/*
 * INET         An implementation of the TCP/IP protocol suite for the LINUX
 *              operating system.  INET is implemented using the  BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              The IP fragmentation functionality.
 *
 * Authors:     Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
 *              Alan Cox <alan@lxorguk.ukuu.org.uk>
 *
 * Fixes:
 *              Alan Cox        :       Split from ip.c , see ip_input.c for history.
 *              David S. Miller :       Begin massive cleanup...
 *              Andi Kleen      :       Add sysctls.
 *              xxxx            :       Overlapfrag bug.
 *              Ultima          :       ip_expire() kernel panic.
 *              Bill Hawes      :       Frag accounting and evictor fixes.
 *              John McDonald   :       0 length frag bug.
 *              Alexey Kuznetsov:       SMP races, threading, cleanup.
 *              Patrick McHardy :       LRU queue of frag heads for evictor.
 */

#define pr_fmt(fmt) "IPv4: " fmt

#include <linux/compiler.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/jiffies.h>
#include <linux/skbuff.h>
#include <linux/list.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <linux/netdevice.h>
#include <linux/jhash.h>
#include <linux/random.h>
#include <linux/slab.h>
#include <net/route.h>
#include <net/dst.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/checksum.h>
#include <net/inetpeer.h>
#include <net/inet_frag.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/inet.h>
#include <linux/netfilter_ipv4.h>
#include <net/inet_ecn.h>

/* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
 * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
 * as well. Or notify me, at least. --ANK
 */

static int sysctl_ipfrag_max_dist __read_mostly = 64;

/* Use skb->cb to track consecutive/adjacent fragments coming at
 * the end of the queue. Nodes in the rb-tree queue will
 * contain "runs" of one or more adjacent fragments.
 *
 * Invariants:
 * - next_frag is NULL at the tail of a "run";
 * - the head of a "run" has the sum of all fragment lengths in frag_run_len.
 */
struct ipfrag_skb_cb
{
        struct inet_skb_parm    h;
        int                     offset;
        struct sk_buff          *next_frag;
        int                     frag_run_len;
};

#define FRAG_CB(skb)    ((struct ipfrag_skb_cb *)((skb)->cb))

static void ip4_frag_init_run(struct sk_buff *skb)
{
        BUILD_BUG_ON(sizeof(struct ipfrag_skb_cb) > sizeof(skb->cb));

        FRAG_CB(skb)->next_frag = NULL;
        FRAG_CB(skb)->frag_run_len = skb->len;
}

/* Append skb to the last "run". */
static void ip4_frag_append_to_last_run(struct inet_frag_queue *q,
                                        struct sk_buff *skb)
{
        RB_CLEAR_NODE(&skb->rbnode);
        FRAG_CB(skb)->next_frag = NULL;

        FRAG_CB(q->last_run_head)->frag_run_len += skb->len;
        FRAG_CB(q->fragments_tail)->next_frag = skb;
        q->fragments_tail = skb;
}

/* Create a new "run" with the skb. */
static void ip4_frag_create_run(struct inet_frag_queue *q, struct sk_buff *skb)
{
        if (q->last_run_head)
                rb_link_node(&skb->rbnode, &q->last_run_head->rbnode,
                             &q->last_run_head->rbnode.rb_right);
        else
                rb_link_node(&skb->rbnode, NULL, &q->rb_fragments.rb_node);
        rb_insert_color(&skb->rbnode, &q->rb_fragments);

        ip4_frag_init_run(skb);
        q->fragments_tail = skb;
        q->last_run_head = skb;
}

