netfilter: nat: Revert "netfilter: nat: convert nat bysrc hash to rhashtable"

This reverts commit 870190a9ec9075205c0fa795a09fa931694a3ff1.

It was not a good idea. The custom hash table was a much better
fit for this purpose.

A fast lookup is not essential, in fact for most cases there is no lookup
at all because original tuple is not taken and can be used as-is.
What needs to be fast is insertion and deletion.

rhlist removal however requires a rhlist walk.
We can have thousands of entries in such a list if source port/addresses
are reused for multiple flows, if this happens removal requests are so
expensive that deletions of a few thousand flows can take several
seconds(!).

The advantages that we got from rhashtable are:
1) table auto-sizing
2) multiple locks

1) would be nice to have, but it is not essential as we have at
most one lookup per new flow, so even a million flows in the bysource
table are not a problem compared to current deletion cost.
2) is easy to add to custom hash table.

I tried to add hlist_node to rhlist to speed up rhltable_remove but this
isn't doable without changing semantics.  rhltable_remove_fast will
check that the to-be-deleted object is part of the table and that
requires a list walk that we want to avoid.

Furthermore, using hlist_node increases size of struct rhlist_head, which
in turn increases nf_conn size.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=196821
Reported-by: Ivan Babrou <ibobrik@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 54 insertions, 80 deletions

diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
index fdc9c64a1c94..8f3bd30511de 100644
--- a/include/net/netfilter/nf_conntrack.h
+++ b/include/net/netfilter/nf_conntrack.h
@@ -17,7 +17,6 @@
 #include <linux/bitops.h>
 #include <linux/compiler.h>
 #include <linux/atomic.h>
-#include <linux/rhashtable.h>
 
 #include <linux/netfilter/nf_conntrack_tcp.h>
 #include <linux/netfilter/nf_conntrack_dccp.h>
@@ -77,7 +76,7 @@ struct nf_conn {
         possible_net_t ct_net;
 
 #if IS_ENABLED(CONFIG_NF_NAT)
-        struct rhlist_head nat_bysource;
+        struct hlist_node       nat_bysource;
 #endif
         /* all members below initialized via memset */
         u8 __nfct_init_offset[0];
diff --git a/include/net/netfilter/nf_nat.h b/include/net/netfilter/nf_nat.h
index 05c82a1a4267..b71701302e61 100644
--- a/include/net/netfilter/nf_nat.h
+++ b/include/net/netfilter/nf_nat.h
@@ -1,6 +1,5 @@
 #ifndef _NF_NAT_H
 #define _NF_NAT_H
-#include <linux/rhashtable.h>
 #include <linux/netfilter_ipv4.h>
 #include <linux/netfilter/nf_nat.h>
 #include <net/netfilter/nf_conntrack_tuple.h>
diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index dc3519cc7209..f090419f5f97 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -30,19 +30,17 @@
 #include <net/netfilter/nf_conntrack_zones.h>
 #include <linux/netfilter/nf_nat.h>
 
+static DEFINE_SPINLOCK(nf_nat_lock);
+
 static DEFINE_MUTEX(nf_nat_proto_mutex);
 static const struct nf_nat_l3proto __rcu *nf_nat_l3protos[NFPROTO_NUMPROTO]
                                                 __read_mostly;
 static const struct nf_nat_l4proto __rcu **nf_nat_l4protos[NFPROTO_NUMPROTO]
                                                 __read_mostly;
 
-struct nf_nat_conn_key {
-        const struct net *net;
-        const struct nf_conntrack_tuple *tuple;
-        const struct nf_conntrack_zone *zone;
-};
-
-static struct rhltable nf_nat_bysource_table;
+static struct hlist_head *nf_nat_bysource __read_mostly;
+static unsigned int nf_nat_htable_size __read_mostly;
+static unsigned int nf_nat_hash_rnd __read_mostly;
 
 inline const struct nf_nat_l3proto *
 __nf_nat_l3proto_find(u8 family)
@@ -118,17 +116,19 @@ int nf_xfrm_me_harder(struct net *net, struct sk_buff *skb, unsigned int family)
 EXPORT_SYMBOL(nf_xfrm_me_harder);
 #endif /* CONFIG_XFRM */
 
