linux-kernel - Re: [PATCH net-next] net/tls: tls_is_tx_ready() checked list

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Date:   Sat, 28 Jan 2023 17:40:08 +0100
From:   Simon Horman <simon.horman@...igine.com>
To:     Pietro Borrello <borrello@...g.uniroma1.it>
Cc:     Boris Pismenny <borisp@...dia.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Vakul Garg <vakul.garg@....com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jkl820.git@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net/tls: tls_is_tx_ready() checked list_entry

On Sat, Jan 28, 2023 at 04:29:17PM +0000, Pietro Borrello wrote:
> tls_is_tx_ready() checks that list_first_entry() does not return NULL.
> This condition can never happen. For empty lists, list_first_entry()
> returns the list_entry() of the head, which is a type confusion.
> Use list_first_entry_or_null() which returns NULL in case of empty
> lists.
> 
> Fixes: a42055e8d2c3 ("net/tls: Add support for async encryption of records for performance")
> Signed-off-by: Pietro Borrello <borrello@...g.uniroma1.it>
> ---
>  net/tls/tls_sw.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> index 9ed978634125..a83d2b4275fa 100644
> --- a/net/tls/tls_sw.c
> +++ b/net/tls/tls_sw.c
> @@ -2427,7 +2427,7 @@ static bool tls_is_tx_ready(struct tls_sw_context_tx *ctx)
>  {
>  	struct tls_rec *rec;
>  
> -	rec = list_first_entry(&ctx->tx_list, struct tls_rec, list);
> +	rec = list_first_entry_or_null(&ctx->tx_list, struct tls_rec, list);
>  	if (!rec)
>  		return false;

Hi Pietro,

I agree this is correct.

However, given that the code has been around for a while,
I feel it's relevant to ask if tx_list can ever be NULL.
If not, perhaps it's better to remove the error path entirely.