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

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

[Li Tuo]

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!

Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>

Best wishes,
Tuo Li

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

[Dave Kleikamp]

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@tsinghua.edu.cn>
> 
> Best wishes,
> Tuo Li

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@tsinghua.edu.cn>
>>
>> Best wishes,
>> Tuo Li