/*
   * 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>

  #define INETFRAGS_EVICT_BUCKETS   128
  #define INETFRAGS_EVICT_MAX	  512

  /* don't rebuild inetfrag table with new secret more often than this */
  #define INETFRAGS_MIN_REBUILD_INTERVAL (5 * HZ)

  /* 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);

  static unsigned int
  inet_frag_hashfn(const struct inet_frags *f, const struct inet_frag_queue *q)
  {
  	return f->hashfn(q) & (INETFRAGS_HASHSZ - 1);
  }

  static bool inet_frag_may_rebuild(struct inet_frags *f)
  {
  	return time_after(jiffies,
  	       f->last_rebuild_jiffies + INETFRAGS_MIN_REBUILD_INTERVAL);
  }
  
  static void inet_frag_secret_rebuild(struct inet_frags *f)

  {

  	int i;

  	write_seqlock_bh(&f->rnd_seqlock);

  
  	if (!inet_frag_may_rebuild(f))
  		goto out;

  	get_random_bytes(&f->rnd, sizeof(u32));

  	for (i = 0; i < INETFRAGS_HASHSZ; i++) {

  		struct inet_frag_bucket *hb;

  		struct inet_frag_queue *q;

  		struct hlist_node *n;

  		hb = &f->hash[i];

  		spin_lock(&hb->chain_lock);

  		hlist_for_each_entry_safe(q, n, &hb->chain, list) {

  			unsigned int hval = inet_frag_hashfn(f, q);

  
  			if (hval != i) {

  				struct inet_frag_bucket *hb_dest;

  				hlist_del(&q->list);
  
  				/* Relink to new hash chain. */

  				hb_dest = &f->hash[hval];

  
  				/* This is the only place where we take
  				 * another chain_lock while already holding
  				 * one.  As this will not run concurrently,
  				 * we cannot deadlock on hb_dest lock below, if its
  				 * already locked it will be released soon since
  				 * other caller cannot be waiting for hb lock
  				 * that we've taken above.
  				 */
  				spin_lock_nested(&hb_dest->chain_lock,
  						 SINGLE_DEPTH_NESTING);

  				hlist_add_head(&q->list, &hb_dest->chain);

  				spin_unlock(&hb_dest->chain_lock);

  			}
  		}

  		spin_unlock(&hb->chain_lock);

  	}

  	f->rebuild = false;
  	f->last_rebuild_jiffies = jiffies;
  out:

  	write_sequnlock_bh(&f->rnd_seqlock);

  }

  static bool inet_fragq_should_evict(const struct inet_frag_queue *q)
  {
  	return q->net->low_thresh == 0 ||
  	       frag_mem_limit(q->net) >= q->net->low_thresh;
  }
  
  static unsigned int
  inet_evict_bucket(struct inet_frags *f, struct inet_frag_bucket *hb)
  {
  	struct inet_frag_queue *fq;
  	struct hlist_node *n;
  	unsigned int evicted = 0;
  	HLIST_HEAD(expired);

  	spin_lock(&hb->chain_lock);
  
  	hlist_for_each_entry_safe(fq, n, &hb->chain, list) {
  		if (!inet_fragq_should_evict(fq))
  			continue;

  		if (!del_timer(&fq->timer))
  			continue;

  		hlist_add_head(&fq->list_evictor, &expired);

  		++evicted;
  	}
  
  	spin_unlock(&hb->chain_lock);

  	hlist_for_each_entry_safe(fq, n, &expired, list_evictor)

  		f->frag_expire((unsigned long) fq);
  
  	return evicted;
  }
  
  static void inet_frag_worker(struct work_struct *work)
  {
  	unsigned int budget = INETFRAGS_EVICT_BUCKETS;
  	unsigned int i, evicted = 0;
  	struct inet_frags *f;
  
  	f = container_of(work, struct inet_frags, frags_work);
  
