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From:   Alexander Shishkin <alexander.shishkin@linux.intel.com>
To:     "Michael S. Tsirkin" <mst@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     jasowang@redhat.com, virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, elena.reshetova@intel.com,
        kirill.shutemov@linux.intel.com, Amit Shah <amit@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        alexander.shishkin@linux.intel.com
Subject: Re: [PATCH v1 4/6] virtio console: Harden control message handling
In-Reply-To: <20230120074120-mutt-send-email-mst@kernel.org>
References: <20230119135721.83345-1-alexander.shishkin@linux.intel.com>
 <20230119135721.83345-5-alexander.shishkin@linux.intel.com>
 <Y8lgIS+jygB7SGrn@kroah.com>
 <20230120074120-mutt-send-email-mst@kernel.org>
Date:   Fri, 20 Jan 2023 18:41:27 +0200
Message-ID: <87y1pxp39k.fsf@ubik.fi.intel.com>
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"Michael S. Tsirkin" <mst@redhat.com> writes:

> 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.

Right, but the code should probably be able to handle bad input on its
own, or what do you think?

> 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.

Well, security was the original motivation, so that's what it said in
the commit message. But we settled on [0] yesterday with Greg, which
would replace this patch and 2/6.

[0] https://lore.kernel.org/all/87a62eqo4h.fsf@ubik.fi.intel.com/

Regards,
--
Alex