/*      6LoWPAN fragment reassembly
 *
 *
 *      Authors:
 *      Alexander Aring         <aar@pengutronix.de>
 *
 *      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.
 */

#define pr_fmt(fmt) "6LoWPAN: " fmt

#include <linux/net.h>
#include <linux/list.h>
#include <linux/netdevice.h>
#include <linux/random.h>
#include <linux/jhash.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/export.h>

#include <net/ieee802154_netdev.h>
#include <net/6lowpan.h>
#include <net/ipv6.h>
#include <net/inet_frag.h>

#include "6lowpan_i.h"

static const char lowpan_frags_cache_name[] = "lowpan-frags";

static struct inet_frags lowpan_frags;

static int lowpan_frag_reasm(struct lowpan_frag_queue *fq,
                             struct sk_buff *prev, struct net_device *ldev);

static unsigned int lowpan_hash_frag(u16 tag, u16 d_size,
                                     const struct ieee802154_addr *saddr,
                                     const struct ieee802154_addr *daddr)
{
        net_get_random_once(&lowpan_frags.rnd, sizeof(lowpan_frags.rnd));
        return jhash_3words(ieee802154_addr_hash(saddr),
                            ieee802154_addr_hash(daddr),
                            (__force u32)(tag + (d_size << 16)),
                            lowpan_frags.rnd);
}

static unsigned int lowpan_hashfn(const struct inet_frag_queue *q)
{
        const struct lowpan_frag_queue *fq;

        fq = container_of(q, struct lowpan_frag_queue, q);
        return lowpan_hash_frag(fq->tag, fq->d_size, &fq->saddr, &fq->daddr);
}

static bool lowpan_frag_match(const struct inet_frag_queue *q, const void *a)
{
        const struct lowpan_frag_queue *fq;
        const struct lowpan_create_arg *arg = a;

        fq = container_of(q, struct lowpan_frag_queue, q);
        return  fq->tag == arg->tag && fq->d_size == arg->d_size &&
                ieee802154_addr_equal(&fq->saddr, arg->src) &&
                ieee802154_addr_equal(&fq->daddr, arg->dst);
}

static void lowpan_frag_init(struct inet_frag_queue *q, const void *a)
{
        const struct lowpan_create_arg *arg = a;
        struct lowpan_frag_queue *fq;

        fq = container_of(q, struct lowpan_frag_queue, q);

        fq->tag = arg->tag;
        fq->d_size = arg->d_size;
        fq->saddr = *arg->src;
        fq->daddr = *arg->dst;
}

static void lowpan_frag_expire(struct timer_list *t)
{
        struct inet_frag_queue *frag = from_timer(frag, t, timer);
        struct frag_queue *fq;
        struct net *net;

        fq = container_of(frag, struct frag_queue, q);
        net = container_of(fq->q.net, struct net, ieee802154_lowpan.frags);

        spin_lock(&fq->q.lock);

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

        inet_frag_kill(&fq->q, &lowpan_frags);
out:
        spin_unlock(&fq->q.lock);
        inet_frag_put(&fq->q, &lowpan_frags);
}

static inline struct lowpan_frag_queue *
fq_find(struct net *net, const struct lowpan_802154_cb *cb,
        const struct ieee802154_addr *src,
        const struct ieee802154_addr *dst)
{
        struct inet_frag_queue *q;
        struct lowpan_create_arg arg;
        unsigned int hash;
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);

        arg.tag = cb->d_tag;
        arg.d_size = cb->d_size;
        arg.src = src;
        arg.dst = dst;

        hash = lowpan_hash_frag(cb->d_tag, cb->d_size, src, dst);

        q = inet_frag_find(&ieee802154_lowpan->frags,
                           &lowpan_frags, &arg, hash);
        if (IS_ERR_OR_NULL(q)) {
                inet_frag_maybe_warn_overflow(q, pr_fmt());
                return NULL;
        }
        return container_of(q, struct lowpan_frag_queue, q);
}

static int lowpan_frag_queue(struct lowpan_frag_queue *fq,
                             struct sk_buff *skb, u8 frag_type)
{
        struct sk_buff *prev, *next;
        struct net_device *ldev;
        int end, offset;

        if (fq->q.flags & INET_FRAG_COMPLETE)
                goto err;

        offset = lowpan_802154_cb(skb)->d_offset << 3;
        end = lowpan_802154_cb(skb)->d_size;

