[PATCH 2/4] HID: wacom: Fix Use-After-Free in wacom_intuos_pad
From: Lee Jones <lee@kernel.org>
Date: 2026-07-07 12:11:07
Also in:
lkml
Subsystem:
hid core layer, hid wacom driver, the rest · Maintainers:
Jiri Kosina, Benjamin Tissoires, Ping Cheng, Jason Gerecke, Linus Torvalds
wacom_intuos_pad() accesses wacom->shared->touch_input locklessly
inside the interrupt handler context. If the Touch sibling device
is disconnected, wacom_remove_shared_data() clears 'touch_input'
outside any lock, creating a Time-of-Check to Time-of-Use (TOCTOU)
race condition where a preempted reader in interrupt context
dereferences the freed pointer, leading to a Use-After-Free.
Resolve this by introducing RCU protection for the touch_input
pointer:
- Annotate 'touch_input' in wacom_shared struct with __rcu
- Wrap all lockless readers in wacom_wac.c with guard(rcu)() and
rcu_dereference() using a unified wacom_report_touch_mute()
helper
- Update writers in wacom_sys.c using rcu_assign_pointer()
- Call synchronize_rcu() in wacom_remove_shared_data() to ensure
all active RCU readers have finished before the input device is
freed
Also wrap wacom_set_shared_values() and touch/pen assignments in
wacom_add_shared_data() inside the wacom_udev_list_lock to serialize
concurrent probe assignments, and verify that 'shared->touch == hdev'
before setting touch_input to prevent concurrent sibling probe state
desynchronization.
Fixes: 961794a00eab ("Input: wacom - add reporting of SW_MUTE_DEVICE events")
Signed-off-by: Lee Jones <lee@kernel.org>
---
v1 -> v2: Split and use RCU as per Dmitry's review
v2 -> v3: Sashiko fixes
v3 -> v4: Dmitry's review [redundant check and guard()]
v4 -> v5: Jason's review [split, remove "awkward if"]
drivers/hid/wacom_sys.c | 35 +++++++++++++++++++++++------------
drivers/hid/wacom_wac.c | 36 ++++++++++++++++++------------------
drivers/hid/wacom_wac.h | 2 +-
3 files changed, 42 insertions(+), 31 deletions(-)
diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c
index 60b380efdfb7..86895f13dbae 100644
--- a/drivers/hid/wacom_sys.c
+++ b/drivers/hid/wacom_sys.c@@ -877,10 +877,16 @@ static void wacom_remove_shared_data(void *res) data = container_of(wacom_wac->shared, struct wacom_hdev_data, shared); - if (wacom_wac->shared->touch == wacom->hdev) - wacom_wac->shared->touch = NULL; - else if (wacom_wac->shared->pen == wacom->hdev) - wacom_wac->shared->pen = NULL; + scoped_guard(mutex, &wacom_udev_list_lock) { + if (wacom_wac->shared->touch == wacom->hdev) { + wacom_wac->shared->touch = NULL; + rcu_assign_pointer(wacom_wac->shared->touch_input, NULL); + } else if (wacom_wac->shared->pen == wacom->hdev) { + wacom_wac->shared->pen = NULL; + } + } + + synchronize_rcu(); kref_put(&data->kref, wacom_release_shared_data); wacom_wac->shared = NULL;
@@ -909,6 +915,11 @@ static int wacom_add_shared_data(struct hid_device *hdev) list_add_tail(&data->list, &wacom_udev_list); } + if (wacom_wac->features.device_type & WACOM_DEVICETYPE_TOUCH) + data->shared.touch = hdev; + else if (wacom_wac->features.device_type & WACOM_DEVICETYPE_PEN) + data->shared.pen = hdev; + mutex_unlock(&wacom_udev_list_lock); wacom_wac->shared = &data->shared;
@@ -917,11 +928,6 @@ static int wacom_add_shared_data(struct hid_device *hdev) if (retval) return retval; - if (wacom_wac->features.device_type & WACOM_DEVICETYPE_TOUCH) - wacom_wac->shared->touch = hdev; - else if (wacom_wac->features.device_type & WACOM_DEVICETYPE_PEN) - wacom_wac->shared->pen = hdev; - return retval; }
@@ -2345,9 +2351,15 @@ static void wacom_release_resources(struct wacom *wacom) static void wacom_set_shared_values(struct wacom_wac *wacom_wac) { + struct wacom *wacom = container_of(wacom_wac, struct wacom, wacom_wac); + + guard(mutex)(&wacom_udev_list_lock); + if (wacom_wac->features.device_type & WACOM_DEVICETYPE_TOUCH) { - wacom_wac->shared->type = wacom_wac->features.type; - wacom_wac->shared->touch_input = wacom_wac->touch_input; + if (wacom_wac->shared->touch == wacom->hdev) { + wacom_wac->shared->type = wacom_wac->features.type; + rcu_assign_pointer(wacom_wac->shared->touch_input, wacom_wac->touch_input); + } } if (wacom_wac->has_mute_touch_switch) {
