[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, 66 insertions, 6 deletions

diff --git a/net/netfilter/nf_conntrack_expect.c b/net/netfilter/nf_conntrack_expect.c
index ad197bccc7ca..0696f87aaef1 100644
--- a/net/netfilter/nf_conntrack_expect.c
+++ b/net/netfilter/nf_conntrack_expect.c
@@ -19,6 +19,7 @@
 #include <linux/err.h>
 #include <linux/percpu.h>
 #include <linux/kernel.h>
+#include <linux/jhash.h>
 
 #include <net/netfilter/nf_conntrack.h>
 #include <net/netfilter/nf_conntrack_core.h>
@@ -29,6 +30,17 @@
 LIST_HEAD(nf_ct_expect_list);
 EXPORT_SYMBOL_GPL(nf_ct_expect_list);
 
+struct hlist_head *nf_ct_expect_hash __read_mostly;
+EXPORT_SYMBOL_GPL(nf_ct_expect_hash);
+
+unsigned int nf_ct_expect_hsize __read_mostly;
+EXPORT_SYMBOL_GPL(nf_ct_expect_hsize);
+
+static unsigned int nf_ct_expect_hash_rnd __read_mostly;
+static unsigned int nf_ct_expect_count;
+static int nf_ct_expect_hash_rnd_initted __read_mostly;
+static int nf_ct_expect_vmalloc;
+
 static struct kmem_cache *nf_ct_expect_cachep __read_mostly;
 static unsigned int nf_ct_expect_next_id;
 
@@ -41,6 +53,9 @@ void nf_ct_unlink_expect(struct nf_conntrack_expect *exp)
         NF_CT_ASSERT(!timer_pending(&exp->timeout));
 
         list_del(&exp->list);
+        hlist_del(&exp->hnode);
+        nf_ct_expect_count--;
+
         NF_CT_STAT_INC(expect_delete);
         master_help->expecting--;
         nf_ct_expect_put(exp);
@@ -57,12 +72,31 @@ static void nf_ct_expectation_timed_out(unsigned long ul_expect)
         nf_ct_expect_put(exp);
 }
 
+static unsigned int nf_ct_expect_dst_hash(const struct nf_conntrack_tuple *tuple)
+{
+        if (unlikely(!nf_ct_expect_hash_rnd_initted)) {
+                get_random_bytes(&nf_ct_expect_hash_rnd, 4);
+                nf_ct_expect_hash_rnd_initted = 1;
+        }
+
+        return jhash2(tuple->dst.u3.all, ARRAY_SIZE(tuple->dst.u3.all),
+                      (((tuple->dst.protonum ^ tuple->src.l3num) << 16) |
+                       tuple->dst.u.all) ^ nf_ct_expect_hash_rnd) %
+               nf_ct_expect_hsize;
+}
+
 struct nf_conntrack_expect *
 __nf_ct_expect_find(const struct nf_conntrack_tuple *tuple)
 {
         struct nf_conntrack_expect *i;
+        struct hlist_node *n;
+        unsigned int h;
+
+        if (!nf_ct_expect_count)
+                return NULL;
 
-        list_for_each_entry(i, &nf_ct_expect_list, list) {
+        h = nf_ct_expect_dst_hash(tuple);
+        hlist_for_each_entry(i, n, &nf_ct_expect_hash[h], hnode) {
                 if (nf_ct_tuple_mask_cmp(tuple, &i->tuple, &i->mask))
                         return i;
         }
@@ -252,10 +286,14 @@ EXPORT_SYMBOL_GPL(nf_ct_expect_put);
 static void nf_ct_expect_insert(struct nf_conntrack_expect *exp)
 {
         struct nf_conn_help *master_help = nfct_help(exp->master);
+        unsigned int h = nf_ct_expect_dst_hash(&exp->tuple);
 
         atomic_inc(&exp->use);
         master_help->expecting++;
+
         list_add(&exp->list, &nf_ct_expect_list);
+        hlist_add_head(&exp->hnode, &nf_ct_expect_hash[h]);
+        nf_ct_expect_count++;
 
         setup_timer(&exp->timeout, nf_ct_expectation_timed_out,
                     (unsigned long)exp);
@@ -300,6 +338,8 @@ int nf_ct_expect_related(struct nf_conntrack_expect *expect)
         struct nf_conntrack_expect *i;
         struct nf_conn *master = expect->master;
         struct nf_conn_help *master_help = nfct_help(master);
+        struct hlist_node *n;
+        unsigned int h;
         int ret;
 
         NF_CT_ASSERT(master_help);
@@ -309,7 +349,8 @@ int nf_ct_expect_related(struct nf_conntrack_expect *expect)
                 ret = -ESHUTDOWN;
                 goto out;
         }
-        list_for_each_entry(i, &nf_ct_expect_list, list) {
+        h = nf_ct_expect_dst_hash(&expect->tuple);
+        hlist_for_each_entry(i, n, &nf_ct_expect_hash[h], hnode) {
                 if (expect_matches(i, expect)) {
                         /* Refresh timer: if it's dying, ignore.. */
                         if (refresh_timer(i)) {
@@ -433,24 +474,41 @@ static void exp_proc_remove(void)
 #endif /* CONFIG_PROC_FS */
 }
 
+module_param_named(expect_hashsize, nf_ct_expect_hsize, uint, 0600);
+
 int __init nf_conntrack_expect_init(void)
 {
-        int err;
+        int err = -ENOMEM;
+
+        if (!nf_ct_expect_hsize) {
+                nf_ct_expect_hsize = nf_conntrack_htable_size / 256;
+                if (!nf_ct_expect_hsize)
+                        nf_ct_expect_hsize = 1;
+        }
+
+        nf_ct_expect_hash = nf_ct_alloc_hashtable(&nf_ct_expect_hsize,
+                                                  &nf_ct_expect_vmalloc);
+        if (nf_ct_expect_hash == NULL)
+                goto err1;
 
         nf_ct_expect_cachep = kmem_cache_create("nf_conntrack_expect",
                                         sizeof(struct nf_conntrack_expect),
                                         0, 0, NULL, NULL);
         if (!nf_ct_expect_cachep)
-                return -ENOMEM;
+                goto err2;
 
         err = exp_proc_init();
         if (err < 0)
-                goto err1;
+                goto err3;
 
         return 0;
 
-err1:
+err3:
+        nf_ct_free_hashtable(nf_ct_expect_hash, nf_ct_expect_vmalloc,
+                             nf_ct_expect_hsize);
+err2:
         kmem_cache_destroy(nf_ct_expect_cachep);
+err1:
         return err;
 }
 
@@ -458,4 +516,6 @@ void nf_conntrack_expect_fini(void)
 {
         exp_proc_remove();
         kmem_cache_destroy(nf_ct_expect_cachep);
+        nf_ct_free_hashtable(nf_ct_expect_hash, nf_ct_expect_vmalloc,
+                             nf_ct_expect_hsize);
 }