CVE-2026-64364

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

HID: multitouch: fix out-of-bounds bit access on mt_io_flags

mt_io_flags is a single unsigned long, but mt_process_slot(),

mt_release_pending_palms() and mt_release_contacts() use it as a

per-slot bitmap indexed by the slot number. That slot number is only

bounded by td->maxcontacts, which is taken from the device's

ContactCountMaximum feature report and can be up to 255, not by

BITS_PER_LONG.

As a result, a multitouch device that advertises a large contact count

makes set_bit()/clear_bit() operate past the mt_io_flags word and

corrupt the adjacent members of struct mt_device. The sticky-fingers

release timer is the easiest way to reach this. mt_release_contacts()

runs

for (i = 0; i < mt->num_slots; i++)

clear_bit(i, &td->mt_io_flags);

with num_slots == maxcontacts. For maxcontacts around 250 the loop

clears the bits that overlap td->applications.next, zeroing that list

head, and the list_for_each_entry() that immediately follows then

dereferences NULL. The kernel panics from timer (softirq) context. On a

KASAN build this shows up as a general protection fault in

mt_release_contacts() with a null-ptr-deref at offset 0x58, which is

offsetof(struct mt_application, num_received).

The state is reachable from an untrusted USB or Bluetooth HID

multitouch device; no local privileges are required.

Store the per-slot active state in a separately allocated bitmap sized

for maxcontacts, the same pattern already used for pending_palm_slots,

and keep only MT_IO_FLAGS_RUNNING in mt_io_flags. The two

"mt_io_flags & MT_IO_SLOTS_MASK" arming checks become

bitmap_empty(td->active_slots, td->maxcontacts).

Move MT_IO_FLAGS_RUNNING back to bit 0. It was bumped to bit 32 by the

same commit to leave the low byte for the slot bits; with the slot bits

gone it fits in bit 0 again, which also keeps it within the unsigned

long on 32-bit.