* [PATCH 2/5] HID: wacom: Advertise SW_MUTE_DEVICE capability prior to registration
2026-08-25 15:12 [PATCH 1/5] HID: wacom: Use hdev->product in wacom_setup_touch_input_capabilities Lee Jones
@ 2026-08-25 15:12 ` Lee Jones
2026-08-25 15:12 ` [PATCH 3/5] HID: wacom: Fix Use-After-Free in wacom_intuos_pad Lee Jones
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Lee Jones @ 2026-08-25 15:12 UTC (permalink / raw)
To: lee, Ping Cheng, Jason Gerecke, Jiri Kosina, Benjamin Tissoires,
Aaron Skomra, Dmitry Torokhov, Peter Hutterer, linux-input,
linux-kernel
Input subsystem guidelines require that device capabilities are advertised
before the input device is registered. The Wacom driver was violating
this by advertising the SW_MUTE_DEVICE capability post-registration in
wacom_set_shared_values() (and duplicating it in device-specific setup
cases).
Resolve this by moving the SW_MUTE_DEVICE capability setup to
wacom_setup_touch_input_capabilities() for all touch devices that support
it.
For generic touch devices whose capabilities depend on mute switch
usages parsed from a sibling Pen/Pad interface, defer registration
with -EPROBE_DEFER until the sibling has parsed its descriptors and
initialized shared capabilities.
Fixes: d2ec58aee8b1 ("HID: wacom: generic: support generic touch switch")
Signed-off-by: Lee Jones <lee@kernel.org>
---
v4 -> v5: New patch used to split out SW_MUTE_DEVICE as per Jason's request
v5 -> v6: Unconditionally advertise SW_MUTE_DEVICE on generic touch devices
v6 -> v7: Only advertise SW_MUTE_DEVICE on composite USB generic touch devices
v7 -> v8: Replace heuristic with probe deferral until sibling Pen/Pad is parsed
Split out 'hdev->product' cleanups into a separate standalone patch
drivers/hid/wacom_sys.c | 46 ++++++++++++++++++++++++++++++++++++-----
drivers/hid/wacom_wac.c | 4 ++++
2 files changed, 45 insertions(+), 5 deletions(-)
diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c
index 0eafa483b7f7..2738d4f515e6 100644
--- a/drivers/hid/wacom_sys.c
+++ b/drivers/hid/wacom_sys.c
@@ -2358,13 +2358,44 @@ 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;
}
+}
- if (wacom_wac->shared->has_mute_touch_switch &&
- wacom_wac->shared->touch_input) {
- set_bit(EV_SW, wacom_wac->shared->touch_input->evbit);
- input_set_capability(wacom_wac->shared->touch_input, EV_SW,
- SW_MUTE_DEVICE);
+static bool wacom_sibling_pending(struct wacom *wacom)
+{
+ struct hid_device *hdev = wacom->hdev;
+ const struct wacom_features *features = &wacom->wacom_wac.features;
+ struct usb_host_config *actconfig;
+ int i;
+
+ if (features->type != HID_GENERIC ||
+ !(features->device_type & WACOM_DEVICETYPE_TOUCH))
+ return false;
+
+ if (wacom->wacom_wac.shared &&
+ rcu_access_pointer(wacom->wacom_wac.shared->pen))
+ return false;
+
+ if (!hid_is_usb(hdev) || !wacom->usbdev)
+ return false;
+
+ if (features->oPid != HID_ANY_ID && features->oPid != 0)
+ return true;
+
+ actconfig = wacom->usbdev->actconfig;
+ if (actconfig && actconfig->desc.bNumInterfaces > 1) {
+ for (i = 0; i < actconfig->desc.bNumInterfaces; i++) {
+ struct usb_interface *sibling_intf = actconfig->interface[i];
+
+ if (!sibling_intf || sibling_intf == wacom->intf)
+ continue;
+
+ if (sibling_intf->cur_altsetting->desc.bInterfaceClass ==
+ USB_INTERFACE_CLASS_HID)
+ return true;
+ }
}
+
+ return false;
}
static int wacom_parse_and_register(struct wacom *wacom, bool wireless)
@@ -2444,6 +2475,11 @@ static int wacom_parse_and_register(struct wacom *wacom, bool wireless)
if (error)
goto fail;
+ if (wacom_sibling_pending(wacom)) {
+ error = -EPROBE_DEFER;
+ goto fail;
+ }
+
error = wacom_setup_inputs(wacom);
if (error)
goto fail;
diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index 4436faf2d2bb..a7e3817aa2c4 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -3965,6 +3965,10 @@ int wacom_setup_touch_input_capabilities(struct input_dev *input_dev,
if (features->type == HID_GENERIC) {
hid_dbg(hdev, "generic touch setup\n");
+ if (wacom_wac->shared && wacom_wac->shared->has_mute_touch_switch) {
+ input_set_capability(input_dev, EV_SW, SW_MUTE_DEVICE);
+ wacom_wac->has_mute_touch_switch = true;
