Re: [PATCH] vhost: Check for valid vdev in vhost_backend_handle_iotlb_msg

[Stefano Garzarella]

On Mon, Feb 01, 2021 at 02:06:53PM +0100, Eugenio Perez Martin wrote:
> On Mon, Feb 1, 2021 at 1:00 PM Stefano Garzarella <sgarzare@redhat.com> wrote:
> > On Fri, Jan 29, 2021 at 10:07:28AM +0100, Eugenio Pérez wrote:
> > >Not checking this can lead to invalid dev->vdev member access in
> > >vhost_device_iotlb_miss if backend issue an iotlb message in a bad
> > >timing, either maliciously or by a bug.
> > >
> > >Reproduced rebooting a guest with testpmd in txonly forward mode.
> > > #0  0x0000559ffff94394 in vhost_device_iotlb_miss (
> > >     dev=dev@entry=0x55a0012f6680, iova=10245279744, write=1)
> > >     at ../hw/virtio/vhost.c:1013
> > > #1  0x0000559ffff9ac31 in vhost_backend_handle_iotlb_msg (
> > >     imsg=0x7ffddcfd32c0, dev=0x55a0012f6680)
> > >     at ../hw/virtio/vhost-backend.c:411
> > > #2  vhost_backend_handle_iotlb_msg (dev=dev@entry=0x55a0012f6680,
> > >     imsg=imsg@entry=0x7ffddcfd32c0)
> > >     at ../hw/virtio/vhost-backend.c:404
> > > #3  0x0000559fffeded7b in slave_read (opaque=0x55a0012f6680)
> > >     at ../hw/virtio/vhost-user.c:1464
> > > #4  0x000055a0000c541b in aio_dispatch_handler (
> > >     ctx=ctx@entry=0x55a0010a2120, node=0x55a0012d9e00)
> > >     at ../util/aio-posix.c:329
> > >
> > >Fixes: 6dcdd06e3b ("spec/vhost-user spec: Add IOMMU support")
> >
> > I'm not sure but IIUC vhost_backend_handle_iotlb_msg() was introduced by
> > commit 020e571b8b, so maybe is better this 'Fixes' line:
> >
> > Fixes: 020e571b8b ("vhost: rework IOTLB messaging")
>
> Hi Stefano.
>
> Thanks for reviewing it :). Actually yes, you are right, I carried the
> previous Fixes line by mistake.
>
> Should I send a new patch?

Maybe Michael can fix it while applying, but I'm not sure, let's see 
what he says :-)

Stefano

> Thanks!
>
>
> > >Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > >---
> > > hw/virtio/vhost-backend.c | 5 +++++
> > > 1 file changed, 5 insertions(+)
> > >
> > >diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> > >index 222bbcc62d..31b33bde37 100644
> > >--- a/hw/virtio/vhost-backend.c
> > >+++ b/hw/virtio/vhost-backend.c
> > >@@ -406,6 +406,11 @@ int vhost_backend_handle_iotlb_msg(struct vhost_dev *dev,
> > > {
> > >     int ret = 0;
> > >
> > >+    if (unlikely(!dev->vdev)) {
> > >+        error_report("Unexpected IOTLB message when virtio device is 
> > stopped");
> > >+        return -EINVAL;
> > >+    }
> > >+
> > >     switch (imsg->type) {
> > >     case VHOST_IOTLB_MISS:
> > >         ret = vhost_device_iotlb_miss(dev, imsg->iova,
> > >--
> > >2.27.0
> > >
> > >
> >
> > The patch LGTM:
> >
> > Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>