  	BUILD_BUG_ON(INETFRAGS_EVICT_BUCKETS >= INETFRAGS_HASHSZ);

  	local_bh_disable();

  
  	for (i = ACCESS_ONCE(f->next_bucket); budget; --budget) {
  		evicted += inet_evict_bucket(f, &f->hash[i]);
  		i = (i + 1) & (INETFRAGS_HASHSZ - 1);
  		if (evicted > INETFRAGS_EVICT_MAX)
  			break;
  	}
  
  	f->next_bucket = i;

  	local_bh_enable();

  	if (f->rebuild && inet_frag_may_rebuild(f))
  		inet_frag_secret_rebuild(f);

  }
  
  static void inet_frag_schedule_worker(struct inet_frags *f)
  {
  	if (unlikely(!work_pending(&f->frags_work)))
  		schedule_work(&f->frags_work);
  }

  int inet_frags_init(struct inet_frags *f)

  {
  	int i;

  	INIT_WORK(&f->frags_work, inet_frag_worker);

  	for (i = 0; i < INETFRAGS_HASHSZ; i++) {
  		struct inet_frag_bucket *hb = &f->hash[i];

  		spin_lock_init(&hb->chain_lock);
  		INIT_HLIST_HEAD(&hb->chain);
  	}

  
  	seqlock_init(&f->rnd_seqlock);

  	f->last_rebuild_jiffies = 0;

  	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)
  {

  	cancel_work_sync(&f->frags_work);

  	kmem_cache_destroy(f->frags_cachep);

  }
  EXPORT_SYMBOL(inet_frags_fini);

  void inet_frags_exit_net(struct netns_frags *nf, struct inet_frags *f)
  {

  	unsigned int seq;

  	int i;

  	nf->low_thresh = 0;

  evict_again:

  	local_bh_disable();

  	seq = read_seqbegin(&f->rnd_seqlock);

  
  	for (i = 0; i < INETFRAGS_HASHSZ ; i++)
  		inet_evict_bucket(f, &f->hash[i]);

  	local_bh_enable();

  	cond_resched();
  
  	if (read_seqretry(&f->rnd_seqlock, seq) ||
  	    percpu_counter_sum(&nf->mem))
  		goto evict_again;

  
  	percpu_counter_destroy(&nf->mem);

  }
  EXPORT_SYMBOL(inet_frags_exit_net);

  static struct inet_frag_bucket *
  get_frag_bucket_locked(struct inet_frag_queue *fq, struct inet_frags *f)
  __acquires(hb->chain_lock)

  {

  	struct inet_frag_bucket *hb;

  	unsigned int seq, hash;
  
   restart:
  	seq = read_seqbegin(&f->rnd_seqlock);

  	hash = inet_frag_hashfn(f, fq);

  	hb = &f->hash[hash];
  
  	spin_lock(&hb->chain_lock);

  	if (read_seqretry(&f->rnd_seqlock, seq)) {
  		spin_unlock(&hb->chain_lock);
  		goto restart;
  	}
  
  	return hb;
  }
  
  static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
  {
  	struct inet_frag_bucket *hb;
  
  	hb = get_frag_bucket_locked(fq, f);

  	hlist_del(&fq->list);

  	fq->flags |= INET_FRAG_COMPLETE;

  	spin_unlock(&hb->chain_lock);

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

  	if (!(fq->flags & INET_FRAG_COMPLETE)) {

  		fq_unlink(fq, f);
  		atomic_dec(&fq->refcnt);

  	}
  }

  EXPORT_SYMBOL(inet_frag_kill);

  void inet_frag_destroy(struct inet_frag_queue *q, struct inet_frags *f)

  {
  	struct sk_buff *fp;

  	struct netns_frags *nf;

  	unsigned int sum, sum_truesize = 0;

  	WARN_ON(!(q->flags & INET_FRAG_COMPLETE));

