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

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

[Purva Yeshi]

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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.

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

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

[Guenter Roeck]

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@gmail.com>
> ---
>  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

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

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@gmail.com>
>> ---
>>   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