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

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[ Upstream commit 8813b06122 ]

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.

Fixes: 46f781e0d1 ("HID: multitouch: fix sticky fingers")
Cc: stable@vger.kernel.org
Signed-off-by: Trung Nguyen <trungnh@cystack.net>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Trung Nguyen
2026-07-24 16:03:50 +02:00
committed by Greg Kroah-Hartman
parent 7c29bc073a
commit a6d5ce2e1a
1 changed files with 20 additions and 12 deletions
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drivers/hid/hid-multitouch.c
+20 -12
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@@ -31,6 +31,7 @@
* [1] https://gitlab.freedesktop.org/libevdev/hid-tools
*/
#include <linux/bitmap.h>
#include <linux/device.h>
#include <linux/hid.h>
#include <linux/module.h>
@@ -83,8 +84,7 @@ enum latency_mode {
HID_LATENCY_HIGH = 1,
};
#define MT_IO_SLOTS_MASK GENMASK(7, 0) /* reserve first 8 bits for slot tracking */
#define MT_IO_FLAGS_RUNNING 32
#define MT_IO_FLAGS_RUNNING 0
static const bool mtrue = true; /* default for true */
static const bool mfalse; /* default for false */
@@ -160,10 +160,9 @@ struct mt_device {
struct mt_class mtclass; /* our mt device class */
struct timer_list release_timer; /* to release sticky fingers */
struct hid_device *hdev; /* hid_device we're attached to */
unsigned long mt_io_flags; /* mt flags (MT_IO_FLAGS_RUNNING)
* first 8 bits are reserved for keeping the slot
* states, this is fine because we only support up
* to 250 slots (MT_MAX_MAXCONTACT)
unsigned long mt_io_flags; /* mt flags (MT_IO_FLAGS_RUNNING) */
unsigned long *active_slots; /* bitmap of slots with an active
* contact, sized for maxcontacts
*/
__u8 inputmode_value; /* InputMode HID feature value */
__u8 maxcontacts;
@@ -947,7 +946,7 @@ static void mt_release_pending_palms(struct mt_device *td,
for_each_set_bit(slotnum, app->pending_palm_slots, td->maxcontacts) {
clear_bit(slotnum, app->pending_palm_slots);
clear_bit(slotnum, &td->mt_io_flags);
clear_bit(slotnum, td->active_slots);
input_mt_slot(input, slotnum);
input_mt_report_slot_inactive(input);
@@ -1153,9 +1152,9 @@ static int mt_process_slot(struct mt_device *td, struct input_dev *input,
input_event(input, EV_ABS, ABS_MT_TOUCH_MAJOR, major);
input_event(input, EV_ABS, ABS_MT_TOUCH_MINOR, minor);
set_bit(slotnum, &td->mt_io_flags);
set_bit(slotnum, td->active_slots);
} else {
clear_bit(slotnum, &td->mt_io_flags);
clear_bit(slotnum, td->active_slots);
}
return 0;
@@ -1290,7 +1289,7 @@ static void mt_touch_report(struct hid_device *hid,
* defect.
*/
if (app->quirks & MT_QUIRK_STICKY_FINGERS) {
if (td->mt_io_flags & MT_IO_SLOTS_MASK)
if (!bitmap_empty(td->active_slots, td->maxcontacts))
mod_timer(&td->release_timer,
jiffies + msecs_to_jiffies(100));
else
@@ -1330,6 +1329,15 @@ static int mt_touch_input_configured(struct hid_device *hdev,
if (td->is_buttonpad)
__set_bit(INPUT_PROP_BUTTONPAD, input->propbit);
if (!td->active_slots) {
td->active_slots = devm_kcalloc(&td->hdev->dev,
BITS_TO_LONGS(td->maxcontacts),
sizeof(long),
GFP_KERNEL);
if (!td->active_slots)
return -ENOMEM;
}
app->pending_palm_slots = devm_kcalloc(&hi->input->dev,
BITS_TO_LONGS(td->maxcontacts),
sizeof(long),
@@ -1738,7 +1746,7 @@ static void mt_release_contacts(struct hid_device *hid)
for (i = 0; i < mt->num_slots; i++) {
input_mt_slot(input_dev, i);
input_mt_report_slot_inactive(input_dev);
clear_bit(i, &td->mt_io_flags);
clear_bit(i, td->active_slots);
}
input_mt_sync_frame(input_dev);
input_sync(input_dev);
@@ -1761,7 +1769,7 @@ static void mt_expired_timeout(struct timer_list *t)
*/
if (test_and_set_bit_lock(MT_IO_FLAGS_RUNNING, &td->mt_io_flags))
return;
if (td->mt_io_flags & MT_IO_SLOTS_MASK)
if (!bitmap_empty(td->active_slots, td->maxcontacts))
mt_release_contacts(hdev);
clear_bit_unlock(MT_IO_FLAGS_RUNNING, &td->mt_io_flags);
}