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Date:   Sun, 24 Sep 2023 12:00:58 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To:     Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        "David S. Miller" <davem@davemloft.net>,
        David Ahern <dsahern@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        netdev@vger.kernel.org
Message-ID: <65105d3a8e70e_12c73e29410@willemb.c.googlers.com.notmuch>
In-Reply-To: <4a096ba9cf981a588aa87235bb91e933ee162b3d.1695542544.git.christophe.jaillet@wanadoo.fr>
References: <4a096ba9cf981a588aa87235bb91e933ee162b3d.1695542544.git.christophe.jaillet@wanadoo.fr>
Subject: Re: [PATCH net-next] udp_tunnel: Use flex array to simplify code
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Christophe JAILLET wrote:
> 'n_tables' is small, UDP_TUNNEL_NIC_MAX_TABLES	= 4 as a maximum. So there
> is no real point to allocate the 'entries' pointers array with a dedicate
> memory allocation.
> 
> Using a flexible array for struct udp_tunnel_nic->entries avoids the
> overhead of an additional memory allocation.
> 
> This also saves an indirection when the array is accessed.
> 
> Finally, __counted_by() can be used for run-time bounds checking if
> configured and supported by the compiler.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
>  net/ipv4/udp_tunnel_nic.c | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
> 
> diff --git a/net/ipv4/udp_tunnel_nic.c b/net/ipv4/udp_tunnel_nic.c
> index 029219749785..b6d2d16189c0 100644
> --- a/net/ipv4/udp_tunnel_nic.c
> +++ b/net/ipv4/udp_tunnel_nic.c
> @@ -47,7 +47,7 @@ struct udp_tunnel_nic {
>  
>  	unsigned int n_tables;
>  	unsigned long missed;
> -	struct udp_tunnel_nic_table_entry **entries;
> +	struct udp_tunnel_nic_table_entry *entries[] __counted_by(n_tables);
>  };
>  
>  /* We ensure all work structs are done using driver state, but not the code.
> @@ -725,16 +725,12 @@ udp_tunnel_nic_alloc(const struct udp_tunnel_nic_info *info,
>  	struct udp_tunnel_nic *utn;
>  	unsigned int i;
>  
> -	utn = kzalloc(sizeof(*utn), GFP_KERNEL);
> +	utn = kzalloc(struct_size(utn, entries, n_tables), GFP_KERNEL);
>  	if (!utn)
>  		return NULL;
>  	utn->n_tables = n_tables;

Should utn->n_tables be initialized before first use of
struct_size(utn, entries, n_tables)?