-static u32 nf_nat_bysource_hash(const void *data, u32 len, u32 seed)
+/* We keep an extra hash for each conntrack, for fast searching. */
+static unsigned int
+hash_by_src(const struct net *n, const struct nf_conntrack_tuple *tuple)
 {
-        const struct nf_conntrack_tuple *t;
-        const struct nf_conn *ct = data;
+        unsigned int hash;
+
+        get_random_once(&nf_nat_hash_rnd, sizeof(nf_nat_hash_rnd));
 
-        t = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
         /* Original src, to ensure we map it consistently if poss. */
+        hash = jhash2((u32 *)&tuple->src, sizeof(tuple->src) / sizeof(u32),
+                      tuple->dst.protonum ^ nf_nat_hash_rnd ^ net_hash_mix(n));
 
-        seed ^= net_hash_mix(nf_ct_net(ct));
-        return jhash2((const u32 *)&t->src, sizeof(t->src) / sizeof(u32),
-                      t->dst.protonum ^ seed);
+        return reciprocal_scale(hash, nf_nat_htable_size);
 }
 
 /* Is this tuple already taken? (not by us) */
@@ -184,28 +184,6 @@ same_src(const struct nf_conn *ct,
                 t->src.u.all == tuple->src.u.all);
 }
 
-static int nf_nat_bysource_cmp(struct rhashtable_compare_arg *arg,
-                               const void *obj)
-{
-        const struct nf_nat_conn_key *key = arg->key;
-        const struct nf_conn *ct = obj;
-
-        if (!same_src(ct, key->tuple) ||
-            !net_eq(nf_ct_net(ct), key->net) ||
-            !nf_ct_zone_equal(ct, key->zone, IP_CT_DIR_ORIGINAL))
-                return 1;
-
-        return 0;
-}
-
-static struct rhashtable_params nf_nat_bysource_params = {
-        .head_offset = offsetof(struct nf_conn, nat_bysource),
-        .obj_hashfn = nf_nat_bysource_hash,
-        .obj_cmpfn = nf_nat_bysource_cmp,
-        .nelem_hint = 256,
-        .min_size = 1024,
-};
-
 /* Only called for SRC manip */
 static int
 find_appropriate_src(struct net *net,
@@ -216,26 +194,22 @@ find_appropriate_src(struct net *net,
                      struct nf_conntrack_tuple *result,
                      const struct nf_nat_range *range)
 {
+        unsigned int h = hash_by_src(net, tuple);
         const struct nf_conn *ct;
-        struct nf_nat_conn_key key = {
-                .net = net,
-                .tuple = tuple,
-                .zone = zone
-        };
-        struct rhlist_head *hl, *h;
-
-        hl = rhltable_lookup(&nf_nat_bysource_table, &key,
-                             nf_nat_bysource_params);
 
-        rhl_for_each_entry_rcu(ct, h, hl, nat_bysource) {
-                nf_ct_invert_tuplepr(result,
-                                     &ct->tuplehash[IP_CT_DIR_REPLY].tuple);
-                result->dst = tuple->dst;
-
-                if (in_range(l3proto, l4proto, result, range))
-                        return 1;
+        hlist_for_each_entry_rcu(ct, &nf_nat_bysource[h], nat_bysource) {
+                if (same_src(ct, tuple) &&
+                    net_eq(net, nf_ct_net(ct)) &&
+                    nf_ct_zone_equal(ct, zone, IP_CT_DIR_ORIGINAL)) {
+                        /* Copy source part from reply tuple. */
+                        nf_ct_invert_tuplepr(result,
+                                       &ct->tuplehash[IP_CT_DIR_REPLY].tuple);
+                        result->dst = tuple->dst;
+
+                        if (in_range(l3proto, l4proto, result, range))
+                                return 1;
+                }
         }
-
         return 0;
 }
 
