/*
 *      IPv6 fragment reassembly
 *      Linux INET6 implementation
 *
 *      Authors:
 *      Pedro Roque             <roque@di.fc.ul.pt>
 *
 *      $Id: reassembly.c,v 1.26 2001/03/07 22:00:57 davem Exp $
 *
 *      Based on: net/ipv4/ip_fragment.c
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */

/*
 *      Fixes:
 *      Andi Kleen      Make it work with multiple hosts.
 *                      More RFC compliance.
 *
 *      Horst von Brand Add missing #include <linux/string.h>
 *      Alexey Kuznetsov        SMP races, threading, cleanup.
 *      Patrick McHardy         LRU queue of frag heads for evictor.
 *      Mitsuru KANDA @USAGI    Register inet6_protocol{}.
 *      David Stevens and
 *      YOSHIFUJI,H. @USAGI     Always remove fragment header to
 *                              calculate ICV correctly.
 */
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/jiffies.h>
#include <linux/net.h>
#include <linux/list.h>
#include <linux/netdevice.h>
#include <linux/in6.h>
#include <linux/ipv6.h>
#include <linux/icmpv6.h>
#include <linux/random.h>
#include <linux/jhash.h>
#include <linux/skbuff.h>

#include <net/sock.h>
#include <net/snmp.h>

#include <net/ipv6.h>
#include <net/ip6_route.h>
#include <net/protocol.h>
#include <net/transp_v6.h>
#include <net/rawv6.h>
#include <net/ndisc.h>
#include <net/addrconf.h>
#include <net/inet_frag.h>

struct ip6frag_skb_cb
{
        struct inet6_skb_parm   h;
        int                     offset;
};

#define FRAG6_CB(skb)   ((struct ip6frag_skb_cb*)((skb)->cb))


/*
 *      Equivalent of ipv4 struct ipq
 */

struct frag_queue
{
        struct inet_frag_queue  q;

        __be32                  id;             /* fragment id          */
        struct in6_addr         saddr;
        struct in6_addr         daddr;

        int                     iif;
        unsigned int            csum;
        __u16                   nhoffset;
};

struct inet_frags_ctl ip6_frags_ctl __read_mostly = {
        .high_thresh     = 256 * 1024,
        .low_thresh      = 192 * 1024,
        .timeout         = IPV6_FRAG_TIMEOUT,
        .secret_interval = 10 * 60 * HZ,
};

static struct inet_frags ip6_frags;

int ip6_frag_nqueues(void)
{
        return ip6_frags.nqueues;
}

int ip6_frag_mem(void)
{
        return atomic_read(&ip6_frags.mem);
}

static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
                          struct net_device *dev);

/*
 * callers should be careful not to use the hash value outside the ipfrag_lock
 * as doing so could race with ipfrag_hash_rnd being recalculated.
 */
static unsigned int ip6qhashfn(__be32 id, struct in6_addr *saddr,
                               struct in6_addr *daddr)
{
        u32 a, b, c;

        a = (__force u32)saddr->s6_addr32[0];
        b = (__force u32)saddr->s6_addr32[1];
        c = (__force u32)saddr->s6_addr32[2];

        a += JHASH_GOLDEN_RATIO;
        b += JHASH_GOLDEN_RATIO;
        c += ip6_frags.rnd;
        __jhash_mix(a, b, c);

        a += (__force u32)saddr->s6_addr32[3];
        b += (__force u32)daddr->s6_addr32[0];
        c += (__force u32)daddr->s6_addr32[1];
        __jhash_mix(a, b, c);

        a += (__force u32)daddr->s6_addr32[2];
        b += (__force u32)daddr->s6_addr32[3];
        c += (__force u32)id;
        __jhash_mix(a, b, c);

        return c & (INETFRAGS_HASHSZ - 1);
}

static unsigned int ip6_hashfn(struct inet_frag_queue *q)
{
        struct frag_queue *fq;

        fq = container_of(q, struct frag_queue, q);
        return ip6qhashfn(fq->id, &fq->saddr, &fq->daddr);
}

int ip6_frag_match(struct inet_frag_queue *q, void *a)
{
        struct frag_queue *fq;
        struct ip6_create_arg *arg = a;

        fq = container_of(q, struct frag_queue, q);
        return (fq->id == arg->id &&
                        ipv6_addr_equal(&fq->saddr, arg->src) &&
                        ipv6_addr_equal(&fq->daddr, arg->dst));
}
EXPORT_SYMBOL(ip6_frag_match);

