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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // 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/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 <asm/unaligned.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
 
 /*
  * 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)
 
 /*
  * Data structure to hold primary network stats for which
  * we want to use 64 bit storage.  Other network stats
  * are stored in dev->stats of the ppp strucute.
  */
 struct ppp_link_stats {
     u64 rx_packets;
     u64 tx_packets;
     u64 rx_bytes;
     u64 tx_bytes;
 };
 
 /*
  * 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 */
     int __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 sk_buff  *xmit_pending;  /* a packet ready to go out 88 */
     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 */
     struct ppp_link_stats stats64;  /* 64 bit network stats */
 };
 
 /*
  * 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  *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 */
     rwlock_t    upl;        /* protects `ppp' and 'bridge' */
     struct channel __rcu *bridge;   /* "bridged" ppp 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 void ppp_send_frame(struct ppp *ppp, struct sk_buff *skb);
 static void ppp_push(struct ppp *ppp);
 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_destroy_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_destroy_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 struct class *ppp_class;
 
 /* 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;
         if (pf->kind == INTERFACE) {
             ppp = PF_TO_PPP(pf);
             rtnl_lock();
             if (file == ppp->owner)
                 unregister_netdevice(ppp->dev);
             rtnl_unlock();
         }
         if (refcount_dec_and_test(&pf->refcnt)) {
             switch (pf->kind) {
             case INTERFACE:
                 ppp_destroy_interface(PF_TO_PPP(pf));
                 break;
             case CHANNEL:
                 ppp_destroy_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, READ, &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 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;
     }
 
     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_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)
 {
     write_lock_bh(&pch->upl);
     if (pch->ppp ||
         rcu_dereference_protected(pch->bridge, lockdep_is_held(&pch->upl))) {
         write_unlock_bh(&pch->upl);
         return -EALREADY;
     }
     refcount_inc(&pchb->file.refcnt);
     rcu_assign_pointer(pch->bridge, pchb);
     write_unlock_bh(&pch->upl);
 
     write_lock_bh(&pchb->upl);
     if (pchb->ppp ||
         rcu_dereference_protected(pchb->bridge, lockdep_is_held(&pchb->upl))) {
         write_unlock_bh(&pchb->upl);
         goto err_unset;
     }
     refcount_inc(&pch->file.refcnt);
     rcu_assign_pointer(pchb->bridge, pch);
     write_unlock_bh(&pchb->upl);
 
     return 0;
 
 err_unset:
     write_lock_bh(&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);
     write_unlock_bh(&pch->upl);
     synchronize_rcu();
 
     if (pchb)
         if (refcount_dec_and_test(&pchb->file.refcnt))
             ppp_destroy_channel(pchb);
 
     return -EALREADY;
 }
 
 static int ppp_unbridge_channels(struct channel *pch)
 {
     struct channel *pchb, *pchbb;
 
     write_lock_bh(&pch->upl);
     pchb = rcu_dereference_protected(pch->bridge, lockdep_is_held(&pch->upl));
     if (!pchb) {
         write_unlock_bh(&pch->upl);
         return -EINVAL;
     }
     RCU_INIT_POINTER(pch->bridge, NULL);
     write_unlock_bh(&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.
      */
     write_lock_bh(&pchb->upl);
     pchbb = rcu_dereference_protected(pchb->bridge, lockdep_is_held(&pchb->upl));
     if (pchbb == pch)
         RCU_INIT_POINTER(pchb->bridge, NULL);
     write_unlock_bh(&pchb->upl);
 
     synchronize_rcu();
 
     if (pchbb == pch)
         if (refcount_dec_and_test(&pch->file.refcnt))
             ppp_destroy_channel(pch);
 
     if (refcount_dec_and_test(&pchb->file.refcnt))
         ppp_destroy_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 */
             if (refcount_dec_and_test(&pchb->file.refcnt))
                 ppp_destroy_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->mru = val;
         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:
         val = ppp->flags | ppp->xstate | ppp->rstate;
         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;
         ppp->debug = val;
         err = 0;
         break;
 
