/* Copyright (C) 2013-2016  B.A.T.M.A.N. contributors:
 *
 * Martin Hundebøll <martin@hundeboll.net>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include "fragmentation.h"
#include "main.h"

#include <linux/atomic.h>
#include <linux/byteorder/generic.h>
#include <linux/etherdevice.h>
#include <linux/fs.h>
#include <linux/if_ether.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/lockdep.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/string.h>

#include "hard-interface.h"
#include "originator.h"
#include "packet.h"
#include "routing.h"
#include "send.h"
#include "soft-interface.h"

/**
 * batadv_frag_clear_chain - delete entries in the fragment buffer chain
 * @head: head of chain with entries.
 *
 * Free fragments in the passed hlist. Should be called with appropriate lock.
 */
static void batadv_frag_clear_chain(struct hlist_head *head)
{
        struct batadv_frag_list_entry *entry;
        struct hlist_node *node;

        hlist_for_each_entry_safe(entry, node, head, list) {
                hlist_del(&entry->list);
                kfree_skb(entry->skb);
                kfree(entry);
        }
}

/**
 * batadv_frag_purge_orig - free fragments associated to an orig
 * @orig_node: originator to free fragments from
 * @check_cb: optional function to tell if an entry should be purged
 */
void batadv_frag_purge_orig(struct batadv_orig_node *orig_node,
                            bool (*check_cb)(struct batadv_frag_table_entry *))
{
        struct batadv_frag_table_entry *chain;
        u8 i;

        for (i = 0; i < BATADV_FRAG_BUFFER_COUNT; i++) {
                chain = &orig_node->fragments[i];
                spin_lock_bh(&chain->lock);

                if (!check_cb || check_cb(chain)) {
                        batadv_frag_clear_chain(&chain->head);
                        chain->size = 0;
                }

                spin_unlock_bh(&chain->lock);
        }
}

/**
 * batadv_frag_size_limit - maximum possible size of packet to be fragmented
 *
 * Return: the maximum size of payload that can be fragmented.
 */
static int batadv_frag_size_limit(void)
{
        int limit = BATADV_FRAG_MAX_FRAG_SIZE;

        limit -= sizeof(struct batadv_frag_packet);
        limit *= BATADV_FRAG_MAX_FRAGMENTS;

        return limit;
}

/**
 * batadv_frag_init_chain - check and prepare fragment chain for new fragment
 * @chain: chain in fragments table to init
 * @seqno: sequence number of the received fragment
 *
 * Make chain ready for a fragment with sequence number "seqno". Delete existing
 * entries if they have an "old" sequence number.
 *
 * Caller must hold chain->lock.
 *
 * Return: true if chain is empty and caller can just insert the new fragment
 * without searching for the right position.
 */
static bool batadv_frag_init_chain(struct batadv_frag_table_entry *chain,
                                   u16 seqno)
{
        lockdep_assert_held(&chain->lock);

        if (chain->seqno == seqno)
                return false;

        if (!hlist_empty(&chain->head))
                batadv_frag_clear_chain(&chain->head);

        chain->size = 0;
        chain->seqno = seqno;

        return true;
}

/**
 * batadv_frag_insert_packet - insert a fragment into a fragment chain
 * @orig_node: originator that the fragment was received from
 * @skb: skb to insert
 * @chain_out: list head to attach complete chains of fragments to
 *
 * Insert a new fragment into the reverse ordered chain in the right table
 * entry. The hash table entry is cleared if "old" fragments exist in it.
 *
 * Return: true if skb is buffered, false on error. If the chain has all the
 * fragments needed to merge the packet, the chain is moved to the passed head
 * to avoid locking the chain in the table.
 */
static bool batadv_frag_insert_packet(struct batadv_orig_node *orig_node,
                                      struct sk_buff *skb,
                                      struct hlist_head *chain_out)
{
        struct batadv_frag_table_entry *chain;
        struct batadv_frag_list_entry *frag_entry_new = NULL, *frag_entry_curr;
        struct batadv_frag_list_entry *frag_entry_last = NULL;
        struct batadv_frag_packet *frag_packet;
        u8 bucket;
        u16 seqno, hdr_size = sizeof(struct batadv_frag_packet);
        bool ret = false;

