/*
 * IPv6 fragment reassembly for connection tracking
 *
 * Copyright (C)2004 USAGI/WIDE Project
 *
 * Author:
 *      Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
 *
 * Based on: net/ipv6/reassembly.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.
 */

#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/slab.h>

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

#include <net/ipv6.h>
#include <net/protocol.h>
#include <net/transp_v6.h>
#include <net/rawv6.h>
#include <net/ndisc.h>
#include <net/addrconf.h>
#include <net/netfilter/ipv6/nf_conntrack_ipv6.h>
#include <linux/sysctl.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv6.h>
#include <linux/kernel.h>
#include <linux/module.h>


struct nf_ct_frag6_skb_cb
{
        struct inet6_skb_parm   h;
        int                     offset;
        struct sk_buff          *orig;
};

#define NFCT_FRAG6_CB(skb)      ((struct nf_ct_frag6_skb_cb*)((skb)->cb))

struct nf_ct_frag6_queue
{
        struct inet_frag_queue  q;

        __be32                  id;             /* fragment id          */
        u32                     user;
        struct in6_addr         saddr;
        struct in6_addr         daddr;

        unsigned int            csum;
        __u16                   nhoffset;
};

static struct inet_frags nf_frags;
static struct netns_frags nf_init_frags;

#ifdef CONFIG_SYSCTL
struct ctl_table nf_ct_frag6_sysctl_table[] = {
        {
                .procname       = "nf_conntrack_frag6_timeout",
                .data           = &nf_init_frags.timeout,
                .maxlen         = sizeof(unsigned int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        {
                .procname       = "nf_conntrack_frag6_low_thresh",
                .data           = &nf_init_frags.low_thresh,
                .maxlen         = sizeof(unsigned int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec,
        },
        {
                .procname       = "nf_conntrack_frag6_high_thresh",
                .data           = &nf_init_frags.high_thresh,
                .maxlen         = sizeof(unsigned int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec,
        },
        { }
};

static struct ctl_table_header *nf_ct_frag6_sysctl_header;
#endif

static unsigned int nf_hashfn(struct inet_frag_queue *q)
{
        const struct nf_ct_frag6_queue *nq;

        nq = container_of(q, struct nf_ct_frag6_queue, q);
        return inet6_hash_frag(nq->id, &nq->saddr, &nq->daddr, nf_frags.rnd);
}

static void nf_skb_free(struct sk_buff *skb)
{
        if (NFCT_FRAG6_CB(skb)->orig)
                kfree_skb(NFCT_FRAG6_CB(skb)->orig);
}

/* Destruction primitives. */

static __inline__ void fq_put(struct nf_ct_frag6_queue *fq)
{
        inet_frag_put(&fq->q, &nf_frags);
}

/* Kill fq entry. It is not destroyed immediately,
 * because caller (and someone more) holds reference count.
 */
static __inline__ void fq_kill(struct nf_ct_frag6_queue *fq)
{
        inet_frag_kill(&fq->q, &nf_frags);
}

static void nf_ct_frag6_evictor(void)
{
        local_bh_disable();
        inet_frag_evictor(&nf_init_frags, &nf_frags);
        local_bh_enable();
}

static void nf_ct_frag6_expire(unsigned long data)
{
        struct nf_ct_frag6_queue *fq;

        fq = container_of((struct inet_frag_queue *)data,
                        struct nf_ct_frag6_queue, q);

        spin_lock(&fq->q.lock);

