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

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Message-ID: <26673670-6e3b-49fc-b66d-26362bde6590@linuxfoundation.org>
Date: Mon, 21 Oct 2024 13:56:45 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Karan Sanghavi <karansanghvi98@...il.com>,
 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, Karan Sanghavi <karansanghavi98@...il.com>,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] iio: chemical: sps30: Add Null pointer check

On 10/19/24 06:08, Karan Sanghavi wrote:
> 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.
>>

This routine checks rsp in the earlier logic

	if (rsp) {
                 /* each two bytes are followed by a crc8 */
                 rsp_size += rsp_size / 2;
         } else {
                 tmp = arg;

                 while (arg_size) {
                         buf[i] = *tmp++;
                         buf[i + 1] = *tmp++;
                         buf[i + 2] = crc8(sps30_i2c_crc8_table, buf + i, 2, CRC8_INIT_VALUE);
                         arg_size -= 2;
                         i += 3;
                 }
         }
  	
	ret = sps30_i2c_xfer(state, buf, i, buf, rsp_size);
         if (ret)
                 return ret;


Looks like the  tmp = rsp; could be reached depending on the
sps30_i2c_xfer() return value?

Maybe this isn't the right fix but looks like the code could
use looking into for accuracy.

>> 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.
> 

thanks,
-- Shuah