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

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Date: Mon, 29 Apr 2024 08:43:14 +0000
From: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
To: Markus Elfring <Markus.Elfring@....de>, "linux-cxl@...r.kernel.org"
	<linux-cxl@...r.kernel.org>, "kernel-janitors@...r.kernel.org"
	<kernel-janitors@...r.kernel.org>, Alison Schofield
	<alison.schofield@...el.com>, Dan Williams <dan.j.williams@...el.com>, Dave
 Jiang <dave.jiang@...el.com>, Davidlohr Bueso <dave@...olabs.net>, Ira Weiny
	<ira.weiny@...el.com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>, Vishal
 Verma <vishal.l.verma@...el.com>
CC: LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] cxl/region: Fix potential invalid pointer dereference



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