) {
			skb = skb_dequeue(&pch->file.xq);
			if (!pch->chan->ops->start_xmit(pch->chan, skb)) {
				/* put the packet back and try again later */
				skb_queue_head(&pch->file.xq, skb);
				break;
			}
		}
	} else {
		/* channel got deregistered */
		skb_queue_purge(&pch->file.xq);
	}
	spin_unlock(&pch->downl);
	/* see if there is anything from the attached unit to be sent */
	if (skb_queue_empty(&pch->file.xq)) {
		if (ppp) {
			ppp_xmit_lock(ppp);
			if (!ppp->closing)
				ppp_xmit_flush(ppp);
			ppp_xmit_unlock(ppp);
		}
	}
}

static void ppp_channel_push(struct channel *pch)
{
	struct ppp_xmit_recursion *xmit_recursion;
	struct ppp *ppp;

	rcu_read_lock_bh();
	ppp = rcu_dereference_bh(pch->ppp);
	if (ppp) {
		xmit_recursion = this_cpu_ptr(ppp->xmit_recursion);
		local_lock_nested_bh(&ppp->xmit_recursion->bh_lock);
		xmit_recursion->owner = current;
		__ppp_channel_push(pch, ppp);
		xmit_recursion->owner = NULL;
		local_unlock_nested_bh(&ppp->xmit_recursion->bh_lock);
	} else {
		__ppp_channel_push(pch, NULL);
	}
	rcu_read_unlock_bh();
}

/*
 * Receive-side routines.
 */

struct ppp_mp_skb_parm {
	u32		sequence;
	u8		BEbits;
};
#define PPP_MP_CB(skb)	((struct ppp_mp_skb_parm *)((skb)->cb))

static inline void
ppp_do_recv(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
{
	ppp_recv_lock(ppp);
	if (!ppp->closing)
		ppp_receive_frame(ppp, skb, pch);
	else
		kfree_skb(skb);
	ppp_recv_unlock(ppp);
}

/**
 * __ppp_decompress_proto - Decompress protocol field, slim version.
 * @skb: Socket buffer where protocol field should be decompressed. It must have
 *	 at least 1 byte of head room and 1 byte of linear data. First byte of
 *	 data must be a protocol field byte.
 *
 * Decompress protocol field in PPP header if it's compressed, e.g. when
 * Protocol-Field-Compression (PFC) was negotiated. No checks w.r.t. skb data
 * length are done in this function.
 */
static void __ppp_decompress_proto(struct sk_buff *skb)
{
	if (ppp_skb_is_compressed_proto(skb))
		*(u8 *)skb_push(skb, 1) = 0x00;
}

/**
 * ppp_decompress_proto - Check skb data room and decompress protocol field.
 * @skb: Socket buffer where protocol field should be decompressed. First byte
 *	 of data must be a protocol field byte.
 *
 * Decompress protocol field in PPP header if it's compressed, e.g. when
 * Protocol-Field-Compression (PFC) was negotiated. This function also makes
 * sure that skb data room is sufficient for Protocol field, before and after
 * decompression.
 *
 * Return: true - decompressed successfully, false - not enough room in skb.
 */
static bool ppp_decompress_proto(struct sk_buff *skb)
{
	/* At least one byte should be present (if protocol is compressed) */
	if (!pskb_may_pull(skb, 1))
		return false;

	__ppp_decompress_proto(skb);

	/* Protocol field should occupy 2 bytes when not compressed */
	return pskb_may_pull(skb, 2);
}

/* Attempt to handle a frame via. a bridged channel, if one exists.
 * If the channel is bridged, the frame is consumed by the bridge.
 * If not, the caller must handle the frame by normal recv mechanisms.
 * Returns true if the frame is consumed, false otherwise.
 */
static bool ppp_channel_bridge_input(struct channel *pch, struct sk_buff *skb)
{
	struct channel *pchb;

	rcu_read_lock();
	pchb = rcu_dereference(pch->bridge);
	if (!pchb)
		goto out_rcu;

	spin_lock_bh(&pchb->downl);
	if (!pchb->chan) {
		/* channel got unregistered */
		kfree_skb(skb);
		goto outl;
	}

	skb_scrub_packet(skb, !net_eq(pch->chan_net, pchb->chan_net));
	if (!pchb->chan->ops->start_xmit(pchb->chan, skb))
		kfree_skb(skb);

outl:
	spin_unlock_bh(&pchb->downl);
out_rcu:
	rcu_read_unlock();

	/* If pchb is set then we've consumed the packet */
	return !!pchb;
}

void
ppp_input(struct ppp_channel *chan, struct sk_buff *skb)
{
	struct channel *pch = chan->ppp;
	struct ppp *ppp;
	int proto;

	if (!pch) {
		kfree_skb(skb);
		return;
	}

	/* If the channel is bridged, transmit via. bridge */
	if (ppp_channel_bridge_input(pch, skb))
		return;

	rcu_read_lock_bh();
	ppp = rcu_dereference_bh(pch->ppp);
	if (!ppp_decompress_proto(skb)) {
		kfree_skb(skb);
		if (ppp) {
			DEV_STATS_INC(ppp->dev, rx_length_errors);
			ppp_receive_error(ppp);
		}
		goto done;
	}

	proto = PPP_PROTO(skb);
	if (!ppp || proto >= 0xc000 || proto == PPP_CCPFRAG) {
		/* put it on the channel queue */
		skb_queue_tail(&pch->file.rq, skb);
		/* drop old frames if queue too long */
		while (pch->file.rq.qlen > PPP_MAX_RQLEN &&
		       (skb = skb_dequeue(&pch->file.rq)))
			kfree_skb(skb);
		wake_up_interruptible(&pch->file.rwait);
	} else {
		ppp_do_recv(ppp, skb, pch);
	}

done:
	rcu_read_unlock_bh();
}

void
ppp_input_error(struct ppp_channel *chan)
{
	struct channel *pch = chan->ppp;
	struct ppp *ppp;

	if (!pch)
		return;

	rcu_read_lock_bh();
	ppp = rcu_dereference_bh(pch->ppp);
	if (ppp) {
		ppp_recv_lock(ppp);
		ppp_receive_error(ppp);
		ppp_recv_unlock(ppp);
	}
	rcu_read_unlock_bh();
}

