linux-kernel - Re: [PATCH] drivers/mmc/card/block.c: fix potential null dereference 'idata'

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Message-ID: <BANLkTimOfmS=tKMY7Z_vRcCWEO6drgwegQ@mail.gmail.com>
Date:	Mon, 9 May 2011 18:13:55 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Vladimir Motyka <vladimir.motyka@...il.com>
Cc:	Julia Lawall <julia@...u.dk>, cjb@...top.org,
	kernel-janitors@...r.kernel.org, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/mmc/card/block.c: fix potential null dereference 'idata'

On Mon, May 9, 2011 at 6:05 PM, Vladimir Motyka
<vladimir.motyka@...il.com> wrote:
> On 05/09/2011 04:32 PM, Julia Lawall wrote:
>> On Mon, 9 May 2011, Vladimir Motyka wrote:
>>
>>> When allocation of idata fails there was a null dereferece.
>>
>> Why not have a different label for the two cases?  That would make the
>> code easier to statically analyze, and perhaps be more understandable as
>> well.
>>
>> julia
>>
> I think You are right. So it could be better like this?
>
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index 3dec493..a03cdc6 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -237,7 +237,7 @@ static struct mmc_blk_ioc_data
> *mmc_blk_ioctl_copy_from_user(
>        idata = kzalloc(sizeof(*idata), GFP_KERNEL);
>        if (!idata) {
>                err = -ENOMEM;
> -               goto copy_err;
> +               goto alloc_err;
>        }
>
>        if (copy_from_user(&idata->ic, user, sizeof(idata->ic))) {
> @@ -266,9 +266,9 @@ static struct mmc_blk_ioc_data
> *mmc_blk_ioctl_copy_from_user(
>        return idata;
>
>  copy_err:
> -       if(idata)
> -               kfree(idata->buf);
> +       kfree(idata->buf);
Make it one patch not series.

>        kfree(idata);
> +alloc_err:
>        return ERR_PTR(err);
>  }
>
> Or it could return right after allocation fails so there needn't be
> goto. It is simplier, but maybe worse looking and to read. What is your
> opinion?
>
> Vladimir Motyka
>
>>
>>> Signed-off-by: Vladimir Motyka <vladimir.motyka@...il.com>
>>>
>>> ---
>>> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
>>> index 407836d..3dec493 100644
>>> --- a/drivers/mmc/card/block.c
>>> +++ b/drivers/mmc/card/block.c
>>> @@ -266,10 +266,10 @@ static struct mmc_blk_ioc_data
>>> *mmc_blk_ioctl_copy_from_user(
>>>      return idata;
>>>
>>>  copy_err:
>>> -    kfree(idata->buf);
>>> +    if(idata)
>>> +            kfree(idata->buf);
>>>      kfree(idata);
>>>      return ERR_PTR(err);
>>> -
>>>  }
>>>
>>>  static int mmc_blk_ioctl_cmd(struct block_device *bdev,
>>> --
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>
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-- 
With Best Regards,
Andy Shevchenko
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