/* Memory Tracking Functions. */
static inline void frag_kfree_skb(struct sk_buff *skb, int *work)
{
        if (work)
                *work -= skb->truesize;
        atomic_sub(skb->truesize, &ip6_frags.mem);
        kfree_skb(skb);
}

void ip6_frag_init(struct inet_frag_queue *q, void *a)
{
        struct frag_queue *fq = container_of(q, struct frag_queue, q);
        struct ip6_create_arg *arg = a;

        fq->id = arg->id;
        ipv6_addr_copy(&fq->saddr, arg->src);
        ipv6_addr_copy(&fq->daddr, arg->dst);
}
EXPORT_SYMBOL(ip6_frag_init);

/* Destruction primitives. */

static __inline__ void fq_put(struct frag_queue *fq)
{
        inet_frag_put(&fq->q, &ip6_frags);
}

/* Kill fq entry. It is not destroyed immediately,
 * because caller (and someone more) holds reference count.
 */
static __inline__ void fq_kill(struct frag_queue *fq)
{
        inet_frag_kill(&fq->q, &ip6_frags);
}

static void ip6_evictor(struct inet6_dev *idev)
{
        int evicted;

        evicted = inet_frag_evictor(&ip6_frags);
        if (evicted)
                IP6_ADD_STATS_BH(idev, IPSTATS_MIB_REASMFAILS, evicted);
}

static void ip6_frag_expire(unsigned long data)
{
        struct frag_queue *fq;
        struct net_device *dev = NULL;

        fq = container_of((struct inet_frag_queue *)data, struct frag_queue, q);

        spin_lock(&fq->q.lock);

        if (fq->q.last_in & COMPLETE)
                goto out;

        fq_kill(fq);

        dev = dev_get_by_index(&init_net, fq->iif);
        if (!dev)
                goto out;

        rcu_read_lock();
        IP6_INC_STATS_BH(__in6_dev_get(dev), IPSTATS_MIB_REASMTIMEOUT);
        IP6_INC_STATS_BH(__in6_dev_get(dev), IPSTATS_MIB_REASMFAILS);
        rcu_read_unlock();

        /* Don't send error if the first segment did not arrive. */
        if (!(fq->q.last_in&FIRST_IN) || !fq->q.fragments)
                goto out;

        /*
           But use as source device on which LAST ARRIVED
           segment was received. And do not use fq->dev
           pointer directly, device might already disappeared.
         */
        fq->q.fragments->dev = dev;
        icmpv6_send(fq->q.fragments, ICMPV6_TIME_EXCEED, ICMPV6_EXC_FRAGTIME, 0, dev);
out:
        if (dev)
                dev_put(dev);
        spin_unlock(&fq->q.lock);
        fq_put(fq);
}

static __inline__ struct frag_queue *
fq_find(__be32 id, struct in6_addr *src, struct in6_addr *dst,
        struct inet6_dev *idev)
{
        struct inet_frag_queue *q;
        struct ip6_create_arg arg;
        unsigned int hash;

        arg.id = id;
        arg.src = src;
        arg.dst = dst;
        hash = ip6qhashfn(id, src, dst);

        q = inet_frag_find(&ip6_frags, &arg, hash);
        if (q == NULL)
                goto oom;

        return container_of(q, struct frag_queue, q);

oom:
        IP6_INC_STATS_BH(idev, IPSTATS_MIB_REASMFAILS);
        return NULL;
}

static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
                           struct frag_hdr *fhdr, int nhoff)
{
        struct sk_buff *prev, *next;
        struct net_device *dev;
        int offset, end;

        if (fq->q.last_in & COMPLETE)
                goto err;

        offset = ntohs(fhdr->frag_off) & ~0x7;
        end = offset + (ntohs(ipv6_hdr(skb)->payload_len) -
                        ((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));

