Hi On Tue, Jul 13, 2021 at 12:51:14PM +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.

Fix this by checking if the divisor is 0

This fix is trying to avoid the situation on a too low layer. Could you please try to look at validating the inputs on a much higher level, in kyro_dev_overlay_viewport_set(). Then the checks are much more obvious and you are more likely to catch a number of similar bugs that the test just fails to trigger for now.

Sam

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@gmail.com

drivers/video/fbdev/kyro/STG4000OverlayDevice.c | 6 ++++++ 1 file changed, 6 insertions(+)

diff --git a/drivers/video/fbdev/kyro/STG4000OverlayDevice.c b/drivers/video/fbdev/kyro/STG4000OverlayDevice.c index 9fde0e3b69ec..29d692fe5e75 100644 --- a/drivers/video/fbdev/kyro/STG4000OverlayDevice.c +++ b/drivers/video/fbdev/kyro/STG4000OverlayDevice.c @@ -407,6 +407,9 @@ int SetOverlayViewPort(volatile STG4000REG __iomem *pSTGReg, ulVertDecFactor = 1; }

• if ((ulDest + 1) == 0)

• return -EINVAL;
  

• ulDacYScale = ((ulSrc - 1) * 2048) / (ulDest + 1);

  tmp = STG_READ_REG(DACOverlayVtDec); /* Decimation */

@@ -471,6 +474,9 @@ int SetOverlayViewPort(volatile STG4000REG __iomem *pSTGReg, */ ulScaleLeft = ulSrcLeft;

• if ((ulRight - ulLeft + 2) == 0)
  

• 	return -EINVAL;
  

• /* shift fxscale until it is in the range of the scaler */ ulhDecim = 0; ulScale = (((ulSrcRight - ulSrcLeft) - 1) << (11 - ulhDecim)) / (ulRight - ulLeft + 2);

-- 2.17.6