linux-kernel - Re: [PATCH v2] staging: gdm724x: Fix DMA from stack

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Date:   Wed, 10 Feb 2021 14:28:11 +0530
From:   Amey Narkhede <ameynarkhede03@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] staging: gdm724x: Fix DMA from stack

On 21/02/10 09:06AM, Greg KH wrote:
> On Wed, Feb 10, 2021 at 01:31:34PM +0530, Amey Narkhede wrote:
> > Stack allocated buffers cannot be used for DMA
> > on all architectures so allocate hci_packet buffer
> > using kzalloc().
> >
> > Signed-off-by: Amey Narkhede <ameynarkhede03@...il.com>
> > ---
> > Changes in v2:
> > 	- Fixed build warning
> > 	- Fixed memory leak using kfree
> >
> >  drivers/staging/gdm724x/gdm_usb.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/staging/gdm724x/gdm_usb.c b/drivers/staging/gdm724x/gdm_usb.c
> > index dc4da66c3..c4a9b90c5 100644
> > --- a/drivers/staging/gdm724x/gdm_usb.c
> > +++ b/drivers/staging/gdm724x/gdm_usb.c
> > @@ -56,11 +56,15 @@ static int gdm_usb_recv(void *priv_dev,
> >
> >  static int request_mac_address(struct lte_udev *udev)
> >  {
> > -	u8 buf[16] = {0,};
> > -	struct hci_packet *hci = (struct hci_packet *)buf;
> > +	u8 *buf;
> > +	struct hci_packet *hci;
> >  	struct usb_device *usbdev = udev->usbdev;
> >  	int actual;
> >  	int ret = -1;
> > +	buf = kzalloc(16, GFP_KERNEL);
>
> checkpatch did not complain about this?
No. checkpatch shows no errors and warnings.
>
> And why do you need 'buf' anymore now?  Why not just allocate hci and
> pass that to the request instead?  Saves you an extra cast and an extra
> pointer.
>
> thanks,
>
> greg k-h
Thanks. I'll send v3. I assume now we don't need kzalloc anymore as we initialize
the hci_packet so kmalloc(sizeof(struct hci_packet),..) will do.

Amey

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