@@ -408,6 +382,7 @@ nf_nat_setup_info(struct nf_conn *ct,
                   const struct nf_nat_range *range,
                   enum nf_nat_manip_type maniptype)
 {
+        struct net *net = nf_ct_net(ct);
         struct nf_conntrack_tuple curr_tuple, new_tuple;
 
         /* Can't setup nat info for confirmed ct. */
@@ -449,19 +424,14 @@ nf_nat_setup_info(struct nf_conn *ct,
         }
 
         if (maniptype == NF_NAT_MANIP_SRC) {
-                struct nf_nat_conn_key key = {
-                        .net = nf_ct_net(ct),
-                        .tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple,
-                        .zone = nf_ct_zone(ct),
-                };
-                int err;
-
-                err = rhltable_insert_key(&nf_nat_bysource_table,
-                                          &key,
-                                          &ct->nat_bysource,
-                                          nf_nat_bysource_params);
-                if (err)
-                        return NF_DROP;
+                unsigned int srchash;
+
+                srchash = hash_by_src(net,
+                                      &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
+                spin_lock_bh(&nf_nat_lock);
+                hlist_add_head_rcu(&ct->nat_bysource,
+                                   &nf_nat_bysource[srchash]);
+                spin_unlock_bh(&nf_nat_lock);
         }
 
         /* It's done. */
@@ -570,8 +540,9 @@ static int nf_nat_proto_clean(struct nf_conn *ct, void *data)
          * will delete entry from already-freed table.
          */
         clear_bit(IPS_SRC_NAT_DONE_BIT, &ct->status);
-        rhltable_remove(&nf_nat_bysource_table, &ct->nat_bysource,
-                        nf_nat_bysource_params);
+        spin_lock_bh(&nf_nat_lock);
+        hlist_del_rcu(&ct->nat_bysource);
+        spin_unlock_bh(&nf_nat_lock);
 
         /* don't delete conntrack.  Although that would make things a lot
          * simpler, we'd end up flushing all conntracks on nat rmmod.
@@ -699,9 +670,11 @@ EXPORT_SYMBOL_GPL(nf_nat_l3proto_unregister);
 /* No one using conntrack by the time this called. */
 static void nf_nat_cleanup_conntrack(struct nf_conn *ct)
 {
-        if (ct->status & IPS_SRC_NAT_DONE)
-                rhltable_remove(&nf_nat_bysource_table, &ct->nat_bysource,
-                                nf_nat_bysource_params);
+        if (ct->status & IPS_SRC_NAT_DONE) {
+                spin_lock_bh(&nf_nat_lock);
+                hlist_del_rcu(&ct->nat_bysource);
+                spin_unlock_bh(&nf_nat_lock);
+        }
 }
 
 static struct nf_ct_ext_type nat_extend __read_mostly = {
@@ -825,13 +798,16 @@ static int __init nf_nat_init(void)
 {
         int ret;
 
-        ret = rhltable_init(&nf_nat_bysource_table, &nf_nat_bysource_params);
-        if (ret)
-                return ret;
+        /* Leave them the same for the moment. */
+        nf_nat_htable_size = nf_conntrack_htable_size;
+
+        nf_nat_bysource = nf_ct_alloc_hashtable(&nf_nat_htable_size, 0);
+        if (!nf_nat_bysource)
+                return -ENOMEM;
 
         ret = nf_ct_extend_register(&nat_extend);
         if (ret < 0) {
-                rhltable_destroy(&nf_nat_bysource_table);
+                nf_ct_free_hashtable(nf_nat_bysource, nf_nat_htable_size);
                 printk(KERN_ERR "nf_nat_core: Unable to register extension\n");
                 return ret;
         }
@@ -865,8 +841,8 @@ static void __exit nf_nat_cleanup(void)
 
         for (i = 0; i < NFPROTO_NUMPROTO; i++)
                 kfree(nf_nat_l4protos[i]);
-
-        rhltable_destroy(&nf_nat_bysource_table);
+        synchronize_net();
+        nf_ct_free_hashtable(nf_nat_bysource, nf_nat_htable_size);
 }
 
 MODULE_LICENSE("GPL");