Re: [PATCH net] gve: ignore nonrelevant GSO type bits when processing TSO headers

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

joshwash@ wrote:
> From: Joshua Washington <joshwash@google.com>
> 
> TSO currently fails when the skb's gso_type field has more than one bit
> set.
> 
> TSO packets can be passed from userspace using PF_PACKET, TUNTAP and a
> few others, using virtio_net_hdr (e.g., PACKET_VNET_HDR). This includes
> virtualization, such as QEMU, a real use-case.
> 
> The gso_type and gso_size fields as passed from userspace in
> virtio_net_hdr are not trusted blindly by the kernel. It adds gso_type
> |= SKB_GSO_DODGY to force the packet to enter the software GSO stack
> for verification.
> 
> This issue might similarly come up when the CWR bit is set in the TCP
> header for congestion control, causing the SKB_GSO_TCP_ECN gso_type bit
> to be set.
> 
> Fixes: a57e5de476be ("gve: DQO: Add TX path")

nit: no empty line

> Signed-off-by: Joshua Washington <joshwash@google.com>
> Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
> Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
> Suggested-by: Eric Dumazet <edumazet@google.com>

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

> ---
>  drivers/net/ethernet/google/gve/gve_tx_dqo.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/ethernet/google/gve/gve_tx_dqo.c b/drivers/net/ethernet/google/gve/gve_tx_dqo.c
> index fe1b26a4d736..04cb43a97c96 100644
> --- a/drivers/net/ethernet/google/gve/gve_tx_dqo.c
> +++ b/drivers/net/ethernet/google/gve/gve_tx_dqo.c
> @@ -555,6 +555,10 @@ static int gve_prep_tso(struct sk_buff *skb)
>  	if (unlikely(skb_shinfo(skb)->gso_size < GVE_TX_MIN_TSO_MSS_DQO))
>  		return -1;
>  
> +	/* We only deal with TCP at this point. */
> +	if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
> +		return -EINVAL;
> +

NETIF_F_TSO and NETIF_F_TSO6 are the only terminal/L4 segmentation
offload types that gve advertises in hw_features. So I think that this
will always be true.

If nothing else, it documents the assumption, so fine to keep.

Careful about comments that just repeat what the code does. More
informative are comments that why non-obvious code exists (where
applicable, which is not here).

>  	/* Needed because we will modify header. */
>  	err = skb_cow_head(skb, 0);
>  	if (err < 0)
> @@ -565,18 +569,10 @@ static int gve_prep_tso(struct sk_buff *skb)
>  	/* Remove payload length from checksum. */
>  	paylen = skb->len - skb_transport_offset(skb);
>  
> -	switch (skb_shinfo(skb)->gso_type) {
> -	case SKB_GSO_TCPV4:
> -	case SKB_GSO_TCPV6:
> -		csum_replace_by_diff(&tcp->check,
> -				     (__force __wsum)htonl(paylen));
> +	csum_replace_by_diff(&tcp->check, (__force __wsum)htonl(paylen));
>  
> -		/* Compute length of segmentation header. */
> -		header_len = skb_tcp_all_headers(skb);
> -		break;
> -	default:
> -		return -EINVAL;
> -	}
> +	/* Compute length of segmentation header. */
> +	header_len = skb_tcp_all_headers(skb);
>  
>  	if (unlikely(header_len > GVE_TX_MAX_HDR_SIZE_DQO))
>  		return -EINVAL;
> -- 
> 2.45.1.288.g0e0cd299f1-goog
>