        /* Linearize packet to avoid linearizing 16 packets in a row when doing
         * the later merge. Non-linear merge should be added to remove this
         * linearization.
         */
        if (skb_linearize(skb) < 0)
                goto err;

        frag_packet = (struct batadv_frag_packet *)skb->data;
        seqno = ntohs(frag_packet->seqno);
        bucket = seqno % BATADV_FRAG_BUFFER_COUNT;

        frag_entry_new = kmalloc(sizeof(*frag_entry_new), GFP_ATOMIC);
        if (!frag_entry_new)
                goto err;

        frag_entry_new->skb = skb;
        frag_entry_new->no = frag_packet->no;

        /* Select entry in the "chain table" and delete any prior fragments
         * with another sequence number. batadv_frag_init_chain() returns true,
         * if the list is empty at return.
         */
        chain = &orig_node->fragments[bucket];
        spin_lock_bh(&chain->lock);
        if (batadv_frag_init_chain(chain, seqno)) {
                hlist_add_head(&frag_entry_new->list, &chain->head);
                chain->size = skb->len - hdr_size;
                chain->timestamp = jiffies;
                chain->total_size = ntohs(frag_packet->total_size);
                ret = true;
                goto out;
        }

        /* Find the position for the new fragment. */
        hlist_for_each_entry(frag_entry_curr, &chain->head, list) {
                /* Drop packet if fragment already exists. */
                if (frag_entry_curr->no == frag_entry_new->no)
                        goto err_unlock;

                /* Order fragments from highest to lowest. */
                if (frag_entry_curr->no < frag_entry_new->no) {
                        hlist_add_before(&frag_entry_new->list,
                                         &frag_entry_curr->list);
                        chain->size += skb->len - hdr_size;
                        chain->timestamp = jiffies;
                        ret = true;
                        goto out;
                }

                /* store current entry because it could be the last in list */
                frag_entry_last = frag_entry_curr;
        }

        /* Reached the end of the list, so insert after 'frag_entry_last'. */
        if (likely(frag_entry_last)) {
                hlist_add_behind(&frag_entry_new->list, &frag_entry_last->list);
                chain->size += skb->len - hdr_size;
                chain->timestamp = jiffies;
                ret = true;
        }

out:
        if (chain->size > batadv_frag_size_limit() ||
            chain->total_size != ntohs(frag_packet->total_size) ||
            chain->total_size > batadv_frag_size_limit()) {
                /* Clear chain if total size of either the list or the packet
                 * exceeds the maximum size of one merged packet. Don't allow
                 * packets to have different total_size.
                 */
                batadv_frag_clear_chain(&chain->head);
                chain->size = 0;
        } else if (ntohs(frag_packet->total_size) == chain->size) {
                /* All fragments received. Hand over chain to caller. */
                hlist_move_list(&chain->head, chain_out);
                chain->size = 0;
        }

err_unlock:
        spin_unlock_bh(&chain->lock);

err:
        if (!ret)
                kfree(frag_entry_new);

        return ret;
}

/**
 * batadv_frag_merge_packets - merge a chain of fragments
 * @chain: head of chain with fragments
 *
 * Expand the first skb in the chain and copy the content of the remaining
 * skb's into the expanded one. After doing so, clear the chain.
 *
 * Return: the merged skb or NULL on error.
 */
static struct sk_buff *
batadv_frag_merge_packets(struct hlist_head *chain)
{
        struct batadv_frag_packet *packet;
        struct batadv_frag_list_entry *entry;
        struct sk_buff *skb_out = NULL;
        int size, hdr_size = sizeof(struct batadv_frag_packet);

        /* Remove first entry, as this is the destination for the rest of the
         * fragments.
         */
        entry = hlist_entry(chain->first, struct batadv_frag_list_entry, list);
        hlist_del(&entry->list);
        skb_out = entry->skb;
        kfree(entry);

        packet = (struct batadv_frag_packet *)skb_out->data;
        size = ntohs(packet->total_size);

        /* Make room for the rest of the fragments. */
        if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {
                kfree_skb(skb_out);
                skb_out = NULL;
                goto free;
        }

        /* Move the existing MAC header to just before the payload. (Override
         * the fragment header.)
         */
        skb_pull_rcsum(skb_out, hdr_size);
        memmove(skb_out->data - ETH_HLEN, skb_mac_header(skb_out), ETH_HLEN);
        skb_set_mac_header(skb_out, -ETH_HLEN);
        skb_reset_network_header(skb_out);
        skb_reset_transport_header(skb_out);

