linux-kernel - Re: [PATCH] iio: addac: ad74115: Fix use of uninitialized variable rate

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Message-ID: <5cb7ab70be67f8b97b5fd09eefab0f2c33d99d20.camel@gmail.com>
Date: Fri, 11 Apr 2025 13:17:22 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Purva Yeshi <purvayeshi550@...il.com>, David Lechner
 <dlechner@...libre.com>, 	cosmin.tanislav@...log.com, lars@...afoo.de,
 Michael.Hennerich@...log.com, 	jic23@...nel.org
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: addac: ad74115: Fix use of uninitialized variable
 rate

On Fri, 2025-04-11 at 14:39 +0530, Purva Yeshi wrote:
> On 11/04/25 11:19, Nuno Sá wrote:
> > On Thu, 2025-04-10 at 09:51 -0500, David Lechner wrote:
> > > On 4/9/25 3:29 PM, Purva Yeshi wrote:
> > > > Fix Smatch-detected error:
> > > > drivers/iio/addac/ad74115.c:823 _ad74115_get_adc_code() error:
> > > > uninitialized symbol 'rate'.
> > > > 
> > > > The variable rate was declared but not given any value before being used
> > > > in a division. If the code reached that point without setting rate, it
> > > > would cause unpredictable behavior.
> > > > 
> > > > Declare and initialize 'rate' to zero inside the 'else' block where it
> > > > is
> > > > used. This ensures 'rate' is always initialized before being passed to
> > > > DIV_ROUND_CLOSEST.
> > > > 
> > > > Signed-off-by: Purva Yeshi <purvayeshi550@...il.com>
> > > > ---
> > > >   drivers/iio/addac/ad74115.c | 2 +-
> > > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/iio/addac/ad74115.c b/drivers/iio/addac/ad74115.c
> > > > index a7e480f2472d..26770c68e5fa 100644
> > > > --- a/drivers/iio/addac/ad74115.c
> > > > +++ b/drivers/iio/addac/ad74115.c
> > > > @@ -814,7 +814,7 @@ static int _ad74115_get_adc_code(struct
> > > > ad74115_state *st,
> > > >   			return -ETIMEDOUT;
> > > >   	} else {
> > > >   		unsigned int regval, wait_time;
> > > > -		int rate;
> > > > +		int rate = 0;
> > > >   
> > > >   		ret = ad74115_get_adc_rate(st, channel, &rate);
> > > >   		if (ret < 0)
> > > 
> > > I don't see how rate could be used uninitialized since we are
> > > returning the error if ad74115_get_adc_rate() fails.
> > > 
> > > Also, initializing to 0 would then cause a divide by 0 error
> > > if that value was actually used later in the code.
> > > 
> > 
> > Agreed... A better check could actually be (in ad74115_get_adc_rate()):
> > 
> > 
> > if (i >= ARRAY_SIZE(ad74115_get_adc_rate))
> >      return -EIO;
> > 
> > Kind of a paranoid check but just making sure a faulty chip does not lead to
> > an out
> > of bounds access.
> > 
> > - Nuno Sá
> 
> Hi Nuno,
> 
> Thank you for your suggestion regarding the paranoid check.
> 
> However, ad74115_get_adc_rate is a function, not an array, pointer, or 
> vector. Therefore, using ARRAY_SIZE on it results in a compilation error.
> 
> I believe the intended check was:
> 
> if (i >= ARRAY_SIZE(ad74115_adc_conv_rate_tbl))
>      return -EIO;
> 

Oh yes, bad copy-paste...

> 
> This ensures that the index i does not exceed the bounds of the 
> ad74115_adc_conv_rate_tbl array, preventing potential out-of-bounds access.
> 
> This check prevents potential out-of-bounds access, it does not address 
> the Smatch warning about the uninitialized variable 'rate'. Smatch may 
> still flag 'rate' as potentially uninitialized if it cannot determine 
> that ad74115_get_adc_rate() always initializes it before use.
> 

Well, as said, this is a false positive...

- Nuno Sá