linux-kernel - Re: [BUG] power: supply: 88pm860x_battery: possible uninitialized-variable access in measure

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Message-ID: <94bb8568-3f3b-b3af-c98f-9d9bf36528e1@gmail.com>
Date:   Fri, 6 Aug 2021 11:29:53 +0800
From:   Tuo Li <islituo@...il.com>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        baijiaju1990@...il.com, "Jett.Zhou" <jtzhou@...vell.com>
Subject: Re: [BUG] power: supply: 88pm860x_battery: possible
 uninitialized-variable access in measure_vbatt()

Thanks for your feedback, and any further feedback about this problem 
would be appreciated.

Best wishes,
Tuo Li

On 2021/8/6 1:49, Sebastian Reichel wrote:
> [adding Jett Zhou to Cc who introduced the driver]
>
> Hi,
>
> On Wed, Jul 28, 2021 at 06:24:12PM +0800, Li Tuo wrote:
>> Our static analysis tool finds a possible uninitialized-variable access in
>> the 88pm860x_battery driver in Linux 5.14.0-rc3:
>>
>> In calc_soc():
>> 369:    int ocv;
>> 376:    switch (state) {
>> 380:    case OCV_MODE_SLEEP:
>> 381:        ret = measure_vbatt(info, OCV_MODE_SLEEP, &ocv);
>>
>> In measure_vbatt(struct pm860x_battery_info *info, int state, int *data)
>> 176:    switch (state) {
>> 184:    case OCV_MODE_SLEEP:
>> 201:        *data = ((*data & 0xff) * 27 * 25) >> 9;
>>
>> If the variable state is OCV_MODE_SLEEP, the function measure_vbatt() is
>> called with the argument &ocv, and the corresponding parameter is data.
>> Thus *data is uninitialized but it is used at line 201.
>>
>> 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@...nghua.edu.cn>
> I suppose the code is suppose to look like this:
>
> 201:        *data = ((ret & 0xff) * 27 * 25) >> 9;
>
> Considering quite some code is spent before to setup ret, which is
> never used. I don't have the device (nor datasheets) though. Considering
> the driver has only seen trivial cleanups over the last 9 years, maybe
> it can just be removed?
>
> -- Sebastian