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

From: Dan Carpenter <dan.carpenter@linaro.org>
To: "Zhijian Li (Fujitsu)" <lizhijian@fujitsu.com>
Cc: "dave@stgolabs.net" <dave@stgolabs.net>,
	"jonathan.cameron@huawei.com" <jonathan.cameron@huawei.com>,
	"dave.jiang@intel.com" <dave.jiang@intel.com>,
	"alison.schofield@intel.com" <alison.schofield@intel.com>,
	"vishal.l.verma@intel.com" <vishal.l.verma@intel.com>,
	"ira.weiny@intel.com" <ira.weiny@intel.com>,
	"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
	"linux-cxl@vger.kernel.org" <linux-cxl@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] cxl/region: Fix potential invalid pointer dereference
Date: Mon, 29 Apr 2024 13:30:28 +0300	[thread overview]
Message-ID: <c6cab703-87df-4152-a5b0-a0ce31e7f057@moroto.mountain> (raw)
In-Reply-To: <576dccd9-1f8d-4c69-bc7f-497413b87b9d@fujitsu.com>

On Mon, Apr 29, 2024 at 10:25:35AM +0000, Zhijian Li (Fujitsu) wrote:
> >    3084          mutex_lock(&cxlrd->range_lock);
> >    3085          region_dev = device_find_child(&cxlrd->cxlsd.cxld.dev, hpa,
> >    3086                                         match_region_by_range);
> >    3087          if (!region_dev) {
> >    3088                  cxlr = construct_region(cxlrd, cxled);
> >    3089                  region_dev = &cxlr->dev;
> >                                       ^^^^^^^^^^^
> > This is not a dereference, it's just pointer math.  In in this case it's
> > the same as saying:
> > 
> > 		region_dev = (void *)cxlr;
> 
> 
> You are right, a equivalent code could be:
> 		region_dev = ((char *)cxlr) + offsetof(struct cxl_region, dev);
> 
> 

Correct.  But offsetof() is zero.  It's the same math that to_cxl_region()
does.

regards,
dan carpenter