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

- From: Zheyu Ma \<hidden\>
- Date: 2021-07-14 04:09:41 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2021/07/1443671
- Thread: https://ratatoskr.run/dri-devel/2021/07/1443671/t.md

```text
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 <redacted>
---
Changes in v2:
    - Validate the inputs on a higher level
---
 drivers/video/fbdev/kyro/fbdev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/video/fbdev/kyro/fbdev.c b/drivers/video/fbdev/kyro/fbdev.c
index 8fbde92ae8b9..eb0cbd1d12d5 100644
--- a/drivers/video/fbdev/kyro/fbdev.c
+++ b/drivers/video/fbdev/kyro/fbdev.c
@@ -372,6 +372,11 @@ static int kyro_dev_overlay_viewport_set(u32 x, u32 y, u32 ulWidth, u32 ulHeight
 		/* probably haven't called CreateOverlay yet */
 		return -EINVAL;
 
+	if (ulWidth == 0 || ulWidth == 0xffffffff ||
+		ulHeight == 0 || ulHeight == 0xffffffff ||
+		(x < 2 && ulWidth + 2 == 0))
+		return -EINVAL;
+
 	/* Stop Ramdac Output */
 	DisableRamdacOutput(deviceInfo.pSTGReg);
 
-- 
2.17.6

```