        if ((unsigned int)end > IPV6_MAXPLEN) {
                IP6_INC_STATS_BH(ip6_dst_idev(skb->dst),
                                 IPSTATS_MIB_INHDRERRORS);
                icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
                                  ((u8 *)&fhdr->frag_off -
                                   skb_network_header(skb)));
                return -1;
        }

        if (skb->ip_summed == CHECKSUM_COMPLETE) {
                const unsigned char *nh = skb_network_header(skb);
                skb->csum = csum_sub(skb->csum,
                                     csum_partial(nh, (u8 *)(fhdr + 1) - nh,
                                                  0));
        }

        /* Is this the final fragment? */
        if (!(fhdr->frag_off & htons(IP6_MF))) {
                /* If we already have some bits beyond end
                 * or have different end, the segment is corrupted.
                 */
                if (end < fq->q.len ||
                    ((fq->q.last_in & LAST_IN) && end != fq->q.len))
                        goto err;
                fq->q.last_in |= LAST_IN;
                fq->q.len = end;
        } else {
                /* Check if the fragment is rounded to 8 bytes.
                 * Required by the RFC.
                 */
                if (end & 0x7) {
                        /* RFC2460 says always send parameter problem in
                         * this case. -DaveM
                         */
                        IP6_INC_STATS_BH(ip6_dst_idev(skb->dst),
                                         IPSTATS_MIB_INHDRERRORS);
                        icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
                                          offsetof(struct ipv6hdr, payload_len));
                        return -1;
                }
                if (end > fq->q.len) {
                        /* Some bits beyond end -> corruption. */
                        if (fq->q.last_in & LAST_IN)
                                goto err;
                        fq->q.len = end;
                }
        }

        if (end == offset)
                goto err;

        /* Point into the IP datagram 'data' part. */
        if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data))
                goto err;

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

        /* Find out which fragments are in front and at the back of us
         * in the chain of fragments so far.  We must know where to put
         * this fragment, right?
         */
        prev = NULL;
        for(next = fq->q.fragments; next != NULL; next = next->next) {
                if (FRAG6_CB(next)->offset >= offset)
                        break;  /* bingo! */
                prev = next;
        }

        /* We found where to put this one.  Check for overlap with
         * preceding fragment, and, if needed, align things so that
         * any overlaps are eliminated.
         */
        if (prev) {
                int i = (FRAG6_CB(prev)->offset + prev->len) - offset;

                if (i > 0) {
                        offset += i;
                        if (end <= offset)
                                goto err;
                        if (!pskb_pull(skb, i))
                                goto err;
                        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
                                skb->ip_summed = CHECKSUM_NONE;
                }
        }

        /* Look for overlap with succeeding segments.
         * If we can merge fragments, do it.
         */
        while (next && FRAG6_CB(next)->offset < end) {
                int i = end - FRAG6_CB(next)->offset; /* overlap is 'i' bytes */

                if (i < next->len) {
                        /* Eat head of the next overlapped fragment
                         * and leave the loop. The next ones cannot overlap.
                         */
                        if (!pskb_pull(next, i))
                                goto err;
                        FRAG6_CB(next)->offset += i;    /* next fragment */
                        fq->q.meat -= i;
                        if (next->ip_summed != CHECKSUM_UNNECESSARY)
                                next->ip_summed = CHECKSUM_NONE;
                        break;
                } else {
                        struct sk_buff *free_it = next;

                        /* Old fragment is completely overridden with
                         * new one drop it.
                         */
                        next = next->next;

                        if (prev)
                                prev->next = next;
                        else
                                fq->q.fragments = next;

                        fq->q.meat -= free_it->len;
                        frag_kfree_skb(free_it, NULL);
                }
        }

        FRAG6_CB(skb)->offset = offset;

        /* Insert this fragment in the chain of fragments. */
        skb->next = next;
        if (prev)
                prev->next = skb;
        else
                fq->q.fragments = skb;

        dev = skb->dev;
        if (dev) {
                fq->iif = dev->ifindex;
                skb->dev = NULL;
        }
        fq->q.stamp = skb->tstamp;
        fq->q.meat += skb->len;
        atomic_add(skb->truesize, &ip6_frags.mem);