/*
 * We come in here to process a received frame.
 * The receive side of the ppp unit is locked.
 */
static void
ppp_receive_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
{
	skb_checksum_complete_unset(skb);
#ifdef CONFIG_PPP_MULTILINK
	/* XXX do channel-level decompression here */
	if (PPP_PROTO(skb) == PPP_MP)
		ppp_receive_mp_frame(ppp, skb, pch);
	else
#endif /* CONFIG_PPP_MULTILINK */
		ppp_receive_nonmp_frame(ppp, skb);
}

static void
ppp_receive_error(struct ppp *ppp)
{
	DEV_STATS_INC(ppp->dev, rx_errors);
	if (ppp->vj)
		slhc_toss(ppp->vj);
}

static void
ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb)
{
	struct sk_buff *ns;
	int proto, len, npi;

	/*
	 * Decompress the frame, if compressed.
	 * Note that some decompressors need to see uncompressed frames
	 * that come in as well as compressed frames.
	 */
	if (ppp->rc_state && (ppp->rstate & SC_DECOMP_RUN) &&
	    (ppp->rstate & (SC_DC_FERROR | SC_DC_ERROR)) == 0)
		skb = ppp_decompress_frame(ppp, skb);

	if (ppp->flags & SC_MUST_COMP && ppp->rstate & SC_DC_FERROR)
		goto err;

	/* At this point the "Protocol" field MUST be decompressed, either in
	 * ppp_input(), ppp_decompress_frame() or in ppp_receive_mp_frame().
	 */
	proto = PPP_PROTO(skb);
	switch (proto) {
	case PPP_VJC_COMP:
		/* decompress VJ compressed packets */
		if (!ppp->vj || (ppp->flags & SC_REJ_COMP_TCP))
			goto err;

		if (skb_tailroom(skb) < 124 || skb_cloned(skb)) {
			/* copy to a new sk_buff with more tailroom */
			ns = dev_alloc_skb(skb->len + 128);
			if (!ns) {
				netdev_err(ppp->dev, "PPP: no memory "
					   "(VJ decomp)\n");
				goto err;
			}
			skb_reserve(ns, 2);
			skb_copy_bits(skb, 0, skb_put(ns, skb->len), skb->len);
			consume_skb(skb);
			skb = ns;
		}
		else
			skb->ip_summed = CHECKSUM_NONE;

		len = slhc_uncompress(ppp->vj, skb->data + 2, skb->len - 2);
		if (len <= 0) {
			netdev_printk(KERN_DEBUG, ppp->dev,
				      "PPP: VJ decompression error\n");
			goto err;
		}
		len += 2;
		if (len > skb->len)
			skb_put(skb, len - skb->len);
		else if (len < skb->len)
			skb_trim(skb, len);
		proto = PPP_IP;
		break;

	case PPP_VJC_UNCOMP:
		if (!ppp->vj || (ppp->flags & SC_REJ_COMP_TCP))
			goto err;

		/* Until we fix the decompressor need to make sure
		 * data portion is linear.
		 */
		if (!pskb_may_pull(skb, skb->len))
			goto err;

		if (slhc_remember(ppp->vj, skb->data + 2, skb->len - 2) <= 0) {
			netdev_err(ppp->dev, "PPP: VJ uncompressed error\n");
			goto err;
		}
		proto = PPP_IP;
		break;

	case PPP_CCP:
		ppp_ccp_peek(ppp, skb, 1);
		break;
	}

	dev_sw_netstats_rx_add(ppp->dev, skb->len - PPP_PROTO_LEN);

	npi = proto_to_npindex(proto);
	if (npi < 0) {
		/* control or unknown frame - pass it to pppd */
		skb_queue_tail(&ppp->file.rq, skb);
		/* limit queue length by dropping old frames */
		while (ppp->file.rq.qlen > PPP_MAX_RQLEN &&
		       (skb = skb_dequeue(&ppp->file.rq)))
			kfree_skb(skb);
		/* wake up any process polling or blocking on read */
		wake_up_interruptible(&ppp->file.rwait);

	} else {
		/* network protocol frame - give it to the kernel */

#ifdef CONFIG_PPP_FILTER
		if (ppp->pass_filter || ppp->active_filter) {
			if (skb_unclone(skb, GFP_ATOMIC))
				goto err;
			/* Check if the packet passes the pass and active filters.
			 * See comment for PPP_FILTER_INBOUND_TAG above.
			 */
			*(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG);
			if (ppp->pass_filter &&
			    bpf_prog_run(ppp->pass_filter, skb) == 0) {
				if (READ_ONCE(ppp->debug) & 1)
					netdev_printk(KERN_DEBUG, ppp->dev,
						      "PPP: inbound frame "
						      "not passed\n");
				kfree_skb(skb);
				return;
			}
			if (!(ppp->active_filter &&
			      bpf_prog_run(ppp->active_filter, skb) == 0))
				WRITE_ONCE(ppp->last_recv, jiffies);
			__skb_pull(skb, 2);
		} else
#endif /* CONFIG_PPP_FILTER */
			WRITE_ONCE(ppp->last_recv, jiffies);

		if ((ppp->dev->flags & IFF_UP) == 0 ||
		    READ_ONCE(ppp->npmode[npi]) != NPMODE_PASS) {
			kfree_skb(skb);
		} else {
			/* chop off protocol */
			skb_pull_rcsum(skb, 2);
			skb->dev = ppp->dev;
			skb->protocol = htons(npindex_to_ethertype[npi]);
			skb_reset_mac_header(skb);
			skb_scrub_packet(skb, !net_eq(ppp->ppp_net,
						      dev_net(ppp->dev)));
			netif_rx(skb);
		}
	}
	return;

 err:
	kfree_skb(skb);
	ppp_receive_error(ppp);
}

static struct sk_buff *
ppp_decompress_frame(struct ppp *ppp, struct sk_buff *skb)
{
	int proto = PPP_PROTO(skb);
	struct sk_buff *ns;
	int len;