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

        /* 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 ||
            lowpan_802154_cb(prev)->d_offset <
            lowpan_802154_cb(skb)->d_offset) {
                next = NULL;
                goto found;
        }
        prev = NULL;
        for (next = fq->q.fragments; next != NULL; next = next->next) {
                if (lowpan_802154_cb(next)->d_offset >=
                    lowpan_802154_cb(skb)->d_offset)
                        break;  /* bingo! */
                prev = next;
        }

found:
        /* 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;

        ldev = skb->dev;
        if (ldev)
                skb->dev = NULL;

        fq->q.stamp = skb->tstamp;
        if (frag_type == LOWPAN_DISPATCH_FRAG1)
                fq->q.flags |= INET_FRAG_FIRST_IN;

        fq->q.meat += skb->len;
        add_frag_mem_limit(fq->q.net, skb->truesize);

        if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
            fq->q.meat == fq->q.len) {
                int res;
                unsigned long orefdst = skb->_skb_refdst;

                skb->_skb_refdst = 0UL;
                res = lowpan_frag_reasm(fq, prev, ldev);
                skb->_skb_refdst = orefdst;
                return res;
        }

        return -1;
err:
        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 lowpan_frag_reasm(struct lowpan_frag_queue *fq, struct sk_buff *prev,
                             struct net_device *ldev)
{
        struct sk_buff *fp, *head = fq->q.fragments;
        int sum_truesize;

        inet_frag_kill(&fq->q, &lowpan_frags);

        /* 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;
                if (!fp->next)
                        fq->q.fragments_tail = fp;
                prev->next = fp;

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

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

        /* Head of list must not be cloned. */
        if (skb_unclone(head, 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_has_frag_list(head)) {
                struct sk_buff *clone;
                int i, plen = 0;

                clone = alloc_skb(0, GFP_ATOMIC);
                if (!clone)
                        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_frag_size(&skb_shinfo(head)->frags[i]);
                clone->len = head->data_len - plen;
                clone->data_len = clone->len;
                head->data_len -= clone->len;
                head->len -= clone->len;
                add_frag_mem_limit(fq->q.net, clone->truesize);
        }

        WARN_ON(head == NULL);

        sum_truesize = head->truesize;
        for (fp = head->next; fp;) {
                bool headstolen;
                int delta;
                struct sk_buff *next = fp->next;

                sum_truesize += fp->truesize;
                if (skb_try_coalesce(head, fp, &headstolen, &delta)) {
                        kfree_skb_partial(fp, headstolen);
                } else {
                        if (!skb_shinfo(head)->frag_list)
                                skb_shinfo(head)->frag_list = fp;
                        head->data_len += fp->len;
                        head->len += fp->len;
                        head->truesize += fp->truesize;
                }
                fp = next;
        }
        sub_frag_mem_limit(fq->q.net, sum_truesize);

        head->next = NULL;
        head->dev = ldev;
        head->tstamp = fq->q.stamp;

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

        return 1;
out_oom:
        net_dbg_ratelimited("lowpan_frag_reasm: no memory for reassembly\n");
        return -1;
}

static int lowpan_frag_rx_handlers_result(struct sk_buff *skb,
                                          lowpan_rx_result res)
{
        switch (res) {
        case RX_QUEUED:
                return NET_RX_SUCCESS;
        case RX_CONTINUE:
                /* nobody cared about this packet */
                net_warn_ratelimited("%s: received unknown dispatch\n",
                                     __func__);

                /* fall-through */
        default:
                /* all others failure */
                return NET_RX_DROP;
        }
}

static lowpan_rx_result lowpan_frag_rx_h_iphc(struct sk_buff *skb)
{
        int ret;

        if (!lowpan_is_iphc(*skb_network_header(skb)))
                return RX_CONTINUE;

        ret = lowpan_iphc_decompress(skb);
        if (ret < 0)
                return RX_DROP;

        return RX_QUEUED;
}

static int lowpan_invoke_frag_rx_handlers(struct sk_buff *skb)
{
        lowpan_rx_result res;

