Re: [bug report] ALSA: usb-audio: Add quirk to enable Avid Mbox 3 support

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

On Sat, Nov 30, 2024 at 01:01:49PM +0300, Dan Carpenter wrote:
> Hello Conner Knox,
> 
> Commit b01104fc62b6 ("ALSA: usb-audio: Add quirk to enable Avid Mbox
> 3 support") from Aug 18, 2022 (linux-next), leads to the following
> Smatch static checker warning:
> 
> sound/usb/quirks.c:1275 snd_usb_mbox3_boot_quirk() error: doing dma on the stack (&new_device_descriptor)
> sound/usb/quirks.c:569 snd_usb_extigy_boot_quirk() error: doing dma on the stack (&new_device_descriptor)
> sound/usb/quirks.c:944 snd_usb_mbox2_boot_quirk() error: doing dma on the stack (&new_device_descriptor)
> 
> sound/usb/quirks.c
>     1259 static int snd_usb_mbox3_boot_quirk(struct usb_device *dev)
>     1260 {
>     1261         struct usb_host_config *config = dev->actconfig;
>     1262         struct usb_device_descriptor new_device_descriptor;
>                                               ^^^^^^^^^^^^^^^^^^^^^^
>     1263         int err;
>     1264         int descriptor_size;
>     1265 
>     1266         descriptor_size = le16_to_cpu(get_cfg_desc(config)->wTotalLength);
>     1267 
>     1268         if (descriptor_size != MBOX3_DESCRIPTOR_SIZE) {
>     1269                 dev_err(&dev->dev, "MBOX3: Invalid descriptor size=%d.\n", descriptor_size);
>     1270                 return -ENODEV;
>     1271         }
>     1272 
>     1273         dev_dbg(&dev->dev, "MBOX3: device initialised!\n");
>     1274 
> --> 1275         err = usb_get_descriptor(dev, USB_DT_DEVICE, 0,
>     1276                 &new_device_descriptor, sizeof(new_device_descriptor));
>                          ^^^^^^^^^^^^^^^^^^^^^^
> The comments in usb_fill_control_urb() say this has to be "suitable for DMA"
> but this is stack data.  It has to be allocated with kmalloc() to be suitable.
> 
> I don't know why I'm only seeing this warning now two years later...
> 

My script looks at the line number for the function and not for the buffer so it
blamed the wrong patch.

Don't stress about this, I'll send a fix in a few hours.

regards,
dan carpenter