Re: [PATCH v1 4/6] virtio console: Harden control message handling

Michael S. Tsirkin
2023-01-20T12:46:04Z

On Thu, Jan 19, 2023 at 04:22:09PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Jan 19, 2023 at 03:57:19PM +0200, Alexander Shishkin wrote:
> > In handle_control_message(), we look at the ->event field twice, which
> > gives a malicious VMM a window in which to switch it from PORT_ADD to
> > PORT_REMOVE, triggering a null dereference further down the line:
>
> How is the other VMM have full control over the full message here?
> Shouldn't this all have been copied into our local memory if we are
> going to be poking around in it? Like I mentioned in my other review,
> copy it all once and then parse it. Don't try to mess with individual
> fields one at a time otherwise that way lies madness...
>
> thanks,
>
> greg k-h

I agree and in fact, it is *already* copied since with malicious
device we generally use a bounce buffer.
Having said that, the patch is actually a cleanup, e.g. it's clearer
to byte-swap only once.
Just don't oversell it as a security thing.

--
MST