// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   * inet fragments management
   *

   * 		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 <linux/rhashtable.h>

  #include <net/sock.h>

  #include <net/inet_frag.h>

  #include <net/inet_ecn.h>

  #include <net/ip.h>
  #include <net/ipv6.h>
  
  /* Use skb->cb to track consecutive/adjacent fragments coming at
   * the end of the queue. Nodes in the rb-tree queue will
   * contain "runs" of one or more adjacent fragments.
   *
   * Invariants:
   * - next_frag is NULL at the tail of a "run";
   * - the head of a "run" has the sum of all fragment lengths in frag_run_len.
   */
  struct ipfrag_skb_cb {
  	union {
  		struct inet_skb_parm	h4;
  		struct inet6_skb_parm	h6;
  	};
  	struct sk_buff		*next_frag;
  	int			frag_run_len;
  };
  
  #define FRAG_CB(skb)		((struct ipfrag_skb_cb *)((skb)->cb))
  
  static void fragcb_clear(struct sk_buff *skb)
  {
  	RB_CLEAR_NODE(&skb->rbnode);
  	FRAG_CB(skb)->next_frag = NULL;
  	FRAG_CB(skb)->frag_run_len = skb->len;
  }
  
  /* Append skb to the last "run". */
  static void fragrun_append_to_last(struct inet_frag_queue *q,
  				   struct sk_buff *skb)
  {
  	fragcb_clear(skb);
  
  	FRAG_CB(q->last_run_head)->frag_run_len += skb->len;
  	FRAG_CB(q->fragments_tail)->next_frag = skb;
  	q->fragments_tail = skb;
  }
  
  /* Create a new "run" with the skb. */
  static void fragrun_create(struct inet_frag_queue *q, struct sk_buff *skb)
  {
  	BUILD_BUG_ON(sizeof(struct ipfrag_skb_cb) > sizeof(skb->cb));
  	fragcb_clear(skb);
  
  	if (q->last_run_head)
  		rb_link_node(&skb->rbnode, &q->last_run_head->rbnode,
  			     &q->last_run_head->rbnode.rb_right);
  	else
  		rb_link_node(&skb->rbnode, NULL, &q->rb_fragments.rb_node);
  	rb_insert_color(&skb->rbnode, &q->rb_fragments);
  
  	q->fragments_tail = skb;
  	q->last_run_head = skb;
  }

  
  /* 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;

  	refcount_set(&f->refcnt, 1);
  	init_completion(&f->completion);

  	return 0;

  }
  EXPORT_SYMBOL(inet_frags_init);
  
  void inet_frags_fini(struct inet_frags *f)
  {

  	if (refcount_dec_and_test(&f->refcnt))
  		complete(&f->completion);
  
  	wait_for_completion(&f->completion);

  	kmem_cache_destroy(f->frags_cachep);

  	f->frags_cachep = NULL;

  }
  EXPORT_SYMBOL(inet_frags_fini);

  /* called from rhashtable_free_and_destroy() at netns_frags dismantle */

  static void inet_frags_free_cb(void *ptr, void *arg)

  {

  	struct inet_frag_queue *fq = ptr;

  	int count;

  	count = del_timer_sync(&fq->timer) ? 1 : 0;

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

  		count++;
  	} else if (fq->flags & INET_FRAG_HASH_DEAD) {
  		count++;

  	}

  	spin_unlock_bh(&fq->lock);

  	if (refcount_sub_and_test(count, &fq->refcnt))
  		inet_frag_destroy(fq);

  }

  static void fqdir_work_fn(struct work_struct *work)

  {

  	struct fqdir *fqdir = container_of(work, struct fqdir, destroy_work);

  	struct inet_frags *f = fqdir->f;

  	rhashtable_free_and_destroy(&fqdir->rhashtable, inet_frags_free_cb, NULL);

  
  	/* We need to make sure all ongoing call_rcu(..., inet_frag_destroy_rcu)
  	 * have completed, since they need to dereference fqdir.
  	 * Would it not be nice to have kfree_rcu_barrier() ? :)
  	 */
  	rcu_barrier();
  
  	if (refcount_dec_and_test(&f->refcnt))
  		complete(&f->completion);

  	kfree(fqdir);