/* Describe an entry in the "incomplete datagrams" queue. */
struct ipq {
        struct inet_frag_queue q;

        u32             user;
        __be32          saddr;
        __be32          daddr;
        __be16          id;
        u8              protocol;
        u8              ecn; /* RFC3168 support */
        u16             max_df_size; /* largest frag with DF set seen */
        int             iif;
        unsigned int    rid;
        struct inet_peer *peer;
};

static inline u8 ip4_frag_ecn(u8 tos)
{
        return 1 << (tos & INET_ECN_MASK);
}

static struct inet_frags ip4_frags;

int ip_frag_nqueues(struct net *net)
{
        return net->ipv4.frags.nqueues;
}

int ip_frag_mem(struct net *net)
{
        return sum_frag_mem_limit(&net->ipv4.frags);
}

static int ip_frag_reasm(struct ipq *qp, struct sk_buff *skb,
                         struct sk_buff *prev_tail, struct net_device *dev);

struct ip4_create_arg {
        struct iphdr *iph;
        u32 user;
};

static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot)
{
        net_get_random_once(&ip4_frags.rnd, sizeof(ip4_frags.rnd));
        return jhash_3words((__force u32)id << 16 | prot,
                            (__force u32)saddr, (__force u32)daddr,
                            ip4_frags.rnd) & (INETFRAGS_HASHSZ - 1);
}

static unsigned int ip4_hashfn(struct inet_frag_queue *q)
{
        struct ipq *ipq;

        ipq = container_of(q, struct ipq, q);
        return ipqhashfn(ipq->id, ipq->saddr, ipq->daddr, ipq->protocol);
}

static bool ip4_frag_match(struct inet_frag_queue *q, void *a)
{
        struct ipq *qp;
        struct ip4_create_arg *arg = a;

        qp = container_of(q, struct ipq, q);
        return  qp->id == arg->iph->id &&
                qp->saddr == arg->iph->saddr &&
                qp->daddr == arg->iph->daddr &&
                qp->protocol == arg->iph->protocol &&
                qp->user == arg->user;
}

static void ip4_frag_init(struct inet_frag_queue *q, void *a)
{
        struct ipq *qp = container_of(q, struct ipq, q);
        struct netns_ipv4 *ipv4 = container_of(q->net, struct netns_ipv4,
                                               frags);
        struct net *net = container_of(ipv4, struct net, ipv4);

        struct ip4_create_arg *arg = a;

        qp->protocol = arg->iph->protocol;
        qp->id = arg->iph->id;
        qp->ecn = ip4_frag_ecn(arg->iph->tos);
        qp->saddr = arg->iph->saddr;
        qp->daddr = arg->iph->daddr;
        qp->user = arg->user;
        qp->peer = sysctl_ipfrag_max_dist ?
                inet_getpeer_v4(net->ipv4.peers, arg->iph->saddr, 1) : NULL;
}

static __inline__ void ip4_frag_free(struct inet_frag_queue *q)
{
        struct ipq *qp;

        qp = container_of(q, struct ipq, q);
        if (qp->peer)
                inet_putpeer(qp->peer);
}


/* Destruction primitives. */

static __inline__ void ipq_put(struct ipq *ipq)
{
        inet_frag_put(&ipq->q, &ip4_frags);
}

/* Kill ipq entry. It is not destroyed immediately,
 * because caller (and someone more) holds reference count.
 */
static void ipq_kill(struct ipq *ipq)
{
        inet_frag_kill(&ipq->q, &ip4_frags);
}

/* Memory limiting on fragments.  Evictor trashes the oldest
 * fragment queue until we are back under the threshold.
 */
static void ip_evictor(struct net *net)
{
        int evicted;

        evicted = inet_frag_evictor(&net->ipv4.frags, &ip4_frags, false);
        if (evicted)
                IP_ADD_STATS_BH(net, IPSTATS_MIB_REASMFAILS, evicted);
}

/*
 * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
 */
static void ip_expire(unsigned long arg)
{
        struct sk_buff *head = NULL;
        const struct iphdr *iph;
        struct ipq *qp;
        struct net *net;
        int err;

        qp = container_of((struct inet_frag_queue *) arg, struct ipq, q);
        net = container_of(qp->q.net, struct net, ipv4.frags);

        spin_lock(&qp->q.lock);

        if (qp->q.last_in & INET_FRAG_COMPLETE)
                goto out;

        ipq_kill(qp);

