Am 23.09.26 um 11:27 schrieb Greg Kroah-Hartman:
On Tue, Sep 22, 2026 at 11:04:46PM +0200, Armin Wolf wrote:
Am 22.09.26 um 15:40 schrieb David Lechner:
On 9/22/26 2:39 AM, Uwe Kleine-König wrote:
On Fri, Sep 18, 2026 at 06:39:02PM +0200, Danilo Krummrich wrote:
On Mon Sep 14, 2026 at 4:30 PM CEST, 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
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.
The flag is 'Y' which was unused, and can remembered as the user is
"yeeting" the device being operated on here (thrown with force without
regard for the thing being thrown).
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.
Fuzzing tools like syzbot, that doesn't have hand-crafted rules to keep
the tool from hitting bind/unbind, should be run with panic_on_taint
enabled so that they fall over and don't continue on, thinking that they
actually found a real issue.
Userspace operations that rely on the bind/unbind files
I agree that this should be avoided.
But I also think the biggest offender really is driver_override. Specifically,
on a hot-pluggable bus a driver must be complient with the device driver
lifecycle rules and hence shouldn't break on bind/unbind. I think it would be
nice to not taint the kernel for such busses, and only taint on driver_override,
as I think we'd still want the bug reports for such cases.
But I think this is fine to leave for a follow-up.
I fully agree. I'm fine and support tainting on driver_override, but
bind/unbind are used occasionally in my bubble and I consider drivers
not handling that properly buggy.
I fully agree with this, drivers should correctly implement the lifecycle model
and not just break when being unbound at a improper time. Drivers suffering from
this can easily break this way when unloading the associated kernel module, so
this
taint is no solution.
It's a "solution" in that it tells the developer "hey, the user did
something odd and unsupported". rmmod is also not a normal operation,
there's no requirement that it actually work as it's usually a "best
effort" type of thing.
From my perspective rmmod and friends are at least expected to not crash the
kernel.
In the IIO subsystem, unbind/rebind is the de-facto way to reset a wedged
chip.
A few examples where other reset methods were reject in favor of unbind/bind:
https://lore.kernel.org/linux-iio/20240727160216.2488ed29@jic23-huawei/
This needs documenting as it's custom ABI. Note that we don't often
accept custom ABI. Particularly not a hook that seems to reset the
device. If you want to do that, unbind and rebind the whole drive[r]
so we are in a known state etc.
https://lore.kernel.org/linux-iio/20240720163440.03c713dc@jic23-huawei/
Firstly as stated below, we don't provide interfaces for this
because it's a heavy weight process that is most of the effort of
unbinding and rebinding the driver. So if you need to reset, do that.
https://lore.kernel.org/linux-iio/20250505200609.54756520@jic23-huawei/
The solution is to run it once at driver bind. Similar to reset
below, if the usecase needs to re do it then unbinding and rebinding
the driver reflects the fact we are taking it effectively offline
for a while.
I also consider bind/unbind to be an official API to interact with devices,
so i want to use them in the future with the WMI subsystem.
Why?
Netlink UAPI <-> generic driver <-> WMI device
User will need to manually bind the generic driver (it really supports all WMI
devices!) to
a given WMI device, something that is only possible with bind/unbind.
AFAIK the underlying reason for this series is that some drivers break when
being bound to unsupported devices. However IMHO drivers should verify that
they support a given device inside their .probe callback, and the associated
bus should only match devices with drivers that explicitly claim support for
those devices (ignoring driver_override).
No, drivers should NOT have to do that in their .probe() function,
that's what we moved away from decades ago! The match function should
handle all of that for you, otherwise it's contant duplication
everywhere that is unneeded.
Please, learn from our history, don't make the same mistakes.
I meant with that, that drivers should be prepared that for example
of_device_get_match_data()
returns a NULL pointer. In Rust drivers would have to check for this anyway, so
i see little
reason why drivers written in C should skip this check and as a result break as
soon as someone
uses driver_override (or they are matched against a non-OF device).
Now I might be convinced that driver_override is the way to go here, but
it still feels really odd as again, bind/unbind was created as a driver
debugging option only, it should NOT be a normal operation that any user
should rely on. The driver should "just work" properly instead, without
requiring manual bind work, as that's not a good model at all.
thanks,
greg k-h
I understand your concerns, but IMHO it turned out that bind/unbind are useful
outside of debugging. I agree that userspace using bind/unbind should not be
considered
normal, but in my opinion its far from being suspicious. Manually unbinding a
specific drivers
in order to bind a generic driver is unusual, but understandable.
I agree with you that driver_override should be the correct place for such a
taint, because
using driver_override indeed overrides the bus-specific matching logic and can
therefore
be dangerous.
Thanks,
Armin Wolf