  }

  int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net)
  {
  	struct fqdir *fqdir = kzalloc(sizeof(*fqdir), GFP_KERNEL);
  	int res;
  
  	if (!fqdir)
  		return -ENOMEM;
  	fqdir->f = f;
  	fqdir->net = net;
  	res = rhashtable_init(&fqdir->rhashtable, &fqdir->f->rhash_params);
  	if (res < 0) {
  		kfree(fqdir);
  		return res;
  	}

  	refcount_inc(&f->refcnt);

  	*fqdirp = fqdir;
  	return 0;
  }
  EXPORT_SYMBOL(fqdir_init);

  void fqdir_exit(struct fqdir *fqdir)
  {

  	INIT_WORK(&fqdir->destroy_work, fqdir_work_fn);
  	queue_work(system_wq, &fqdir->destroy_work);

  }

  EXPORT_SYMBOL(fqdir_exit);

  void inet_frag_kill(struct inet_frag_queue *fq)

  {
  	if (del_timer(&fq->timer))

  		refcount_dec(&fq->refcnt);

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

  		struct fqdir *fqdir = fq->fqdir;

  
  		fq->flags |= INET_FRAG_COMPLETE;

  		rcu_read_lock();

  		/* The RCU read lock provides a memory barrier
  		 * guaranteeing that if fqdir->dead is false then
  		 * the hash table destruction will not start until
  		 * after we unlock.  Paired with inet_frags_exit_net().

  		 */

  		if (!fqdir->dead) {

  			rhashtable_remove_fast(&fqdir->rhashtable, &fq->node,
  					       fqdir->f->rhash_params);
  			refcount_dec(&fq->refcnt);
  		} else {
  			fq->flags |= INET_FRAG_HASH_DEAD;
  		}
  		rcu_read_unlock();

  	}
  }

  EXPORT_SYMBOL(inet_frag_kill);

  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->fqdir->f;

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

  unsigned int inet_frag_rbtree_purge(struct rb_root *root)
  {
  	struct rb_node *p = rb_first(root);
  	unsigned int sum = 0;
  
  	while (p) {
  		struct sk_buff *skb = rb_entry(p, struct sk_buff, rbnode);
  
  		p = rb_next(p);
  		rb_erase(&skb->rbnode, root);
  		while (skb) {
  			struct sk_buff *next = FRAG_CB(skb)->next_frag;
  
  			sum += skb->truesize;
  			kfree_skb(skb);
  			skb = next;
  		}
  	}
  	return sum;
  }
  EXPORT_SYMBOL(inet_frag_rbtree_purge);

  void inet_frag_destroy(struct inet_frag_queue *q)

  {

  	struct fqdir *fqdir;

  	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. */

  	fqdir = q->fqdir;
  	f = fqdir->f;

  	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(fqdir, sum);

  }
  EXPORT_SYMBOL(inet_frag_destroy);

  static struct inet_frag_queue *inet_frag_alloc(struct fqdir *fqdir,

  					       struct inet_frags *f,
  					       void *arg)

  {
  	struct inet_frag_queue *q;

  	q = kmem_cache_zalloc(f->frags_cachep, GFP_ATOMIC);

  	if (!q)

  		return NULL;

  	q->fqdir = fqdir;

  	f->constructor(q, arg);

  	add_frag_mem_limit(fqdir, f->qsize);

  	timer_setup(&q->timer, f->frag_expire, 0);

  	spin_lock_init(&q->lock);

  	refcount_set(&q->refcnt, 3);

  
  	return q;
  }

  static struct inet_frag_queue *inet_frag_create(struct fqdir *fqdir,

  						void *arg,
  						struct inet_frag_queue **prev)

  {

  	struct inet_frags *f = fqdir->f;

  	struct inet_frag_queue *q;

  	q = inet_frag_alloc(fqdir, f, arg);

  	if (!q) {
  		*prev = ERR_PTR(-ENOMEM);

  		return NULL;

  	}

  	mod_timer(&q->timer, jiffies + fqdir->timeout);

  	*prev = rhashtable_lookup_get_insert_key(&fqdir->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;

