CVE-2026-98859: HID: multitouch: stop the release timer from being rearmed on remove

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

HID: multitouch: stop the release timer from being rearmed on remove

mt_remove() quiesces the sticky-finger timer before stopping the
hardware:

    timer_delete_sync(&td->release_timer);

    sysfs_remove_group(&hdev->dev.kobj, &mt_attribute_group);
    hid_hw_stop(hdev);

timer_delete_sync() waits for a running callback and dequeues the timer,
but it does not stop the timer from being armed again. The transport is
still delivering reports at that point, and the report path rearms it:

    if (app->quirks & MT_QUIRK_STICKY_FINGERS) {
        if (td->mt_io_flags & MT_IO_SLOTS_MASK)
            mod_timer(&td->release_timer,
                      jiffies + msecs_to_jiffies(100));

A report that arrives after timer_delete_sync() has returned therefore
leaves the timer queued. td is allocated with devm_kzalloc() against
hdev->dev, so it is freed when the driver is unbound, after mt_remove()
returns. When the timer fires afterwards, mt_expired_timeout()
dereferences the freed td:

    struct mt_device *td = timer_container_of(td, t, release_timer);
    struct hid_device *hdev = td->hdev;

    if (test_and_set_bit_lock(MT_IO_FLAGS_RUNNING, &td->mt_io_flags))

Simply moving the teardown after hid_hw_stop() does not fix this on its
own, because mt_expired_timeout() calls mt_release_contacts(), which
walks hdev->inputs; the timer still has to be quiesced before
hid_hw_stop() tears the input devices down.

Use timer_shutdown_sync() instead, which additionally makes any later
mod_timer() a no-op, so neither ordering constraint has to be traded off
against the other. This is the final-teardown pattern the function was
introduced for, and hid-wiimote already uses it for the same reason.

The Linux kernel CVE team has assigned CVE-2026-98859 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.13 with commit 4f4001bc76fd1a138a501fbd3d68cce72cbf96ce and fixed in 6.12.113 with commit 1f1bd9a3117f082eb891c0986c4f0e04cd974c9a
	Issue introduced in 4.13 with commit 4f4001bc76fd1a138a501fbd3d68cce72cbf96ce and fixed in 6.18.56 with commit 0c19a6c1d25fd5ed66d1f80dc6f6e56cc1f0a787
	Issue introduced in 4.13 with commit 4f4001bc76fd1a138a501fbd3d68cce72cbf96ce and fixed in 7.2.10 with commit a0125ca86e405b8a704e96157a6c10ca51087652
	Issue introduced in 4.13 with commit 4f4001bc76fd1a138a501fbd3d68cce72cbf96ce and fixed in 7.3-rc6 with commit 5acb2dace582f061aab5e14c399ac9480315f44b

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-98859
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/hid/hid-multitouch.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/1f1bd9a3117f082eb891c0986c4f0e04cd974c9a
	https://git.kernel.org/stable/c/0c19a6c1d25fd5ed66d1f80dc6f6e56cc1f0a787
	https://git.kernel.org/stable/c/a0125ca86e405b8a704e96157a6c10ca51087652
	https://git.kernel.org/stable/c/5acb2dace582f061aab5e14c399ac9480315f44b