        /* The first fragment.
         * nhoffset is obtained from the first fragment, of course.
         */
        if (offset == 0) {
                fq->nhoffset = nhoff;
                fq->q.last_in |= FIRST_IN;
        }

        if (fq->q.last_in == (FIRST_IN | LAST_IN) && fq->q.meat == fq->q.len)
                return ip6_frag_reasm(fq, prev, dev);

        write_lock(&ip6_frags.lock);
        list_move_tail(&fq->q.lru_list, &ip6_frags.lru_list);
        write_unlock(&ip6_frags.lock);
        return -1;

err:
        IP6_INC_STATS(ip6_dst_idev(skb->dst), IPSTATS_MIB_REASMFAILS);
        kfree_skb(skb);
        return -1;
}

/*
 *      Check if this packet is complete.
 *      Returns NULL on failure by any reason, and pointer
 *      to current nexthdr field in reassembled frame.
 *
 *      It is called with locked fq, and caller must check that
 *      queue is eligible for reassembly i.e. it is not COMPLETE,
 *      the last and the first frames arrived and all the bits are here.
 */
static int ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
                          struct net_device *dev)
{
        struct sk_buff *fp, *head = fq->q.fragments;
        int    payload_len;
        unsigned int nhoff;

        fq_kill(fq);

        /* Make the one we just received the head. */
        if (prev) {
                head = prev->next;
                fp = skb_clone(head, GFP_ATOMIC);

                if (!fp)
                        goto out_oom;

                fp->next = head->next;
                prev->next = fp;

                skb_morph(head, fq->q.fragments);
                head->next = fq->q.fragments->next;

                kfree_skb(fq->q.fragments);
                fq->q.fragments = head;
        }

        BUG_TRAP(head != NULL);
        BUG_TRAP(FRAG6_CB(head)->offset == 0);

        /* Unfragmented part is taken from the first segment. */
        payload_len = ((head->data - skb_network_header(head)) -
                       sizeof(struct ipv6hdr) + fq->q.len -
                       sizeof(struct frag_hdr));
        if (payload_len > IPV6_MAXPLEN)
                goto out_oversize;

        /* Head of list must not be cloned. */
        if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
                goto out_oom;

        /* 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_shinfo(head)->frag_list) {
                struct sk_buff *clone;
                int i, plen = 0;

                if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
                        goto out_oom;
                clone->next = head->next;
                head->next = clone;
                skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
                skb_shinfo(head)->frag_list = NULL;
                for (i=0; i<skb_shinfo(head)->nr_frags; i++)
                        plen += skb_shinfo(head)->frags[i].size;
                clone->len = clone->data_len = head->data_len - plen;
                head->data_len -= clone->len;
                head->len -= clone->len;
                clone->csum = 0;
                clone->ip_summed = head->ip_summed;
                atomic_add(clone->truesize, &ip6_frags.mem);
        }

        /* We have to remove fragment header from datagram and to relocate
         * header in order to calculate ICV correctly. */
        nhoff = fq->nhoffset;
        skb_network_header(head)[nhoff] = skb_transport_header(head)[0];
        memmove(head->head + sizeof(struct frag_hdr), head->head,
                (head->data - head->head) - sizeof(struct frag_hdr));
        head->mac_header += sizeof(struct frag_hdr);
        head->network_header += sizeof(struct frag_hdr);

        skb_shinfo(head)->frag_list = head->next;
        skb_reset_transport_header(head);
        skb_push(head, head->data - skb_network_header(head));
        atomic_sub(head->truesize, &ip6_frags.mem);

        for (fp=head->next; fp; fp = fp->next) {
                head->data_len += fp->len;
                head->len += fp->len;
                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);
                head->truesize += fp->truesize;
                atomic_sub(fp->truesize, &ip6_frags.mem);
        }

        head->next = NULL;
        head->dev = dev;
        head->tstamp = fq->q.stamp;
        ipv6_hdr(head)->payload_len = htons(payload_len);
        IP6CB(head)->nhoff = nhoff;

