Re: [PATCH 1/2] cxl/region: Fix potential invalid pointer dereference

["Zhijian Li (Fujitsu)" <lizhijian@fujitsu.com>]

On 29/04/2024 15:50, Markus Elfring wrote:
> I would usually expect a corresponding cover letter for patch series.



> 
> 
>> construct_region() could return a PTR_ERR() which cannot be derefernced.
> 
> I hope that a typo will be avoided in the last word of this sentence.

Thanks, hate my fat fingers, I will fix it later.




> 
> 
>> Moving the dereference behind the error checking to make sure the
>> pointer is valid.
> 
> Please choose an imperative wording for an improved change description.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.9-rc5#n94
> 
> 
> …
>> +++ b/drivers/cxl/core/region.c
>> @@ -3086,10 +3086,9 @@ int cxl_add_to_region(struct cxl_port *root, struct cxl_endpoint_decoder *cxled)
>>   	mutex_lock(&cxlrd->range_lock);
>>   	region_dev = device_find_child(&cxlrd->cxlsd.cxld.dev, hpa,
>>   				       match_region_by_range);
>> -	if (!region_dev) {
>> +	if (!region_dev)
>>   		cxlr = construct_region(cxlrd, cxled);
>> -		region_dev = &cxlr->dev;
>> -	} else
>> +	else
>>   		cxlr = to_cxl_region(region_dev);
>>   	mutex_unlock(&cxlrd->range_lock);
> 
> I suggest to simplify such source code by using a conditional operator expression.

Thanks for your suggestion. Do you mean something like:
cxlr = region_dev ? to_cxl_region(region_dev) : construct_region(cxlrd, cxled);

If so, I'm open to this option, but the kernel does not always obey this convention.
For example,
static inline int __must_check PTR_ERR_OR_ZERO(__force const void *ptr)
{
         if (IS_ERR(ptr))
                 return PTR_ERR(ptr);
         else
                 return 0;
}

Thanks
Zhijian

> 
> Regards,
> Markus