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

Joe Perches
2019-08-02T10:04:37Z

On Fri, 2019-08-02 at 11:40 +0200, Greg Kroah-Hartman wrote:
> From: Luke Nowakowski-Krijger <lnowakow@eng.ucsd.edu>
>
> 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@syzkaller.appspotmail.com
>
> Signed-off-by: Luke Nowakowski-Krijger <lnowakow@eng.ucsd.edu>
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> [hverkuil-cisco@xs4all.nl: cleaned up two small checkpatch.pl warnings]
> [hverkuil-cisco@xs4all.nl: prefix subject with driver name]
> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> ---
> 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;
> }
>
>
>