linux-kernel - Re: [PATCH v4 1/7] cxl/region: Avoid null pointer dereference in is_cxl

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Message-ID: <e13cace9-1ab3-4c22-88f7-0d020423c430@amd.com>
Date: Wed, 4 Jun 2025 14:56:22 -0500
From: Nathan Fontenot <nathan.fontenot@....com>
To: Dave Jiang <dave.jiang@...el.com>,
 Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
 linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
 nvdimm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
 linux-pm@...r.kernel.org
Cc: Davidlohr Bueso <dave@...olabs.net>,
 Jonathan Cameron <jonathan.cameron@...wei.com>,
 Alison Schofield <alison.schofield@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>,
 Dan Williams <dan.j.williams@...el.com>, Matthew Wilcox
 <willy@...radead.org>, Jan Kara <jack@...e.cz>,
 "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <len.brown@...el.com>,
 Pavel Machek <pavel@...nel.org>, Li Ming <ming.li@...omail.com>,
 Jeff Johnson <jeff.johnson@....qualcomm.com>,
 Ying Huang <huang.ying.caritas@...il.com>,
 Yao Xingtao <yaoxt.fnst@...itsu.com>, Peter Zijlstra <peterz@...radead.org>,
 Greg KH <gregkh@...uxfoundation.org>, Terry Bowman <terry.bowman@....com>,
 Robert Richter <rrichter@....com>,
 Benjamin Cheatham <benjamin.cheatham@....com>,
 PradeepVineshReddy Kodamati <PradeepVineshReddy.Kodamati@....com>,
 Zhijian Li <lizhijian@...itsu.com>
Subject: Re: [PATCH v4 1/7] cxl/region: Avoid null pointer dereference in
 is_cxl_region()

On 6/3/2025 6:49 PM, Dave Jiang wrote:
> 
> 
> On 6/3/25 3:19 PM, Smita Koralahalli wrote:
>> Add a NULL check in is_cxl_region() to prevent potential null pointer
>> dereference if a caller passes a NULL device. This change ensures the
>> function safely returns false instead of triggering undefined behavior
>> when dev is NULL.
> 
> Don't think this change is necessary. The code paths should not be hitting any NULL region devices unless it's a programming error.

I originally added this to the patchset during some initial development to handle possible
NULL dev pointers when updating soft reserve resources, see cxl_region_softreserv_update()
in patch 5/7.

In the current form of the that routine it appears we shouldn't execute the while loop
if dev is NULL so this could get from the patch set.

-Nathan 

> 
>>
>> Co-developed-by: Nathan Fontenot <Nathan.Fontenot@....com>
>> Signed-off-by: Nathan Fontenot <Nathan.Fontenot@....com>
>> Co-developed-by: Terry Bowman <terry.bowman@....com>
>> Signed-off-by: Terry Bowman <terry.bowman@....com>
>> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
>> ---
>>  drivers/cxl/core/region.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index c3f4dc244df7..109b8a98c4c7 100644
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> @@ -2333,7 +2333,7 @@ const struct device_type cxl_region_type = {
>>  
>>  bool is_cxl_region(struct device *dev)
>>  {
>> -	return dev->type == &cxl_region_type;
>> +	return dev && dev->type == &cxl_region_type;
>>  }
>>  EXPORT_SYMBOL_NS_GPL(is_cxl_region, "CXL");
>>  
>