        /* Copy the payload of the each fragment into the last skb */
        hlist_for_each_entry(entry, chain, list) {
                size = entry->skb->len - hdr_size;
                memcpy(skb_put(skb_out, size), entry->skb->data + hdr_size,
                       size);
        }

free:
        /* Locking is not needed, because 'chain' is not part of any orig. */
        batadv_frag_clear_chain(chain);
        return skb_out;
}

/**
 * batadv_frag_skb_buffer - buffer fragment for later merge
 * @skb: skb to buffer
 * @orig_node_src: originator that the skb is received from
 *
 * Add fragment to buffer and merge fragments if possible.
 *
 * There are three possible outcomes: 1) Packet is merged: Return true and
 * set *skb to merged packet; 2) Packet is buffered: Return true and set *skb
 * to NULL; 3) Error: Return false and leave skb as is.
 *
 * Return: true when packet is merged or buffered, false when skb is not not
 * used.
 */
bool batadv_frag_skb_buffer(struct sk_buff **skb,
                            struct batadv_orig_node *orig_node_src)
{
        struct sk_buff *skb_out = NULL;
        struct hlist_head head = HLIST_HEAD_INIT;
        bool ret = false;

        /* Add packet to buffer and table entry if merge is possible. */
        if (!batadv_frag_insert_packet(orig_node_src, *skb, &head))
                goto out_err;

        /* Leave if more fragments are needed to merge. */
        if (hlist_empty(&head))
                goto out;

        skb_out = batadv_frag_merge_packets(&head);
        if (!skb_out)
                goto out_err;

out:
        *skb = skb_out;
        ret = true;
out_err:
        return ret;
}

/**
 * batadv_frag_skb_fwd - forward fragments that would exceed MTU when merged
 * @skb: skb to forward
 * @recv_if: interface that the skb is received on
 * @orig_node_src: originator that the skb is received from
 *
 * Look up the next-hop of the fragments payload and check if the merged packet
 * will exceed the MTU towards the next-hop. If so, the fragment is forwarded
 * without merging it.
 *
 * Return: true if the fragment is consumed/forwarded, false otherwise.
 */
bool batadv_frag_skb_fwd(struct sk_buff *skb,
                         struct batadv_hard_iface *recv_if,
                         struct batadv_orig_node *orig_node_src)
{
        struct batadv_priv *bat_priv = netdev_priv(recv_if->soft_iface);
        struct batadv_orig_node *orig_node_dst = NULL;
        struct batadv_neigh_node *neigh_node = NULL;
        struct batadv_frag_packet *packet;
        u16 total_size;
        bool ret = false;

        packet = (struct batadv_frag_packet *)skb->data;
        orig_node_dst = batadv_orig_hash_find(bat_priv, packet->dest);
        if (!orig_node_dst)
                goto out;

        neigh_node = batadv_find_router(bat_priv, orig_node_dst, recv_if);
        if (!neigh_node)
                goto out;

        /* Forward the fragment, if the merged packet would be too big to
         * be assembled.
         */
        total_size = ntohs(packet->total_size);
        if (total_size > neigh_node->if_incoming->net_dev->mtu) {
                batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_FWD);
                batadv_add_counter(bat_priv, BATADV_CNT_FRAG_FWD_BYTES,
                                   skb->len + ETH_HLEN);

                packet->ttl--;
                batadv_send_unicast_skb(skb, neigh_node);
                ret = true;
        }

out:
        if (orig_node_dst)
                batadv_orig_node_put(orig_node_dst);
        if (neigh_node)
                batadv_neigh_node_put(neigh_node);
        return ret;
}

/**
 * batadv_frag_create - create a fragment from skb
 * @skb: skb to create fragment from
 * @frag_head: header to use in new fragment
 * @mtu: size of new fragment
 *
 * Split the passed skb into two fragments: A new one with size matching the
 * passed mtu and the old one with the rest. The new skb contains data from the
 * tail of the old skb.
 *
 * Return: the new fragment, NULL on error.
 */
static struct sk_buff *batadv_frag_create(struct sk_buff *skb,
                                          struct batadv_frag_packet *frag_head,
                                          unsigned int mtu)
{
        struct sk_buff *skb_fragment;
        unsigned int header_size = sizeof(*frag_head);
        unsigned int fragment_size = mtu - header_size;

        skb_fragment = netdev_alloc_skb(NULL, mtu + ETH_HLEN);
        if (!skb_fragment)
                goto err;

        skb_fragment->priority = skb->priority;

