Re: [PATCH net v4 1/2] net: validate virtio checksum start after network header

[David Ahern]

On 9/19/26 6:47 PM, Paulos Yibelo wrote:
> __virtio_net_hdr_to_skb() rejects a CHECKSUM_PARTIAL start smaller than an
> estimated minimum network-header length. The comparison currently uses the
> offset from skb->data rather than the offset from skb_network_header().
> 
> For an AF_PACKET frame, skb->data can still point at the Ethernet header
> while skb_network_header() points past nested link-layer headers. A
> checksum start at the network header can therefore pass, then target byte
> zero after those headers are removed.
> 
> This does not require a virtual-machine guest. A TUN device with
> virtio-net header support can supply the same checksum metadata.
> 
> Keep the existing data-relative lower bound and also require checksum
> start to follow the estimated minimum relative to skb_network_header().
> 
> Fixes: 49d14b54a527 ("net: test for not too small csum_start in virtio_net_hdr_to_skb()")
> Reported-by: Paulos Yibelo <habte.yibelo@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Assisted-by: LLM
> Signed-off-by: Paulos Yibelo <habte.yibelo@xxxxxxxxx>
> Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> Changes in v4:
> - State explicitly that a TUN device is sufficient and no guest is required,
>   as noted by Michael S. Tsirkin. No code changes.
> 
> Changes in v3:
> - Keep the network-relative comparison on one line for readability, as
>   requested by David Ahern.
> 
> Changes in v2:
> - Make nh_min_len an int and remove the casts, as suggested by Michael S.
>   Tsirkin.
> 
>  include/linux/virtio_net.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 

Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>