        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMTIMEOUT);
        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);

        if (!(qp->q.last_in & INET_FRAG_FIRST_IN))
                goto out;

        /* sk_buff::dev and sk_buff::rbnode are unionized. So we
         * pull the head out of the tree in order to be able to
         * deal with head->dev.
         */
        if (qp->q.fragments) {
                head = qp->q.fragments;
                qp->q.fragments = head->next;
        } else {
                head = skb_rb_first(&qp->q.rb_fragments);
                if (!head)
                        goto out;
                if (FRAG_CB(head)->next_frag)
                        rb_replace_node(&head->rbnode,
                                        &FRAG_CB(head)->next_frag->rbnode,
                                        &qp->q.rb_fragments);
                else
                        rb_erase(&head->rbnode, &qp->q.rb_fragments);
                memset(&head->rbnode, 0, sizeof(head->rbnode));
                barrier();
        }
        if (head == qp->q.fragments_tail)
                qp->q.fragments_tail = NULL;

        sub_frag_mem_limit(&qp->q, head->truesize);

        rcu_read_lock();
        head->dev = dev_get_by_index_rcu(net, qp->iif);
        if (!head->dev)
                goto out_rcu_unlock;

        /* skb has no dst, perform route lookup again */
        iph = ip_hdr(head);
        err = ip_route_input_noref(head, iph->daddr, iph->saddr,
                                   iph->tos, head->dev);
        if (err)
                goto out_rcu_unlock;

        /*
         * Only an end host needs to send an ICMP
         * "Fragment Reassembly Timeout" message, per RFC792.
         */
        if (qp->user == IP_DEFRAG_AF_PACKET ||
            (qp->user == IP_DEFRAG_CONNTRACK_IN &&
             skb_rtable(head)->rt_type != RTN_LOCAL))
                goto out_rcu_unlock;

        /* Send an ICMP "Fragment Reassembly Timeout" message. */
        icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
out_rcu_unlock:
        rcu_read_unlock();
out:
        spin_unlock(&qp->q.lock);
        if (head)
                kfree_skb(head);
        ipq_put(qp);
}

/* Find the correct entry in the "incomplete datagrams" queue for
 * this IP datagram, and create new one, if nothing is found.
 */
static inline struct ipq *ip_find(struct net *net, struct iphdr *iph, u32 user)
{
        struct inet_frag_queue *q;
        struct ip4_create_arg arg;
        unsigned int hash;

        arg.iph = iph;
        arg.user = user;

        read_lock(&ip4_frags.lock);
        hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol);

        q = inet_frag_find(&net->ipv4.frags, &ip4_frags, &arg, hash);
        if (IS_ERR_OR_NULL(q)) {
                inet_frag_maybe_warn_overflow(q, pr_fmt());
                return NULL;
        }
        return container_of(q, struct ipq, q);
}

/* Is the fragment too far ahead to be part of ipq? */
static inline int ip_frag_too_far(struct ipq *qp)
{
        struct inet_peer *peer = qp->peer;
        unsigned int max = sysctl_ipfrag_max_dist;
        unsigned int start, end;

        int rc;

        if (!peer || !max)
                return 0;

        start = qp->rid;
        end = atomic_inc_return(&peer->rid);
        qp->rid = end;

        rc = qp->q.fragments_tail && (end - start) > max;

        if (rc) {
                struct net *net;

                net = container_of(qp->q.net, struct net, ipv4.frags);
                IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
        }

        return rc;
}

static int ip_frag_reinit(struct ipq *qp)
{
        unsigned int sum_truesize = 0;

        if (!mod_timer(&qp->q.timer, jiffies + qp->q.net->timeout)) {
                atomic_inc(&qp->q.refcnt);
                return -ETIMEDOUT;
        }

        sum_truesize = inet_frag_rbtree_purge(&qp->q.rb_fragments);
        sub_frag_mem_limit(&qp->q, sum_truesize);

