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: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/ip.h b/include/net/ip.h
index 2d3cce7..be89967 100644 (file)
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -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);

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index bfd0ca5..d03eb4a 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -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;