Re: [PATCH net] vrf: Stop corrupting skb->csum when capturing CHECKSUM_COMPLETE packets

[David Ahern <dsahern@kernel.org>]

On 9/22/26 7:12 AM, Ido Schimmel wrote:
> The VRF device is an Ethernet device but it can have non-Ethernet ports
> such as IP tunnels. Before the cited commit, capturing packets from such
> ports on the VRF device resulted in these packets being detected as
> malformed since they lack an Ethernet header.
> 
> The cited commit fixed it by pushing a dummy Ethernet header to such
> packets before the capture and pulling it afterwards. In the case of
> CHECKSUM_COMPLETE packets it also updated skb->csum with the checksum of
> the dummy Ethernet header. This is wrong as skb->csum should not include
> the checksum of the Ethernet header ("checksum of the _whole_ packet as
> seen by netif_rx()").
> 
> This also means that L4 protocols receive a corrupted skb->csum and
> potentially drop the packet, as is the case with UDP packets whose
> checksum was completed by software.
> 
> Fix by removing the unnecessary call to skb_postpush_rcsum().
> 
> Fixes: 048939088220 ("vrf: add mac header for tunneled packets when sniffer is attached")
> Reported-by: Stefano Sasso <stesasso@gmail.com>
> Closes: https://lore.kernel.org/netdev/CALtE316UtL3x7LL6uxfXzx8rW6AbzYPeDOb478hqJCr_-dj=Wg@mail.gmail.com/
> Signed-off-by: Ido Schimmel <idosch@nvidia.com>
> ---
>  drivers/net/vrf.c | 2 --
>  1 file changed, 2 deletions(-)
> 

Reviewed-by: David Ahern <dsahern@kernel.org>

Thanks, Ido.