	/* Until we fix all the decompressor's need to make sure
	 * data portion is linear.
	 */
	if (!pskb_may_pull(skb, skb->len))
		goto err;

	if (proto == PPP_COMP) {
		int obuff_size;

		switch(ppp->rcomp->compress_proto) {
		case CI_MPPE:
			obuff_size = ppp->mru + PPP_HDRLEN + 1;
			break;
		default:
			obuff_size = ppp->mru + PPP_HDRLEN;
			break;
		}

		ns = dev_alloc_skb(obuff_size);
		if (!ns) {
			netdev_err(ppp->dev, "ppp_decompress_frame: "
				   "no memory\n");
			goto err;
		}
		/* the decompressor still expects the A/C bytes in the hdr */
		len = ppp->rcomp->decompress(ppp->rc_state, skb->data - 2,
				skb->len + 2, ns->data, obuff_size);
		if (len < 0) {
			/* Pass the compressed frame to pppd as an
			   error indication. */
			if (len == DECOMP_FATALERROR)
				ppp->rstate |= SC_DC_FERROR;
			kfree_skb(ns);
			goto err;
		}

		consume_skb(skb);
		skb = ns;
		skb_put(skb, len);
		skb_pull(skb, 2);	/* pull off the A/C bytes */

		/* Don't call __ppp_decompress_proto() here, but instead rely on
		 * corresponding algo (mppe/bsd/deflate) to decompress it.
		 */
	} else {
		/* Uncompressed frame - pass to decompressor so it
		   can update its dictionary if necessary. */
		if (ppp->rcomp->incomp)
			ppp->rcomp->incomp(ppp->rc_state, skb->data - 2,
					   skb->len + 2);
	}

	return skb;

 err:
	ppp->rstate |= SC_DC_ERROR;
	ppp_receive_error(ppp);
	return skb;
}

#ifdef CONFIG_PPP_MULTILINK
/*
 * Receive a multilink frame.
 * We put it on the reconstruction queue and then pull off
 * as many completed frames as we can.
 */
static void
ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch)
{
	u32 mask, seq;
	struct channel *ch;
	int mphdrlen = (ppp->flags & SC_MP_SHORTSEQ)? MPHDRLEN_SSN: MPHDRLEN;

	if (!pskb_may_pull(skb, mphdrlen + 1) || ppp->mrru == 0)
		goto err;		/* no good, throw it away */

	/* Decode sequence number and begin/end bits */
	if (ppp->flags & SC_MP_SHORTSEQ) {
		seq = ((skb->data[2] & 0x0f) << 8) | skb->data[3];
		mask = 0xfff;
	} else {
		seq = (skb->data[3] << 16) | (skb->data[4] << 8)| skb->data[5];
		mask = 0xffffff;
	}
	PPP_MP_CB(skb)->BEbits = skb->data[2];
	skb_pull(skb, mphdrlen);	/* pull off PPP and MP headers */

	/*
	 * Do protocol ID decompression on the first fragment of each packet.
	 * We have to do that here, because ppp_receive_nonmp_frame() expects
	 * decompressed protocol field.
	 */
	if (PPP_MP_CB(skb)->BEbits & B)
		__ppp_decompress_proto(skb);

	/*
	 * Expand sequence number to 32 bits, making it as close
	 * as possible to ppp->minseq.
	 */
	seq |= ppp->minseq & ~mask;
	if ((int)(ppp->minseq - seq) > (int)(mask >> 1))
		seq += mask + 1;
	else if ((int)(seq - ppp->minseq) > (int)(mask >> 1))
		seq -= mask + 1;	/* should never happen */
	PPP_MP_CB(skb)->sequence = seq;
	pch->lastseq = seq;

	/*
	 * If this packet comes before the next one we were expecting,
	 * drop it.
	 */
	if (seq_before(seq, ppp->nextseq)) {
		kfree_skb(skb);
		DEV_STATS_INC(ppp->dev, rx_dropped);
		ppp_receive_error(ppp);
		return;
	}

	/*
	 * Reevaluate minseq, the minimum over all channels of the
	 * last sequence number received on each channel.  Because of
	 * the increasing sequence number rule, we know that any fragment
	 * before `minseq' which hasn't arrived is never going to arrive.
	 * The list of channels can't change because we have the receive
	 * side of the ppp unit locked.
	 */
	list_for_each_entry(ch, &ppp->channels, clist) {
		if (seq_before(ch->lastseq, seq))
			seq = ch->lastseq;
	}
	if (seq_before(ppp->minseq, seq))
		ppp->minseq = seq;

	/* Put the fragment on the reconstruction queue */
	ppp_mp_insert(ppp, skb);

	/* If the queue is getting long, don't wait any longer for packets
	   before the start of the queue. */
	if (skb_queue_len(&ppp->mrq) >= PPP_MP_MAX_QLEN) {
		struct sk_buff *mskb = skb_peek(&ppp->mrq);
		if (seq_before(ppp->minseq, PPP_MP_CB(mskb)->sequence))
			ppp->minseq = PPP_MP_CB(mskb)->sequence;
	}