        qp->q.last_in = 0;
        qp->q.len = 0;
        qp->q.meat = 0;
        qp->q.fragments = NULL;
        qp->q.rb_fragments = RB_ROOT;
        qp->q.fragments_tail = NULL;
        qp->q.last_run_head = NULL;
        qp->iif = 0;
        qp->ecn = 0;

        return 0;
}

/* Add new segment to existing queue. */
static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
{
        struct net *net = container_of(qp->q.net, struct net, ipv4.frags);
        struct rb_node **rbn, *parent;
        struct sk_buff *skb1, *prev_tail;
        struct net_device *dev;
        unsigned int fragsize;
        int flags, offset;
        int ihl, end;
        int err = -ENOENT;
        u8 ecn;

        if (qp->q.last_in & INET_FRAG_COMPLETE)
                goto err;

        if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
            unlikely(ip_frag_too_far(qp)) &&
            unlikely(err = ip_frag_reinit(qp))) {
                ipq_kill(qp);
                goto err;
        }

        ecn = ip4_frag_ecn(ip_hdr(skb)->tos);
        offset = ntohs(ip_hdr(skb)->frag_off);
        flags = offset & ~IP_OFFSET;
        offset &= IP_OFFSET;
        offset <<= 3;           /* offset is in 8-byte chunks */
        ihl = ip_hdrlen(skb);

        /* Determine the position of this fragment. */
        end = offset + skb->len - skb_network_offset(skb) - ihl;
        err = -EINVAL;

        /* Is this the final fragment? */
        if ((flags & IP_MF) == 0) {
                /* If we already have some bits beyond end
                 * or have different end, the segment is corrupted.
                 */
                if (end < qp->q.len ||
                    ((qp->q.last_in & INET_FRAG_LAST_IN) && end != qp->q.len))
                        goto err;
                qp->q.last_in |= INET_FRAG_LAST_IN;
                qp->q.len = end;
        } else {
                if (end&7) {
                        end &= ~7;
                        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
                                skb->ip_summed = CHECKSUM_NONE;
                }
                if (end > qp->q.len) {
                        /* Some bits beyond end -> corruption. */
                        if (qp->q.last_in & INET_FRAG_LAST_IN)
                                goto err;
                        qp->q.len = end;
                }
        }
        if (end == offset)
                goto err;

        err = -ENOMEM;
        if (!pskb_pull(skb, skb_network_offset(skb) + ihl))
                goto err;

        err = pskb_trim_rcsum(skb, end - offset);
        if (err)
                goto err;

        /* Note : skb->rbnode and skb->dev share the same location. */
        dev = skb->dev;
        /* Makes sure compiler wont do silly aliasing games */
        barrier();

        /* RFC5722, Section 4, amended by Errata ID : 3089
         *                          When reassembling an IPv6 datagram, if
         *   one or more its constituent fragments is determined to be an
         *   overlapping fragment, the entire datagram (and any constituent
         *   fragments) MUST be silently discarded.
         *
         * We do the same here for IPv4 (and increment an snmp counter).
         */

        /* Find out where to put this fragment.  */
        prev_tail = qp->q.fragments_tail;
        if (!prev_tail)
                ip4_frag_create_run(&qp->q, skb);  /* First fragment. */
        else if (FRAG_CB(prev_tail)->offset + prev_tail->len < end) {
                /* This is the common case: skb goes to the end. */
                /* Detect and discard overlaps. */
                if (offset < FRAG_CB(prev_tail)->offset + prev_tail->len)
                        goto discard_qp;
                if (offset == FRAG_CB(prev_tail)->offset + prev_tail->len)
                        ip4_frag_append_to_last_run(&qp->q, skb);
                else
                        ip4_frag_create_run(&qp->q, skb);
        } else {
                /* Binary search. Note that skb can become the first fragment,
                 * but not the last (covered above).
                 */
                rbn = &qp->q.rb_fragments.rb_node;
                do {
                        parent = *rbn;
                        skb1 = rb_to_skb(parent);
                        if (end <= FRAG_CB(skb1)->offset)
                                rbn = &parent->rb_left;
                        else if (offset >= FRAG_CB(skb1)->offset +
                                                FRAG_CB(skb1)->frag_run_len)
                                rbn = &parent->rb_right;
                        else /* Found an overlap with skb1. */
                                goto discard_qp;
                } while (*rbn);
                /* Here we have parent properly set, and rbn pointing to
                 * one of its NULL left/right children. Insert skb.
                 */
                ip4_frag_init_run(skb);
                rb_link_node(&skb->rbnode, parent, rbn);
                rb_insert_color(&skb->rbnode, &qp->q.rb_fragments);
        }

