linux-kernel - Re: [Line6linux-devel] [PATCH] line6: Use kmemdup rather than duplicating its implementation

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Date:	Mon, 3 Dec 2012 17:34:07 +0100
From:	Stefan Hajnoczi <stefanha@...il.com>
To:	Laurent Navet <laurent.navet@...il.com>
Cc:	devel@...verdev.osuosl.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"line6linux-devel@...ts.sourceforge.net" 
	<line6linux-devel@...ts.sourceforge.net>,
	kernel-janitors@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [Line6linux-devel] [PATCH] line6: Use kmemdup rather than
 duplicating its implementation

On Mon, Dec 3, 2012 at 2:20 PM, Laurent Navet <laurent.navet@...il.com> wrote:
> staging: line6: driver.c
>  The semantic patch that makes this output is available
>  in scripts/coccinelle/api/memdup.cocci.
>
> Signed-off-by: Laurent Navet <laurent.navet@...il.com>
> ---
>  drivers/staging/line6/driver.c |    5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/line6/driver.c b/drivers/staging/line6/driver.c
> index f5c19b2..e1d6241 100644
> --- a/drivers/staging/line6/driver.c
> +++ b/drivers/staging/line6/driver.c
> @@ -331,14 +331,13 @@ int line6_version_request_async(struct usb_line6 *line6)
>         char *buffer;
>         int retval;
>
> -       buffer = kmalloc(sizeof(line6_request_version), GFP_ATOMIC);
> +       buffer = kmemdup(line6_request_version,
> +                       sizeof(line6_request_version), GFP_ATOMIC);
>         if (buffer == NULL) {
>                 dev_err(line6->ifcdev, "Out of memory");
>                 return -ENOMEM;
>         }
>
> -       memcpy(buffer, line6_request_version, sizeof(line6_request_version));
> -
>         retval = line6_send_raw_message_async(line6, buffer,
>                                               sizeof(line6_request_version));
>         kfree(buffer);
> --
> 1.7.10.4

Your change is fine but I'm not sure whether we should allocate memory
in the first place:

line6_send_raw_message_async() returns before the transfer is
complete.  It submits one or more URBs but I cannot see a guarantee
that the buffer is no longer needed.  It seems unsafe to kfree(buffer)
before the request is complete.

Since we already have const char line6_request_version[] we should
pass it directly without a temporary kmemdup() buffer.

Stefan
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