	/* Pull completed packets off the queue and receive them. */
	while ((skb = ppp_mp_reconstruct(ppp))) {
		if (pskb_may_pull(skb, 2))
			ppp_receive_nonmp_frame(ppp, skb);
		else {
			DEV_STATS_INC(ppp->dev, rx_length_errors);
			kfree_skb(skb);
			ppp_receive_error(ppp);
		}
	}

	return;

 err:
	kfree_skb(skb);
	ppp_receive_error(ppp);
}

/*
 * Insert a fragment on the MP reconstruction queue.
 * The queue is ordered by increasing sequence number.
 */
static void
ppp_mp_insert(struct ppp *ppp, struct sk_buff *skb)
{
	struct sk_buff *p;
	struct sk_buff_head *list = &ppp->mrq;
	u32 seq = PPP_MP_CB(skb)->sequence;

	/* N.B. we don't need to lock the list lock because we have the
	   ppp unit receive-side lock. */
	skb_queue_walk(list, p) {
		if (seq_before(seq, PPP_MP_CB(p)->sequence))
			break;
	}
	__skb_queue_before(list, p, skb);
}

/*
 * Reconstruct a packet from the MP fragment queue.
 * We go through increasing sequence numbers until we find a
 * complete packet, or we get to the sequence number for a fragment
 * which hasn't arrived but might still do so.
 */
static struct sk_buff *
ppp_mp_reconstruct(struct ppp *ppp)
{
	u32 seq = ppp->nextseq;
	u32 minseq = ppp->minseq;
	struct sk_buff_head *list = &ppp->mrq;
	struct sk_buff *p, *tmp;
	struct sk_buff *head, *tail;
	struct sk_buff *skb = NULL;
	int lost = 0, len = 0;

	if (ppp->mrru == 0)	/* do nothing until mrru is set */
		return NULL;
	head = __skb_peek(list);
	tail = NULL;
	skb_queue_walk_safe(list, p, tmp) {
	again:
		if (seq_before(PPP_MP_CB(p)->sequence, seq)) {
			/* this can't happen, anyway ignore the skb */
			netdev_err(ppp->dev, "ppp_mp_reconstruct bad "
				   "seq %u < %u\n",
				   PPP_MP_CB(p)->sequence, seq);
			__skb_unlink(p, list);
			kfree_skb(p);
			continue;
		}
		if (PPP_MP_CB(p)->sequence != seq) {
			u32 oldseq;
			/* Fragment `seq' is missing.  If it is after
			   minseq, it might arrive later, so stop here. */
			if (seq_after(seq, minseq))
				break;
			/* Fragment `seq' is lost, keep going. */
			lost = 1;
			oldseq = seq;
			seq = seq_before(minseq, PPP_MP_CB(p)->sequence)?
				minseq + 1: PPP_MP_CB(p)->sequence;

			if (READ_ONCE(ppp->debug) & 1)
				netdev_printk(KERN_DEBUG, ppp->dev,
					      "lost frag %u..%u\n",
					      oldseq, seq-1);

			goto again;
		}

		/*
		 * At this point we know that all the fragments from
		 * ppp->nextseq to seq are either present or lost.
		 * Also, there are no complete packets in the queue
		 * that have no missing fragments and end before this
		 * fragment.
		 */

		/* B bit set indicates this fragment starts a packet */
		if (PPP_MP_CB(p)->BEbits & B) {
			head = p;
			lost = 0;
			len = 0;
		}

		len += p->len;

		/* Got a complete packet yet? */
		if (lost == 0 && (PPP_MP_CB(p)->BEbits & E) &&
		    (PPP_MP_CB(head)->BEbits & B)) {
			if (len > ppp->mrru + 2) {
				DEV_STATS_INC(ppp->dev, rx_length_errors);
				netdev_printk(KERN_DEBUG, ppp->dev,
					      "PPP: reconstructed packet"
					      " is too long (%d)\n", len);
			} else {
				tail = p;
				break;
			}
			ppp->nextseq = seq + 1;
		}

		/*
		 * If this is the ending fragment of a packet,
		 * and we haven't found a complete valid packet yet,
		 * we can discard up to and including this fragment.
		 */
		if (PPP_MP_CB(p)->BEbits & E) {
			struct sk_buff *tmp2;

			skb_queue_reverse_walk_from_safe(list, p, tmp2) {
				if (READ_ONCE(ppp->debug) & 1)
					netdev_printk(KERN_DEBUG, ppp->dev,
						      "discarding frag %u\n",
						      PPP_MP_CB(p)->sequence);
				__skb_unlink(p, list);
				kfree_skb(p);
			}
			head = skb_peek(list);
			if (!head)
				break;
		}
		++seq;
	}

	/* If we have a complete packet, copy it all into one skb. */
	if (tail != NULL) {
		/* If we have discarded any fragments,
		   signal a receive error. */
		if (PPP_MP_CB(head)->sequence != ppp->nextseq) {
			skb_queue_walk_safe(list, p, tmp) {
				if (p == head)
					break;
				if (READ_ONCE(ppp->debug) & 1)
					netdev_printk(KERN_DEBUG, ppp->dev,
						      "discarding frag %u\n",
						      PPP_MP_CB(p)->sequence);
				__skb_unlink(p, list);
				kfree_skb(p);
			}

			if (READ_ONCE(ppp->debug) & 1)
				netdev_printk(KERN_DEBUG, ppp->dev,
					      "  missed pkts %u..%u\n",
					      ppp->nextseq,
					      PPP_MP_CB(head)->sequence-1);
			DEV_STATS_INC(ppp->dev, rx_dropped);
			ppp_receive_error(ppp);
		}

		skb = head;
		if (head != tail) {
			struct sk_buff **fragpp = &skb_shinfo(skb)->frag_list;
			p = skb_queue_next(list, head);
			__skb_unlink(skb, list);
			skb_queue_walk_from_safe(list, p, tmp) {
				__skb_unlink(p, list);
				*fragpp = p;
				p->next = NULL;
				fragpp = &p->next;

				skb->len += p->len;
				skb->data_len += p->len;
				skb->truesize += p->truesize;

				if (p == tail)
					break;
			}
		} else {
			__skb_unlink(skb, list);
		}

		ppp->nextseq = PPP_MP_CB(tail)->sequence + 1;
	}

	return skb;
}
#endif /* CONFIG_PPP_MULTILINK */

/*
 * Channel interface.
 */

/* Create a new, unattached ppp channel. */
int ppp_register_channel(struct ppp_channel *chan)
{
	return ppp_register_net_channel(current->nsproxy->net_ns, chan);
}