        if (dev) {
                qp->iif = dev->ifindex;
                skb->dev = NULL;
        }
        FRAG_CB(skb)->offset = offset;

        qp->q.stamp = skb->tstamp;
        qp->q.meat += skb->len;
        qp->ecn |= ecn;
        add_frag_mem_limit(&qp->q, skb->truesize);
        if (offset == 0)
                qp->q.last_in |= INET_FRAG_FIRST_IN;

        fragsize = skb->len + ihl;

        if (fragsize > qp->q.max_size)
                qp->q.max_size = fragsize;

        if (ip_hdr(skb)->frag_off & htons(IP_DF) &&
            fragsize > qp->max_df_size)
                qp->max_df_size = fragsize;

        if (qp->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
            qp->q.meat == qp->q.len) {
                unsigned long orefdst = skb->_skb_refdst;

                skb->_skb_refdst = 0UL;
                err = ip_frag_reasm(qp, skb, prev_tail, dev);
                skb->_skb_refdst = orefdst;
                return err;
        }

        skb_dst_drop(skb);
        inet_frag_lru_move(&qp->q);
        return -EINPROGRESS;

discard_qp:
        ipq_kill(qp);
        err = -EINVAL;
        IP_INC_STATS_BH(net, IPSTATS_MIB_REASM_OVERLAPS);
err:
        kfree_skb(skb);
        return err;
}

static bool ip_frag_coalesce_ok(const struct ipq *qp)
{
        return qp->user == IP_DEFRAG_LOCAL_DELIVER;
}

/* Build a new IP datagram from all its fragments. */
static int ip_frag_reasm(struct ipq *qp, struct sk_buff *skb,
                         struct sk_buff *prev_tail, struct net_device *dev)
{
        struct net *net = container_of(qp->q.net, struct net, ipv4.frags);
        struct iphdr *iph;
        struct sk_buff *fp, *head = skb_rb_first(&qp->q.rb_fragments);
        struct sk_buff **nextp; /* To build frag_list. */
        struct rb_node *rbn;
        int sum_truesize;
        int len;
        int ihlen;
        int err;
        u8 ecn;

        ipq_kill(qp);

        ecn = ip_frag_ecn_table[qp->ecn];
        if (unlikely(ecn == 0xff)) {
                err = -EINVAL;
                goto out_fail;
        }
        /* Make the one we just received the head. */
        if (head != skb) {
                fp = skb_clone(skb, GFP_ATOMIC);
                if (!fp)
                        goto out_nomem;
                FRAG_CB(fp)->next_frag = FRAG_CB(skb)->next_frag;
                if (RB_EMPTY_NODE(&skb->rbnode))
                        FRAG_CB(prev_tail)->next_frag = fp;
                else
                        rb_replace_node(&skb->rbnode, &fp->rbnode,
                                        &qp->q.rb_fragments);
                if (qp->q.fragments_tail == skb)
                        qp->q.fragments_tail = fp;
                skb_morph(skb, head);
                FRAG_CB(skb)->next_frag = FRAG_CB(head)->next_frag;
                rb_replace_node(&head->rbnode, &skb->rbnode,
                                &qp->q.rb_fragments);
                consume_skb(head);
                head = skb;
        }