+ }
/* setup has already been done */
return 0;
}
--
2.55.0.887.g758fc8c411-goog
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH 3/5] HID: wacom: Fix Use-After-Free in wacom_intuos_pad
2026-08-25 15:12 [PATCH 1/5] HID: wacom: Use hdev->product in wacom_setup_touch_input_capabilities Lee Jones
2026-08-25 15:12 ` [PATCH 2/5] HID: wacom: Advertise SW_MUTE_DEVICE capability prior to registration Lee Jones
@ 2026-08-25 15:12 ` Lee Jones
2026-08-25 15:12 ` [PATCH 4/5] HID: wacom: Fix Use-After-Free in wacom_bamboo_pad Lee Jones
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Lee Jones @ 2026-08-25 15:12 UTC (permalink / raw)
To: lee, Ping Cheng, Jason Gerecke, Jiri Kosina, Benjamin Tissoires,
Aaron Skomra, Peter Hutterer, Dmitry Torokhov, linux-input,
linux-kernel
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"]
v5 -> v6: No change
v6 -> v7: No change
v7 -> v8: No functional change - cleaned up a stray whitespace/blank line deletion hunk
drivers/hid/wacom_sys.c | 34 +++++++++++++++++++++++-----------
drivers/hid/wacom_wac.c | 36 ++++++++++++++++++------------------
drivers/hid/wacom_wac.h | 2 +-
3 files changed, 42 insertions(+), 30 deletions(-)
diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c
index 2738d4f515e6..b88726cbbb4e 100644
--- a/drivers/hid/wacom_sys.c
+++ b/drivers/hid/wacom_sys.c
@@ -875,10 +875,16 @@ 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;
@@ -907,6 +913,11 @@ 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;
@@ -915,11 +926,6 @@ 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;
}
@@ -2343,9 +2349,15 @@ 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) {
diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index a7e3817aa2c4..f953851ad6bc 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);
@@ -2155,7 +2163,7 @@ 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)
@@ -2163,9 +2171,7 @@ 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;
}
@@ -3383,11 +3389,8 @@ 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]);
@@ -3422,11 +3425,8 @@ 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;
--
2.55.0.887.g758fc8c411-goog
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH 4/5] HID: wacom: Fix Use-After-Free in wacom_bamboo_pad
2026-08-25 15:12 [PATCH 1/5] HID: wacom: Use hdev->product in wacom_setup_touch_input_capabilities Lee Jones
2026-08-25 15:12 ` [PATCH 2/5] HID: wacom: Advertise SW_MUTE_DEVICE capability prior to registration Lee Jones
2026-08-25 15:12 ` [PATCH 3/5] HID: wacom: Fix Use-After-Free in wacom_intuos_pad Lee Jones
@ 2026-08-25 15:12 ` Lee Jones
2026-08-25 15:12 ` [PATCH 5/5] HID: wacom: Redesign shared sibling data lifecycle Lee Jones
2026-08-27 2:48 ` [PATCH 1/5] HID: wacom: Use hdev->product in wacom_setup_touch_input_capabilities Ping Cheng
4 siblings, 0 replies; 6+ messages in thread
From: Lee Jones @ 2026-08-25 15:12 UTC (permalink / raw)
To: lee, Ping Cheng, Jason Gerecke, Jiri Kosina, Benjamin Tissoires,
Aaron Skomra, Dmitry Torokhov, Peter Hutterer, linux-input,
linux-kernel
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
v5 -> v6: No change
v6 -> v7: No change
v7 -> v8: 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 b88726cbbb4e..79fd397e044a 100644
--- a/drivers/hid/wacom_sys.c
+++ b/drivers/hid/wacom_sys.c
@@ -876,11 +876,18 @@ 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);
}
}
@@ -914,9 +921,9 @@ 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);
@@ -2354,7 +2361,11 @@ 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);
}
@@ -2836,16 +2847,19 @@ 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 f953851ad6bc..884d1cf7401c 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -3294,6 +3294,7 @@ 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;
/*
@@ -3306,13 +3307,11 @@ 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;
};
--
2.55.0.887.g758fc8c411-goog
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH 5/5] HID: wacom: Redesign shared sibling data lifecycle
2026-08-25 15:12 [PATCH 1/5] HID: wacom: Use hdev->product in wacom_setup_touch_input_capabilities Lee Jones
` (2 preceding siblings ...)
