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

[Stefano Garzarella <sgarzare@redhat.com>]

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>
>>
>