  }

  /* TODO : call from rcu_read_lock() and no longer use refcount_inc_not_zero() */

  struct inet_frag_queue *inet_frag_find(struct fqdir *fqdir, void *key)

  {

  	struct inet_frag_queue *fq = NULL, *prev;

  	if (!fqdir->high_thresh || frag_mem_limit(fqdir) > fqdir->high_thresh)

  		return NULL;

  	rcu_read_lock();

  	prev = rhashtable_lookup(&fqdir->rhashtable, key, fqdir->f->rhash_params);

  	if (!prev)

  		fq = inet_frag_create(fqdir, key, &prev);

  	if (!IS_ERR_OR_NULL(prev)) {

  		fq = prev;

  		if (!refcount_inc_not_zero(&fq->refcnt))
  			fq = NULL;

  	}

  	rcu_read_unlock();

  	return fq;

  }
  EXPORT_SYMBOL(inet_frag_find);

  
  int inet_frag_queue_insert(struct inet_frag_queue *q, struct sk_buff *skb,
  			   int offset, int end)
  {
  	struct sk_buff *last = q->fragments_tail;
  
  	/* RFC5722, Section 4, amended by Errata ID : 3089
  	 *                          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) MUST be silently discarded.
  	 *
  	 * Duplicates, however, should be ignored (i.e. skb dropped, but the
  	 * queue/fragments kept for later reassembly).
  	 */
  	if (!last)
  		fragrun_create(q, skb);  /* First fragment. */
  	else if (last->ip_defrag_offset + last->len < end) {
  		/* This is the common case: skb goes to the end. */
  		/* Detect and discard overlaps. */
  		if (offset < last->ip_defrag_offset + last->len)
  			return IPFRAG_OVERLAP;
  		if (offset == last->ip_defrag_offset + last->len)
  			fragrun_append_to_last(q, skb);
  		else
  			fragrun_create(q, skb);
  	} else {
  		/* Binary search. Note that skb can become the first fragment,
  		 * but not the last (covered above).
  		 */
  		struct rb_node **rbn, *parent;
  
  		rbn = &q->rb_fragments.rb_node;
  		do {
  			struct sk_buff *curr;
  			int curr_run_end;
  
  			parent = *rbn;
  			curr = rb_to_skb(parent);
  			curr_run_end = curr->ip_defrag_offset +
  					FRAG_CB(curr)->frag_run_len;
  			if (end <= curr->ip_defrag_offset)
  				rbn = &parent->rb_left;
  			else if (offset >= curr_run_end)
  				rbn = &parent->rb_right;
  			else if (offset >= curr->ip_defrag_offset &&
  				 end <= curr_run_end)
  				return IPFRAG_DUP;
  			else
  				return IPFRAG_OVERLAP;
  		} while (*rbn);
  		/* Here we have parent properly set, and rbn pointing to
  		 * one of its NULL left/right children. Insert skb.
  		 */
  		fragcb_clear(skb);
  		rb_link_node(&skb->rbnode, parent, rbn);
  		rb_insert_color(&skb->rbnode, &q->rb_fragments);
  	}
  
  	skb->ip_defrag_offset = offset;
  
  	return IPFRAG_OK;
  }
  EXPORT_SYMBOL(inet_frag_queue_insert);
  
  void *inet_frag_reasm_prepare(struct inet_frag_queue *q, struct sk_buff *skb,
  			      struct sk_buff *parent)
  {
  	struct sk_buff *fp, *head = skb_rb_first(&q->rb_fragments);
  	struct sk_buff **nextp;
  	int delta;
  
  	if (head != skb) {
  		fp = skb_clone(skb, GFP_ATOMIC);
  		if (!fp)
  			return NULL;
  		FRAG_CB(fp)->next_frag = FRAG_CB(skb)->next_frag;
  		if (RB_EMPTY_NODE(&skb->rbnode))
  			FRAG_CB(parent)->next_frag = fp;
  		else
  			rb_replace_node(&skb->rbnode, &fp->rbnode,
  					&q->rb_fragments);
  		if (q->fragments_tail == skb)
  			q->fragments_tail = fp;
  		skb_morph(skb, head);
  		FRAG_CB(skb)->next_frag = FRAG_CB(head)->next_frag;
  		rb_replace_node(&head->rbnode, &skb->rbnode,
  				&q->rb_fragments);
  		consume_skb(head);
  		head = skb;
  	}
  	WARN_ON(head->ip_defrag_offset != 0);
  
  	delta = -head->truesize;
  
