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

[Pablo Neira Ayuso]

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");
> 
>