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

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Message-ID: <CAN1soZwM6qNTJn3vvMdc6TR1eJHc=K+_c0WuWOBBuFYMWB_oCA@mail.gmail.com>
Date:	Tue, 5 Feb 2013 09:14:08 +0800
From:	Haojian Zhuang <haojian.zhuang@...il.com>
To:	Cong Ding <dinggnu@...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 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.

Regards
Haojian
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