        /* Eat the last mtu-bytes of the skb */
        skb_reserve(skb_fragment, header_size + ETH_HLEN);
        skb_split(skb, skb_fragment, skb->len - fragment_size);

        /* Add the header */
        skb_push(skb_fragment, header_size);
        memcpy(skb_fragment->data, frag_head, header_size);

err:
        return skb_fragment;
}

/**
 * batadv_frag_send_packet - create up to 16 fragments from the passed skb
 * @skb: skb to create fragments from
 * @orig_node: final destination of the created fragments
 * @neigh_node: next-hop of the created fragments
 *
 * Return: the netdev tx status or -1 in case of error.
 * When -1 is returned the skb is not consumed.
 */
int batadv_frag_send_packet(struct sk_buff *skb,
                            struct batadv_orig_node *orig_node,
                            struct batadv_neigh_node *neigh_node)
{
        struct batadv_priv *bat_priv;
        struct batadv_hard_iface *primary_if = NULL;
        struct batadv_frag_packet frag_header;
        struct sk_buff *skb_fragment;
        unsigned int mtu = neigh_node->if_incoming->net_dev->mtu;
        unsigned int header_size = sizeof(frag_header);
        unsigned int max_fragment_size, max_packet_size;
        int ret = -1;

        /* To avoid merge and refragmentation at next-hops we never send
         * fragments larger than BATADV_FRAG_MAX_FRAG_SIZE
         */
        mtu = min_t(unsigned int, mtu, BATADV_FRAG_MAX_FRAG_SIZE);
        max_fragment_size = mtu - header_size;
        max_packet_size = max_fragment_size * BATADV_FRAG_MAX_FRAGMENTS;

        /* Don't even try to fragment, if we need more than 16 fragments */
        if (skb->len > max_packet_size)
                goto out;

        bat_priv = orig_node->bat_priv;
        primary_if = batadv_primary_if_get_selected(bat_priv);
        if (!primary_if)
                goto out;

        /* Create one header to be copied to all fragments */
        frag_header.packet_type = BATADV_UNICAST_FRAG;
        frag_header.version = BATADV_COMPAT_VERSION;
        frag_header.ttl = BATADV_TTL;
        frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
        frag_header.reserved = 0;
        frag_header.no = 0;
        frag_header.total_size = htons(skb->len);

        /* skb->priority values from 256->263 are magic values to
         * directly indicate a specific 802.1d priority.  This is used
         * to allow 802.1d priority to be passed directly in from VLAN
         * tags, etc.
         */
        if (skb->priority >= 256 && skb->priority <= 263)
                frag_header.priority = skb->priority - 256;

        ether_addr_copy(frag_header.orig, primary_if->net_dev->dev_addr);
        ether_addr_copy(frag_header.dest, orig_node->orig);

        /* Eat and send fragments from the tail of skb */
        while (skb->len > max_fragment_size) {
                skb_fragment = batadv_frag_create(skb, &frag_header, mtu);
                if (!skb_fragment)
                        goto out;

                batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
                batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
                                   skb_fragment->len + ETH_HLEN);
                ret = batadv_send_unicast_skb(skb_fragment, neigh_node);
                if (ret != NET_XMIT_SUCCESS) {
                        /* return -1 so that the caller can free the original
                         * skb
                         */
                        ret = -1;
                        goto out;
                }

                frag_header.no++;

                /* The initial check in this function should cover this case */
                if (frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1) {
                        ret = -1;
                        goto out;
                }
        }

        /* Make room for the fragment header. */
        if (batadv_skb_head_push(skb, header_size) < 0 ||
            pskb_expand_head(skb, header_size + ETH_HLEN, 0, GFP_ATOMIC) < 0)
                goto out;

        memcpy(skb->data, &frag_header, header_size);

        /* Send the last fragment */
        batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
        batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
                           skb->len + ETH_HLEN);
        ret = batadv_send_unicast_skb(skb, neigh_node);

out:
        if (primary_if)
                batadv_hardif_put(primary_if);

        return ret;
}