        WARN_ON(FRAG_CB(head)->offset != 0);

        /* Allocate a new buffer for the datagram. */
        ihlen = ip_hdrlen(head);
        len = ihlen + qp->q.len;

        err = -E2BIG;
        if (len > 65535)
                goto out_oversize;

        /* Head of list must not be cloned. */
        if (skb_unclone(head, GFP_ATOMIC))
                goto out_nomem;

        /* If the first fragment is fragmented itself, we split
         * it to two chunks: the first with data and paged part
         * and the second, holding only fragments. */
        if (skb_has_frag_list(head)) {
                struct sk_buff *clone;
                int i, plen = 0;

                if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
                        goto out_nomem;
                skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
                skb_frag_list_init(head);
                for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
                        plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
                clone->len = clone->data_len = head->data_len - plen;
                head->truesize += clone->truesize;
                clone->csum = 0;
                clone->ip_summed = head->ip_summed;
                add_frag_mem_limit(&qp->q, clone->truesize);
                skb_shinfo(head)->frag_list = clone;
                nextp = &clone->next;
        } else {
                nextp = &skb_shinfo(head)->frag_list;
        }

        skb_push(head, head->data - skb_network_header(head));

        /* Traverse the tree in order, to build frag_list. */
        fp = FRAG_CB(head)->next_frag;
        rbn = rb_next(&head->rbnode);
        rb_erase(&head->rbnode, &qp->q.rb_fragments);

        sum_truesize = head->truesize;
        while (rbn || fp) {
                /* fp points to the next sk_buff in the current run;
                 * rbn points to the next run.
                 */
                /* Go through the current run. */
                while (fp) {
                        struct sk_buff *next_frag = FRAG_CB(fp)->next_frag;
                        bool stolen;
                        int delta;

                        sum_truesize += fp->truesize;
                        if (head->ip_summed != fp->ip_summed)
                                head->ip_summed = CHECKSUM_NONE;
                        else if (head->ip_summed == CHECKSUM_COMPLETE)
                                head->csum = csum_add(head->csum, fp->csum);

                        if (ip_frag_coalesce_ok(qp) &&
                            skb_try_coalesce(head, fp, &stolen, &delta)) {
                                kfree_skb_partial(fp, stolen);
                        } else {
                                fp->prev = NULL;
                                memset(&fp->rbnode, 0, sizeof(fp->rbnode));

                                head->data_len += fp->len;
                                head->len += fp->len;
                                head->truesize += fp->truesize;

                                *nextp = fp;
                                nextp = &fp->next;
                        }

                        fp = next_frag;
                }
                /* Move to the next run. */
                if (rbn) {
                        struct rb_node *rbnext = rb_next(rbn);

                        fp = rb_to_skb(rbn);
                        rb_erase(rbn, &qp->q.rb_fragments);
                        rbn = rbnext;
                }
        }
        sub_frag_mem_limit(&qp->q, sum_truesize);

        *nextp = NULL;
        head->next = NULL;
        head->prev = NULL;
        head->dev = dev;
        head->tstamp = qp->q.stamp;
        IPCB(head)->frag_max_size = max(qp->max_df_size, qp->q.max_size);

        iph = ip_hdr(head);
        iph->tot_len = htons(len);
        iph->tos |= ecn;

        /* When we set IP_DF on a refragmented skb we must also force a
         * call to ip_fragment to avoid forwarding a DF-skb of size s while
         * original sender only sent fragments of size f (where f < s).
         *
         * We only set DF/IPSKB_FRAG_PMTU if such DF fragment was the largest
         * frag seen to avoid sending tiny DF-fragments in case skb was built
         * from one very small df-fragment and one large non-df frag.
         */
        if (qp->max_df_size == qp->q.max_size) {
                IPCB(head)->flags |= IPSKB_FRAG_PMTU;
                iph->frag_off = htons(IP_DF);
        } else {
                iph->frag_off = 0;
        }

        ip_send_check(iph);