  	/* Head of list must not be cloned. */
  	if (skb_unclone(head, GFP_ATOMIC))
  		return NULL;
  
  	delta += head->truesize;
  	if (delta)

  		add_frag_mem_limit(q->fqdir, delta);

  
  	/* 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)
  			return NULL;
  		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->data_len = head->data_len - plen;
  		clone->len = clone->data_len;
  		head->truesize += clone->truesize;
  		clone->csum = 0;
  		clone->ip_summed = head->ip_summed;

  		add_frag_mem_limit(q->fqdir, clone->truesize);

  		skb_shinfo(head)->frag_list = clone;
  		nextp = &clone->next;
  	} else {
  		nextp = &skb_shinfo(head)->frag_list;
  	}
  
  	return nextp;
  }
  EXPORT_SYMBOL(inet_frag_reasm_prepare);
  
  void inet_frag_reasm_finish(struct inet_frag_queue *q, struct sk_buff *head,

  			    void *reasm_data, bool try_coalesce)

  {
  	struct sk_buff **nextp = (struct sk_buff **)reasm_data;
  	struct rb_node *rbn;
  	struct sk_buff *fp;

  	int sum_truesize;

  
  	skb_push(head, head->data - skb_network_header(head));
  
  	/* Traverse the tree in order, to build frag_list. */
  	fp = FRAG_CB(head)->next_frag;
  	rbn = rb_next(&head->rbnode);
  	rb_erase(&head->rbnode, &q->rb_fragments);

  
  	sum_truesize = head->truesize;

  	while (rbn || fp) {
  		/* fp points to the next sk_buff in the current run;
  		 * rbn points to the next run.
  		 */
  		/* Go through the current run. */
  		while (fp) {

  			struct sk_buff *next_frag = FRAG_CB(fp)->next_frag;
  			bool stolen;
  			int delta;
  
  			sum_truesize += fp->truesize;

  			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);

  
  			if (try_coalesce && skb_try_coalesce(head, fp, &stolen,
  							     &delta)) {
  				kfree_skb_partial(fp, stolen);
  			} else {
  				fp->prev = NULL;
  				memset(&fp->rbnode, 0, sizeof(fp->rbnode));
  				fp->sk = NULL;
  
  				head->data_len += fp->len;
  				head->len += fp->len;
  				head->truesize += fp->truesize;
  
  				*nextp = fp;
  				nextp = &fp->next;
  			}
  
  			fp = next_frag;

  		}
  		/* Move to the next run. */
  		if (rbn) {
  			struct rb_node *rbnext = rb_next(rbn);
  
  			fp = rb_to_skb(rbn);
  			rb_erase(rbn, &q->rb_fragments);
  			rbn = rbnext;
  		}
  	}

  	sub_frag_mem_limit(q->fqdir, sum_truesize);

  
  	*nextp = NULL;
  	skb_mark_not_on_list(head);
  	head->prev = NULL;
  	head->tstamp = q->stamp;
  }
  EXPORT_SYMBOL(inet_frag_reasm_finish);
  
  struct sk_buff *inet_frag_pull_head(struct inet_frag_queue *q)
  {

  	struct sk_buff *head, *skb;

  	head = skb_rb_first(&q->rb_fragments);
  	if (!head)
  		return NULL;
  	skb = FRAG_CB(head)->next_frag;
  	if (skb)
  		rb_replace_node(&head->rbnode, &skb->rbnode,
  				&q->rb_fragments);
  	else
  		rb_erase(&head->rbnode, &q->rb_fragments);
  	memset(&head->rbnode, 0, sizeof(head->rbnode));
  	barrier();

  	if (head == q->fragments_tail)
  		q->fragments_tail = NULL;

  	sub_frag_mem_limit(q->fqdir, head->truesize);

  
  	return head;
  }
  EXPORT_SYMBOL(inet_frag_pull_head);