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netfilter: nf_dup4: remove redundant checksum recalculation

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IP header checksum will be recalculated at ip_local_out, so
there's no need to calculated it here, remove it. Also update
code comments to illustrate it, and delete the misleading
comments about checksum recalculation.

Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Liping Zhang 2016-07-30 19:44:12 +08:00 committed by Pablo Neira Ayuso
parent ceee4091d6
commit 9f7c824a44
1 changed files with 4 additions and 6 deletions
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10
net/ipv4/netfilter/nf_dup_ipv4.c
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@ -74,21 +74,19 @@ void nf_dup_ipv4(struct net *net, struct sk_buff *skb, unsigned int hooknum,
nf_conntrack_get(skb->nfct);
#endif
/*
* If we are in PREROUTING/INPUT, the checksum must be recalculated
* since the length could have changed as a result of defragmentation.
*
* We also decrease the TTL to mitigate potential loops between two
* hosts.
* If we are in PREROUTING/INPUT, decrease the TTL to mitigate potential
* loops between two hosts.
*
* Set %IP_DF so that the original source is notified of a potentially
* decreased MTU on the clone route. IPv6 does this too.
*
* IP header checksum will be recalculated at ip_local_out.
*/
iph = ip_hdr(skb);
iph->frag_off |= htons(IP_DF);
if (hooknum == NF_INET_PRE_ROUTING ||
hooknum == NF_INET_LOCAL_IN)
--iph->ttl;
ip_send_check(iph);
if (nf_dup_ipv4_route(net, skb, gw, oif)) {
__this_cpu_write(nf_skb_duplicated, true);