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

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Message-ID: <YCOit8SI7k1Gv7dl@kroah.com>
Date:   Wed, 10 Feb 2021 10:09:11 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Amey Narkhede <ameynarkhede03@...il.com>
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] staging: gdm724x: Fix DMA from stack

On Wed, Feb 10, 2021 at 02:28:11PM +0530, Amey Narkhede wrote:
> 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.

Please add a blank line after variables and before logic.

> > 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.

Why is it needed now?  And why would that change?

thanks,

greg k-h