        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMOKS);
        qp->q.fragments = NULL;
        qp->q.rb_fragments = RB_ROOT;
        qp->q.fragments_tail = NULL;
        qp->q.last_run_head = NULL;
        return 0;

out_nomem:
        LIMIT_NETDEBUG(KERN_ERR pr_fmt("queue_glue: no memory for gluing queue %p\n"),
                       qp);
        err = -ENOMEM;
        goto out_fail;
out_oversize:
        net_info_ratelimited("Oversized IP packet from %pI4\n", &qp->saddr);
out_fail:
        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
        return err;
}

/* Process an incoming IP datagram fragment. */
int ip_defrag(struct sk_buff *skb, u32 user)
{
        struct ipq *qp;
        struct net *net;

        net = skb->dev ? dev_net(skb->dev) : dev_net(skb_dst(skb)->dev);
        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMREQDS);
        skb_orphan(skb);

        /* Start by cleaning up the memory. */
        ip_evictor(net);

        /* Lookup (or create) queue header */
        if ((qp = ip_find(net, ip_hdr(skb), user)) != NULL) {
                int ret;

                spin_lock(&qp->q.lock);

                ret = ip_frag_queue(qp, skb);

                spin_unlock(&qp->q.lock);
                ipq_put(qp);
                return ret;
        }

        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
        kfree_skb(skb);
        return -ENOMEM;
}
EXPORT_SYMBOL(ip_defrag);

struct sk_buff *ip_check_defrag(struct sk_buff *skb, u32 user)
{
        struct iphdr iph;
        int netoff;
        u32 len;

        if (skb->protocol != htons(ETH_P_IP))
                return skb;

        netoff = skb_network_offset(skb);

        if (skb_copy_bits(skb, netoff, &iph, sizeof(iph)) < 0)
                return skb;

        if (iph.ihl < 5 || iph.version != 4)
                return skb;

        len = ntohs(iph.tot_len);
        if (skb->len < netoff + len || len < (iph.ihl * 4))
                return skb;

        if (ip_is_fragment(&iph)) {
                skb = skb_share_check(skb, GFP_ATOMIC);
                if (skb) {
                        if (!pskb_may_pull(skb, netoff + iph.ihl * 4))
                                return skb;
                        if (pskb_trim_rcsum(skb, netoff + len))
                                return skb;
                        memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
                        if (ip_defrag(skb, user))
                                return NULL;
                        skb_clear_hash(skb);
                }
        }
        return skb;
}
EXPORT_SYMBOL(ip_check_defrag);

unsigned int inet_frag_rbtree_purge(struct rb_root *root)
{
        struct rb_node *p = rb_first(root);
        unsigned int sum = 0;

        while (p) {
                struct sk_buff *skb = rb_entry(p, struct sk_buff, rbnode);

                p = rb_next(p);
                rb_erase(&skb->rbnode, root);
                while (skb) {
                        struct sk_buff *next = FRAG_CB(skb)->next_frag;

                        sum += skb->truesize;
                        kfree_skb(skb);
                        skb = next;
                }
        }
        return sum;
}
EXPORT_SYMBOL(inet_frag_rbtree_purge);

#ifdef CONFIG_SYSCTL
static int zero;

static struct ctl_table ip4_frags_ns_ctl_table[] = {
        {
                .procname       = "ipfrag_high_thresh",
                .data           = &init_net.ipv4.frags.high_thresh,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec
        },
        {
                .procname       = "ipfrag_low_thresh",
                .data           = &init_net.ipv4.frags.low_thresh,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec
        },
        {
                .procname       = "ipfrag_time",
                .data           = &init_net.ipv4.frags.timeout,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        { }
};

static struct ctl_table ip4_frags_ctl_table[] = {
        {
                .procname       = "ipfrag_secret_interval",
                .data           = &ip4_frags.secret_interval,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        {
                .procname       = "ipfrag_max_dist",
                .data           = &sysctl_ipfrag_max_dist,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &zero
        },
        { }
};

