netdev - Re: [PATCH v2 net] af_unix: Do not call kmemdup() for init

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Date:   Sun, 26 Jun 2022 11:43:27 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Kuniyuki Iwashima <kuniyu@...zon.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Pavel Emelyanov <xemul@...nvz.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Kuniyuki Iwashima <kuni1840@...il.com>,
        <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net] af_unix: Do not call kmemdup() for init_net's
 sysctl table.

Kuniyuki Iwashima <kuniyu@...zon.com> writes:

> While setting up init_net's sysctl table, we need not duplicate the global
> table and can use it directly.

Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

I am not quite certain the savings of a single entry table justivies
the complexity.  But the looks correct.

Eric


>
> Fixes: 1597fbc0faf8 ("[UNIX]: Make the unix sysctl tables per-namespace")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
> v2:
>   * Fix NULL comparison style by checkpatch.pl
>
> v1: https://lore.kernel.org/all/20220626074454.28944-1-kuniyu@amazon.com/
> ---
> ---
>  net/unix/sysctl_net_unix.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/net/unix/sysctl_net_unix.c b/net/unix/sysctl_net_unix.c
> index 01d44e2598e2..4bd856d05135 100644
> --- a/net/unix/sysctl_net_unix.c
> +++ b/net/unix/sysctl_net_unix.c
> @@ -26,11 +26,16 @@ int __net_init unix_sysctl_register(struct net *net)
>  {
>  	struct ctl_table *table;
>  
> -	table = kmemdup(unix_table, sizeof(unix_table), GFP_KERNEL);
> -	if (table == NULL)
> -		goto err_alloc;
> +	if (net_eq(net, &init_net)) {
> +		table = unix_table;
> +	} else {
> +		table = kmemdup(unix_table, sizeof(unix_table), GFP_KERNEL);
> +		if (!table)
> +			goto err_alloc;
> +
> +		table[0].data = &net->unx.sysctl_max_dgram_qlen;
> +	}
>  
> -	table[0].data = &net->unx.sysctl_max_dgram_qlen;
>  	net->unx.ctl = register_net_sysctl(net, "net/unix", table);
>  	if (net->unx.ctl == NULL)
>  		goto err_reg;
> @@ -38,7 +43,8 @@ int __net_init unix_sysctl_register(struct net *net)
>  	return 0;
>  
>  err_reg:
> -	kfree(table);
> +	if (net_eq(net, &init_net))
> +		kfree(table);
>  err_alloc:
>  	return -ENOMEM;
>  }