Re: [PATCH] uio: Fix use-after-free in uio_open

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Dec 21, 2023 at 12:26:48PM +0800, Guanghui Feng wrote:
> core-1					core-2
> -------------------------------------------------------------
> uio_unregister_device			uio_open
> 					idev = idr_find()
> device_unregister(&idev->dev)
> put_device(&idev->dev)
> uio_device_release
> 					get_device(&idev->dev)
> kfree(idev)
> uio_free_minor(minor)
> 					uio_release
> 					put_device(&idev->dev)
> 					kfree(idev)
> -------------------------------------------------------------
> 
> In the core-1 uio_unregister_device(), the device_unregister will kfree idev
> when the idev->dev kobject ref is one. But after core-1 device_unregister,
> put_device and before doing kfree, the core-2 may get_device. Then:
> 1. After core-1 kfree idev, the core-2 will do use-after-free for idev.
> 2. When core-2 do uio_release and put_device, the idev will be double freed.
> 
> To address this issue, we can get idev atomic & inc idev reference with minor_lock.

Nit, can you wrap your lines at 72 columns?

Anyway, nice fix, how did you find this?

> Signed-off-by: Guanghui Feng <guanghuifeng@linux.alibaba.com>

What commit id does this fix?

thanks,

greg k-h