[PATCH 3/4] HID: wacom: Fix Use-After-Free in wacom_bamboo_pad
From: Lee Jones <lee@kernel.org>
Date: 2026-07-07 12:11:10
Also in:
lkml
Subsystem:
hid core layer, hid wacom driver, the rest · Maintainers:
Jiri Kosina, Benjamin Tissoires, Ping Cheng, Jason Gerecke, Linus Torvalds
wacom_bamboo_pad_pen_event() accesses wacom->shared->pen locklessly
relative to wacom_remove_shared_data() which nullifies it. This
can lead to a Use-After-Free if the sibling device is removed while
events are being processed.
Resolve this by introducing RCU protection for pen and touch
pointers:
- Annotate 'pen' and 'touch' in wacom_shared struct with __rcu.
- Wrap lockless readers in wacom_bamboo_pad_pen_event() with
rcu_read_lock() and rcu_dereference().
- Update writers in wacom_sys.c using rcu_assign_pointer().
- Use rcu_dereference_protected for comparisons under
wacom_udev_list_lock.
- Also use rcu_access_pointer in wacom_mode_change_work() to avoid
warnings (while lockless access there remains a pre-existing issue).
Fixes: 8c97a765467c ("HID: wacom: add full support of the Wacom Bamboo PAD")
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 [guard()]
v4 -> v5: No change
drivers/hid/wacom_sys.c | 36 +++++++++++++++++++++++++-----------
drivers/hid/wacom_wac.c | 13 ++++++-------
drivers/hid/wacom_wac.h | 4 ++--
3 files changed, 33 insertions(+), 20 deletions(-)
diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c
index 86895f13dbae..3990d8d0b40c 100644
--- a/drivers/hid/wacom_sys.c
+++ b/drivers/hid/wacom_sys.c@@ -878,11 +878,18 @@ static void wacom_remove_shared_data(void *res) shared); scoped_guard(mutex, &wacom_udev_list_lock) { - if (wacom_wac->shared->touch == wacom->hdev) { - wacom_wac->shared->touch = NULL; + struct hid_device *touch = + rcu_dereference_protected(wacom_wac->shared->touch, + lockdep_is_held(&wacom_udev_list_lock)); + struct hid_device *pen = + rcu_dereference_protected(wacom_wac->shared->pen, + lockdep_is_held(&wacom_udev_list_lock)); + + if (touch == wacom->hdev) { + rcu_assign_pointer(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; + } else if (pen == wacom->hdev) { + rcu_assign_pointer(wacom_wac->shared->pen, NULL); } }
@@ -916,9 +923,9 @@ static int wacom_add_shared_data(struct hid_device *hdev) } if (wacom_wac->features.device_type & WACOM_DEVICETYPE_TOUCH) - data->shared.touch = hdev; + rcu_assign_pointer(data->shared.touch, hdev); else if (wacom_wac->features.device_type & WACOM_DEVICETYPE_PEN) - data->shared.pen = hdev; + rcu_assign_pointer(data->shared.pen, hdev); mutex_unlock(&wacom_udev_list_lock);
@@ -2356,7 +2363,11 @@ static void wacom_set_shared_values(struct wacom_wac *wacom_wac) guard(mutex)(&wacom_udev_list_lock); if (wacom_wac->features.device_type & WACOM_DEVICETYPE_TOUCH) { - if (wacom_wac->shared->touch == wacom->hdev) { + struct hid_device *touch = + rcu_dereference_protected(wacom_wac->shared->touch, + lockdep_is_held(&wacom_udev_list_lock)); + + if (touch == wacom->hdev) { wacom_wac->shared->type = wacom_wac->features.type; rcu_assign_pointer(wacom_wac->shared->touch_input, wacom_wac->touch_input); }
@@ -2795,16 +2806,19 @@ static void wacom_mode_change_work(struct work_struct *work) bool is_direct = wacom->wacom_wac.is_direct_mode; int error = 0; - if (shared->pen) { - wacom1 = hid_get_drvdata(shared->pen); + struct hid_device *pen = rcu_access_pointer(shared->pen); + struct hid_device *touch = rcu_access_pointer(shared->touch); + + if (pen) { + wacom1 = hid_get_drvdata(pen); wacom_release_resources(wacom1); hid_hw_stop(wacom1->hdev); wacom1->wacom_wac.has_mode_change = true; wacom1->wacom_wac.is_direct_mode = is_direct; } - if (shared->touch) { - wacom2 = hid_get_drvdata(shared->touch); + if (touch) { + wacom2 = hid_get_drvdata(touch); wacom_release_resources(wacom2); hid_hw_stop(wacom2->hdev); wacom2->wacom_wac.has_mode_change = true;
diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index f3429a2c8f36..8581c33fac59 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c@@ -3292,6 +3292,7 @@ static int wacom_bpt_irq(struct wacom_wac *wacom, size_t len) static void wacom_bamboo_pad_pen_event(struct wacom_wac *wacom, unsigned char *data) { + struct hid_device *pen; unsigned char prefix; /*
@@ -3304,13 +3305,11 @@ static void wacom_bamboo_pad_pen_event(struct wacom_wac *wacom, prefix = data[0]; data[0] = WACOM_REPORT_BPAD_PEN; - /* - * actually reroute the event. - * No need to check if wacom->shared->pen is valid, hid_input_report() - * will check for us. - */ - hid_input_report(wacom->shared->pen, HID_INPUT_REPORT, data, - WACOM_PKGLEN_PENABLED, 1); + guard(rcu)(); + pen = rcu_dereference(wacom->shared->pen); + if (pen) + hid_input_report(pen, HID_INPUT_REPORT, data, + WACOM_PKGLEN_PENABLED, 1); data[0] = prefix; }
diff --git a/drivers/hid/wacom_wac.h b/drivers/hid/wacom_wac.h
index a8bbba4a6f37..170d6adbe02a 100644
--- a/drivers/hid/wacom_wac.h
+++ b/drivers/hid/wacom_wac.h@@ -286,8 +286,8 @@ struct wacom_shared { unsigned touch_max; int type; struct input_dev __rcu *touch_input; - struct hid_device *pen; - struct hid_device *touch; + struct hid_device __rcu *pen; + struct hid_device __rcu *touch; bool has_mute_touch_switch; bool is_touch_on; };
--
2.55.0.rc2.803.g1fd1e6609c-goog