[PATCH] staging: comedi: drivers: usbduxsigma.c: fix DMA buffers on stack

[PATCH] staging: comedi: drivers: usbduxsigma.c: fix DMA buffers on stack

[Kumar Amit Mehta]

This patch fixes an instance of DMA buffer on stack(being passed to
usb_control_msg)for the USB-DUXsigma Board driver. Found using smatch.

Signed-off-by: Kumar Amit Mehta <gmate.amit@gmail.com>
---
 drivers/staging/comedi/drivers/usbduxsigma.c |   37 +++++++++++++++++---------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/drivers/staging/comedi/drivers/usbduxsigma.c b/drivers/staging/comedi/drivers/usbduxsigma.c
index dc6b017..46137e8 100644
--- a/drivers/staging/comedi/drivers/usbduxsigma.c
+++ b/drivers/staging/comedi/drivers/usbduxsigma.c
@@ -681,10 +681,14 @@ static void usbduxsub_ao_IsocIrq(struct urb *urb)
 static int usbduxsub_start(struct usbduxsub *usbduxsub)
 {
 	int errcode = 0;
-	uint8_t local_transfer_buffer[16];
-
+	uint8_t *local_transfer_buffer;
+	local_transfer_buffer = kmalloc(16, GFP_KERNEL);
+	if (!local_transfer_buffer) {
+		errcode = -ENOMEM;
+		goto exit;
+	}
 	/* 7f92 to zero */
-	local_transfer_buffer[0] = 0;
+	*local_transfer_buffer = 0;
 	errcode = usb_control_msg(usbduxsub->usbdev,
 				  /* create a pipe for a control transfer */
 				  usb_sndctrlpipe(usbduxsub->usbdev, 0),
@@ -702,22 +706,28 @@ static int usbduxsub_start(struct usbduxsub *usbduxsub)
 				  1,
 				  /* Timeout */
 				  BULK_TIMEOUT);
-	if (errcode < 0) {
+	if (errcode < 0)
 		dev_err(&usbduxsub->interface->dev,
 			"comedi_: control msg failed (start)\n");
-		return errcode;
-	}
-	return 0;
+
+	kfree(local_transfer_buffer);
+exit:
+	return errcode;
 }
 
 static int usbduxsub_stop(struct usbduxsub *usbduxsub)
 {
 	int errcode = 0;
 
-	uint8_t local_transfer_buffer[16];
+	uint8_t *local_transfer_buffer;
+	local_transfer_buffer = kmalloc(16, GFP_KERNEL);
+	if (!local_transfer_buffer) {
+		errcode = -ENOMEM;
+		goto exit;
+	}
 
 	/* 7f92 to one */
-	local_transfer_buffer[0] = 1;
+	*local_transfer_buffer = 1;
 	errcode = usb_control_msg(usbduxsub->usbdev,
 				  usb_sndctrlpipe(usbduxsub->usbdev, 0),
 				  /* bRequest, "Firmware" */
@@ -732,12 +742,13 @@ static int usbduxsub_stop(struct usbduxsub *usbduxsub)
 				  1,
 				  /* Timeout */
 				  BULK_TIMEOUT);
-	if (errcode < 0) {
+	if (errcode < 0)
 		dev_err(&usbduxsub->interface->dev,
 			"comedi_: control msg failed (stop)\n");
-		return errcode;
-	}
-	return 0;
+
+	kfree(local_transfer_buffer);
+exit:
+	return errcode;
 }
 
 static int usbduxsub_upload(struct usbduxsub *usbduxsub,
-- 
1.7.9.5

Re: [PATCH] staging: comedi: drivers: usbduxsigma.c: fix DMA buffers on stack

[Dan Carpenter]

A couple small style issues.

On Thu, Feb 21, 2013 at 09:47:06AM -0800, Kumar Amit Mehta wrote:
> This patch fixes an instance of DMA buffer on stack(being passed to
> usb_control_msg)for the USB-DUXsigma Board driver. Found using smatch.
> 
> Signed-off-by: Kumar Amit Mehta <gmate.amit@gmail.com>
> ---
>  drivers/staging/comedi/drivers/usbduxsigma.c |   37 +++++++++++++++++---------
>  1 file changed, 24 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/staging/comedi/drivers/usbduxsigma.c b/drivers/staging/comedi/drivers/usbduxsigma.c
> index dc6b017..46137e8 100644
> --- a/drivers/staging/comedi/drivers/usbduxsigma.c
> +++ b/drivers/staging/comedi/drivers/usbduxsigma.c
> @@ -681,10 +681,14 @@ static void usbduxsub_ao_IsocIrq(struct urb *urb)
>  static int usbduxsub_start(struct usbduxsub *usbduxsub)
>  {
>  	int errcode = 0;
> -	uint8_t local_transfer_buffer[16];
> -
> +	uint8_t *local_transfer_buffer;

Put a blank line here between the declaration and the code.

> +	local_transfer_buffer = kmalloc(16, GFP_KERNEL);
> +	if (!local_transfer_buffer) {
> +		errcode = -ENOMEM;
> +		goto exit;

Just return directly.

> +	}
>  	/* 7f92 to zero */
> -	local_transfer_buffer[0] = 0;
> +	*local_transfer_buffer = 0;

The original is sort of nicer.  local_transfer is an array and we're
setting the first element.  It seems more clear to me.  Also I
already had to argue with everyone to get comedi to use arrays
instead of pointer math.  :P

I wonder why we have a 16 byte array when we only use the first
byte and we pass 1 as the length to usb_control_msg().  Odd.
Perhaps it shouldn't be an array after all.

regards,
dan carpenter
>  static int usbduxsub_stop(struct usbduxsub *usbduxsub)
>  {
>  	int errcode = 0;
>  

Delete this blank line...

> -	uint8_t local_transfer_buffer[16];
> +	uint8_t *local_transfer_buffer;
> +	local_transfer_buffer = kmalloc(16, GFP_KERNEL);
> +	if (!local_transfer_buffer) {
> +		errcode = -ENOMEM;
> +		goto exit;
> +	}
>  

regards,
dan carpenter