Re: [PATCH net v3] net: Clear old fragment checksum value in napi_reuse_skb

["Nelson, Shannon" <shannon.nelson@amd.com>]

On 2/25/2025 3:28 AM, Mohammad Heib wrote:
> 
> In certain cases, napi_get_frags() returns an skb that points to an old
> received fragment, This skb may have its skb->ip_summed, csum, and other
> fields set from previous fragment handling.
> 
> Some network drivers set skb->ip_summed to either CHECKSUM_COMPLETE or
> CHECKSUM_UNNECESSARY when getting skb from napi_get_frags(), while
> others only set skb->ip_summed when RX checksum offload is enabled on
> the device, and do not set any value for skb->ip_summed when hardware
> checksum offload is disabled, assuming that the skb->ip_summed
> initiated to zero by napi_reuse_skb, ionic driver for example will
> ignore/unset any value for the ip_summed filed if HW checksum offload is
> disabled, and if we have a situation where the user disables the
> checksum offload during a traffic that could lead to the following
> errors shown in the kernel logs:
> <IRQ>
> dump_stack_lvl+0x34/0x48
>   __skb_gro_checksum_complete+0x7e/0x90
> tcp6_gro_receive+0xc6/0x190
> ipv6_gro_receive+0x1ec/0x430
> dev_gro_receive+0x188/0x360
> ? ionic_rx_clean+0x25a/0x460 [ionic]
> napi_gro_frags+0x13c/0x300
> ? __pfx_ionic_rx_service+0x10/0x10 [ionic]
> ionic_rx_service+0x67/0x80 [ionic]
> ionic_cq_service+0x58/0x90 [ionic]
> ionic_txrx_napi+0x64/0x1b0 [ionic]
>   __napi_poll+0x27/0x170
> net_rx_action+0x29c/0x370
> handle_softirqs+0xce/0x270
> __irq_exit_rcu+0xa3/0xc0
> common_interrupt+0x80/0xa0
> </IRQ>
> 
> This inconsistency sometimes leads to checksum validation issues in the
> upper layers of the network stack.
> 
> To resolve this, this patch clears the skb->ip_summed value for each
> reused skb in by napi_reuse_skb(), ensuring that the caller is responsible
> for setting the correct checksum status. This eliminates potential
> checksum validation issues caused by improper handling of
> skb->ip_summed.
> 
> Fixes: 76620aafd66f ("gro: New frags interface to avoid copying shinfo")
> Signed-off-by: Mohammad Heib <mheib@redhat.com>

Thanks!

Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>


> ---
>   net/core/gro.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/net/core/gro.c b/net/core/gro.c
> index 78b320b63174..0ad549b07e03 100644
> --- a/net/core/gro.c
> +++ b/net/core/gro.c
> @@ -653,6 +653,7 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
>          skb->pkt_type = PACKET_HOST;
> 
>          skb->encapsulation = 0;
> +       skb->ip_summed = CHECKSUM_NONE;
>          skb_shinfo(skb)->gso_type = 0;
>          skb_shinfo(skb)->gso_size = 0;
>          if (unlikely(skb->slow_gro)) {
> --
> 2.48.1
> 
>