linux-kernel - Re: [PATCH net-next v3] inet: fix fast path in __inet_hash

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Message-ID: <cf3c7895be29d46e814d356bb5afad1203815253.camel@redhat.com>
Date:   Tue, 17 Jan 2023 11:21:39 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Pietro Borrello <borrello@...g.uniroma1.it>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>
Cc:     Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jkl820.git@...il.com>,
        Kuniyuki Iwashima <kuniyu@...zon.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3] inet: fix fast path in __inet_hash_connect()

On Sat, 2023-01-14 at 13:11 +0000, Pietro Borrello wrote:
> __inet_hash_connect() has a fast path taken if sk_head(&tb->owners) is
> equal to the sk parameter.
> sk_head() returns the hlist_entry() with respect to the sk_node field.
> However entries in the tb->owners list are inserted with respect to the
> sk_bind_node field with sk_add_bind_node().
> Thus the check would never pass and the fast path never execute.
> 
> This fast path has never been executed or tested as this bug seems
> to be present since commit 1da177e4c3f4 ("Linux-2.6.12-rc2"), thus
> remove it to reduce code complexity.
> 
> Signed-off-by: Pietro Borrello <borrello@...g.uniroma1.it>
> ---
> Changes in v3:
> - remove the fast path to reduce code complexity
> - Link to v2: https://lore.kernel.org/r/20230112-inet_hash_connect_bind_head-v2-1-5ec926ddd985@diag.uniroma1.it
> 
> Changes in v2:
> - nit: s/list_entry/hlist_entry/
> - Link to v1: https://lore.kernel.org/r/20230112-inet_hash_connect_bind_head-v1-1-7e3c770157c8@diag.uniroma1.it
> ---
>  net/ipv4/inet_hashtables.c | 12 +-----------
>  1 file changed, 1 insertion(+), 11 deletions(-)
> 
> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> index d039b4e732a3..b832e7a545d4 100644
> --- a/net/ipv4/inet_hashtables.c
> +++ b/net/ipv4/inet_hashtables.c
> @@ -994,17 +994,7 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
>  	u32 index;
>  
>  	if (port) {
> -		head = &hinfo->bhash[inet_bhashfn(net, port,
> -						  hinfo->bhash_size)];
> -		tb = inet_csk(sk)->icsk_bind_hash;
> -		spin_lock_bh(&head->lock);
> -		if (sk_head(&tb->owners) == sk && !sk->sk_bind_node.next) {
> -			inet_ehash_nolisten(sk, NULL, NULL);
> -			spin_unlock_bh(&head->lock);
> -			return 0;
> -		}
> -		spin_unlock(&head->lock);
> -		/* No definite answer... Walk to established hash table */
> +		local_bh_disable();
>  		ret = check_established(death_row, sk, port, NULL);
>  		local_bh_enable();
>  		return ret;

LGTM, thanks!

Eric, do you have any additional comment?

Cheers,

Paolo