Re: [PATCH 4.9 85/87] netfilter: nat: Revert "netfilter: nat: convert nat bysrc hash to rhashtable"

From: Pablo Neira Ayuso
Date: Tue Nov 14 2017 - 10:55:43 EST

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Hi again,

Cc'ing Sebastian Gottschall too.

See below for details. Thanks.

On Tue, Nov 14, 2017 at 04:54:10PM +0100, Pablo Neira Ayuso wrote:
> Hi Greg,
>
> Please, hold on a bit with this revert patch entitled:
>
> nat: Revert "netfilter: nat: convert nat bysrc hash to rhashtable")
>
>
> for 4.9-stable.
>
> Until we clarify what is going on.
>
> Guillame (he's on Cc) is reporting some problems after this.
>
> Thanks!
>
> On Mon, Nov 13, 2017 at 01:56:42PM +0100, Greg Kroah-Hartman wrote:
> > 4.9-stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: Florian Westphal <fw@xxxxxxxxx>
> >
> > commit e1bf1687740ce1a3598a1c5e452b852ff2190682 upstream.
> >
> > 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@xxxxxxxxx>
> > Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
> > Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> >
> >
> > ---
> > include/net/netfilter/nf_conntrack.h | 3
> > include/net/netfilter/nf_nat.h | 1
> > net/netfilter/nf_nat_core.c | 131 ++++++++++++++---------------------
> > 3 files changed, 56 insertions(+), 79 deletions(-)
> >
> > --- 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>
> > @@ -101,7 +100,7 @@ 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];
> > --- 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>
> > --- 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)
> > @@ -121,17 +119,19 @@ int nf_xfrm_me_harder(struct net *net, s
> > 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 inline 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) */
> > @@ -187,28 +187,6 @@ 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,
> > @@ -219,26 +197,22 @@ 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;
> > + 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;
> > + if (in_range(l3proto, l4proto, result, range))
> > + return 1;
> > + }
> > }
> > -
> > return 0;
> > }
> >
> > @@ -411,6 +385,7 @@ 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;
> > struct nf_conn_nat *nat;
> >
> > @@ -452,19 +427,16 @@ 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);
> > + /* nf_conntrack_alter_reply might re-allocate extension aera */
> > + nat = nfct_nat(ct);
> > + hlist_add_head_rcu(&ct->nat_bysource,
> > + &nf_nat_bysource[srchash]);
> > + spin_unlock_bh(&nf_nat_lock);
> > }
> >
> > /* It's done. */
> > @@ -578,9 +550,10 @@ static int nf_nat_proto_clean(struct nf_
> > * Else, when the conntrack is destoyed, nf_nat_cleanup_conntrack()
> > * will delete entry from already-freed table.
> > */
> > + spin_lock_bh(&nf_nat_lock);
> > + hlist_del_rcu(&ct->nat_bysource);
> > ct->status &= ~IPS_NAT_DONE_MASK;
> > - rhltable_remove(&nf_nat_bysource_table, &ct->nat_bysource,
> > - nf_nat_bysource_params);
> > + 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.
> > @@ -710,8 +683,11 @@ static void nf_nat_cleanup_conntrack(str
> > if (!nat)
> > return;
> >
> > - rhltable_remove(&nf_nat_bysource_table, &ct->nat_bysource,
> > - nf_nat_bysource_params);
> > + NF_CT_ASSERT(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 = {
> > @@ -846,13 +822,16 @@ 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;
> > }
> > @@ -876,7 +855,7 @@ static int __init nf_nat_init(void)
> > return 0;
> >
> > cleanup_extend:
> > - rhltable_destroy(&nf_nat_bysource_table);
> > + nf_ct_free_hashtable(nf_nat_bysource, nf_nat_htable_size);
> > nf_ct_extend_unregister(&nat_extend);
> > return ret;
> > }
> > @@ -896,8 +875,8 @@ 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");
> >
> >

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