Re: [PATCH net] flow_dissector: fix byteorder of dissected ICMP ID

[Jakub Sitnicki <jakub@cloudflare.com>]

On Fri, Mar 12, 2021 at 09:08 PM CET, Alexander Lobakin wrote:
> flow_dissector_key_icmp::id is of type u16 (CPU byteorder),
> ICMP header has its ID field in network byteorder obviously.
> Sparse says:
>
> net/core/flow_dissector.c:178:43: warning: restricted __be16 degrades to integer
>
> Convert ID value to CPU byteorder when storing it into
> flow_dissector_key_icmp.
>
> Fixes: 5dec597e5cd0 ("flow_dissector: extract more ICMP information")
> Signed-off-by: Alexander Lobakin <alobakin@pm.me>
> ---
>  net/core/flow_dissector.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index 2ef2224b3bff..a96a4f5de0ce 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
> @@ -176,7 +176,7 @@ void skb_flow_get_icmp_tci(const struct sk_buff *skb,
>  	 * avoid confusion with packets without such field
>  	 */
>  	if (icmp_has_id(ih->type))
> -		key_icmp->id = ih->un.echo.id ? : 1;
> +		key_icmp->id = ih->un.echo.id ? ntohs(ih->un.echo.id) : 1;
>  	else
>  		key_icmp->id = 0;
>  }

Smells like a breaking change for existing consumers of this value.

How about we change the type of flow_dissector_key_icmp{}.id to __be16
instead to make sparse happy?