Re: [PATCH net] net: virtio_net: decode tunnel csum_start as little-endian

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Oct 23, 2026 at 04:09:57PM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Low] net: virtio_net: sparse __virtio16 mismatch in virtio_net_hdr_tnl_to_skb()
> --
> 
> commit ba7ce0ae4b2dfb77c6b110ada68faaf66de9237f
> Author: Cheng Yongkang <teel4res@gmail.com>
> 
> net: virtio_net: decode tunnel csum_start as little-endian
> 
> This commit changes virtio_net_hdr_tnl_to_skb() in include/linux/virtio_net.h
> to always decode hdr->csum_start as little-endian during tunnel header offset
> validation, matching the subsequent call to __virtio_net_hdr_to_skb().
> 
> > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> > index d6466f96cdd00..ddc6341747e53 100644
> > --- a/include/linux/virtio_net.h
> > +++ b/include/linux/virtio_net.h
> > @@ -324,7 +324,7 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb,
> >  	inner_l3min = virtio_l3min(inner_isv6);
> >  	outer_l3min = ETH_HLEN + virtio_l3min(outer_isv6);
> >  
> > -	inner_th = __virtio16_to_cpu(little_endian, hdr->csum_start);
> > +	inner_th = le16_to_cpu(hdr->csum_start);
> >  	inner_nh = le16_to_cpu(vhdr->inner_nh_offset);
> >  	outer_th = le16_to_cpu(vhdr->outer_th_offset);
> >  	if (outer_th < outer_l3min ||
> 
> [Severity: Low]
> Does passing hdr->csum_start directly to le16_to_cpu() in
> virtio_net_hdr_tnl_to_skb() trigger sparse endianness warnings when building
> callers such as drivers/net/virtio_net.c and drivers/net/tun.c with C=1?
> 
> Unlike vhdr->inner_nh_offset and vhdr->outer_th_offset, which are declared as
> __le16 in struct virtio_net_hdr_v1_hash_tunnel, hdr->csum_start is declared as
> __virtio16 in include/uapi/linux/virtio_net.h:
> 
> struct virtio_net_hdr {
> 	...
> 	__virtio16 csum_start;	/* Position to start checksumming from */
> 	__virtio16 csum_offset;	/* Offset after that to place checksum */
> };
> 
> In include/linux/virtio_byteorder.h, __virtio16_to_cpu() performs the forced
> cast from __virtio16 to __le16 before calling le16_to_cpu():
> 
> static inline u16 __virtio16_to_cpu(bool little_endian, __virtio16 val)
> {
> 	if (little_endian)
> 		return le16_to_cpu((__force __le16)val);
> 	else
> 		return be16_to_cpu((__force __be16)val);
> }
> 
> Should this use __virtio16_to_cpu(true, hdr->csum_start) instead, matching the
> __virtio_net_hdr_to_skb(skb, hdr, true, ...) call below and
> __cpu_to_virtio16(true, hdr_len) in __virtio_net_set_tnl_hdrlen()?


Ugh. In fact it does. Should be __virtio16_to_cpu(true, hdr->csum_start)
and I had exactly that in v5. Not sure at what point I picked
an old version of that (

It's just a warning - functionally the same - so if v6 goes in, I'll fix
it by a patch on top.

> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/179268538303.70821.1734486381476363942@gmail.com?part=1