/*
 * inet fragments management
 *
 *		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.
 *
 * 		Authors:	Pavel Emelyanov <xemul@openvz.org>
 *				Started as consolidation of ipv4/ip_fragment.c,
 *				ipv6/reassembly. and ipv6 nf conntrack reassembly
 */

#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/module.h>
#include <linux/timer.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
#include <linux/slab.h>

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

/* Given the OR values of all fragments, apply RFC 3168 5.3 requirements
 * Value : 0xff if frame should be dropped.
 *         0 or INET_ECN_CE value, to be ORed in to final iph->tos field
 */
const u8 ip_frag_ecn_table[16] = {
	/* at least one fragment had CE, and others ECT_0 or ECT_1 */
	[IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0]			= INET_ECN_CE,
	[IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1]			= INET_ECN_CE,
	[IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1]	= INET_ECN_CE,

	/* invalid combinations : drop frame */
	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE] = 0xff,
	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0] = 0xff,
	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_1] = 0xff,
	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0] = 0xff,
	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1] = 0xff,
	[IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
};
EXPORT_SYMBOL(ip_frag_ecn_table);

int inet_frags_init(struct inet_frags *f)
{
	f->frags_cachep = kmem_cache_create(f->frags_cache_name, f->qsize, 0, 0,
					    NULL);
	if (!f->frags_cachep)
		return -ENOMEM;

	return 0;
}
EXPORT_SYMBOL(inet_frags_init);

void inet_frags_fini(struct inet_frags *f)
{
	/* We must wait that all inet_frag_destroy_rcu() have completed. */
	rcu_barrier();

	kmem_cache_destroy(f->frags_cachep);
	f->frags_cachep = NULL;
}
EXPORT_SYMBOL(inet_frags_fini);

static void inet_frags_free_cb(void *ptr, void *arg)
{
	struct inet_frag_queue *fq = ptr;

	/* If we can not cancel the timer, it means this frag_queue
	 * is already disappearing, we have nothing to do.
	 * Otherwise, we own a refcount until the end of this function.
	 */
	if (!del_timer(&fq->timer))
		return;

	spin_lock_bh(&fq->lock);
	if (!(fq->flags & INET_FRAG_COMPLETE)) {
		fq->flags |= INET_FRAG_COMPLETE;
		atomic_dec(&fq->refcnt);
	}
	spin_unlock_bh(&fq->lock);

	inet_frag_put(fq);
}

void inet_frags_exit_net(struct netns_frags *nf)
{
	nf->high_thresh = 0; /* prevent creation of new frags */

	rhashtable_free_and_destroy(&nf->rhashtable, inet_frags_free_cb, NULL);
}
EXPORT_SYMBOL(inet_frags_exit_net);

void inet_frag_kill(struct inet_frag_queue *fq)
{
	if (del_timer(&fq->timer))
		atomic_dec(&fq->refcnt);

	if (!(fq->flags & INET_FRAG_COMPLETE)) {
		struct netns_frags *nf = fq->net;

		fq->flags |= INET_FRAG_COMPLETE;
		rhashtable_remove_fast(&nf->rhashtable, &fq->node, nf->f->rhash_params);
		atomic_dec(&fq->refcnt);
	}
}
EXPORT_SYMBOL(inet_frag_kill);

static inline void frag_kfree_skb(struct netns_frags *nf, struct inet_frags *f,
				  struct sk_buff *skb)
{
	if (f->skb_free)
		f->skb_free(skb);
	kfree_skb(skb);
}

static void inet_frag_destroy_rcu(struct rcu_head *head)
{
	struct inet_frag_queue *q = container_of(head, struct inet_frag_queue,
						 rcu);
	struct inet_frags *f = q->net->f;

	if (f->destructor)
		f->destructor(q);
	kmem_cache_free(f->frags_cachep, q);
}

void inet_frag_destroy(struct inet_frag_queue *q)
{
	struct sk_buff *fp;
	struct netns_frags *nf;
	unsigned int sum, sum_truesize = 0;
	struct inet_frags *f;

	WARN_ON(!(q->flags & INET_FRAG_COMPLETE));
	WARN_ON(del_timer(&q->timer) != 0);

	/* Release all fragment data. */
	fp = q->fragments;
	nf = q->net;
	f = nf->f;
	if (fp) {
		do {
			struct sk_buff *xp = fp->next;

			sum_truesize += fp->truesize;
			frag_kfree_skb(nf, f, fp);
			fp = xp;
		} while (fp);
	} else {
		sum_truesize = inet_frag_rbtree_purge(&q->rb_fragments);
	}
	sum = sum_truesize + f->qsize;

	call_rcu(&q->rcu, inet_frag_destroy_rcu);

	sub_frag_mem_limit(nf, sum);
}
EXPORT_SYMBOL(inet_frag_destroy);

static struct inet_frag_queue *inet_frag_alloc(struct netns_frags *nf,
					       struct inet_frags *f,
					       void *arg)
{
	struct inet_frag_queue *q;

	if (!nf->high_thresh || frag_mem_limit(nf) > nf->high_thresh)
		return NULL;
	q = kmem_cache_zalloc(f->frags_cachep, GFP_ATOMIC);
	if (!q)
		return NULL;

	q->net = nf;
	f->constructor(q, arg);
	add_frag_mem_limit(nf, f->qsize);

	setup_timer(&q->timer, f->frag_expire, (unsigned long)q);
	spin_lock_init(&q->lock);
	atomic_set(&q->refcnt, 3);

	return q;
}

static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
						void *arg,
						struct inet_frag_queue **prev)
{
	struct inet_frags *f = nf->f;
	struct inet_frag_queue *q;

	q = inet_frag_alloc(nf, f, arg);
	if (!q) {
		*prev = ERR_PTR(-ENOMEM);
		return NULL;
	}
	mod_timer(&q->timer, jiffies + nf->timeout);

	*prev = rhashtable_lookup_get_insert_key(&nf->rhashtable, &q->key,
						 &q->node, f->rhash_params);
	if (*prev) {
		q->flags |= INET_FRAG_COMPLETE;
		inet_frag_kill(q);
		inet_frag_destroy(q);
		return NULL;
	}
	return q;
}
EXPORT_SYMBOL(inet_frag_create);

/* TODO : call from rcu_read_lock() and no longer use refcount_inc_not_zero() */
struct inet_frag_queue *inet_frag_find(struct netns_frags *nf, void *key)
{
	struct inet_frag_queue *fq = NULL, *prev;

	rcu_read_lock();
	prev = rhashtable_lookup(&nf->rhashtable, key, nf->f->rhash_params);
	if (!prev)
		fq = inet_frag_create(nf, key, &prev);
	if (prev && !IS_ERR(prev)) {
		fq = prev;
		if (!atomic_inc_not_zero(&fq->refcnt))
			fq = NULL;
	}
	rcu_read_unlock();
	return fq;
}
EXPORT_SYMBOL(inet_frag_find);