netfilter: nfnetlink_queue: add NAT TCP sequence adjustment if packet mangled
User-space programs that receive traffic via NFQUEUE may mangle packets.
If NAT is enabled, this usually puzzles sequence tracking, leading to
traffic disruptions.
With this patch, nfnl_queue will make the corresponding NAT TCP sequence
adjustment if:
1) The packet has been mangled,
2) the NFQA_CFG_F_CONNTRACK flag has been set, and
3) NAT is detected.
There are some records on the Internet complaning about this issue:
http://stackoverflow.com/questions/260757/packet-mangling-utilities-besides-iptables
By now, we only support TCP since we have no helpers for DCCP or SCTP.
Better to add this if we ever have some helper over those layer 4 protocols.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index ba65bfb..dca19e6 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -401,6 +401,8 @@
size_t (*build_size)(const struct nf_conn *ct);
int (*build)(struct sk_buff *skb, struct nf_conn *ct);
int (*parse)(const struct nlattr *attr, struct nf_conn *ct);
+ void (*seq_adjust)(struct sk_buff *skb, struct nf_conn *ct,
+ u32 ctinfo, int off);
};
extern struct nfq_ct_hook *nfq_ct_hook;
#else