     case PPPIOCGDEBUG:
         if (put_user(ppp->debug, p))
             break;
         err = 0;
         break;
 
     case PPPIOCGIDLE32:
                 idle32.xmit_idle = (jiffies - ppp->last_xmit) / HZ;
                 idle32.recv_idle = (jiffies - ppp->last_recv) / HZ;
                 if (copy_to_user(argp, &idle32, sizeof(idle32)))
             break;
         err = 0;
         break;
 
     case PPPIOCGIDLE64:
         idle64.xmit_idle = (jiffies - ppp->last_xmit) / HZ;
         idle64.recv_idle = (jiffies - 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 {
             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;
 
     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 __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_net(struct net *net)
 {
     struct ppp_net *pn = net_generic(net, ppp_net_id);
     struct net_device *dev;
     struct net_device *aux;
     struct ppp *ppp;
     LIST_HEAD(list);
     int id;
 
     rtnl_lock();
     for_each_netdev_safe(net, dev, aux) {
         if (dev->netdev_ops == &ppp_netdev_ops)
             unregister_netdevice_queue(dev, &list);
     }
 
     idr_for_each_entry(&pn->units_idr, ppp, id)
         /* Skip devices already unregistered by previous loop */
         if (!net_eq(dev_net(ppp->dev), net))
             unregister_netdevice_queue(ppp->dev, &list);
 
     unregister_netdevice_many(&list);
     rtnl_unlock();
 
     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 = 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(int);
     if (!ppp->xmit_recursion) {
         err = -ENOMEM;
         goto err1;
     }
     for_each_possible_cpu(cpu)
         (*per_cpu_ptr(ppp->xmit_recursion, cpu)) = 0;
 
 #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 *src_net, struct net_device *dev,
               struct nlattr *tb[], struct nlattr *data[],
               struct netlink_ext_ack *extack)
 {
     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(src_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 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;
     }
 
     ppp_class = class_create(THIS_MODULE, "ppp");
     if (IS_ERR(ppp_class)) {
         err = PTR_ERR(ppp_class);
         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_destroy(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 (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.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)
 {
     struct ppp *ppp = netdev_priv(dev);
 
     ppp_recv_lock(ppp);
     stats64->rx_packets = ppp->stats64.rx_packets;
     stats64->rx_bytes   = ppp->stats64.rx_bytes;
     ppp_recv_unlock(ppp);
 
     ppp_xmit_lock(ppp);
     stats64->tx_packets = ppp->stats64.tx_packets;
     stats64->tx_bytes   = ppp->stats64.tx_bytes;
     ppp_xmit_unlock(ppp);
 
     stats64->rx_errors        = dev->stats.rx_errors;
     stats64->tx_errors        = dev->stats.tx_errors;
     stats64->rx_dropped       = dev->stats.rx_dropped;
     stats64->tx_dropped       = dev->stats.tx_dropped;
     stats64->rx_length_errors = dev->stats.rx_length_errors;
 }
 
 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);
     if (refcount_dec_and_test(&ppp->file.refcnt))
         ppp_destroy_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;
 
     if (list_empty(&ppp->channels))
         return -ENODEV;
 
     pch = list_first_entry(&ppp->channels, struct channel, clist);
     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 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->features |= NETIF_F_LLTX;
 
     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;
     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_process(struct ppp *ppp, struct sk_buff *skb)
 {
     ppp_xmit_lock(ppp);
     if (!ppp->closing) {
         ppp_push(ppp);
 
         if (skb)
             skb_queue_tail(&ppp->file.xq, skb);
         while (!ppp->xmit_pending &&
                (skb = skb_dequeue(&ppp->file.xq)))
             ppp_send_frame(ppp, skb);
         /* If there's no work left to do, tell the core net
            code that we can accept some more. */
         if (!ppp->xmit_pending && !skb_peek(&ppp->file.xq))
             netif_wake_queue(ppp->dev);
         else
             netif_stop_queue(ppp->dev);
     } else {
         kfree_skb(skb);
     }
     ppp_xmit_unlock(ppp);
 }
 
 static void ppp_xmit_process(struct ppp *ppp, struct sk_buff *skb)
 {
     local_bh_disable();
 
     if (unlikely(*this_cpu_ptr(ppp->xmit_recursion)))
         goto err;
 