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

        fq_kill(fq);

out:
        spin_unlock(&fq->q.lock);
        fq_put(fq);
}

/* Creation primitives. */

static __inline__ struct nf_ct_frag6_queue *
fq_find(__be32 id, u32 user, struct in6_addr *src, struct in6_addr *dst)
{
        struct inet_frag_queue *q;
        struct ip6_create_arg arg;
        unsigned int hash;

        arg.id = id;
        arg.user = user;
        arg.src = src;
        arg.dst = dst;

        read_lock_bh(&nf_frags.lock);
        hash = inet6_hash_frag(id, src, dst, nf_frags.rnd);

        q = inet_frag_find(&nf_init_frags, &nf_frags, &arg, hash);
        local_bh_enable();
        if (q == NULL)
                goto oom;

        return container_of(q, struct nf_ct_frag6_queue, q);

oom:
        pr_debug("Can't alloc new queue\n");
        return NULL;
}


static int nf_ct_frag6_queue(struct nf_ct_frag6_queue *fq, struct sk_buff *skb,
                             const struct frag_hdr *fhdr, int nhoff)
{
        struct sk_buff *prev, *next;
        int offset, end;

        if (fq->q.last_in & INET_FRAG_COMPLETE) {
                pr_debug("Already completed\n");
                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) {
                pr_debug("offset is too large.\n");
                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 & INET_FRAG_LAST_IN) && end != fq->q.len)) {
                        pr_debug("already received last fragment\n");
                        goto err;
                }
                fq->q.last_in |= INET_FRAG_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
                         */
                        pr_debug("end of fragment not rounded to 8 bytes.\n");
                        return -1;
                }
                if (end > fq->q.len) {
                        /* Some bits beyond end -> corruption. */
                        if (fq->q.last_in & INET_FRAG_LAST_IN) {
                                pr_debug("last packet already reached.\n");
                                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)) {
                pr_debug("queue: message is too short.\n");
                goto err;
        }
        if (pskb_trim_rcsum(skb, end - offset)) {
                pr_debug("Can't trim\n");
                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 = fq->q.fragments_tail;
        if (!prev || NFCT_FRAG6_CB(prev)->offset < offset) {
                next = NULL;
                goto found;
        }
        prev = NULL;
        for (next = fq->q.fragments; next != NULL; next = next->next) {
                if (NFCT_FRAG6_CB(next)->offset >= offset)
                        break;  /* bingo! */
                prev = next;
        }

found:
        /* RFC5722, Section 4:
         *                                  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, including those not yet received) MUST be silently
         *   discarded.
         */

        /* Check for overlap with preceding fragment. */
        if (prev &&
            (NFCT_FRAG6_CB(prev)->offset + prev->len) > offset)
                goto discard_fq;

        /* Look for overlap with succeeding segment. */
        if (next && NFCT_FRAG6_CB(next)->offset < end)
                goto discard_fq;

        NFCT_FRAG6_CB(skb)->offset = offset;

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

        skb->dev = NULL;
        fq->q.stamp = skb->tstamp;
        fq->q.meat += skb->len;
        atomic_add(skb->truesize, &nf_init_frags.mem);

        /* The first fragment.
         * nhoffset is obtained from the first fragment, of course.
         */
        if (offset == 0) {
                fq->nhoffset = nhoff;
                fq->q.last_in |= INET_FRAG_FIRST_IN;
        }
        write_lock(&nf_frags.lock);
        list_move_tail(&fq->q.lru_list, &nf_init_frags.lru_list);
        write_unlock(&nf_frags.lock);
        return 0;

discard_fq:
        fq_kill(fq);
err:
        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 struct sk_buff *
nf_ct_frag6_reasm(struct nf_ct_frag6_queue *fq, struct net_device *dev)
{
        struct sk_buff *fp, *op, *head = fq->q.fragments;
        int    payload_len;

        fq_kill(fq);

        WARN_ON(head == NULL);
        WARN_ON(NFCT_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) {
                pr_debug("payload len is too large.\n");
                goto out_oversize;
        }

        /* Head of list must not be cloned. */
        if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC)) {
                pr_debug("skb is cloned but can't expand head");
                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_has_frag_list(head)) {
                struct sk_buff *clone;
                int i, plen = 0;

                if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL) {
                        pr_debug("Can't alloc skb\n");
                        goto out_oom;
                }
                clone->next = head->next;
                head->next = clone;
                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_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;

                NFCT_FRAG6_CB(clone)->orig = NULL;
                atomic_add(clone->truesize, &nf_init_frags.mem);
        }

