Re: [PATCH] usb: misc: yurex: fix ordering of usb_deregister_dev() and usb_set_intfdata()

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Apr 28, 2026 at 12:54:22PM +0800, Ginger wrote:
> In yurex_disconnect(), usb_set_intfdata(interface, NULL) was called
> before usb_deregister_dev(interface, &yurex_class).  This opens a race
> window with usb_open() in the USB core:
> 
>   T0 (yurex_disconnect)               T1 (usb_open)
>   --------------------------           -------------------------
>   usb_set_intfdata(iface, NULL) [t0]
>                                        fops = usb_minors[minor]  [t1]
>                                        /* fops still valid here */
>   usb_deregister_dev()
>     usb_minors[minor] = NULL   [t2]
>                                        file->f_op->open(inode, file)
>                                          yurex_open()
>                                            dev = usb_get_intfdata() [t3]
>                                            /* dev is NULL */
> 
> Because t0 precedes t1 precedes t2 precedes t3, T1 can obtain the
> file_operations pointer for the device (t1, while the minor is still
> registered), then continue into yurex_open() where it calls
> usb_get_intfdata() and gets NULL back, leading to a NULL dereference.
> 
> Fix the race by calling usb_deregister_dev() first, which removes the
> device from usb_minors[] before the interface data pointer is cleared.
> Concurrent usb_open() that arrives after usb_deregister_dev() returns
> will fail to look up the fops and will never reach yurex_open().
> 
> Reported-by: Ginger <ginger.jzllee@gmail.com>
> Closes: https://lore.kernel.org/linux-usb/2026042718-unwieldy-dicing-626f@gregkh
> Signed-off-by: Ginger <ginger.jzllee@gmail.com>
> ---
>  drivers/usb/misc/yurex.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/misc/yurex.c b/drivers/usb/misc/yurex.c
> index 6d03e689850a..b5484ab77e91 100644
> --- a/drivers/usb/misc/yurex.c
> +++ b/drivers/usb/misc/yurex.c
> @@ -310,11 +310,12 @@ static void yurex_disconnect(struct
> usb_interface *interface)
>     int minor = interface->minor;
> 
>     dev = usb_get_intfdata(interface);
> -   usb_set_intfdata(interface, NULL);
> 
>     /* give back our minor */
>     usb_deregister_dev(interface, &yurex_class);
> 
> +   usb_set_intfdata(interface, NULL);
> +
>     /* prevent more I/O from starting */
>     usb_poison_urb(dev->urb);
>     usb_poison_urb(dev->cntl_urb);
> --
> 2.39.5
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
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created.  Hopefully you will not take offence and will fix the problem
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