Re: [PATCH RFC v5 05/10] tun: Pad virtio header with zero

[Jason Wang]

On Tue, Oct 8, 2024 at 2:55 PM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:
>
> tun used to simply advance iov_iter when it needs to pad virtio header,
> which leaves the garbage in the buffer as is. This is especially
> problematic when tun starts to allow enabling the hash reporting
> feature; even if the feature is enabled, the packet may lack a hash
> value and may contain a hole in the virtio header because the packet
> arrived before the feature gets enabled or does not contain the
> header fields to be hashed. If the hole is not filled with zero, it is
> impossible to tell if the packet lacks a hash value.
>
> In theory, a user of tun can fill the buffer with zero before calling
> read() to avoid such a problem, but leaving the garbage in the buffer is
> awkward anyway so fill the buffer in tun.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>

This sounds like an independent fix that is worth going to -net first.

Thanks

> ---
>  drivers/net/tun_vnet.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
> index 7c7f3f6d85e9..c40bde0fdf8c 100644
> --- a/drivers/net/tun_vnet.h
> +++ b/drivers/net/tun_vnet.h
> @@ -138,7 +138,8 @@ static inline int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
>         if (copy_to_iter(hdr, sizeof(*hdr), iter) != sizeof(*hdr))
>                 return -EFAULT;
>
> -       iov_iter_advance(iter, sz - sizeof(*hdr));
> +       if (iov_iter_zero(sz - sizeof(*hdr), iter) != sz - sizeof(*hdr))
> +               return -EFAULT;
>
>         return 0;
>  }
>
> --
> 2.46.2
>