static int __net_init ip4_frags_ns_ctl_register(struct net *net)
{
        struct ctl_table *table;
        struct ctl_table_header *hdr;

        table = ip4_frags_ns_ctl_table;
        if (!net_eq(net, &init_net)) {
                table = kmemdup(table, sizeof(ip4_frags_ns_ctl_table), GFP_KERNEL);
                if (table == NULL)
                        goto err_alloc;

                table[0].data = &net->ipv4.frags.high_thresh;
                table[1].data = &net->ipv4.frags.low_thresh;
                table[2].data = &net->ipv4.frags.timeout;

                /* Don't export sysctls to unprivileged users */
                if (net->user_ns != &init_user_ns)
                        table[0].procname = NULL;
        }

        hdr = register_net_sysctl(net, "net/ipv4", table);
        if (hdr == NULL)
                goto err_reg;

        net->ipv4.frags_hdr = hdr;
        return 0;

err_reg:
        if (!net_eq(net, &init_net))
                kfree(table);
err_alloc:
        return -ENOMEM;
}

static void __net_exit ip4_frags_ns_ctl_unregister(struct net *net)
{
        struct ctl_table *table;

        table = net->ipv4.frags_hdr->ctl_table_arg;
        unregister_net_sysctl_table(net->ipv4.frags_hdr);
        kfree(table);
}

static void ip4_frags_ctl_register(void)
{
        register_net_sysctl(&init_net, "net/ipv4", ip4_frags_ctl_table);
}
#else
static inline int ip4_frags_ns_ctl_register(struct net *net)
{
        return 0;
}

static inline void ip4_frags_ns_ctl_unregister(struct net *net)
{
}

static inline void ip4_frags_ctl_register(void)
{
}
#endif

static int __net_init ipv4_frags_init_net(struct net *net)
{
        /* Fragment cache limits.
         *
         * The fragment memory accounting code, (tries to) account for
         * the real memory usage, by measuring both the size of frag
         * queue struct (inet_frag_queue (ipv4:ipq/ipv6:frag_queue))
         * and the SKB's truesize.
         *
         * A 64K fragment consumes 129736 bytes (44*2944)+200
         * (1500 truesize == 2944, sizeof(struct ipq) == 200)
         *
         * We will commit 4MB at one time. Should we cross that limit
         * we will prune down to 3MB, making room for approx 8 big 64K
         * fragments 8x128k.
         */
        net->ipv4.frags.high_thresh = 4 * 1024 * 1024;
        net->ipv4.frags.low_thresh  = 3 * 1024 * 1024;
        /*
         * Important NOTE! Fragment queue must be destroyed before MSL expires.
         * RFC791 is wrong proposing to prolongate timer each fragment arrival
         * by TTL.
         */
        net->ipv4.frags.timeout = IP_FRAG_TIME;

        inet_frags_init_net(&net->ipv4.frags);

        return ip4_frags_ns_ctl_register(net);
}

static void __net_exit ipv4_frags_exit_net(struct net *net)
{
        ip4_frags_ns_ctl_unregister(net);
        inet_frags_exit_net(&net->ipv4.frags, &ip4_frags);
}

static struct pernet_operations ip4_frags_ops = {
        .init = ipv4_frags_init_net,
        .exit = ipv4_frags_exit_net,
};

void __init ipfrag_init(void)
{
        ip4_frags_ctl_register();
        register_pernet_subsys(&ip4_frags_ops);
        ip4_frags.hashfn = ip4_hashfn;
        ip4_frags.constructor = ip4_frag_init;
        ip4_frags.destructor = ip4_frag_free;
        ip4_frags.skb_free = NULL;
        ip4_frags.qsize = sizeof(struct ipq);
        ip4_frags.match = ip4_frag_match;
        ip4_frags.frag_expire = ip_expire;
        ip4_frags.secret_interval = 10 * 60 * HZ;

        inet_frags_init(&ip4_frags);
}