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

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Message-ID: <CACGkMEt054F1AZP7V0ocbUce_AvQV_Cw-K21y7Ky1gWa=eSpCA@mail.gmail.com>
Date: Wed, 9 Oct 2024 15:44:30 +0800
From: Jason Wang <jasowang@...hat.com>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: Jonathan Corbet <corbet@....net>, Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, kvm@...r.kernel.org, 
	virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org, 
	Yuri Benditovich <yuri.benditovich@...nix.com>, Andrew Melnychenko <andrew@...nix.com>, 
	Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com
Subject: Re: [PATCH RFC v5 05/10] tun: Pad virtio header with zero

On Tue, Oct 8, 2024 at 2:55 PM Akihiko Odaki <akihiko.odaki@...nix.com> 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@...nix.com>

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
>