/* Create a new, unattached ppp channel for specified net. */
int ppp_register_net_channel(struct net *net, struct ppp_channel *chan)
{
	struct channel *pch;
	struct ppp_net *pn;

	pch = kzalloc_obj(struct channel);
	if (!pch)
		return -ENOMEM;

	pn = ppp_pernet(net);

	pch->chan = chan;
	pch->chan_net = get_net_track(net, &pch->ns_tracker, GFP_KERNEL);
	chan->ppp = pch;
	init_ppp_file(&pch->file, CHANNEL);
	pch->file.hdrlen = chan->hdrlen;
#ifdef CONFIG_PPP_MULTILINK
	pch->lastseq = -1;
#endif /* CONFIG_PPP_MULTILINK */
	init_rwsem(&pch->chan_sem);
	spin_lock_init(&pch->downl);
	spin_lock_init(&pch->upl);

	spin_lock_bh(&pn->all_channels_lock);
	pch->file.index = ++pn->last_channel_index;
	list_add(&pch->list, &pn->new_channels);
	atomic_inc(&channel_count);
	spin_unlock_bh(&pn->all_channels_lock);

	return 0;
}

/*
 * Return the index of a channel.
 */
int ppp_channel_index(struct ppp_channel *chan)
{
	struct channel *pch = chan->ppp;

	if (pch)
		return pch->file.index;
	return -1;
}

/*
 * Return the PPP unit number to which a channel is connected.
 */
int ppp_unit_number(struct ppp_channel *chan)
{
	struct channel *pch = chan->ppp;
	struct ppp *ppp;
	int unit = -1;

	if (pch) {
		rcu_read_lock();
		ppp = rcu_dereference(pch->ppp);
		if (ppp)
			unit = ppp->file.index;
		rcu_read_unlock();
	}
	return unit;
}

/*
 * Return the PPP device interface name of a channel.
 * Caller must hold RCU read lock.
 */
char *ppp_dev_name(struct ppp_channel *chan)
{
	struct channel *pch = chan->ppp;
	char *name = NULL;
	struct ppp *ppp;

	if (pch) {
		ppp = rcu_dereference(pch->ppp);
		if (ppp && ppp->dev)
			name = ppp->dev->name;
	}
	return name;
}


/*
 * Disconnect a channel from the generic layer.
 * This must be called in process context.
 */
void
ppp_unregister_channel(struct ppp_channel *chan)
{
	struct channel *pch = chan->ppp;
	struct ppp_net *pn;

	if (!pch)
		return;		/* should never happen */

	chan->ppp = NULL;

	/*
	 * This ensures that we have returned from any calls into
	 * the channel's start_xmit or ioctl routine before we proceed.
	 */
	ppp_disconnect_channel(pch);
	down_write(&pch->chan_sem);
	spin_lock_bh(&pch->downl);
	pch->chan = NULL;
	spin_unlock_bh(&pch->downl);
	up_write(&pch->chan_sem);

	pn = ppp_pernet(pch->chan_net);
	spin_lock_bh(&pn->all_channels_lock);
	list_del(&pch->list);
	spin_unlock_bh(&pn->all_channels_lock);

	ppp_unbridge_channels(pch);

	pch->file.dead = 1;
	wake_up_interruptible(&pch->file.rwait);

	ppp_release_channel(pch);
}

/*
 * Callback from a channel when it can accept more to transmit.
 * This should be called at BH/softirq level, not interrupt level.
 */
void
ppp_output_wakeup(struct ppp_channel *chan)
{
	struct channel *pch = chan->ppp;

	if (!pch)
		return;
	ppp_channel_push(pch);
}

/*
 * Compression control.
 */

/* Process the PPPIOCSCOMPRESS ioctl. */
static int
ppp_set_compress(struct ppp *ppp, struct ppp_option_data *data)
{
	int err = -EFAULT;
	struct compressor *cp, *ocomp;
	void *state, *ostate;
	unsigned char ccp_option[CCP_MAX_OPTION_LENGTH];

	if (data->length > CCP_MAX_OPTION_LENGTH)
		goto out;
	if (copy_from_user(ccp_option, data->ptr, data->length))
		goto out;

	err = -EINVAL;
	if (data->length < 2 || ccp_option[1] < 2 || ccp_option[1] > data->length)
		goto out;

	cp = try_then_request_module(
		find_compressor(ccp_option[0]),
		"ppp-compress-%d", ccp_option[0]);
	if (!cp)
		goto out;

	err = -ENOBUFS;
	if (data->transmit) {
		state = cp->comp_alloc(ccp_option, data->length);
		if (state) {
			ppp_xmit_lock(ppp);
			ppp->xstate &= ~SC_COMP_RUN;
			ocomp = ppp->xcomp;
			ostate = ppp->xc_state;
			ppp->xcomp = cp;
			ppp->xc_state = state;
			ppp_xmit_unlock(ppp);
			if (ostate) {
				ocomp->comp_free(ostate);
				module_put(ocomp->owner);
			}
			err = 0;
		} else
			module_put(cp->owner);

