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

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Message-ID: <20210805174908.ctg6n5iwmg5izap3@earth.universe>
Date:   Thu, 5 Aug 2021 19:49:08 +0200
From:   Sebastian Reichel <sre@...nel.org>
To:     Li Tuo <islituo@...il.com>
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()

[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

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