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Message-ID: <20230120074120-mutt-send-email-mst@kernel.org>
Date: Fri, 20 Jan 2023 07:45:05 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, elena.reshetova@...el.com,
kirill.shutemov@...ux.intel.com, Amit Shah <amit@...nel.org>,
Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v1 4/6] virtio console: Harden control message handling
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
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