reassembly.c

linux 内核源代码

		}
	}

	if (end == offset)
		goto err;

	/* Point into the IP datagram 'data' part. */
	if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data))
		goto err;

	if (pskb_trim_rcsum(skb, end - offset))
		goto err;

	/* 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 = NULL;
	for(next = fq->q.fragments; next != NULL; next = next->next) {
		if (FRAG6_CB(next)->offset >= offset)
			break;	/* bingo! */
		prev = next;
	}

	/* We found where to put this one.  Check for overlap with
	 * preceding fragment, and, if needed, align things so that
	 * any overlaps are eliminated.
	 */
	if (prev) {
		int i = (FRAG6_CB(prev)->offset + prev->len) - offset;

		if (i > 0) {
			offset += i;
			if (end <= offset)
				goto err;
			if (!pskb_pull(skb, i))
				goto err;
			if (skb->ip_summed != CHECKSUM_UNNECESSARY)
				skb->ip_summed = CHECKSUM_NONE;
		}
	}

	/* Look for overlap with succeeding segments.
	 * If we can merge fragments, do it.
	 */
	while (next && FRAG6_CB(next)->offset < end) {
		int i = end - FRAG6_CB(next)->offset; /* overlap is 'i' bytes */

		if (i < next->len) {
			/* Eat head of the next overlapped fragment
			 * and leave the loop. The next ones cannot overlap.
			 */
			if (!pskb_pull(next, i))
				goto err;
			FRAG6_CB(next)->offset += i;	/* next fragment */
			fq->q.meat -= i;
			if (next->ip_summed != CHECKSUM_UNNECESSARY)
				next->ip_summed = CHECKSUM_NONE;
			break;
		} else {
			struct sk_buff *free_it = next;

			/* Old fragment is completely overridden with
			 * new one drop it.
			 */
			next = next->next;

			if (prev)
				prev->next = next;
			else
				fq->q.fragments = next;

			fq->q.meat -= free_it->len;
			frag_kfree_skb(free_it, NULL);
		}
	}

	FRAG6_CB(skb)->offset = offset;

	/* Insert this fragment in the chain of fragments. */
	skb->next = next;
	if (prev)
		prev->next = skb;
	else
		fq->q.fragments = skb;

	dev = skb->dev;
	if (dev) {
		fq->iif = dev->ifindex;
		skb->dev = NULL;
	}
	fq->q.stamp = skb->tstamp;
	fq->q.meat += skb->len;
	atomic_add(skb->truesize, &ip6_frags.mem);

	/* The first fragment.
	 * nhoffset is obtained from the first fragment, of course.
	 */
	if (offset == 0) {
		fq->nhoffset = nhoff;
		fq->q.last_in |= FIRST_IN;
	}

	if (fq->q.last_in == (FIRST_IN | LAST_IN) && fq->q.meat == fq->q.len)
		return ip6_frag_reasm(fq, prev, dev);

	write_lock(&ip6_frags.lock);
	list_move_tail(&fq->q.lru_list, &ip6_frags.lru_list);
	write_unlock(&ip6_frags.lock);
	return -1;

err:
	IP6_INC_STATS(ip6_dst_idev(skb->dst), IPSTATS_MIB_REASMFAILS);
	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 ip6_frag_reasm(struct frag_queue *fq, struct sk_buff *prev,
			  struct net_device *dev)
{
	struct sk_buff *fp, *head = fq->q.fragments;
	int    payload_len;
	unsigned int nhoff;

	fq_kill(fq);

	/* 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;
		prev->next = fp;

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

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

	BUG_TRAP(head != NULL);
	BUG_TRAP(FRAG6_CB(head)->offset == 0);

	/* Unfragmented part is taken from the first segment. */
	payload_len = ((head->data - skb_network_header(head)) -
		       sizeof(struct ipv6hdr) + fq->q.len -
		       sizeof(struct frag_hdr));
	if (payload_len > IPV6_MAXPLEN)
		goto out_oversize;

	/* Head of list must not be cloned. */
	if (skb_cloned(head) && pskb_expand_head(head, 0, 0, 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_shinfo(head)->frag_list) {
		struct sk_buff *clone;
		int i, plen = 0;

		if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
			goto out_oom;
		clone->next = head->next;
		head->next = clone;
		skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
		skb_shinfo(head)->frag_list = NULL;
		for (i=0; i<skb_shinfo(head)->nr_frags; i++)
			plen += skb_shinfo(head)->frags[i].size;
		clone->len = clone->data_len = head->data_len - plen;
		head->data_len -= clone->len;
		head->len -= clone->len;
		clone->csum = 0;
		clone->ip_summed = head->ip_summed;
		atomic_add(clone->truesize, &ip6_frags.mem);
	}