	} else {
		state = cp->decomp_alloc(ccp_option, data->length);
		if (state) {
			ppp_recv_lock(ppp);
			ppp->rstate &= ~SC_DECOMP_RUN;
			ocomp = ppp->rcomp;
			ostate = ppp->rc_state;
			ppp->rcomp = cp;
			ppp->rc_state = state;
			ppp_recv_unlock(ppp);
			if (ostate) {
				ocomp->decomp_free(ostate);
				module_put(ocomp->owner);
			}
			err = 0;
		} else
			module_put(cp->owner);
	}

 out:
	return err;
}

/*
 * Look at a CCP packet and update our state accordingly.
 * We assume the caller has the xmit or recv path locked.
 */
static void
ppp_ccp_peek(struct ppp *ppp, struct sk_buff *skb, int inbound)
{
	unsigned char *dp;
	int len;

	if (!pskb_may_pull(skb, CCP_HDRLEN + 2))
		return;	/* no header */
	dp = skb->data + 2;

	switch (CCP_CODE(dp)) {
	case CCP_CONFREQ:

		/* A ConfReq starts negotiation of compression
		 * in one direction of transmission,
		 * and hence brings it down...but which way?
		 *
		 * Remember:
		 * A ConfReq indicates what the sender would like to receive
		 */
		if(inbound)
			/* He is proposing what I should send */
			ppp->xstate &= ~SC_COMP_RUN;
		else
			/* I am proposing to what he should send */
			ppp->rstate &= ~SC_DECOMP_RUN;

		break;

	case CCP_TERMREQ:
	case CCP_TERMACK:
		/*
		 * CCP is going down, both directions of transmission
		 */
		ppp->rstate &= ~SC_DECOMP_RUN;
		ppp->xstate &= ~SC_COMP_RUN;
		break;

	case CCP_CONFACK:
		if ((ppp->flags & (SC_CCP_OPEN | SC_CCP_UP)) != SC_CCP_OPEN)
			break;
		len = CCP_LENGTH(dp);
		if (!pskb_may_pull(skb, len + 2))
			return;		/* too short */
		dp += CCP_HDRLEN;
		len -= CCP_HDRLEN;
		if (len < CCP_OPT_MINLEN || len < CCP_OPT_LENGTH(dp))
			break;
		if (inbound) {
			/* we will start receiving compressed packets */
			if (!ppp->rc_state)
				break;
			if (ppp->rcomp->decomp_init(ppp->rc_state, dp, len,
						ppp->file.index, 0, ppp->mru,
						READ_ONCE(ppp->debug))) {
				ppp->rstate |= SC_DECOMP_RUN;
				ppp->rstate &= ~(SC_DC_ERROR | SC_DC_FERROR);
			}
		} else {
			/* we will soon start sending compressed packets */
			if (!ppp->xc_state)
				break;
			if (ppp->xcomp->comp_init(ppp->xc_state, dp, len,
						  ppp->file.index, 0,
						  READ_ONCE(ppp->debug)))
				ppp->xstate |= SC_COMP_RUN;
		}
		break;

	case CCP_RESETACK:
		/* reset the [de]compressor */
		if ((ppp->flags & SC_CCP_UP) == 0)
			break;
		if (inbound) {
			if (ppp->rc_state && (ppp->rstate & SC_DECOMP_RUN)) {
				ppp->rcomp->decomp_reset(ppp->rc_state);
				ppp->rstate &= ~SC_DC_ERROR;
			}
		} else {
			if (ppp->xc_state && (ppp->xstate & SC_COMP_RUN))
				ppp->xcomp->comp_reset(ppp->xc_state);
		}
		break;
	}
}

/* Free up compression resources. */
static void
ppp_ccp_closed(struct ppp *ppp)
{
	void *xstate, *rstate;
	struct compressor *xcomp, *rcomp;

	ppp_lock(ppp);
	ppp->flags &= ~(SC_CCP_OPEN | SC_CCP_UP);
	ppp->xstate = 0;
	xcomp = ppp->xcomp;
	xstate = ppp->xc_state;
	ppp->xc_state = NULL;
	ppp->rstate = 0;
	rcomp = ppp->rcomp;
	rstate = ppp->rc_state;
	ppp->rc_state = NULL;
	ppp_unlock(ppp);

	if (xstate) {
		xcomp->comp_free(xstate);
		module_put(xcomp->owner);
	}
	if (rstate) {
		rcomp->decomp_free(rstate);
		module_put(rcomp->owner);
	}
}

/* List of compressors. */
static LIST_HEAD(compressor_list);
static DEFINE_SPINLOCK(compressor_list_lock);

struct compressor_entry {
	struct list_head list;
	struct compressor *comp;
};

static struct compressor_entry *
find_comp_entry(int proto)
{
	struct compressor_entry *ce;

	list_for_each_entry(ce, &compressor_list, list) {
		if (ce->comp->compress_proto == proto)
			return ce;
	}
	return NULL;
}

/* Register a compressor */
int
ppp_register_compressor(struct compressor *cp)
{
	struct compressor_entry *ce;
	int ret;
	spin_lock(&compressor_list_lock);
	ret = -EEXIST;
	if (find_comp_entry(cp->compress_proto))
		goto out;
	ret = -ENOMEM;
	ce = kmalloc_obj(struct compressor_entry, GFP_ATOMIC);
	if (!ce)
		goto out;
	ret = 0;
	ce->comp = cp;
	list_add(&ce->list, &compressor_list);
 out:
	spin_unlock(&compressor_list_lock);
	return ret;
}

/* Unregister a compressor */
void
ppp_unregister_compressor(struct compressor *cp)
{
	struct compressor_entry *ce;

	spin_lock(&compressor_list_lock);
	ce = find_comp_entry(cp->compress_proto);
	if (ce && ce->comp == cp) {
		list_del(&ce->list);
		kfree(ce);
	}
	spin_unlock(&compressor_list_lock);
}

/* Find a compressor. */
static struct compressor *
find_compressor(int type)
{
	struct compressor_entry *ce;
	struct compressor *cp = NULL;

	spin_lock(&compressor_list_lock);
	ce = find_comp_entry(type);
	if (ce) {
		cp = ce->comp;
		if (!try_module_get(cp->owner))
			cp = NULL;
	}
	spin_unlock(&compressor_list_lock);
	return cp;
}

