Commit c8b17be0 authored by Pablo Neira Ayuso's avatar Pablo Neira Ayuso Committed by David S. Miller
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net: ipv4: add skbuff fraglist splitter 



This patch adds the skbuff fraglist splitter. This API provides an
iterator to transform the fraglist into single skbuff objects, it
consists of:

* ip_fraglist_init(), that initializes the internal state of the
  fraglist splitter.
* ip_fraglist_prepare(), that restores the IPv4 header on the
  fragments.
* ip_fraglist_next(), that retrieves the fragment from the fraglist and
  it updates the internal state of the splitter to point to the next
  fragment skbuff in the fraglist.

The ip_fraglist_iter object stores the internal state of the iterator.

This code has been extracted from ip_do_fragment(). Symbols are also
exported to allow to reuse this iterator from the bridge codepath to
build its own refragmentation routine by reusing the existing codebase.

Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d48ecb40

include/net/ip.h

+23 −0
Original line number Diff line number Diff line
@@ -165,6 +165,29 @@ int ip_output(struct net *net, struct sock *sk, struct sk_buff *skb); 
int ip_mc_output(struct net *net, struct sock *sk, struct sk_buff *skb);

int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,

		   int (*output)(struct net *, struct sock *, struct sk_buff *));



struct ip_fraglist_iter {

	struct sk_buff	*frag_list;

	struct sk_buff	*frag;

	struct iphdr	*iph;

	int		offset;

	unsigned int	hlen;

};



void ip_fraglist_init(struct sk_buff *skb, struct iphdr *iph,

		      unsigned int hlen, struct ip_fraglist_iter *iter);

void ip_fraglist_prepare(struct sk_buff *skb, struct ip_fraglist_iter *iter);



static inline struct sk_buff *ip_fraglist_next(struct ip_fraglist_iter *iter)

{

	struct sk_buff *skb = iter->frag;



	iter->frag = skb->next;

	skb_mark_not_on_list(skb);



	return skb;

}



void ip_send_check(struct iphdr *ip);

int __ip_local_out(struct net *net, struct sock *sk, struct sk_buff *skb);

int ip_local_out(struct net *net, struct sock *sk, struct sk_buff *skb);

net/ipv4/ip_output.c

+55 −33
Original line number Diff line number Diff line
@@ -561,6 +561,54 @@ static int ip_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, 
	return ip_do_fragment(net, sk, skb, output);

}



void ip_fraglist_init(struct sk_buff *skb, struct iphdr *iph,

		      unsigned int hlen, struct ip_fraglist_iter *iter)

{

	unsigned int first_len = skb_pagelen(skb);



	iter->frag_list = skb_shinfo(skb)->frag_list;

	iter->frag = iter->frag_list;

	skb_frag_list_init(skb);



	iter->offset = 0;

	iter->iph = iph;

	iter->hlen = hlen;



	skb->data_len = first_len - skb_headlen(skb);

	skb->len = first_len;

	iph->tot_len = htons(first_len);

	iph->frag_off = htons(IP_MF);

	ip_send_check(iph);

}

EXPORT_SYMBOL(ip_fraglist_init);



void ip_fraglist_prepare(struct sk_buff *skb, struct ip_fraglist_iter *iter)

{

	unsigned int hlen = iter->hlen;

	struct iphdr *iph = iter->iph;

	struct sk_buff *frag;



	frag = iter->frag;

	frag->ip_summed = CHECKSUM_NONE;

	skb_reset_transport_header(frag);

	__skb_push(frag, hlen);

	skb_reset_network_header(frag);

	memcpy(skb_network_header(frag), iph, hlen);

	iter->iph = ip_hdr(frag);

	iph = iter->iph;

	iph->tot_len = htons(frag->len);

	ip_copy_metadata(frag, skb);

	if (iter->offset == 0)

		ip_options_fragment(frag);

	iter->offset += skb->len - hlen;

	iph->frag_off = htons(iter->offset >> 3);

	if (frag->next)

		iph->frag_off |= htons(IP_MF);

	/* Ready, complete checksum */

	ip_send_check(iph);

}

EXPORT_SYMBOL(ip_fraglist_prepare);



/*

 *	This IP datagram is too large to be sent in one piece.  Break it up into

 *	smaller pieces (each of size equal to IP header plus
@@ -578,6 +626,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, 
	int offset;

	__be16 not_last_frag;

	struct rtable *rt = skb_rtable(skb);

	struct ip_fraglist_iter iter;

	int err = 0;



	/* for offloaded checksums cleanup checksum before fragmentation */
@@ -642,49 +691,22 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, 
		}



		/* Everything is OK. Generate! */



		err = 0;

		offset = 0;

		frag = skb_shinfo(skb)->frag_list;

		skb_frag_list_init(skb);

		skb->data_len = first_len - skb_headlen(skb);

		skb->len = first_len;

		iph->tot_len = htons(first_len);

		iph->frag_off = htons(IP_MF);

		ip_send_check(iph);

		ip_fraglist_init(skb, iph, hlen, &iter);



		for (;;) {

			/* Prepare header of the next frame,

			 * before previous one went down. */

			if (frag) {

				frag->ip_summed = CHECKSUM_NONE;

				skb_reset_transport_header(frag);

				__skb_push(frag, hlen);

				skb_reset_network_header(frag);

				memcpy(skb_network_header(frag), iph, hlen);

				iph = ip_hdr(frag);

				iph->tot_len = htons(frag->len);

				ip_copy_metadata(frag, skb);

				if (offset == 0)

					ip_options_fragment(frag);

				offset += skb->len - hlen;

				iph->frag_off = htons(offset>>3);

				if (frag->next)

					iph->frag_off |= htons(IP_MF);

				/* Ready, complete checksum */

				ip_send_check(iph);

			}

			if (iter.frag)

				ip_fraglist_prepare(skb, &iter);



			err = output(net, sk, skb);



			if (!err)

				IP_INC_STATS(net, IPSTATS_MIB_FRAGCREATES);

			if (err || !frag)

			if (err || !iter.frag)

				break;



			skb = frag;

			frag = skb->next;

			skb_mark_not_on_list(skb);

			skb = ip_fraglist_next(&iter);

		}



		if (err == 0) {
@@ -692,7 +714,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, 
			return 0;

		}



		kfree_skb_list(frag);

		kfree_skb_list(iter.frag_list);



		IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);

		return err;

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