linux-kernel - Re: dm: ioctl: use kvfree

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Date:	Mon, 11 Apr 2016 11:34:32 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:	Alasdair Kergon <agk@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>,
	Shaohua Li <shli@...nel.org>, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, linux-raid@...r.kernel.org
Subject: Re: dm: ioctl: use kvfree

On Mon, Apr 11, 2016 at 08:44:37PM +0530, Sudip Mukherjee wrote:
> We can use kvfree() instead of calling kfree() and vfree() based on
> if-else and param_flags. kvfree() will check the type of address and
> will call the respective function to free it.
> Additionally we can also remove the use of DM_PARAMS_KMALLOC and
> DM_PARAMS_VMALLOC.
> 
> Signed-off-by: Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>
> 
> ---
> drivers/md/dm-ioctl.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> index 2adf81d..d5df3a5 100644
> --- a/drivers/md/dm-ioctl.c
> +++ b/drivers/md/dm-ioctl.c
> @@ -1670,8 +1670,6 @@ static int check_version(unsigned int cmd, struct dm_ioctl __user *user)
>  	return r;
>  }
>  
> -#define DM_PARAMS_KMALLOC	0x0001	/* Params alloced with kmalloc */
> -#define DM_PARAMS_VMALLOC	0x0002	/* Params alloced with vmalloc */
>  #define DM_WIPE_BUFFER		0x0010	/* Wipe input buffer before returning from ioctl */
>  
>  static void free_params(struct dm_ioctl *param, size_t param_size, int param_flags)
> @@ -1679,10 +1677,7 @@ static void free_params(struct dm_ioctl *param, size_t param_size, int param_fla
>  	if (param_flags & DM_WIPE_BUFFER)
>  		memset(param, 0, param_size);
>  
> -	if (param_flags & DM_PARAMS_KMALLOC)
> -		kfree(param);
> -	if (param_flags & DM_PARAMS_VMALLOC)
> -		vfree(param);
> +	kvfree(param);

That won't work: param is not always allocated. See code path leading to
the "data_copied:" label in copy_params().

This is the second time this patch has been submitted. Maybe someone should
add a comment explaining why a conditional flag is needed.

Guenter

>  }
>  
>  static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kernel,
> @@ -1716,8 +1711,6 @@ static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kern
>  	dmi = NULL;
>  	if (param_kernel->data_size <= KMALLOC_MAX_SIZE) {
>  		dmi = kmalloc(param_kernel->data_size, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
> -		if (dmi)
> -			*param_flags |= DM_PARAMS_KMALLOC;
>  	}
>  
>  	if (!dmi) {
> @@ -1725,8 +1718,6 @@ static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kern
>  		noio_flag = memalloc_noio_save();
>  		dmi = __vmalloc(param_kernel->data_size, GFP_NOIO | __GFP_REPEAT | __GFP_HIGH | __GFP_HIGHMEM, PAGE_KERNEL);
>  		memalloc_noio_restore(noio_flag);
> -		if (dmi)
> -			*param_flags |= DM_PARAMS_VMALLOC;
>  	}
>  
>  	if (!dmi) {