        /* Yes, and fold redundant checksum back. 8) */
        if (head->ip_summed == CHECKSUM_COMPLETE)
                head->csum = csum_partial(skb_network_header(head),
                                          skb_network_header_len(head),
                                          head->csum);

        rcu_read_lock();
        IP6_INC_STATS_BH(__in6_dev_get(dev), IPSTATS_MIB_REASMOKS);
        rcu_read_unlock();
        fq->q.fragments = NULL;
        return 1;

out_oversize:
        if (net_ratelimit())
                printk(KERN_DEBUG "ip6_frag_reasm: payload len = %d\n", payload_len);
        goto out_fail;
out_oom:
        if (net_ratelimit())
                printk(KERN_DEBUG "ip6_frag_reasm: no memory for reassembly\n");
out_fail:
        rcu_read_lock();
        IP6_INC_STATS_BH(__in6_dev_get(dev), IPSTATS_MIB_REASMFAILS);
        rcu_read_unlock();
        return -1;
}

static int ipv6_frag_rcv(struct sk_buff *skb)
{
        struct frag_hdr *fhdr;
        struct frag_queue *fq;
        struct ipv6hdr *hdr = ipv6_hdr(skb);

        IP6_INC_STATS_BH(ip6_dst_idev(skb->dst), IPSTATS_MIB_REASMREQDS);

        /* Jumbo payload inhibits frag. header */
        if (hdr->payload_len==0) {
                IP6_INC_STATS(ip6_dst_idev(skb->dst), IPSTATS_MIB_INHDRERRORS);
                icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
                                  skb_network_header_len(skb));
                return -1;
        }
        if (!pskb_may_pull(skb, (skb_transport_offset(skb) +
                                 sizeof(struct frag_hdr)))) {
                IP6_INC_STATS(ip6_dst_idev(skb->dst), IPSTATS_MIB_INHDRERRORS);
                icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
                                  skb_network_header_len(skb));
                return -1;
        }

        hdr = ipv6_hdr(skb);
        fhdr = (struct frag_hdr *)skb_transport_header(skb);

        if (!(fhdr->frag_off & htons(0xFFF9))) {
                /* It is not a fragmented frame */
                skb->transport_header += sizeof(struct frag_hdr);
                IP6_INC_STATS_BH(ip6_dst_idev(skb->dst), IPSTATS_MIB_REASMOKS);

                IP6CB(skb)->nhoff = (u8 *)fhdr - skb_network_header(skb);
                return 1;
        }

        if (atomic_read(&ip6_frags.mem) > ip6_frags_ctl.high_thresh)
                ip6_evictor(ip6_dst_idev(skb->dst));

        if ((fq = fq_find(fhdr->identification, &hdr->saddr, &hdr->daddr,
                          ip6_dst_idev(skb->dst))) != NULL) {
                int ret;

                spin_lock(&fq->q.lock);

                ret = ip6_frag_queue(fq, skb, fhdr, IP6CB(skb)->nhoff);

                spin_unlock(&fq->q.lock);
                fq_put(fq);
                return ret;
        }

        IP6_INC_STATS_BH(ip6_dst_idev(skb->dst), IPSTATS_MIB_REASMFAILS);
        kfree_skb(skb);
        return -1;
}

static struct inet6_protocol frag_protocol =
{
        .handler        =       ipv6_frag_rcv,
        .flags          =       INET6_PROTO_NOPOLICY,
};

void __init ipv6_frag_init(void)
{
        if (inet6_add_protocol(&frag_protocol, IPPROTO_FRAGMENT) < 0)
                printk(KERN_ERR "ipv6_frag_init: Could not register protocol\n");

        ip6_frags.ctl = &ip6_frags_ctl;
        ip6_frags.hashfn = ip6_hashfn;
        ip6_frags.constructor = ip6_frag_init;
        ip6_frags.destructor = NULL;
        ip6_frags.skb_free = NULL;
        ip6_frags.qsize = sizeof(struct frag_queue);
        ip6_frags.match = ip6_frag_match;
        ip6_frags.frag_expire = ip6_frag_expire;
        inet_frags_init(&ip6_frags);
}