[NETFILTER]: nf_conntrack: use hashtable for expectations

Currently all expectations are kept on a global list that

- needs to be searched for every new conncetion
- needs to be walked for evicting expectations when a master connection
  has reached its limit
- needs to be walked on connection destruction for connections that
  have open expectations

This is obviously not good, especially when considering helpers like
H.323 that register *lots* of expectations and can set up permanent
expectations, but it also allows for an easy DoS against firewalls
using connection tracking helpers.

Use a hashtable for expectations to avoid incurring the search overhead
for every new connection. The default hash size is 1/256 of the conntrack
hash table size, this can be overriden using a module parameter.

This patch only introduces the hash table for expectation lookups and
keeps other users to reduce the noise, the following patches will get
rid of it completely.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/net/netfilter/nf_conntrack_expect.h b/include/net/netfilter/nf_conntrack_expect.h
index cf6a619664e8..424d4bdb9848 100644
--- a/include/net/netfilter/nf_conntrack_expect.h
+++ b/include/net/netfilter/nf_conntrack_expect.h
@@ -7,12 +7,17 @@
 #include <net/netfilter/nf_conntrack.h>
 
 extern struct list_head nf_ct_expect_list;
+extern struct hlist_head *nf_ct_expect_hash;
+extern unsigned int nf_ct_expect_hsize;
 
 struct nf_conntrack_expect
 {
 	/* Internal linked list (global expectation list) */
 	struct list_head list;
 
+	/* Hash member */
+	struct hlist_node hnode;
+
 	/* We expect this tuple, with the following mask */
 	struct nf_conntrack_tuple tuple;
 	struct nf_conntrack_tuple_mask mask;