linux-kernel - Re: [PATCH 1/2] mmc-block: Use memdup_user() rather than duplicating its implementation

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Date:   Sat, 20 Aug 2016 11:25:15 +0200
From:   walter harms <wharms@....de>
To:     unlisted-recipients:; (no To-header on input)
CC:     linux-mmc@...r.kernel.org, Adrian Hunter <adrian.hunter@...el.com>,
        Grant Grundler <grundler@...omium.org>,
        Jens Axboe <axboe@...com>, Jon Hunter <jonathanh@...dia.com>,
        Mike Christie <mchristi@...hat.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH 1/2] mmc-block: Use memdup_user() rather than duplicating
 its implementation



Am 19.08.2016 23:10, schrieb SF Markus Elfring:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Fri, 19 Aug 2016 22:46:38 +0200
> 
> * Reuse existing functionality from memdup_user() instead of keeping
>   duplicate source code.
> 
>   This issue was detected by using the Coccinelle software.
> 
> * Delete the integer variable "err" then because the pointer
>   variable "idata" should be sufficient to handle return values alone
>   in this function.
> 
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  drivers/mmc/card/block.c | 26 +++++++++-----------------
>  1 file changed, 9 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index 48a5dd7..6ce9492 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -337,22 +337,21 @@ static struct mmc_blk_ioc_data *mmc_blk_ioctl_copy_from_user(
>  	struct mmc_ioc_cmd __user *user)
>  {
>  	struct mmc_blk_ioc_data *idata;
> -	int err;
>  
>  	idata = kmalloc(sizeof(*idata), GFP_KERNEL);
>  	if (!idata) {
> -		err = -ENOMEM;
> +		idata = ERR_PTR(-ENOMEM);
>  		goto out;
>  	}
>  
>  	if (copy_from_user(&idata->ic, user, sizeof(idata->ic))) {
> -		err = -EFAULT;
> +		idata = ERR_PTR(-EFAULT);
>  		goto idata_err;
>  	}
>  
>  	idata->buf_bytes = (u64) idata->ic.blksz * idata->ic.blocks;
>  	if (idata->buf_bytes > MMC_IOC_MAX_BYTES) {
> -		err = -EOVERFLOW;
> +		idata = ERR_PTR(-EOVERFLOW);
>  		goto idata_err;
>  	}
>  
> @@ -361,26 +360,19 @@ static struct mmc_blk_ioc_data *mmc_blk_ioctl_copy_from_user(
>  		return idata;
>  	}
>  
> -	idata->buf = kmalloc(idata->buf_bytes, GFP_KERNEL);
> -	if (!idata->buf) {
> -		err = -ENOMEM;
> +	idata->buf = memdup_user((void __user *)(unsigned long)
> +				 idata->ic.data_ptr,
> +				 idata->buf_bytes);
> +	if (IS_ERR(idata->buf)) {
> +		idata = (void *) idata->buf;
>  		goto idata_err;
>  	}
> -
> -	if (copy_from_user(idata->buf, (void __user *)(unsigned long)
> -					idata->ic.data_ptr, idata->buf_bytes)) {
> -		err = -EFAULT;
> -		goto copy_err;
> -	}
> -
>  	return idata;
>  
> -copy_err:
> -	kfree(idata->buf);
>  idata_err:
>  	kfree(idata);
>  out:
> -	return ERR_PTR(err);
> +	return idata;
>  }


This looks strange, returning a freed pointer is a bad idea. I suggest a
idata=NULL after kfree().

re,
 wh

>  
>  static int mmc_blk_ioctl_copy_to_user(struct mmc_ioc_cmd __user *ic_ptr,