     (*this_cpu_ptr(ppp->xmit_recursion))++;
     __ppp_xmit_process(ppp, skb);
     (*this_cpu_ptr(ppp->xmit_recursion))--;
 
     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;
     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");
         kfree_skb(skb);
         consume_skb(new_skb);
         new_skb = NULL;
     }
     return new_skb;
 }
 
 /*
  * Compress and send a frame.
  * The caller should have locked the xmit path,
  * and xmit_pending should be 0.
  */
 static void
 ppp_send_frame(struct ppp *ppp, struct sk_buff *skb)
 {
     int proto = PPP_PROTO(skb);
     struct sk_buff *new_skb;
     int len;
     unsigned char *cp;
 
     if (proto < 0x8000) {
 #ifdef CONFIG_PPP_FILTER
         /* check if we should pass this packet */
         /* the filter instructions are constructed assuming
            a four-byte PPP header on each packet */
         *(u8 *)skb_push(skb, 2) = 1;
         if (ppp->pass_filter &&
             bpf_prog_run(ppp->pass_filter, skb) == 0) {
             if (ppp->debug & 1)
                 netdev_printk(KERN_DEBUG, ppp->dev,
                           "PPP: outbound frame "
                           "not passed\n");
             kfree_skb(skb);
             return;
         }
         /* if this packet passes the active filter, record the time */
         if (!(ppp->active_filter &&
               bpf_prog_run(ppp->active_filter, skb) == 0))
             ppp->last_xmit = jiffies;
         skb_pull(skb, 2);
 #else
         /* for data packets, record the time */
         ppp->last_xmit = jiffies;
 #endif /* CONFIG_PPP_FILTER */
     }
 
     ++ppp->stats64.tx_packets;
     ppp->stats64.tx_bytes += skb->len - PPP_PROTO_LEN;
 
     switch (proto) {
     case PPP_IP:
         if (!ppp->vj || (ppp->flags & SC_COMP_TCP) == 0)
             break;
         /* 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;
             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;
         }
         skb = pad_compress_skb(ppp, skb);
         if (!skb)
             goto drop;
     }
 
     /*
      * 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;
     }
 
     ppp->xmit_pending = skb;
     ppp_push(ppp);
     return;
 
  drop:
     kfree_skb(skb);
     ++ppp->dev->stats.tx_errors;
 }
 
 /*
  * Try to send the frame in xmit_pending.
  * The caller should have the xmit path locked.
  */
 static void
 ppp_push(struct ppp *ppp)
 {
     struct list_head *list;
     struct channel *pch;
     struct sk_buff *skb = ppp->xmit_pending;
 
     if (!skb)
         return;
 
     list = &ppp->channels;
     if (list_empty(list)) {
         /* nowhere to send the packet, just drop it */
         ppp->xmit_pending = NULL;
         kfree_skb(skb);
         return;
     }
 
     if ((ppp->flags & SC_MULTILINK) == 0) {
         /* not doing multilink: send it down the first channel */
         list = list->next;
         pch = list_entry(list, struct channel, clist);
 
         spin_lock(&pch->downl);
         if (pch->chan) {
             if (pch->chan->ops->start_xmit(pch->chan, skb))
                 ppp->xmit_pending = NULL;
         } else {
             /* channel got unregistered */
             kfree_skb(skb);
             ppp->xmit_pending = NULL;
         }
         spin_unlock(&pch->downl);
         return;
     }
 
 #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;
 #endif /* CONFIG_PPP_MULTILINK */
 
     ppp->xmit_pending = NULL;
     kfree_skb(skb);
 }
 
 #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) {
         if (pch->chan) {
             pch->avail = 1;
             navail++;
             pch->speed = pch->chan->speed;
         } else {
             pch->avail = 0;
         }
         if (pch->avail) {
             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 xmit_pending */
 
