Re: [PATCH net v2] tap: fix incorrect variable used for USO check in set_offload()

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Rongguang Wei wrote:
> From: Rongguang Wei <weirongguang@kylinos.cn>
> 
> The USO features in set_offload() incorrectly uses feature_mask and
> features argument.
> 
> The USO feature was written to the local features variable instead of
> feature_mask. All other offload bits (TSO, TSO_ECN) are stored in
> feature_mask which becomes tap->tap_features and is used by
> tap_handle_frame() for GSO segmentation. Without NETIF_F_GSO_UDP_L4
> in tap->tap_features, making USO on tap effectively non-functional.
> 
> Keeping the USO handling inside the TUN_F_CSUM block avoids enabling
> GRO/LRO when userspace requests USO without CSUM.
> 
> Fixes: 399e0827642f ("driver/net/tun: Added features for USO.")
> Signed-off-by: Rongguang Wei <weirongguang@kylinos.cn>
> Reviewed-by: Willem de Bruijn <willemb@google.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>

Substantially changed patch, please don't keep Reviewed-by tags across
non-trivial changes. That said, I do agree, so adding it again.

> ---
> v2: Fix more incorrect variable in USO check.
>     https://lore.kernel.org/netdev/20260806163949.2807698-1-kuba@kernel.org/
> v1: https://lore.kernel.org/netdev/20260805072121.117472-1-clementwei90@163.com/
> ---
>  drivers/net/tap.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/tap.c b/drivers/net/tap.c
> index 5d2d34d24ce8..d4ca2fee538b 100644
> --- a/drivers/net/tap.c
> +++ b/drivers/net/tap.c
> @@ -883,7 +883,7 @@ static int set_offload(struct tap_queue *q, unsigned long arg)
>  
>  		/* TODO: for now USO4 and USO6 should work simultaneously */
>  		if ((arg & (TUN_F_USO4 | TUN_F_USO6)) == (TUN_F_USO4 | TUN_F_USO6))
> -			features |= NETIF_F_GSO_UDP_L4;
> +			feature_mask |= NETIF_F_GSO_UDP_L4;

Drivers/net/tun seems to have this same issue.

Do you want to take a look or shall I?


>  	}
>  
>  	/* tun/tap driver inverts the usage for TSO offloads, where
> @@ -894,8 +894,7 @@ static int set_offload(struct tap_queue *q, unsigned long arg)
>  	 * When user space turns off TSO, we turn off GSO/LRO so that
>  	 * user-space will not receive TSO frames.
>  	 */
> -	if (feature_mask & (NETIF_F_TSO | NETIF_F_TSO6) ||
> -	    (feature_mask & (TUN_F_USO4 | TUN_F_USO6)) == (TUN_F_USO4 | TUN_F_USO6))
> +	if (feature_mask & (NETIF_F_TSO | NETIF_F_TSO6 | NETIF_F_GSO_UDP_L4))
>  		features |= RX_OFFLOADS;
>  	else
>  		features &= ~RX_OFFLOADS;