CVE-2026-64364HID: multitouch: fix out-of-bounds bit access on mt_io_flags

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/12e90656e330ff8bbaf2f29c535fdb8a11cc6f55
• https://git.kernel.org/stable/c/152983d87387f6a8ae72b73474cfa55fbcf1ec75
• https://git.kernel.org/stable/c/b5c037d6b807017e74a115288f81bc9cd5a5aab8
• https://git.kernel.org/stable/c/a6d5ce2e1a2d7bf189bde8a659d04b65f0b0725d
• https://git.kernel.org/stable/c/e24918ee67c4dc3d20d4670750e46e9b160365f4
• https://git.kernel.org/stable/c/37daa8c96bd563d03150e23f094cb60703594a6d
• https://git.kernel.org/stable/c/6493ebf9489efef0105078377b973ab33d51af22
• https://git.kernel.org/stable/c/8813b0612275cc61fe9e6603d0ee019247ade6be