/*
 * Miscelleneous stuff.
 */

static void
ppp_get_stats(struct ppp *ppp, struct ppp_stats *st)
{
	struct slcompress *vj = ppp->vj;
	int cpu;

	memset(st, 0, sizeof(*st));
	for_each_possible_cpu(cpu) {
		struct pcpu_sw_netstats *p = per_cpu_ptr(ppp->dev->tstats, cpu);
		u64 rx_packets, rx_bytes, tx_packets, tx_bytes;

		rx_packets = u64_stats_read(&p->rx_packets);
		rx_bytes = u64_stats_read(&p->rx_bytes);
		tx_packets = u64_stats_read(&p->tx_packets);
		tx_bytes = u64_stats_read(&p->tx_bytes);

		st->p.ppp_ipackets += rx_packets;
		st->p.ppp_ibytes += rx_bytes;
		st->p.ppp_opackets += tx_packets;
		st->p.ppp_obytes += tx_bytes;
	}
	st->p.ppp_ierrors = DEV_STATS_READ(ppp->dev, rx_errors);
	st->p.ppp_oerrors = DEV_STATS_READ(ppp->dev, tx_errors);
	if (!vj)
		return;
	st->vj.vjs_packets = vj->sls_o_compressed + vj->sls_o_uncompressed;
	st->vj.vjs_compressed = vj->sls_o_compressed;
	st->vj.vjs_searches = vj->sls_o_searches;
	st->vj.vjs_misses = vj->sls_o_misses;
	st->vj.vjs_errorin = vj->sls_i_error;
	st->vj.vjs_tossed = vj->sls_i_tossed;
	st->vj.vjs_uncompressedin = vj->sls_i_uncompressed;
	st->vj.vjs_compressedin = vj->sls_i_compressed;
}

/*
 * Stuff for handling the lists of ppp units and channels
 * and for initialization.
 */

/*
 * Create a new ppp interface unit.  Fails if it can't allocate memory
 * or if there is already a unit with the requested number.
 * unit == -1 means allocate a new number.
 */
static int ppp_create_interface(struct net *net, struct file *file, int *unit)
{
	struct ppp_config conf = {
		.file = file,
		.unit = *unit,
		.ifname_is_set = false,
	};
	struct net_device *dev;
	struct ppp *ppp;
	int err;

	dev = alloc_netdev(sizeof(struct ppp), "", NET_NAME_ENUM, ppp_setup);
	if (!dev) {
		err = -ENOMEM;
		goto err;
	}
	dev_net_set(dev, net);
	dev->rtnl_link_ops = &ppp_link_ops;

	rtnl_lock();

	err = ppp_dev_configure(net, dev, &conf);
	if (err < 0)
		goto err_dev;
	ppp = netdev_priv(dev);
	*unit = ppp->file.index;

	rtnl_unlock();

	return 0;

err_dev:
	rtnl_unlock();
	free_netdev(dev);
err:
	return err;
}

/*
 * Initialize a ppp_file structure.
 */
static void
init_ppp_file(struct ppp_file *pf, int kind)
{
	pf->kind = kind;
	skb_queue_head_init(&pf->xq);
	skb_queue_head_init(&pf->rq);
	refcount_set(&pf->refcnt, 1);
	init_waitqueue_head(&pf->rwait);
}

/*
 * Drop a reference to a ppp unit and free its memory if the refcount reaches
 * zero.
 */
static void ppp_release_interface(struct ppp *ppp)
{
	if (!refcount_dec_and_test(&ppp->file.refcnt))
		return;

	atomic_dec(&ppp_unit_count);

	if (!ppp->file.dead || ppp->n_channels) {
		/* "can't happen" */
		netdev_err(ppp->dev, "ppp: destroying ppp struct %p "
			   "but dead=%d n_channels=%d !\n",
			   ppp, ppp->file.dead, ppp->n_channels);
		return;
	}

	ppp_ccp_closed(ppp);
	if (ppp->vj) {
		slhc_free(ppp->vj);
		ppp->vj = NULL;
	}
	skb_queue_purge(&ppp->file.xq);
	skb_queue_purge(&ppp->file.rq);
#ifdef CONFIG_PPP_MULTILINK
	skb_queue_purge(&ppp->mrq);
#endif /* CONFIG_PPP_MULTILINK */
#ifdef CONFIG_PPP_FILTER
	if (ppp->pass_filter) {
		bpf_prog_destroy(ppp->pass_filter);
		ppp->pass_filter = NULL;
	}

	if (ppp->active_filter) {
		bpf_prog_destroy(ppp->active_filter);
		ppp->active_filter = NULL;
	}
#endif /* CONFIG_PPP_FILTER */

	free_percpu(ppp->xmit_recursion);

	free_netdev(ppp->dev);
}

/*
 * Locate an existing ppp unit.
 * The caller should have locked the all_ppp_mutex.
 */
static struct ppp *
ppp_find_unit(struct ppp_net *pn, int unit)
{
	return unit_find(&pn->units_idr, unit);
}

/*
 * Locate an existing ppp channel.
 * The caller should have locked the all_channels_lock.
 * First we look in the new_channels list, then in the
 * all_channels list.  If found in the new_channels list,
 * we move it to the all_channels list.  This is for speed
 * when we have a lot of channels in use.
 */
static struct channel *
ppp_find_channel(struct ppp_net *pn, int unit)
{
	struct channel *pch;

	list_for_each_entry(pch, &pn->new_channels, list) {
		if (pch->file.index == unit) {
			list_move(&pch->list, &pn->all_channels);
			return pch;
		}
	}

	list_for_each_entry(pch, &pn->all_channels, list) {
		if (pch->file.index == unit)
			return pch;
	}

	return NULL;
}

/*
 * Connect a PPP channel to a PPP interface unit.
 */
static int
ppp_connect_channel(struct channel *pch, int unit)
{
	struct ppp *ppp;
	struct ppp_net *pn;
	int ret = -ENXIO;
	int hdrlen;

