Re: [Qemu-devel] [PATCH 1/4] ui: avoid risk of 32-bit int overflow in VNC buffer check

[Laszlo Ersek]

On 02/05/18 12:49, Daniel P. Berrangé wrote:
> For very large framebuffers, it is theoretically possible for the result
> of 'vs->throttle_output_offset * VNC_THROTTLE_OUTPUT_LIMIT_SCALE' to
> exceed the size of a 32-bit int. For this to happen in practice, the
> video RAM would have to be set to a large enough value, which is not
> likely today. None the less we can be paranoid against future growth by
> using division instead of multiplication when checking the limits.
> 
> Reported-by: Laszlo Ersek <address@hidden>
> Signed-off-by: Daniel P. Berrangé <address@hidden>
> ---
>  ui/vnc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/ui/vnc.c b/ui/vnc.c
> index 93731accb6..e14e524764 100644
> --- a/ui/vnc.c
> +++ b/ui/vnc.c
> @@ -1572,8 +1572,8 @@ void vnc_write(VncState *vs, const void *data, size_t 
> len)
>       * handshake, or from the job thread's VncState clone
>       */
>      if (vs->throttle_output_offset != 0 &&
> -        vs->output.offset > (vs->throttle_output_offset *
> -                             VNC_THROTTLE_OUTPUT_LIMIT_SCALE)) {
> +        (vs->output.offset / VNC_THROTTLE_OUTPUT_LIMIT_SCALE) >
> +        vs->throttle_output_offset) {
>          trace_vnc_client_output_limit(vs, vs->ioc, vs->output.offset,
>                                        vs->throttle_output_offset);
>          vnc_disconnect_start(vs);
> 

Reviewed-by: Laszlo Ersek <address@hidden>