Re: [PATCH] hwmon: max31827: Fix uninitialized variable lsb_idx in max31827_init_client

[Purva Yeshi]

On 11/04/25 01:31, Guenter Roeck wrote:
> On Fri, Apr 11, 2025 at 01:18:33AM +0530, Purva Yeshi wrote:
> > Fix Smatch-detected issue:
> > drivers/hwmon/max31827.c:564 max31827_init_client() error:
> > uninitialized symbol 'lsb_idx'.
> >
> > ​In the max31827_init_client() function, the variable lsb_idx is assigned
> > a value only when data has exactly one bit set (hweight32(data) == 1).
> > If this condition isn't met, lsb_idx remains uninitialized, leading to
> > undefined behavior when it's subsequently used.
>
> That is not correct.
>
> > Ensure that data is non-zero and has exactly one bit set before
> > calling __ffs(data) to determine lsb_idx. Additionally, verify that
> > lsb_idx does not exceed 4. This approach prevents the use of an
> > uninitialized lsb_idx and resolves the Smatch warning.
> >
> > Signed-off-by: Purva Yeshi <purvayeshi550@xxxxxxxxx>
> > ---
> >   drivers/hwmon/max31827.c | 9 ++++++---
> >   1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/hwmon/max31827.c b/drivers/hwmon/max31827.c
> > index 48e8f8ba4d05..c62eaf186d9d 100644
> > --- a/drivers/hwmon/max31827.c
> > +++ b/drivers/hwmon/max31827.c
> > @@ -558,10 +558,13 @@ static int max31827_init_client(struct max31827_state *st,
> >   		/*
> >   		 * Convert the desired fault queue into register bits.
> >   		 */
> > -		if (data != 0)
> > -			lsb_idx = __ffs(data);
>
> lsb_idx is assigned if data != 0, not if hweight32(data) == 1 ...
>
> > +		if (data == 0 || hweight32(data) != 1) {
> > +			dev_err(dev, "Invalid data in adi,fault-q\n");
> > +			return -EINVAL;
> > +		}
> >   
> > -		if (hweight32(data) != 1 || lsb_idx > 4) {
>
> ... and if hweight32(data) != 1, it bails out here before using lsb_idx.
> The problem you describe does not exist.
>
> Guenter

Thank you for reviewing the patch and clarifying the behavior regarding 
lsb_idx. I understand the existing control flow.​

> > +		lsb_idx = __ffs(data);
> > +		if (lsb_idx > 4) {
> >   			dev_err(dev, "Invalid data in adi,fault-q\n");
> >   			return -EINVAL;
> >   		}
> > --
> > 2.34.1

Best regards,
Purva