        /* We have to remove fragment header from datagram and to relocate
         * header in order to calculate ICV correctly. */
        skb_network_header(head)[fq->nhoffset] = 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));

        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(head->truesize, &nf_init_frags.mem);

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

        /* 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);

        fq->q.fragments = NULL;
        fq->q.fragments_tail = NULL;

        /* all original skbs are linked into the NFCT_FRAG6_CB(head).orig */
        fp = skb_shinfo(head)->frag_list;
        if (fp && NFCT_FRAG6_CB(fp)->orig == NULL)
                /* at above code, head skb is divided into two skbs. */
                fp = fp->next;

        op = NFCT_FRAG6_CB(head)->orig;
        for (; fp; fp = fp->next) {
                struct sk_buff *orig = NFCT_FRAG6_CB(fp)->orig;

                op->next = orig;
                op = orig;
                NFCT_FRAG6_CB(fp)->orig = NULL;
        }

        return head;

out_oversize:
        if (net_ratelimit())
                printk(KERN_DEBUG "nf_ct_frag6_reasm: payload len = %d\n", payload_len);
        goto out_fail;
out_oom:
        if (net_ratelimit())
                printk(KERN_DEBUG "nf_ct_frag6_reasm: no memory for reassembly\n");
out_fail:
        return NULL;
}

/*
 * find the header just before Fragment Header.
 *
 * if success return 0 and set ...
 * (*prevhdrp): the value of "Next Header Field" in the header
 *              just before Fragment Header.
 * (*prevhoff): the offset of "Next Header Field" in the header
 *              just before Fragment Header.
 * (*fhoff)   : the offset of Fragment Header.
 *
 * Based on ipv6_skip_hdr() in net/ipv6/exthdr.c
 *
 */
static int
find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff)
{
        u8 nexthdr = ipv6_hdr(skb)->nexthdr;
        const int netoff = skb_network_offset(skb);
        u8 prev_nhoff = netoff + offsetof(struct ipv6hdr, nexthdr);
        int start = netoff + sizeof(struct ipv6hdr);
        int len = skb->len - start;
        u8 prevhdr = NEXTHDR_IPV6;

        while (nexthdr != NEXTHDR_FRAGMENT) {
                struct ipv6_opt_hdr hdr;
                int hdrlen;

                if (!ipv6_ext_hdr(nexthdr)) {
                        return -1;
                }
                if (nexthdr == NEXTHDR_NONE) {
                        pr_debug("next header is none\n");
                        return -1;
                }
                if (len < (int)sizeof(struct ipv6_opt_hdr)) {
                        pr_debug("too short\n");
                        return -1;
                }
                if (skb_copy_bits(skb, start, &hdr, sizeof(hdr)))
                        BUG();
                if (nexthdr == NEXTHDR_AUTH)
                        hdrlen = (hdr.hdrlen+2)<<2;
                else
                        hdrlen = ipv6_optlen(&hdr);

                prevhdr = nexthdr;
                prev_nhoff = start;

                nexthdr = hdr.nexthdr;
                len -= hdrlen;
                start += hdrlen;
        }

        if (len < 0)
                return -1;

        *prevhdrp = prevhdr;
        *prevhoff = prev_nhoff;
        *fhoff = start;

        return 0;
}

struct sk_buff *nf_ct_frag6_gather(struct sk_buff *skb, u32 user)
{
        struct sk_buff *clone;
        struct net_device *dev = skb->dev;
        struct frag_hdr *fhdr;
        struct nf_ct_frag6_queue *fq;
        struct ipv6hdr *hdr;
        int fhoff, nhoff;
        u8 prevhdr;
        struct sk_buff *ret_skb = NULL;

        /* Jumbo payload inhibits frag. header */
        if (ipv6_hdr(skb)->payload_len == 0) {
                pr_debug("payload len = 0\n");
                return skb;
        }

        if (find_prev_fhdr(skb, &prevhdr, &nhoff, &fhoff) < 0)
                return skb;

        clone = skb_clone(skb, GFP_ATOMIC);
        if (clone == NULL) {
                pr_debug("Can't clone skb\n");
                return skb;
        }

