Re: [PATCH 5.2 10/20] media: radio-raremono: change devm_k*alloc to k*alloc

[Joe Perches]

On Fri, 2019-08-02 at 11:40 +0200, Greg Kroah-Hartman wrote:
> From: Luke Nowakowski-Krijger <lnowakow@xxxxxxxxxxxx>
> 
> commit c666355e60ddb4748ead3bdd983e3f7f2224aaf0 upstream.
> 
> Change devm_k*alloc to k*alloc to manually allocate memory
> 
> The manual allocation and freeing of memory is necessary because when
> the USB radio is disconnected, the memory associated with devm_k*alloc
> is freed. Meaning if we still have unresolved references to the radio
> device, then we get use-after-free errors.
> 
> This patch fixes this by manually allocating memory, and freeing it in
> the v4l2.release callback that gets called when the last radio device
> exits.

This really should be commented in the code
and not just in the commit changelog as some
unsuspecting person will likely undo this in
the future without one.

> Reported-and-tested-by: syzbot+a4387f5b6b799f6becbf@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> Signed-off-by: Luke Nowakowski-Krijger <lnowakow@xxxxxxxxxxxx>
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
> [hverkuil-cisco@xxxxxxxxx: cleaned up two small checkpatch.pl warnings]
> [hverkuil-cisco@xxxxxxxxx: prefix subject with driver name]
> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@xxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> 
> ---
>  drivers/media/radio/radio-raremono.c |   30 +++++++++++++++++++++++-------
>  1 file changed, 23 insertions(+), 7 deletions(-)
> 
> --- a/drivers/media/radio/radio-raremono.c
> +++ b/drivers/media/radio/radio-raremono.c
> @@ -271,6 +271,14 @@ static int vidioc_g_frequency(struct fil
>  	return 0;
>  }
>  
> +static void raremono_device_release(struct v4l2_device *v4l2_dev)
> +{
> +	struct raremono_device *radio = to_raremono_dev(v4l2_dev);
> +
> +	kfree(radio->buffer);
> +	kfree(radio);
> +}
> +
>  /* File system interface */
>  static const struct v4l2_file_operations usb_raremono_fops = {
>  	.owner		= THIS_MODULE,
> @@ -295,12 +303,14 @@ static int usb_raremono_probe(struct usb
>  	struct raremono_device *radio;
>  	int retval = 0;
>  
> -	radio = devm_kzalloc(&intf->dev, sizeof(struct raremono_device), GFP_KERNEL);
> -	if (radio)
> -		radio->buffer = devm_kmalloc(&intf->dev, BUFFER_LENGTH, GFP_KERNEL);
> -
> -	if (!radio || !radio->buffer)
> +	radio = kzalloc(sizeof(*radio), GFP_KERNEL);
> +	if (!radio)
> +		return -ENOMEM;
> +	radio->buffer = kmalloc(BUFFER_LENGTH, GFP_KERNEL);
> +	if (!radio->buffer) {
> +		kfree(radio);
>  		return -ENOMEM;
> +	}
>  
>  	radio->usbdev = interface_to_usbdev(intf);
>  	radio->intf = intf;
> @@ -324,7 +334,8 @@ static int usb_raremono_probe(struct usb
>  	if (retval != 3 ||
>  	    (get_unaligned_be16(&radio->buffer[1]) & 0xfff) == 0x0242) {
>  		dev_info(&intf->dev, "this is not Thanko's Raremono.\n");
> -		return -ENODEV;
> +		retval = -ENODEV;
> +		goto free_mem;
>  	}
>  
>  	dev_info(&intf->dev, "Thanko's Raremono connected: (%04X:%04X)\n",
> @@ -333,7 +344,7 @@ static int usb_raremono_probe(struct usb
>  	retval = v4l2_device_register(&intf->dev, &radio->v4l2_dev);
>  	if (retval < 0) {
>  		dev_err(&intf->dev, "couldn't register v4l2_device\n");
> -		return retval;
> +		goto free_mem;
>  	}
>  
>  	mutex_init(&radio->lock);
> @@ -345,6 +356,7 @@ static int usb_raremono_probe(struct usb
>  	radio->vdev.ioctl_ops = &usb_raremono_ioctl_ops;
>  	radio->vdev.lock = &radio->lock;
>  	radio->vdev.release = video_device_release_empty;
> +	radio->v4l2_dev.release = raremono_device_release;
>  
>  	usb_set_intfdata(intf, &radio->v4l2_dev);
>  
> @@ -360,6 +372,10 @@ static int usb_raremono_probe(struct usb
>  	}
>  	dev_err(&intf->dev, "could not register video device\n");
>  	v4l2_device_unregister(&radio->v4l2_dev);
> +
> +free_mem:
> +	kfree(radio->buffer);
> +	kfree(radio);
>  	return retval;
>  }
>  
> 
>