[PATCH] netfilter: nat: remove rcu_read_lock in __nf_nat_decode_session.

[PATCH] netfilter: nat: remove rcu_read_lock in __nf_nat_decode_session.

[Taehee Yoo]

__nf_nat_decode_session is called from nf_nat_decode_session as decodefn.
before calling decodefn, it already set rcu_read_lock. so rcu_read_lock in
__nf_nat_decode_session can be removed.

Signed-off-by: Taehee Yoo <ap420073@gmail.com>
---
 net/netfilter/nf_nat_core.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index 94b14c5..9b68676 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -71,11 +71,10 @@ static void __nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl)
 	if (ct == NULL)
 		return;
 
-	family = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.l3num;
-	rcu_read_lock();
+	family = nf_ct_l3num(ct);
 	l3proto = __nf_nat_l3proto_find(family);
 	if (l3proto == NULL)
-		goto out;
+		return;
 
 	dir = CTINFO2DIR(ctinfo);
 	if (dir == IP_CT_DIR_ORIGINAL)
@@ -84,8 +83,6 @@ static void __nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl)
 		statusbit = IPS_SRC_NAT;
 
 	l3proto->decode_session(skb, ct, dir, statusbit, fl);
-out:
-	rcu_read_unlock();
 }
 
 int nf_xfrm_me_harder(struct net *net, struct sk_buff *skb, unsigned int family)
-- 
2.9.3

Re: [PATCH] netfilter: nat: remove rcu_read_lock in __nf_nat_decode_session.

[Pablo Neira Ayuso]

On Tue, Mar 28, 2017 at 12:28:50AM +0900, Taehee Yoo wrote:
> __nf_nat_decode_session is called from nf_nat_decode_session as decodefn.
> before calling decodefn, it already set rcu_read_lock. so rcu_read_lock in
> __nf_nat_decode_session can be removed.

Could you have close look at the tree to confirm if we have more spots
where rcu_read_lock is unnecessary?

$ git grep rcu_read_lock net/netfilter/ | wc -l
158
$ git grep rcu_read_lock
net/ipv4/netfilter/ | wc -l
3
$ git grep rcu_read_lock
net/ipv6/netfilter/ | wc -l
2
$ git grep rcu_read_lock
net/bridge/netfilter/ | wc -l

It's a fair good amount, it would take me around one hour probably to
evaluate those here.

If you can help us on verifying this, it would be simply great.

Thanks!

Re: [PATCH] netfilter: nat: remove rcu_read_lock in __nf_nat_decode_session.

[Taehee Yoo]

Thank you for your review!

2017-04-07 4:51 GMT+09:00 Pablo Neira Ayuso <pablo@netfilter.org>:
> On Tue, Mar 28, 2017 at 12:28:50AM +0900, Taehee Yoo wrote:
>> __nf_nat_decode_session is called from nf_nat_decode_session as decodefn.
>> before calling decodefn, it already set rcu_read_lock. so rcu_read_lock in
>> __nf_nat_decode_session can be removed.
>
> Could you have close look at the tree to confirm if we have more spots
> where rcu_read_lock is unnecessary?
>
> $ git grep rcu_read_lock net/netfilter/ | wc -l
> 158
> $ git grep rcu_read_lock
> net/ipv4/netfilter/ | wc -l
> 3
> $ git grep rcu_read_lock
> net/ipv6/netfilter/ | wc -l
> 2
> $ git grep rcu_read_lock
> net/bridge/netfilter/ | wc -l
>
> It's a fair good amount, it would take me around one hour probably to
> evaluate those here.
>
> If you can help us on verifying this, it would be simply great.
>
> Thanks!

okay, I confirm whole rcu_read_lock then I will resend a single patch
as soon as possible.
may be it needs a week.

Re: [PATCH] netfilter: nat: remove rcu_read_lock in __nf_nat_decode_session.

[Pablo Neira Ayuso]

On Tue, Mar 28, 2017 at 12:28:50AM +0900, Taehee Yoo wrote:
> __nf_nat_decode_session is called from nf_nat_decode_session as decodefn.
> before calling decodefn, it already set rcu_read_lock. so rcu_read_lock in
> __nf_nat_decode_session can be removed.

Applied, thanks.