     /* Do protocol field compression */
     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;
         }
 
         /* check the channel's mtu and whether it is still attached. */
         spin_lock(&pch->downl);
         if (pch->chan == NULL) {
             /* can't use this channel, it's being deregistered */
             if (pch->speed == 0)
                 nzero--;
             else
                 totspeed -= pch->speed;
 
             spin_unlock(&pch->downl);
             pch->avail = 0;
             totlen = len;
             totfree--;
             nfree--;
             if (--navail == 0)
                 break;
             continue;
         }
 
         /*
         *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);
     if (ppp->debug & 1)
         netdev_err(ppp->dev, "PPP: no memory (fragment)\n");
     ++ppp->dev->stats.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 sk_buff *skb;
     struct ppp *ppp;
 
     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)) {
         ppp = pch->ppp;
         if (ppp)
             __ppp_xmit_process(ppp, NULL);
     }
 }
 
 static void ppp_channel_push(struct channel *pch)
 {
     read_lock_bh(&pch->upl);
     if (pch->ppp) {
         (*this_cpu_ptr(pch->ppp->xmit_recursion))++;
         __ppp_channel_push(pch);
         (*this_cpu_ptr(pch->ppp->xmit_recursion))--;
     } else {
         __ppp_channel_push(pch);
     }
     read_unlock_bh(&pch->upl);
 }
 
 /*
  * 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 (skb->data[0] & 0x01)
         *(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(&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(&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;
     int proto;
 
     if (!pch) {
         kfree_skb(skb);
         return;
     }
 
     /* If the channel is bridged, transmit via. bridge */
     if (ppp_channel_bridge_input(pch, skb))
         return;
 
     read_lock_bh(&pch->upl);
     if (!ppp_decompress_proto(skb)) {
         kfree_skb(skb);
         if (pch->ppp) {
             ++pch->ppp->dev->stats.rx_length_errors;
             ppp_receive_error(pch->ppp);
         }
         goto done;
     }
 
     proto = PPP_PROTO(skb);
     if (!pch->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(pch->ppp, skb, pch);
     }
 
 done:
     read_unlock_bh(&pch->upl);
 }
 
 /* Put a 0-length skb in the receive queue as an error indication */
 void
 ppp_input_error(struct ppp_channel *chan, int code)
 {
     struct channel *pch = chan->ppp;
     struct sk_buff *skb;
 
     if (!pch)
         return;
 
     read_lock_bh(&pch->upl);
     if (pch->ppp) {
         skb = alloc_skb(0, GFP_ATOMIC);
         if (skb) {
             skb->len = 0;       /* probably unnecessary */
             skb->cb[0] = code;
             ppp_do_recv(pch->ppp, skb, pch);
         }
     }
     read_unlock_bh(&pch->upl);
 }
 
 /*
  * 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)
 {
     /* note: a 0-length skb is used as an error indication */
     if (skb->len > 0) {
         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);
     } else {
         kfree_skb(skb);
         ppp_receive_error(ppp);
     }
 }
 
 static void
 ppp_receive_error(struct ppp *ppp)
 {
     ++ppp->dev->stats.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;
     }
 
     ++ppp->stats64.rx_packets;
     ppp->stats64.rx_bytes += skb->len - 2;
 
     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
         /* check if the packet passes the pass and active filters */
         /* the filter instructions are constructed assuming
            a four-byte PPP header on each packet */
         if (ppp->pass_filter || ppp->active_filter) {
             if (skb_unclone(skb, GFP_ATOMIC))
                 goto err;
 