#define CALL_RXH(rxh)                   \
        do {                            \
                res = rxh(skb); \
                if (res != RX_CONTINUE) \
                        goto rxh_next;  \
        } while (0)

        /* likely at first */
        CALL_RXH(lowpan_frag_rx_h_iphc);
        CALL_RXH(lowpan_rx_h_ipv6);

rxh_next:
        return lowpan_frag_rx_handlers_result(skb, res);
#undef CALL_RXH
}

#define LOWPAN_FRAG_DGRAM_SIZE_HIGH_MASK        0x07
#define LOWPAN_FRAG_DGRAM_SIZE_HIGH_SHIFT       8

static int lowpan_get_cb(struct sk_buff *skb, u8 frag_type,
                         struct lowpan_802154_cb *cb)
{
        bool fail;
        u8 high = 0, low = 0;
        __be16 d_tag = 0;

        fail = lowpan_fetch_skb(skb, &high, 1);
        fail |= lowpan_fetch_skb(skb, &low, 1);
        /* remove the dispatch value and use first three bits as high value
         * for the datagram size
         */
        cb->d_size = (high & LOWPAN_FRAG_DGRAM_SIZE_HIGH_MASK) <<
                LOWPAN_FRAG_DGRAM_SIZE_HIGH_SHIFT | low;
        fail |= lowpan_fetch_skb(skb, &d_tag, 2);
        cb->d_tag = ntohs(d_tag);

        if (frag_type == LOWPAN_DISPATCH_FRAGN) {
                fail |= lowpan_fetch_skb(skb, &cb->d_offset, 1);
        } else {
                skb_reset_network_header(skb);
                cb->d_offset = 0;
                /* check if datagram_size has ipv6hdr on FRAG1 */
                fail |= cb->d_size < sizeof(struct ipv6hdr);
                /* check if we can dereference the dispatch value */
                fail |= !skb->len;
        }

        if (unlikely(fail))
                return -EIO;

        return 0;
}

int lowpan_frag_rcv(struct sk_buff *skb, u8 frag_type)
{
        struct lowpan_frag_queue *fq;
        struct net *net = dev_net(skb->dev);
        struct lowpan_802154_cb *cb = lowpan_802154_cb(skb);
        struct ieee802154_hdr hdr;
        int err;

        if (ieee802154_hdr_peek_addrs(skb, &hdr) < 0)
                goto err;

        err = lowpan_get_cb(skb, frag_type, cb);
        if (err < 0)
                goto err;

        if (frag_type == LOWPAN_DISPATCH_FRAG1) {
                err = lowpan_invoke_frag_rx_handlers(skb);
                if (err == NET_RX_DROP)
                        goto err;
        }

        if (cb->d_size > IPV6_MIN_MTU) {
                net_warn_ratelimited("lowpan_frag_rcv: datagram size exceeds MTU\n");
                goto err;
        }

        fq = fq_find(net, cb, &hdr.source, &hdr.dest);
        if (fq != NULL) {
                int ret;

                spin_lock(&fq->q.lock);
                ret = lowpan_frag_queue(fq, skb, frag_type);
                spin_unlock(&fq->q.lock);

                inet_frag_put(&fq->q, &lowpan_frags);
                return ret;
        }

err:
        kfree_skb(skb);
        return -1;
}

#ifdef CONFIG_SYSCTL
static int zero;

static struct ctl_table lowpan_frags_ns_ctl_table[] = {
        {
                .procname       = "6lowpanfrag_high_thresh",
                .data           = &init_net.ieee802154_lowpan.frags.high_thresh,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &init_net.ieee802154_lowpan.frags.low_thresh
        },
        {
                .procname       = "6lowpanfrag_low_thresh",
                .data           = &init_net.ieee802154_lowpan.frags.low_thresh,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &zero,
                .extra2         = &init_net.ieee802154_lowpan.frags.high_thresh
        },
        {
                .procname       = "6lowpanfrag_time",
                .data           = &init_net.ieee802154_lowpan.frags.timeout,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        { }
};