	/* We have to remove fragment header from datagram and to relocate
	 * header in order to calculate ICV correctly. */
	nhoff = fq->nhoffset;
	skb_network_header(head)[nhoff] = skb_transport_header(head)[0];
	memmove(head->head + sizeof(struct frag_hdr), head->head,
		(head->data - head->head) - sizeof(struct frag_hdr));
	head->mac_header += sizeof(struct frag_hdr);
	head->network_header += sizeof(struct frag_hdr);

	skb_shinfo(head)->frag_list = head->next;
	skb_reset_transport_header(head);
	skb_push(head, head->data - skb_network_header(head));
	atomic_sub(head->truesize, &ip6_frags.mem);

	for (fp=head->next; fp; fp = fp->next) {
		head->data_len += fp->len;
		head->len += fp->len;
		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);
		head->truesize += fp->truesize;
		atomic_sub(fp->truesize, &ip6_frags.mem);
	}

	head->next = NULL;
	head->dev = dev;
	head->tstamp = fq->q.stamp;
	ipv6_hdr(head)->payload_len = htons(payload_len);
	IP6CB(head)->nhoff = nhoff;

	/* Yes, and fold redundant checksum back. 8) */
	if (head->ip_summed == CHECKSUM_COMPLETE)
		head->csum = csum_partial(skb_network_header(head),
					  skb_network_header_len(head),
					  head->csum);

	rcu_read_lock();
	IP6_INC_STATS_BH(__in6_dev_get(dev), IPSTATS_MIB_REASMOKS);
	rcu_read_unlock();
	fq->q.fragments = NULL;
	return 1;

out_oversize:
	if (net_ratelimit())
		printk(KERN_DEBUG "ip6_frag_reasm: payload len = %d\n", payload_len);
	goto out_fail;
out_oom:
	if (net_ratelimit())
		printk(KERN_DEBUG "ip6_frag_reasm: no memory for reassembly\n");
out_fail:
	rcu_read_lock();
	IP6_INC_STATS_BH(__in6_dev_get(dev), IPSTATS_MIB_REASMFAILS);
	rcu_read_unlock();
	return -1;
}

static int ipv6_frag_rcv(struct sk_buff *skb)
{
	struct frag_hdr *fhdr;
	struct frag_queue *fq;
	struct ipv6hdr *hdr = ipv6_hdr(skb);

	IP6_INC_STATS_BH(ip6_dst_idev(skb->dst), IPSTATS_MIB_REASMREQDS);

	/* Jumbo payload inhibits frag. header */
	if (hdr->payload_len==0) {
		IP6_INC_STATS(ip6_dst_idev(skb->dst), IPSTATS_MIB_INHDRERRORS);
		icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
				  skb_network_header_len(skb));
		return -1;
	}
	if (!pskb_may_pull(skb, (skb_transport_offset(skb) +
				 sizeof(struct frag_hdr)))) {
		IP6_INC_STATS(ip6_dst_idev(skb->dst), IPSTATS_MIB_INHDRERRORS);
		icmpv6_param_prob(skb, ICMPV6_HDR_FIELD,
				  skb_network_header_len(skb));
		return -1;
	}

	hdr = ipv6_hdr(skb);
	fhdr = (struct frag_hdr *)skb_transport_header(skb);

	if (!(fhdr->frag_off & htons(0xFFF9))) {
		/* It is not a fragmented frame */
		skb->transport_header += sizeof(struct frag_hdr);
		IP6_INC_STATS_BH(ip6_dst_idev(skb->dst), IPSTATS_MIB_REASMOKS);

		IP6CB(skb)->nhoff = (u8 *)fhdr - skb_network_header(skb);
		return 1;
	}

	if (atomic_read(&ip6_frags.mem) > ip6_frags_ctl.high_thresh)
		ip6_evictor(ip6_dst_idev(skb->dst));

	if ((fq = fq_find(fhdr->identification, &hdr->saddr, &hdr->daddr,
			  ip6_dst_idev(skb->dst))) != NULL) {
		int ret;

		spin_lock(&fq->q.lock);

		ret = ip6_frag_queue(fq, skb, fhdr, IP6CB(skb)->nhoff);

		spin_unlock(&fq->q.lock);
		fq_put(fq);
		return ret;
	}

	IP6_INC_STATS_BH(ip6_dst_idev(skb->dst), IPSTATS_MIB_REASMFAILS);
	kfree_skb(skb);
	return -1;
}

static struct inet6_protocol frag_protocol =
{
	.handler	=	ipv6_frag_rcv,
	.flags		=	INET6_PROTO_NOPOLICY,
};

void __init ipv6_frag_init(void)
{
	if (inet6_add_protocol(&frag_protocol, IPPROTO_FRAGMENT) < 0)
		printk(KERN_ERR "ipv6_frag_init: Could not register protocol\n");

	ip6_frags.ctl = &ip6_frags_ctl;
	ip6_frags.hashfn = ip6_hashfn;
	ip6_frags.constructor = ip6_frag_init;
	ip6_frags.destructor = NULL;
	ip6_frags.skb_free = NULL;
	ip6_frags.qsize = sizeof(struct frag_queue);
	ip6_frags.match = ip6_frag_match;
	ip6_frags.frag_expire = ip6_frag_expire;
	inet_frags_init(&ip6_frags);
}