Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [BUG] jfs: possible uninitialized-variable access in xtSplitUp()
To:     Dave Kleikamp <dave.kleikamp@oracle.com>
Cc:     jfs-discussion@lists.sourceforge.net, linux-kernel@vger.kernel.org,
        baijiaju1990@gmail.com
References: <6b3b3a56-b77c-aff7-c9f1-94a99d4929d2@gmail.com>
 <a01909f1-19d9-8b3e-f772-3aa03b9b139c@oracle.com>
From:   Li Tuo <islituo@gmail.com>
Message-ID: <09905e41-c450-df22-45bb-746be314ecc5@gmail.com>
Date:   Tue, 3 Aug 2021 10:46:28 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.12.0
MIME-Version: 1.0
In-Reply-To: <a01909f1-19d9-8b3e-f772-3aa03b9b139c@oracle.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Precedence: bulk

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