Re: [Qemu-devel] [PULL 10/14] ui: fix VNC client throttling when audio capture is active

[Paolo Bonzini <pbonzini@redhat.com>]

On 18/01/2018 17:06, Thomas Huth wrote:
> On 18.01.2018 16:33, Paolo Bonzini wrote:
>> On 18/01/2018 15:50, Peter Maydell wrote:
>>> On 18 January 2018 at 14:46, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>> On 18/01/2018 15:12, Daniel P. Berrange wrote:
>>>>>> In addition to that, do we support a >= 2 GiB framebuffer at all? (Even
>>>>>> with unsigned ints, Coverity would rightly complain about a truncated
>>>>>> 32-bit multiplication being assigned to a 64-bit value).
>>>>> client_width/client_height are values that are initialized from the
>>>>> graphics card frontend config, and thus limited by amount of video
>>>>> RAM QEMU allows.   bytes_per_pixel is limited to 8/16/32.
>>>>>
>>>>> So I think we're safe from 2GB overflow in any normal case.
>>>>>
>>>>> That said, VGA RAM size is configurable, so I'm curious what would happen
>>>>> if someone configured an insanely large VGA RAM and asked for a big frame
>>>>> buffer in guest.
>>>>>
>>>>> VNC is protocol limited to uint16 for width/height size, and so is X11
>>>>> so I imagine some exploding behavour would follow :-)
>>>>
>>>> Indeed, and even 2^16 x 2^16 * 32bpp is already 34 bits.  So perhaps we
>>>> should limit VNC to 16384 pixels on each axis (maximum frame buffer size
>>>> 1 GiB).
>>>
>>> Google says you can already get graphics cards that can do 15360x8640,
>>> which is really quite close to that 16384 limit...
>>
>> Then we can do 32767 * 16384 * 4, but I'm a bit afraid of off-by-ones.
> 
> Simply limit it to 30000 * 20000 ?

That's too much (exceeds 2^31-1 at 32bpp), but yeah, 30720*17280 is
twice what Peter found and it's safe.

Paolo