RE: [Intel-wired-lan] [PATCH iwl-net v1] i40e: don't advertise IFF_SUPP_NOFCS

["Loktionov, Aleksandr" <aleksandr.loktionov@intel.com>]

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@osuosl.org> On Behalf
> Of Kohei Enju
> Sent: Wednesday, March 25, 2026 9:50 PM
> To: intel-wired-lan@lists.osuosl.org; netdev@vger.kernel.org
> Cc: Nguyen, Anthony L <anthony.l.nguyen@intel.com>; Kitszel,
> Przemyslaw <przemyslaw.kitszel@intel.com>; Andrew Lunn
> <andrew+netdev@lunn.ch>; David S. Miller <davem@davemloft.net>; Eric
> Dumazet <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>; Paolo
> Abeni <pabeni@redhat.com>; Shannon Nelson <sln@onemain.com>; Jesse
> Brandeburg <jesse.brandeburg@intel.com>; kohei.enju@gmail.com; Kohei
> Enju <kohei@enjuk.jp>
> Subject: [Intel-wired-lan] [PATCH iwl-net v1] i40e: don't advertise
> IFF_SUPP_NOFCS
> 
> i40e advertises IFF_SUPP_NOFCS, allowing users to use the SO_NOFCS
> socket option. However, this option is silently ignored, as the driver
> does not check skb->no_fcs, and always enables FCS insertion offload.
> 
> Fix this by removing the advertisement of IFF_SUPP_NOFCS.
> 
> This behavior can be reproduced with a simple AF_PACKET socket:
> 
>   import socket
>   s = socket.socket(socket.AF_PACKET, socket.SOCK_RAW)
>   s.setsockopt(socket.SOL_SOCKET, 43, 1) # SO_NOFCS
>   s.bind(("eth0", 0))
>   s.send(b'\xff' * 64)
> 
> Previously, send() succeeds but the driver ignores SO_NOFCS.
> With this change, send() fails with -EPROTONOSUPPORT, as expected.
> 
> Fixes: 41c445ff0f48 ("i40e: main driver core")
> Signed-off-by: Kohei Enju <kohei@enjuk.jp>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c
> b/drivers/net/ethernet/intel/i40e/i40e_main.c
> index 3749f32ef95a..a3c52aa6255b 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -13831,7 +13831,6 @@ static int i40e_config_netdev(struct i40e_vsi
> *vsi)
>  	netdev->neigh_priv_len = sizeof(u32) * 4;
> 
>  	netdev->priv_flags |= IFF_UNICAST_FLT;
> -	netdev->priv_flags |= IFF_SUPP_NOFCS;
>  	/* Setup netdev TC information */
>  	i40e_vsi_config_netdev_tc(vsi, vsi->tc_config.enabled_tc);
> 
> --
> 2.51.0

I'd recommend to add Cc: stable@vger.kernel.org

Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>