[PATCH v2] video: fbdev: kyro: fix a DoS bug by restricting user input

[Sam Ravnborg]

Hi Zheyu,
On Wed, Jul 14, 2021 at 04:09:22AM +0000, Zheyu Ma wrote:
> The user can pass in any value to the driver through the 'ioctl'
> interface. The driver dost not check, which may cause DoS bugs.
> 
> The following log reveals it:
> 
> divide error: 0000 [#1] PREEMPT SMP KASAN PTI
> RIP: 0010:SetOverlayViewPort+0x133/0x5f0 drivers/video/fbdev/kyro/STG4000OverlayDevice.c:476
> Call Trace:
>  kyro_dev_overlay_viewport_set drivers/video/fbdev/kyro/fbdev.c:378 [inline]
>  kyrofb_ioctl+0x2eb/0x330 drivers/video/fbdev/kyro/fbdev.c:603
>  do_fb_ioctl+0x1f3/0x700 drivers/video/fbdev/core/fbmem.c:1171
>  fb_ioctl+0xeb/0x130 drivers/video/fbdev/core/fbmem.c:1185
>  vfs_ioctl fs/ioctl.c:48 [inline]
>  __do_sys_ioctl fs/ioctl.c:753 [inline]
>  __se_sys_ioctl fs/ioctl.c:739 [inline]
>  __x64_sys_ioctl+0x19b/0x220 fs/ioctl.c:739
>  do_syscall_64+0x32/0x80 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Signed-off-by: Zheyu Ma <zheyuma97 at gmail.com>
> ---
> Changes in v2:
>     - Validate the inputs on a higher level

Much better, thanks.
When a line is continued like here the statement shall aling with the
opening brace. I fixed it up when applying the patch to drm-misc-next so
no need to do anything this time.

	Sam