netdev - Re: [PATCH 1/1] vhost: Added pad cleanup if vnet

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Date: Mon, 26 Feb 2024 12:30:27 +0200
From: Andrew Melnichenko <andrew@...nix.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: jasowang@...hat.com, kvm@...r.kernel.org, virtualization@...ts.linux.dev, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	yuri.benditovich@...nix.com, yan@...nix.com
Subject: Re: [PATCH 1/1] vhost: Added pad cleanup if vnet_hdr is not present.

Hi all,
Ok, let me prepare a new patch v2, where I'll write a
description/analysis of the issue in the commit message.

On Thu, Feb 22, 2024 at 10:02 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Mon, Jan 15, 2024 at 05:32:25PM -0500, Michael S. Tsirkin wrote:
> > 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@...nix.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 ...
>
>
> Could you post this analysis pls?
>
> > > --
> > > 2.43.0
>