/* secret interval has been deprecated */
static int lowpan_frags_secret_interval_unused;
static struct ctl_table lowpan_frags_ctl_table[] = {
        {
                .procname       = "6lowpanfrag_secret_interval",
                .data           = &lowpan_frags_secret_interval_unused,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        { }
};

static int __net_init lowpan_frags_ns_sysctl_register(struct net *net)
{
        struct ctl_table *table;
        struct ctl_table_header *hdr;
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);

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

                table[0].data = &ieee802154_lowpan->frags.high_thresh;
                table[0].extra1 = &ieee802154_lowpan->frags.low_thresh;
                table[0].extra2 = &init_net.ieee802154_lowpan.frags.high_thresh;
                table[1].data = &ieee802154_lowpan->frags.low_thresh;
                table[1].extra2 = &ieee802154_lowpan->frags.high_thresh;
                table[2].data = &ieee802154_lowpan->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/ieee802154/6lowpan", table);
        if (hdr == NULL)
                goto err_reg;

        ieee802154_lowpan->sysctl.frags_hdr = hdr;
        return 0;

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

static void __net_exit lowpan_frags_ns_sysctl_unregister(struct net *net)
{
        struct ctl_table *table;
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);

        table = ieee802154_lowpan->sysctl.frags_hdr->ctl_table_arg;
        unregister_net_sysctl_table(ieee802154_lowpan->sysctl.frags_hdr);
        if (!net_eq(net, &init_net))
                kfree(table);
}

static struct ctl_table_header *lowpan_ctl_header;

static int __init lowpan_frags_sysctl_register(void)
{
        lowpan_ctl_header = register_net_sysctl(&init_net,
                                                "net/ieee802154/6lowpan",
                                                lowpan_frags_ctl_table);
        return lowpan_ctl_header == NULL ? -ENOMEM : 0;
}

static void lowpan_frags_sysctl_unregister(void)
{
        unregister_net_sysctl_table(lowpan_ctl_header);
}
#else
static inline int lowpan_frags_ns_sysctl_register(struct net *net)
{
        return 0;
}

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

static inline int __init lowpan_frags_sysctl_register(void)
{
        return 0;
}

static inline void lowpan_frags_sysctl_unregister(void)
{
}
#endif

static int __net_init lowpan_frags_init_net(struct net *net)
{
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);

        ieee802154_lowpan->frags.high_thresh = IPV6_FRAG_HIGH_THRESH;
        ieee802154_lowpan->frags.low_thresh = IPV6_FRAG_LOW_THRESH;
        ieee802154_lowpan->frags.timeout = IPV6_FRAG_TIMEOUT;

        inet_frags_init_net(&ieee802154_lowpan->frags);

        return lowpan_frags_ns_sysctl_register(net);
}

static void __net_exit lowpan_frags_exit_net(struct net *net)
{
        struct netns_ieee802154_lowpan *ieee802154_lowpan =
                net_ieee802154_lowpan(net);

        lowpan_frags_ns_sysctl_unregister(net);
        inet_frags_exit_net(&ieee802154_lowpan->frags, &lowpan_frags);
}

static struct pernet_operations lowpan_frags_ops = {
        .init = lowpan_frags_init_net,
        .exit = lowpan_frags_exit_net,
};

int __init lowpan_net_frag_init(void)
{
        int ret;

        ret = lowpan_frags_sysctl_register();
        if (ret)
                return ret;

        ret = register_pernet_subsys(&lowpan_frags_ops);
        if (ret)
                goto err_pernet;

        lowpan_frags.hashfn = lowpan_hashfn;
        lowpan_frags.constructor = lowpan_frag_init;
        lowpan_frags.destructor = NULL;
        lowpan_frags.qsize = sizeof(struct frag_queue);
        lowpan_frags.match = lowpan_frag_match;
        lowpan_frags.frag_expire = lowpan_frag_expire;
        lowpan_frags.frags_cache_name = lowpan_frags_cache_name;
        ret = inet_frags_init(&lowpan_frags);
        if (ret)
                goto err_pernet;

        return ret;
err_pernet:
        lowpan_frags_sysctl_unregister();
        return ret;
}

void lowpan_net_frag_exit(void)
{
        inet_frags_fini(&lowpan_frags);
        lowpan_frags_sysctl_unregister();
        unregister_pernet_subsys(&lowpan_frags_ops);
}