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SubjectRe: [PATCH 1/1] vhost: Added pad cleanup if vnet_hdr is not present.
On Mon, Jan 15, 2024 at 09:48:40PM +0200, Andrew Melnychenko wrote:
> When the Qemu launched with vhost but without tap vnet_hdr,
> vhost tries to copy vnet_hdr from socket iter with size 0
> to the page that may contain some trash.
> That trash can be interpreted as unpredictable values for
> vnet_hdr.
> That leads to dropping some packets and in some cases to
> stalling vhost routine when the vhost_net tries to process
> packets and fails in a loop.
>
> Qemu options:
> -netdev tap,vhost=on,vnet_hdr=off,...
>
> Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
> ---
> drivers/vhost/net.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index f2ed7167c848..57411ac2d08b 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -735,6 +735,9 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
> hdr = buf;
> gso = &hdr->gso;
>
> + if (!sock_hlen)
> + memset(buf, 0, pad);
> +
> if ((gso->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
> vhost16_to_cpu(vq, gso->csum_start) +
> vhost16_to_cpu(vq, gso->csum_offset) + 2 >


Hmm need to analyse it to make sure there are no cases where we leak
some data to guest here in case where sock_hlen is set ...
> --
> 2.43.0


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