Re: [PATCH] HID: usbhid: sanitize hid->uniq against non-printable bytes

[Greg KH]

On Thu, Apr 23, 2026 at 05:55:00AM +0000, Eric Naim wrote:
> On 4/18/26 3:14 PM, Greg KH wrote:
> > On Sat, Apr 18, 2026 at 02:58:23PM +1200, Taylor Hewetson wrote:
> >> Some USB HID devices (observed on ASUS ROG Azoth via its 2.4GHz
> >> dongle, USB ID 0b05:1a85) report an iSerialNumber string whose
> >> USB string descriptor declares a longer length than the actual
> >> serial, leaving uninitialized firmware memory - including control
> >> characters such as 0x18 - appended to the returned string.
> >>
> >> These non-printable bytes propagate into hid->uniq, which in turn
> >> populates /sys/class/input/inputN/uniq. Downstream userspace
> >> components (systemd sd-device property_is_valid(), and by extension
> >> mutter input enumeration on GNOME Wayland sessions) reject devices
> >> with control characters in their uniq, rendering otherwise-
> >> functional input devices unusable in graphical sessions despite
> >> the kernel input layer correctly translating keypresses.
> >>
> >> Truncate hid->uniq at the first byte outside the printable ASCII
> >> range (0x20..0x7e) after the serial is read.
> > 
> > Why aren't we doing this in the USB core instead of forcing all users of
> > this to do it instead?
> 
> Should it be up to the kernel to do this as well? Currently this is only a
> problem with systemd because they added this check, and it looks like they
> have something in mind to fix it as well [1].
> 
> [1] https://github.com/systemd/systemd/issues/41339#issuecomment-4266429563

It's either up to the kernel, or every single userspace program that
reads the strings from a device.  Might as well do it in one place,
right?

thanks,

greg k-h