Received-SPF: pass (google.com: domain of linux-kernel+bounces-57756-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Precedence: bulk
MIME-Version: 1.0
References: <20240115194840.1183077-1-andrew@daynix.com> <20240115172837-mutt-send-email-mst@kernel.org>
In-Reply-To: <20240115172837-mutt-send-email-mst@kernel.org>
From: Yuri Benditovich <yuri.benditovich@daynix.com>
Date: Thu, 8 Feb 2024 11:34:53 +0200
Message-ID: <CAOEp5OfKUs+Q+Nq3YywYR=oihSw8Nr=jYSC6a7CN1MTMzJVtHQ@mail.gmail.com>
Subject: Re: [PATCH 1/1] vhost: Added pad cleanup if vnet_hdr is not present.
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Andrew Melnychenko <andrew@daynix.com>, jasowang@redhat.com, kvm@vger.kernel.org, 
	virtualization@lists.linux.dev, netdev@vger.kernel.org, 
	linux-kernel@vger.kernel.org, yan@daynix.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Just polite ping

On Tue, Jan 16, 2024 at 12:32=E2=80=AFAM Michael S. Tsirkin <mst@redhat.com=
> 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=3Don,vnet_hdr=3Doff,...
> >
> > 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_vir=
tqueue *nvq,
> >       hdr =3D buf;
> >       gso =3D &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
>