[Spice-devel] [PATCH spice-gtk] Run-time check monitor per display count <= 256

[Uri Lublin]

Hi Marc-Andre,

On 07/17/2012 08:11 PM, Marc-André Lureau wrote:
> Limit range of monitors, to avoid potential crashes lead by invalid
> received MonitorConfig values (could be misconfigured or misbehaving
> guest)
>
> This is a a client-side implementation limitation. Eventually, the
> range could be inscreased (or unlimited == 0) in the future...
> ---
>   gtk/channel-display.c |   14 +++++++++++++-
>   1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/gtk/channel-display.c b/gtk/channel-display.c
> index d77447a..345d26e 100644
> --- a/gtk/channel-display.c
> +++ b/gtk/channel-display.c
> @@ -275,7 +275,7 @@ static void spice_display_channel_class_init(SpiceDisplayChannelClass *klass)
>            g_param_spec_uint("monitors-max",
>                              "Max display monitors",
>                              "The current maximum number of monitors",
> -                           1, G_MAXINT16, 1,
> +                           1, 256, 1,

A good idea is to have 256 as a constant.

>                              G_PARAM_READABLE |
>                              G_PARAM_STATIC_STRINGS));
>
> @@ -1493,6 +1493,8 @@ static void display_handle_surface_destroy(SpiceChannel *channel, SpiceMsgIn *in
>       free(surface);
>   }
>
> +#define CLAMP_CHECK(x, low, high)  (((x)>  (high)) ? TRUE : (((x)<  (low)) ? TRUE : FALSE))
> +
>   /* coroutine context */
>   static void display_handle_monitors_config(SpiceChannel *channel, SpiceMsgIn *in)
>   {
> @@ -1506,6 +1508,16 @@ static void display_handle_monitors_config(SpiceChannel *channel, SpiceMsgIn *in
>       SPICE_DEBUG("monitors config: n: %d/%d", config->count, config->max_allowed);
>
>       c->monitors_max = config->max_allowed;
> +    if (CLAMP_CHECK(c->monitors_max, 1, 256)) {
> +        g_warning("MonitorConfig max_allowed is not within permitted range, clamping");
> +        c->monitors_max = CLAMP(c->monitors_max, 1, 256);

I'm not sure it's a good idea to continue and process the message once 
it was
found to have an invalid number for monitors_max.
For example if we that value is 1024, CLAMP would make it 256, and the
loop below would fill 256 entries with possibly bad values.

> +    }
> +
> +    if (CLAMP_CHECK(config->count, 1, c->monitors_max)) {
> +        g_warning("MonitorConfig count is not within permitted range, clamping");
> +        config->count = CLAMP(config->count, 1, c->monitors_max);
> +    }
> +
>       c->monitors = g_array_set_size(c->monitors, config->count);
>
>       for (i = 0; i<  config->count; i++) {