        NFCT_FRAG6_CB(clone)->orig = skb;

        if (!pskb_may_pull(clone, fhoff + sizeof(*fhdr))) {
                pr_debug("message is too short.\n");
                goto ret_orig;
        }

        skb_set_transport_header(clone, fhoff);
        hdr = ipv6_hdr(clone);
        fhdr = (struct frag_hdr *)skb_transport_header(clone);

        if (atomic_read(&nf_init_frags.mem) > nf_init_frags.high_thresh)
                nf_ct_frag6_evictor();

        fq = fq_find(fhdr->identification, user, &hdr->saddr, &hdr->daddr);
        if (fq == NULL) {
                pr_debug("Can't find and can't create new queue\n");
                goto ret_orig;
        }

        spin_lock_bh(&fq->q.lock);

        if (nf_ct_frag6_queue(fq, clone, fhdr, nhoff) < 0) {
                spin_unlock_bh(&fq->q.lock);
                pr_debug("Can't insert skb to queue\n");
                fq_put(fq);
                goto ret_orig;
        }

        if (fq->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
            fq->q.meat == fq->q.len) {
                ret_skb = nf_ct_frag6_reasm(fq, dev);
                if (ret_skb == NULL)
                        pr_debug("Can't reassemble fragmented packets\n");
        }
        spin_unlock_bh(&fq->q.lock);

        fq_put(fq);
        return ret_skb;

ret_orig:
        kfree_skb(clone);
        return skb;
}

void nf_ct_frag6_output(unsigned int hooknum, struct sk_buff *skb,
                        struct net_device *in, struct net_device *out,
                        int (*okfn)(struct sk_buff *))
{
        struct sk_buff *s, *s2;

        for (s = NFCT_FRAG6_CB(skb)->orig; s;) {
                nf_conntrack_put_reasm(s->nfct_reasm);
                nf_conntrack_get_reasm(skb);
                s->nfct_reasm = skb;

                s2 = s->next;
                s->next = NULL;

                NF_HOOK_THRESH(NFPROTO_IPV6, hooknum, s, in, out, okfn,
                               NF_IP6_PRI_CONNTRACK_DEFRAG + 1);
                s = s2;
        }
        nf_conntrack_put_reasm(skb);
}

int nf_ct_frag6_init(void)
{
        nf_frags.hashfn = nf_hashfn;
        nf_frags.constructor = ip6_frag_init;
        nf_frags.destructor = NULL;
        nf_frags.skb_free = nf_skb_free;
        nf_frags.qsize = sizeof(struct nf_ct_frag6_queue);
        nf_frags.match = ip6_frag_match;
        nf_frags.frag_expire = nf_ct_frag6_expire;
        nf_frags.secret_interval = 10 * 60 * HZ;
        nf_init_frags.timeout = IPV6_FRAG_TIMEOUT;
        nf_init_frags.high_thresh = IPV6_FRAG_HIGH_THRESH;
        nf_init_frags.low_thresh = IPV6_FRAG_LOW_THRESH;
        inet_frags_init_net(&nf_init_frags);
        inet_frags_init(&nf_frags);

#ifdef CONFIG_SYSCTL
        nf_ct_frag6_sysctl_header = register_sysctl_paths(nf_net_netfilter_sysctl_path,
                                                          nf_ct_frag6_sysctl_table);
        if (!nf_ct_frag6_sysctl_header) {
                inet_frags_fini(&nf_frags);
                return -ENOMEM;
        }
#endif

        return 0;
}

void nf_ct_frag6_cleanup(void)
{
#ifdef CONFIG_SYSCTL
        unregister_sysctl_table(nf_ct_frag6_sysctl_header);
        nf_ct_frag6_sysctl_header = NULL;
#endif
        inet_frags_fini(&nf_frags);

        nf_init_frags.low_thresh = 0;
        nf_ct_frag6_evictor();
}