linux-kernel - Re: [PATCH v3][next] counter: Add default statement to switch() in quad8_function

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Date:   Wed, 22 Sep 2021 07:51:45 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Tim Gardner <tim.gardner@...onical.com>
Cc:     linux-iio@...r.kernel.org,
        Syed Nayyar Waris <syednwaris@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3][next] counter: Add default statement to switch() in
 quad8_function_read()

On Tue, Sep 21, 2021 at 07:37:49AM -0600, Tim Gardner wrote:
> Coverity complains of a possible use of an uninitialized variable in
> quad8_action_read().
> 
> CID 119643 (#1 of 1): Uninitialized scalar variable (UNINIT)
> 4. uninit_use: Using uninitialized value function.
> 346        switch (function) {
> 
> The call to quad8_function_read() could theoretically return without assigning
> a value to '*function', thus causing the use of an ininitialized variable
> 'function' in quad8_action_read().
> 
> Fix this by adding a default statement to the switch in quad8_function_read()
> and setting a return error code.
> 
> Cc: William Breathitt Gray <vilhelm.gray@...il.com>
> Cc: Syed Nayyar Waris <syednwaris@...il.com>
> Cc: linux-iio@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Tim Gardner <tim.gardner@...onical.com>

Thank you for noticing the mutex. Although this case is simple, I'd
still prefer for this function to return early when an error is found
rather than hold a return value until the end. Please adjust the default
case to unlock the mutex directly and return immediately with -EINVAL.
With that change feel free to add my Ack-by line:

Acked-by: William Breathitt Gray <vilhelm.gray@...il.com>

> ---
> v2 - Add the correct Cc's
> v3 - Add comment to the default switch statement. Also noticed v2 would have
>      returned with a lock held. Fix that by returning a variable return code.
> ---
>  drivers/counter/104-quad-8.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
> index c587f295d720..7faca6b760e7 100644
> --- a/drivers/counter/104-quad-8.c
> +++ b/drivers/counter/104-quad-8.c
> @@ -201,6 +201,7 @@ static int quad8_function_read(struct counter_device *counter,
>  {
>  	struct quad8 *const priv = counter->priv;
>  	const int id = count->id;
> +	int ret = 0;
>  
>  	mutex_lock(&priv->lock);
>  
> @@ -215,13 +216,16 @@ static int quad8_function_read(struct counter_device *counter,
>  		case 2:
>  			*function = COUNTER_FUNCTION_QUADRATURE_X4;
>  			break;
> +		default:
> +			/* should never reach this path */
> +			ret = -EINVAL;
>  		}
>  	else
>  		*function = COUNTER_FUNCTION_PULSE_DIRECTION;
>  
>  	mutex_unlock(&priv->lock);
>  
> -	return 0;
> +	return ret;
>  }
>  
>  static int quad8_function_write(struct counter_device *counter,
> -- 
> 2.33.0
> 

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