linux-kernel - Re: [PATCH v2] i2c: busses/i2c-pxa.c: fix potential null pointer dereference error

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Message-ID: <20130205102540.GC9969@gmail.com>
Date:	Tue, 5 Feb 2013 11:25:40 +0100
From:	Cong Ding <dinggnu@...il.com>
To:	Haojian Zhuang <haojian.zhuang@...il.com>
Cc:	Kyungmin Park <kmpark@...radead.org>,
	Wolfram Sang <w.sang@...gutronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Karol Lewandowski <k.lewandowsk@...sung.com>,
	Haojian Zhuang <haojian.zhuang@...vell.com>,
	linux-i2c@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] i2c: busses/i2c-pxa.c: fix potential null pointer
 dereference error

On Tue, Feb 05, 2013 at 09:14:08AM +0800, Haojian Zhuang wrote:
> On Tue, Feb 5, 2013 at 8:05 AM, Cong Ding <dinggnu@...il.com> wrote:
> > If it goes to eclk through line 1107, the variable res would be NULL. It will
> > cause a null pointer dereference error if we call release_mem_region.
> >
> > Signed-off-by: Cong Ding <dinggnu@...il.com>
> > ---
> >  drivers/i2c/busses/i2c-pxa.c |    3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-pxa.c b/drivers/i2c/busses/i2c-pxa.c
> > index 1034d93..00df535 100644
> > --- a/drivers/i2c/busses/i2c-pxa.c
> > +++ b/drivers/i2c/busses/i2c-pxa.c
> > @@ -1211,7 +1211,8 @@ eremap:
> >  eclk:
> >         kfree(i2c);
> >  emalloc:
> > -       release_mem_region(res->start, resource_size(res));
> > +       if (res)
> > +               release_mem_region(res->start, resource_size(res));
> >         return ret;
> >  }
> >
> >
> 
> No. I don't agree on this. Your fix can't resolve all potential issues.
> 
>         i2c = kzalloc(sizeof(struct pxa_i2c), GFP_KERNEL);
>         if (!i2c) {
>                 ret = -ENOMEM;
>                 goto emalloc;
>         }
> 
>         ret = i2c_pxa_probe_dt(dev, i2c, &i2c_type);
>         if (ret > 0)
>                 ret = i2c_pxa_probe_pdata(dev, i2c, &i2c_type);
>         if (ret < 0)
>                 goto eclk;
> 
>         res = platform_get_resource(dev, IORESOURCE_MEM, 0);
>         irq = platform_get_irq(dev, 0);
>         if (res == NULL || irq < 0) {
>                 ret = -ENODEV;
>                 goto eclk;
>         }
> 
>         if (!request_mem_region(res->start, resource_size(res), res->name)) {
>                 ret = -ENOMEM;
>                 goto eclk;
>         }
> 
> We shouldn't jump to eclk for these error cases. Then we needn't to add
> checking on res.
So what do you suggest to do for these error cases?
 - cong

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