Re: [PATCH v2] usb: usbtest: disable dynamic ID support

On Thu, Aug 6, 2026 at 4:43 PM Greg Kroah-Hartman
<[email protected]> wrote:
>
> On Thu, Aug 06, 2026 at 04:35:12PM +0200, Aleksandr Nogikh wrote:
> > On Thu, Aug 6, 2026 at 4:32 PM Greg Kroah-Hartman
> > <[email protected]> wrote:
> > >
> > > On Thu, Aug 06, 2026 at 02:25:11PM +0000, Aleksandr Nogikh wrote:
> > > > The usbtest driver relies on the driver_info field of struct usb_device_id
> > > > to point to a valid struct usbtest_info descriptor. This structure contains
> > > > essential test configurations, such as endpoint addresses and test modes,
> > > > which are required during probe.
> > > >
> > > > When a user dynamically adds a new device ID via the sysfs new_id
> > > > interface without specifying a reference device, the USB core initializes
> > > > driver_info to 0 (NULL). When a matching device is subsequently probed,
> > > > usbtest_probe() unconditionally casts driver_info to a struct usbtest_info
> > > > pointer and dereferences it, leading to a NULL pointer dereference crash:
> > > >
> > > >   Oops: general protection fault, probably for non-canonical address
> > > >   0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI
> > > >   KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
> > > >   RIP: 0010:usbtest_probe+0x3b9/0x1280 drivers/usb/misc/usbtest.c:2822
> > > >
> > > > Because usbtest strictly requires pre-defined usbtest_info descriptors
> > > > to function, dynamic ID binding via sysfs is fundamentally unsupported
> > > > for this driver.
> > > >
> > > > Fix this by setting .no_dynamic_id = 1 on usbtest_driver. This instructs
> > > > the USB core to skip creating the new_id and remove_id sysfs interfaces
> > > > for usbtest, preventing invalid dynamic ID entries from being created.
> > > >
> > > > Reported-by: [email protected]
> > > > Closes: https://syzkaller.appspot.com/bug?extid=7e1e5911f9eac50bedc7
> > > > Signed-off-by: Aleksandr Nogikh <[email protected]>
> > >
> > > Shouldn't this also get a cc: stable?
> >
> > Is there (in general) value in cc: stable without a Fixes: tag?
>
> Very much so.  Don't you want this in stable trees so that your syzbot
> runs on the older kernels don't fail horribly?  If not, then hey,
> waiting for newer releases is fine with me, but I got the impression
> this was a good thing to fix :)

I see, thanks for the clarification!
I've sent a v3 that Cc's stable.

>
> thanks,
>
> greg k-h