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

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Date: Mon, 29 Apr 2024 13:30:28 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
Cc: "dave@...olabs.net" <dave@...olabs.net>,
	"jonathan.cameron@...wei.com" <jonathan.cameron@...wei.com>,
	"dave.jiang@...el.com" <dave.jiang@...el.com>,
	"alison.schofield@...el.com" <alison.schofield@...el.com>,
	"vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
	"ira.weiny@...el.com" <ira.weiny@...el.com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] cxl/region: Fix potential invalid pointer dereference

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