Re: [PATCH 2/2] driver core: add TAINT_FORCED_BIND for when userspace manually messes with devices and drivers

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Thu, Aug 27, 2026 at 03:33:19PM +0200, Johan Hovold wrote:
> On Wed, Aug 26, 2026 at 11:19:33AM +0200, Greg Kroah-Hartman wrote:
> > The ability to add and remove devices from a driver through the sysfs
> > "bind" and "unbind" files was created all those decades ago as a way
> > that kernel developers can iterate faster, and provide a debugging way
> > for users to attempt to add a new device to a driver without having to
> > rebuild their kernel.
> > 
> > This api over the years has been abused and recently come under a major
> > fuzzing "attack" through tools like syzbot which decided that it would
> > attempt to just randomly bind any driver to any type of device, causing
> > loads of unneeded errors and pointless kernel patches to be generated by
> > unsuspecting new developers.
> > 
> > Handle all of this by adding a new taint flag, TAINT_FORCED_BIND, which
> > will be set on the driver if the bind/unbind sysfs files are ever
> > successfully written to.  This lets kernel developers "know" that a user
> > is attempting to do something that is not normal, and as such, if the
> > kernel breaks they get to keep the shiny pieces laying around on the
> > floor.
> > 
> > Note, the taint flag gets set _BEFORE_ the bind/unbind callback happens,
> > as many times crashes/oops/warnings/failures happen within the callback,
> > and the taint flag needs to be there to show what was being attempted.
> > If it were to be set after the callback happens, the oops report would
> > not properly reflect what foolishness was being attempted.
> > 
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> This makes it clear that this is a development tool, and it is a good
> compromise preferable to adding unnecessary complexity or suppressing
> the attributes completely just to prevent root from shooting themselves
> in the foot:
> 
> Reviewed-by: Johan Hovold <johan@kernel.org>
> Tested-by: Johan Hovold <johan@kernel.org>

bind/unbind without overrides should not necessarily be treated as a
development tool. For example with I2C devices you may want to unbind
the functional driver, perform firmware update from userspace, and bind
the device again. This will ensure that driver is not confused and at
the same time you do not need to put into the kernel code that is
dormant 99.9999 percent of the time.

Thanks.

-- 
Dmitry