Re: [PATCH] video: fbdev: smscufx: Fix use-after-free in ufx_ops_open()

[Helge Deller <deller@gmx.de>]

On 9/25/22 13:03, Hyunwoo Kim wrote:
> A race condition may occur if the user physically removes the
> USB device while calling open() for this device node.
>
> This is a race condition between the ufx_ops_open() function and
> the ufx_usb_disconnect() function, which may eventually result in UAF.
>
> So, add a mutex to the ufx_ops_open() and ufx_usb_disconnect() functions
> to avoid race contidion of krefs.
>
> Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
> ---
>   drivers/video/fbdev/smscufx.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> diff --git a/drivers/video/fbdev/smscufx.c b/drivers/video/fbdev/smscufx.c
> index d7aa5511c361..a4378a7241f7 100644
> --- a/drivers/video/fbdev/smscufx.c
> +++ b/drivers/video/fbdev/smscufx.c
> @@ -1065,6 +1067,8 @@ static int ufx_ops_open(struct fb_info *info, int user)
>   {
>   	struct ufx_data *dev = info->par;
>
> +	mutex_lock(&disconnect_mutex);
> +

The next few lines show:
         if (user == 0 && !console)
                 return -EBUSY;

in this case this function exits with the mutex held.

Please check all possible exit paths and unlock the mutex
where necessary.

Helge