@@ -2360,7 +2372,6 @@ static void wacom_set_shared_values(struct wacom_wac *wacom_wac) if (wacom_wac->is_soft_touch_switch) wacom_wac->shared->is_touch_on = true; } - } static int wacom_parse_and_register(struct wacom *wacom, bool wireless)
diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index a31325be50f8..f3429a2c8f36 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c@@ -510,6 +510,18 @@ static void wacom_intuos_schedule_prox_event(struct wacom_wac *wacom_wac) } } +static void wacom_report_touch_mute(struct wacom_wac *wacom_wac, bool mute) +{ + struct input_dev *touch_input; + + guard(rcu)(); + touch_input = rcu_dereference(wacom_wac->shared->touch_input); + if (touch_input) { + input_report_switch(touch_input, SW_MUTE_DEVICE, mute); + input_sync(touch_input); + } +} + static int wacom_intuos_pad(struct wacom_wac *wacom) { struct wacom_features *features = &wacom->features;
@@ -650,12 +662,8 @@ static int wacom_intuos_pad(struct wacom_wac *wacom) input_report_key(input, KEY_CONTROLPANEL, menu); input_report_key(input, KEY_INFO, info); - if (wacom->shared && wacom->shared->touch_input) { - input_report_switch(wacom->shared->touch_input, - SW_MUTE_DEVICE, - !wacom->shared->is_touch_on); - input_sync(wacom->shared->touch_input); - } + if (wacom->shared) + wacom_report_touch_mute(wacom, !wacom->shared->is_touch_on); input_report_abs(input, ABS_RX, strip1); input_report_abs(input, ABS_RY, strip2);
@@ -2153,7 +2161,7 @@ static void wacom_wac_pad_event(struct hid_device *hdev, struct hid_field *field */ if ((equivalent_usage == WACOM_HID_WD_MUTE_DEVICE) || (equivalent_usage == WACOM_HID_WD_TOUCHONOFF)) { - if (wacom_wac->shared->touch_input) { + if (wacom_wac->shared) { bool *is_touch_on = &wacom_wac->shared->is_touch_on; if (equivalent_usage == WACOM_HID_WD_MUTE_DEVICE && value)
@@ -2161,9 +2169,7 @@ static void wacom_wac_pad_event(struct hid_device *hdev, struct hid_field *field else if (equivalent_usage == WACOM_HID_WD_TOUCHONOFF) *is_touch_on = value; - input_report_switch(wacom_wac->shared->touch_input, - SW_MUTE_DEVICE, !(*is_touch_on)); - input_sync(wacom_wac->shared->touch_input); + wacom_report_touch_mute(wacom_wac, !(*is_touch_on)); } return; }
@@ -3381,11 +3387,8 @@ static int wacom_wireless_irq(struct wacom_wac *wacom, size_t len) if ((wacom->shared->type == INTUOSHT || wacom->shared->type == INTUOSHT2) && - wacom->shared->touch_input && wacom->shared->touch_max) { - input_report_switch(wacom->shared->touch_input, - SW_MUTE_DEVICE, data[5] & 0x40); - input_sync(wacom->shared->touch_input); + wacom_report_touch_mute(wacom, data[5] & 0x40); } pid = get_unaligned_be16(&data[6]);
@@ -3420,11 +3423,8 @@ static int wacom_status_irq(struct wacom_wac *wacom_wac, size_t len) if ((features->type == INTUOSHT || features->type == INTUOSHT2) && - wacom_wac->shared->touch_input && features->touch_max) { - input_report_switch(wacom_wac->shared->touch_input, - SW_MUTE_DEVICE, data[8] & 0x40); - input_sync(wacom_wac->shared->touch_input); + wacom_report_touch_mute(wacom_wac, data[8] & 0x40); } if (data[9] & 0x02) { /* wireless module is attached */
diff --git a/drivers/hid/wacom_wac.h b/drivers/hid/wacom_wac.h
index 126bec6e5c0c..a8bbba4a6f37 100644
--- a/drivers/hid/wacom_wac.h
+++ b/drivers/hid/wacom_wac.h@@ -285,7 +285,7 @@ struct wacom_shared { /* for wireless device to access USB interfaces */ unsigned touch_max; int type; - struct input_dev *touch_input; + struct input_dev __rcu *touch_input; struct hid_device *pen; struct hid_device *touch; bool has_mute_touch_switch;
--
2.55.0.rc2.803.g1fd1e6609c-goog