Re: [BUG] jfs: possible uninitialized-variable access in xtSplitUp()

[Li Tuo]

Thanks for your feedback, and any feedback about the further check would 
be appreciated!

Best wishes,
Tuo Li

On 2021/8/3 3:04, Dave Kleikamp wrote:
> On 7/31/21 1:31 AM, Li Tuo wrote:
> > Hello,
> >
> > Our static analysis tool finds a possible uninitialized-variable 
> > access in the jfs driver in Linux 5.14.0-rc3:
> >
> > At the beginning of the function xtSplitUp(), the variable rbn is not 
> > initialized.
> > If sp->header.flag & BT_ROOT is true,
> > 780:    rc = (sp->header.flag & BT_ROOT) ? xtSplitRoot(tid, ip, 
> > split, &rmp) : xtSplitPage(tid, ip, split, &rmp, &rbn);
> >
> > the varialbe rbn will remain uninitialized.
> > However, it is accessed through:
> > 814:    rcbn = rbn;
> >
> > 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!
>
> I think the logic that protects us is that in the case where rbn is 
> uninitialized, sp->header.flag & BT_ROOT, which means it SHOULD BE the 
> last entry in btstack, so we shouldn't enter the loop:
>     while ((parent = BT_POP(btstack)) != NULL) {
>
> It does seem that some type of sanity check is warranted. I'll take a 
> closer look and see if I can add some kind of error path if things are 
> out of sync.
>
> > Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx>
> >
> > Best wishes,
> > Tuo Li