	pn = ppp_pernet(pch->chan_net);

	mutex_lock(&pn->all_ppp_mutex);
	ppp = ppp_find_unit(pn, unit);
	if (!ppp)
		goto out;
	spin_lock(&pch->upl);
	ret = -EINVAL;
	if (rcu_dereference_protected(pch->ppp, lockdep_is_held(&pch->upl)) ||
	    rcu_dereference_protected(pch->bridge, lockdep_is_held(&pch->upl)))
		goto outl;

	ppp_lock(ppp);
	spin_lock_bh(&pch->downl);
	if (!pch->chan) {
		/* Don't connect unregistered channels */
		spin_unlock_bh(&pch->downl);
		ppp_unlock(ppp);
		ret = -ENOTCONN;
		goto outl;
	}
	if (pch->chan->direct_xmit)
		ppp->dev->priv_flags |= IFF_NO_QUEUE;
	else
		ppp->dev->priv_flags &= ~IFF_NO_QUEUE;
	spin_unlock_bh(&pch->downl);
	if (pch->file.hdrlen > ppp->file.hdrlen)
		ppp->file.hdrlen = pch->file.hdrlen;
	hdrlen = pch->file.hdrlen + 2;	/* for protocol bytes */
	if (hdrlen > ppp->dev->hard_header_len)
		ppp->dev->hard_header_len = hdrlen;
	list_add_tail_rcu(&pch->clist, &ppp->channels);
	++ppp->n_channels;
	rcu_assign_pointer(pch->ppp, ppp);
	refcount_inc(&ppp->file.refcnt);
	ppp_unlock(ppp);
	ret = 0;

 outl:
	spin_unlock(&pch->upl);
 out:
	mutex_unlock(&pn->all_ppp_mutex);
	return ret;
}

/*
 * Disconnect a channel from its ppp unit.
 */
static int
ppp_disconnect_channel(struct channel *pch)
{
	struct ppp *ppp;
	int err = -EINVAL;

	spin_lock(&pch->upl);
	ppp = rcu_replace_pointer(pch->ppp, NULL, lockdep_is_held(&pch->upl));
	spin_unlock(&pch->upl);
	if (ppp) {
		/* remove it from the ppp unit's list */
		ppp_lock(ppp);
		list_del_rcu(&pch->clist);
		if (--ppp->n_channels == 0)
			wake_up_interruptible(&ppp->file.rwait);
		ppp_unlock(ppp);
		synchronize_net();
		ppp_release_interface(ppp);
		err = 0;
	}
	return err;
}

/* Purge after the grace period: a late ppp_input() may still queue an
 * skb on pch->file.rq before the last RCU reader drains.
 */
static void ppp_release_channel_free(struct rcu_head *rcu)
{
	struct channel *pch = container_of(rcu, struct channel, rcu);

	skb_queue_purge(&pch->file.xq);
	skb_queue_purge(&pch->file.rq);
	kfree(pch);
}

/*
 * Drop a reference to a ppp channel and free its memory if the refcount reaches
 * zero.
 */
static void ppp_release_channel(struct channel *pch)
{
	if (!refcount_dec_and_test(&pch->file.refcnt))
		return;

	put_net_track(pch->chan_net, &pch->ns_tracker);
	pch->chan_net = NULL;

	atomic_dec(&channel_count);

	if (!pch->file.dead) {
		/* "can't happen" */
		pr_err("ppp: destroying undead channel %p !\n", pch);
		return;
	}
	call_rcu(&pch->rcu, ppp_release_channel_free);
}

static void __exit ppp_cleanup(void)
{
	/* should never happen */
	if (atomic_read(&ppp_unit_count) || atomic_read(&channel_count))
		pr_err("PPP: removing module but units remain!\n");
	rtnl_link_unregister(&ppp_link_ops);
	unregister_chrdev(PPP_MAJOR, "ppp");
	device_destroy(&ppp_class, MKDEV(PPP_MAJOR, 0));
	class_unregister(&ppp_class);
	unregister_pernet_device(&ppp_net_ops);
	rcu_barrier(); /* wait for RCU callbacks before module unload */
}

/*
 * Units handling. Caller must protect concurrent access
 * by holding all_ppp_mutex
 */

/* associate pointer with specified number */
static int unit_set(struct idr *p, void *ptr, int n)
{
	int unit;

	unit = idr_alloc(p, ptr, n, n + 1, GFP_KERNEL);
	if (unit == -ENOSPC)
		unit = -EINVAL;
	return unit;
}

/* get new free unit number and associate pointer with it */
static int unit_get(struct idr *p, void *ptr, int min)
{
	return idr_alloc(p, ptr, min, 0, GFP_KERNEL);
}

/* put unit number back to a pool */
static void unit_put(struct idr *p, int n)
{
	idr_remove(p, n);
}

/* get pointer associated with the number */
static void *unit_find(struct idr *p, int n)
{
	return idr_find(p, n);
}

/* Module/initialization stuff */

module_init(ppp_init);
module_exit(ppp_cleanup);

EXPORT_SYMBOL(ppp_register_net_channel);
EXPORT_SYMBOL(ppp_register_channel);
EXPORT_SYMBOL(ppp_unregister_channel);
EXPORT_SYMBOL(ppp_channel_index);
EXPORT_SYMBOL(ppp_unit_number);
EXPORT_SYMBOL(ppp_dev_name);
EXPORT_SYMBOL(ppp_input);
EXPORT_SYMBOL(ppp_input_error);
EXPORT_SYMBOL(ppp_output_wakeup);
EXPORT_SYMBOL(ppp_register_compressor);
EXPORT_SYMBOL(ppp_unregister_compressor);
MODULE_DESCRIPTION("Generic PPP layer driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_CHARDEV(PPP_MAJOR, 0);
MODULE_ALIAS_RTNL_LINK("ppp");
MODULE_ALIAS("devname:ppp");