linux-kernel - Re: [PATCH] iio: chemical: sps30: Add Null pointer check

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Message-ID: <upme6hy6sroszgdhj7ucg6iksxuim26grhgaypegu2vzdtsp6z@ne33c5yhbhe2>
Date: Sat, 19 Oct 2024 12:08:55 +0000
From: Karan Sanghavi <karansanghvi98@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Tomasz Duszynski <tduszyns@...il.com>, 
	Lars-Peter Clausen <lars@...afoo.de>, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Shuah Khan <skhan@...uxfoundation.org>, Karan Sanghavi <karansanghavi98@...il.com>
Subject: Re: [PATCH] iio: chemical: sps30: Add Null pointer check

On Sat, Oct 19, 2024 at 12:21:33PM +0100, Jonathan Cameron wrote:
> On Fri, 18 Oct 2024 18:54:42 +0000
> Karan Sanghavi <karansanghvi98@...il.com> wrote:
> 
> > Add a Null pointer check before assigning and incrementing
> > the null pointer
> > 
> > Signed-off-by: Karan Sanghavi <karansanghvi98@...il.com>
> 
> It would be a bug if rsp_size was anything other than 0 and rsp is NULL.
> So this looks like a false positive as the loop will never be
> entered.
> 
> How did you find it, in particular have you managed to trigger this
> in the driver?
> 
> Jonathan
> 
>

I found this bug in Coverity scan with Cid: 1504707.
Link below, for the same.
https://scan7.scan.coverity.com/#/project-view/51946/11354?selectedIssue=1504707

Rsp here is a void pointer received from the function arguments 
which can be NULL for a no respone call.
Thus incrementing the NULL pointer can lead to some unexpected 
behavior which cross my mind thus added the check. 


> > ---
> >  drivers/iio/chemical/sps30_i2c.c | 20 +++++++++++---------
> >  1 file changed, 11 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/iio/chemical/sps30_i2c.c b/drivers/iio/chemical/sps30_i2c.c
> > index 1b21b6bcd0e7..d2142e4c748c 100644
> > --- a/drivers/iio/chemical/sps30_i2c.c
> > +++ b/drivers/iio/chemical/sps30_i2c.c
> > @@ -105,16 +105,18 @@ static int sps30_i2c_command(struct sps30_state *state, u16 cmd, void *arg, size
> >  		return ret;
> >  
> >  	/* validate received data and strip off crc bytes */
> > -	tmp = rsp;
> > -	for (i = 0; i < rsp_size; i += 3) {
> > -		crc = crc8(sps30_i2c_crc8_table, buf + i, 2, CRC8_INIT_VALUE);
> > -		if (crc != buf[i + 2]) {
> > -			dev_err(state->dev, "data integrity check failed\n");
> > -			return -EIO;
> > +	if (rsp) {
> > +		tmp = rsp;
> > +		for (i = 0; i < rsp_size; i += 3) {
> > +			crc = crc8(sps30_i2c_crc8_table, buf + i, 2, CRC8_INIT_VALUE);
> > +			if (crc != buf[i + 2]) {
> > +				dev_err(state->dev, "data integrity check failed\n");
> > +				return -EIO;
> > +			}
> > +
> > +			*tmp++ = buf[i];
> > +			*tmp++ = buf[i + 1];
> >  		}
> > -
> > -		*tmp++ = buf[i];
> > -		*tmp++ = buf[i + 1];
> >  	}
> >  
> >  	return 0;
> > 
> > ---
> > base-commit: f2493655d2d3d5c6958ed996b043c821c23ae8d3
> > change-id: 20241018-cid1593398badshift-9c512a3b92d9
> > 
> > Best regards,
>
Thank you,
Karan.