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

  
  	/* Release all fragment data. */
  	fp = q->fragments;

  	nf = q->net;

  	while (fp) {
  		struct sk_buff *xp = fp->next;

  		sum_truesize += fp->truesize;

  		kfree_skb(fp);

  		fp = xp;
  	}

  	sum = sum_truesize + f->qsize;

  	if (f->destructor)
  		f->destructor(q);

  	kmem_cache_free(f->frags_cachep, q);

  
  	sub_frag_mem_limit(nf, sum);

  }
  EXPORT_SYMBOL(inet_frag_destroy);

  static struct inet_frag_queue *inet_frag_intern(struct netns_frags *nf,

  						struct inet_frag_queue *qp_in,
  						struct inet_frags *f,
  						void *arg)

  {

  	struct inet_frag_bucket *hb = get_frag_bucket_locked(qp_in, f);

  	struct inet_frag_queue *qp;

  #ifdef CONFIG_SMP
  	/* With SMP race we have to recheck hash table, because

  	 * such entry could have been created on other cpu before
  	 * we acquired hash bucket lock.

  	 */

  	hlist_for_each_entry(qp, &hb->chain, list) {

  		if (qp->net == nf && f->match(qp, arg)) {

  			atomic_inc(&qp->refcnt);

  			spin_unlock(&hb->chain_lock);

  			qp_in->flags |= INET_FRAG_COMPLETE;

  			inet_frag_put(qp_in, f);
  			return qp;
  		}
  	}
  #endif
  	qp = qp_in;

  	if (!mod_timer(&qp->timer, jiffies + nf->timeout))

  		atomic_inc(&qp->refcnt);
  
  	atomic_inc(&qp->refcnt);

  	hlist_add_head(&qp->list, &hb->chain);

  	spin_unlock(&hb->chain_lock);

  	return qp;
  }

  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) {

  		inet_frag_schedule_worker(f);

  		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, 1);
  
  	return q;
  }

  static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,

  						struct inet_frags *f,
  						void *arg)

  {
  	struct inet_frag_queue *q;

  	q = inet_frag_alloc(nf, f, arg);

  	if (!q)

  		return NULL;

  	return inet_frag_intern(nf, q, f, arg);

  }

  struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,

  				       struct inet_frags *f, void *key,
  				       unsigned int hash)

  {

  	struct inet_frag_bucket *hb;

  	struct inet_frag_queue *q;

  	int depth = 0;

  	if (frag_mem_limit(nf) > nf->low_thresh)
  		inet_frag_schedule_worker(f);

  	hash &= (INETFRAGS_HASHSZ - 1);

  	hb = &f->hash[hash];
  
  	spin_lock(&hb->chain_lock);
  	hlist_for_each_entry(q, &hb->chain, list) {

  		if (q->net == nf && f->match(q, key)) {

  			atomic_inc(&q->refcnt);

  			spin_unlock(&hb->chain_lock);

  			return q;
  		}

  		depth++;

  	}

  	spin_unlock(&hb->chain_lock);

  	if (depth <= INETFRAGS_MAXDEPTH)
  		return inet_frag_create(nf, f, key);

  
  	if (inet_frag_may_rebuild(f)) {

  		if (!f->rebuild)
  			f->rebuild = true;

  		inet_frag_schedule_worker(f);
  	}
  
  	return ERR_PTR(-ENOBUFS);

  }
  EXPORT_SYMBOL(inet_frag_find);

  
  void inet_frag_maybe_warn_overflow(struct inet_frag_queue *q,
  				   const char *prefix)
  {
  	static const char msg[] = "inet_frag_find: Fragment hash bucket"
  		" list length grew over limit " __stringify(INETFRAGS_MAXDEPTH)
  		". Dropping fragment.
  ";
  
  	if (PTR_ERR(q) == -ENOBUFS)

  		net_dbg_ratelimited("%s%s", prefix, msg);

  }
  EXPORT_SYMBOL(inet_frag_maybe_warn_overflow);