             *(u8 *)skb_push(skb, 2) = 0;
             if (ppp->pass_filter &&
                 bpf_prog_run(ppp->pass_filter, skb) == 0) {
                 if (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))
                 ppp->last_recv = jiffies;
             __skb_pull(skb, 2);
         } else
 #endif /* CONFIG_PPP_FILTER */
             ppp->last_recv = jiffies;
 
         if ((ppp->dev->flags & IFF_UP) == 0 ||
             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);
         ++ppp->dev->stats.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 {
             ++ppp->dev->stats.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 (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) {
                 ++ppp->dev->stats.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 (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 (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 (ppp->debug & 1)
                 netdev_printk(KERN_DEBUG, ppp->dev,
                           "  missed pkts %u..%u\n",
                           ppp->nextseq,
                           PPP_MP_CB(head)->sequence-1);
             ++ppp->dev->stats.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(sizeof(struct channel), GFP_KERNEL);
     if (!pch)
         return -ENOMEM;
 
     pn = ppp_pernet(net);
 
     pch->ppp = NULL;
     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);
     rwlock_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;
     int unit = -1;
 
     if (pch) {
         read_lock_bh(&pch->upl);
         if (pch->ppp)
             unit = pch->ppp->file.index;
         read_unlock_bh(&pch->upl);
     }
     return unit;
 }
 
 /*
  * Return the PPP device interface name of a channel.
  */
 char *ppp_dev_name(struct ppp_channel *chan)
 {
     struct channel *pch = chan->ppp;
     char *name = NULL;
 
     if (pch) {
         read_lock_bh(&pch->upl);
         if (pch->ppp && pch->ppp->dev)
             name = pch->ppp->dev->name;
         read_unlock_bh(&pch->upl);
     }
     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.
      */
     down_write(&pch->chan_sem);
     spin_lock_bh(&pch->downl);
     pch->chan = NULL;
     spin_unlock_bh(&pch->downl);
     up_write(&pch->chan_sem);
     ppp_disconnect_channel(pch);
 
     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);
 
     if (refcount_dec_and_test(&pch->file.refcnt))
         ppp_destroy_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, 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, 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(sizeof(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;
 
     memset(st, 0, sizeof(*st));
     st->p.ppp_ipackets = ppp->stats64.rx_packets;
     st->p.ppp_ierrors = ppp->dev->stats.rx_errors;
     st->p.ppp_ibytes = ppp->stats64.rx_bytes;
     st->p.ppp_opackets = ppp->stats64.tx_packets;
     st->p.ppp_oerrors = ppp->dev->stats.tx_errors;
     st->p.ppp_obytes = ppp->stats64.tx_bytes;
     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);
 }
 
 /*
  * Free the memory used by a ppp unit.  This is only called once
  * there are no channels connected to the unit and no file structs
  * that reference the unit.
  */
 static void ppp_destroy_interface(struct ppp *ppp)
 {
     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 */
 
     kfree_skb(ppp->xmit_pending);
     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;
     write_lock_bh(&pch->upl);
     ret = -EINVAL;
     if (pch->ppp ||
         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;
     }
     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(&pch->clist, &ppp->channels);
     ++ppp->n_channels;
     pch->ppp = ppp;
     refcount_inc(&ppp->file.refcnt);
     ppp_unlock(ppp);
     ret = 0;
 
  outl:
     write_unlock_bh(&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;
 
     write_lock_bh(&pch->upl);
     ppp = pch->ppp;
     pch->ppp = NULL;
     write_unlock_bh(&pch->upl);
     if (ppp) {
         /* remove it from the ppp unit's list */
         ppp_lock(ppp);
         list_del(&pch->clist);
         if (--ppp->n_channels == 0)
             wake_up_interruptible(&ppp->file.rwait);
         ppp_unlock(ppp);
         if (refcount_dec_and_test(&ppp->file.refcnt))
             ppp_destroy_interface(ppp);
         err = 0;
     }
     return err;
 }
 
 /*
  * Free up the resources used by a ppp channel.
  */
 static void ppp_destroy_channel(struct channel *pch)
 {
     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;
     }
     skb_queue_purge(&pch->file.xq);
     skb_queue_purge(&pch->file.rq);
     kfree(pch);
 }
 
 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_destroy(ppp_class);
     unregister_pernet_device(&ppp_net_ops);
 }
 
 /*
  * 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_LICENSE("GPL");
 MODULE_ALIAS_CHARDEV(PPP_MAJOR, 0);
 MODULE_ALIAS_RTNL_LINK("ppp");
 MODULE_ALIAS("devname:ppp");