[BUG] video: fbdev: sis: possible uninitialized-variable access in SiS_SetCRT2FIFO_300()

[Sam Ravnborg]

Hi Tuo Li,

On Sat, Jul 31, 2021 at 02:28:39PM +0800, Li Tuo wrote:
> Hello,
> 
> Our static analysis tool finds a possible uninitialized-variable access in
> the sis driver in Linux 5.14.0-rc3:
> 
> At the beginning of the function SiS_SetCRT2FIFO_300(), the variable
> modeidindex is not initialized.
> If the following conditions are false, it remains uninitialized.
> 5346:    if(!SiS_Pr->CRT1UsesCustomMode)
> 5438:    if(!SiS_Pr->UseCustomMode)
> 
> But it is accessed at:
> 5466:    colorth = SiS_GetColorDepth(SiS_Pr,CRT2ModeNo,modeidindex) >> 1;
> 
> I am not quite sure whether this possible uninitialized-variable access is
> real and how to fix it if it is real.
> Any feedback would be appreciated, thanks!

First, the report looks correct. There is a path where modeindex may not
be initilized.
But I find it very hard to care for such an ancient driver.
If this was somethign we hit is real life we had heard about it - and
the risk of introducing bugs is higher than the the cance that this
fixes a real life bug.

So my advice, find something more relevant to look at.

	Sam