2026-08-25 15:12 ` [PATCH 4/5] HID: wacom: Fix Use-After-Free in wacom_bamboo_pad Lee Jones
@ 2026-08-25 15:12 ` Lee Jones
2026-08-27 2:48 ` [PATCH 1/5] HID: wacom: Use hdev->product in wacom_setup_touch_input_capabilities Ping Cheng
4 siblings, 0 replies; 6+ messages in thread
From: Lee Jones @ 2026-08-25 15:12 UTC (permalink / raw)
To: lee, Ping Cheng, Jason Gerecke, Jiri Kosina, Benjamin Tissoires,
Aaron Skomra, Dmitry Torokhov, Peter Hutterer, linux-input,
linux-kernel
The Wacom driver coordinates state between sibling interfaces of
the same physical device using a shared structure 'wacom_shared'
inside 'wacom_hdev_data'. The driver kept a volatile representative
pointer 'data->dev' pointing to a sibling 'hid_device' for physical
path comparisons during sibling matching.
This pointer management is fragile. When the representative device
is disconnected, wacom_remove_shared_data() failed to clear/update
'data->dev', leading to a Use-After-Free vulnerability when
subsequent sibling probes dereference the dangling 'data->dev'
pointer.
Resolve this issue by redesigning the sibling data lifecycle:
- Eliminate the volatile 'data->dev' representative pointer
completely
- Redesign 'wacom_hdev_data' to store stable static copies of the
required attributes upon first allocation: 'phys' path string,
'vendor', 'product' IDs and the sibling's 'device_type'
- Use these static attributes for stable sibling matching in
wacom_are_sibling() and wacom_get_hdev_data()
This ensures sibling matching remains safe and stable even if
individual siblings are dynamically added or removed.
To secure the lifecycle against concurrent probe/disconnect races:
- Switch kref_put() to kref_put_mutex() in
wacom_remove_shared_data() to serialize refcount drops with list
traversal and lookup
- Modify wacom_release_shared_data() to assume the list lock is
already held
Also, do not accumulate the 'device_type' capability flag during
subsequent sibling probes. Keeping only the first probed sibling's
device_type exactly preserves the original sibling matching behavior
without introducing side effects.
Fixes: 4492efffffeb ("Input: wacom - share pen info with touch of the same ID")
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: No change
v4 -> v5: No change
v5 -> v6: No change
v6 -> v7: No change
v7 -> v8: No change
drivers/hid/wacom_sys.c | 70 +++++++++++++++++++++++++++--------------
1 file changed, 46 insertions(+), 24 deletions(-)
diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c
index 79fd397e044a..d4b6dc9eb0c8 100644
--- a/drivers/hid/wacom_sys.c
+++ b/drivers/hid/wacom_sys.c
@@ -757,27 +757,47 @@ static void wacom_retrieve_hid_descriptor(struct hid_device *hdev,
struct wacom_hdev_data {
struct list_head list;
struct kref kref;
- struct hid_device *dev;
+ char phys[64];
+ __u32 vendor;
+ __u32 product;
+ __u32 device_type;
struct wacom_shared shared;
};
+static bool wacom_compare_device_paths(struct hid_device *hdev_a,
+ const char *phys_b, char separator)
+{
+ const char *p1 = strrchr(hdev_a->phys, separator);
+ const char *p2 = strrchr(phys_b, separator);
+ int n1, n2;
+
+ if (!p1 || !p2)
+ return false;
+
+ n1 = p1 - hdev_a->phys;
+ n2 = p2 - phys_b;
+
+ if (n1 != n2 || n1 <= 0 || n2 <= 0)
+ return false;
+
+ return !strncmp(hdev_a->phys, phys_b, n1);
+}
+
static LIST_HEAD(wacom_udev_list);
static DEFINE_MUTEX(wacom_udev_list_lock);
static bool wacom_are_sibling(struct hid_device *hdev,
- struct hid_device *sibling)
+ struct wacom_hdev_data *data)
{
struct wacom *wacom = hid_get_drvdata(hdev);
struct wacom_features *features = &wacom->wacom_wac.features;
- struct wacom *sibling_wacom = hid_get_drvdata(sibling);
- struct wacom_features *sibling_features = &sibling_wacom->wacom_wac.features;
__u32 oVid = features->oVid ? features->oVid : hdev->vendor;
__u32 oPid = features->oPid ? features->oPid : hdev->product;
/* The defined oVid/oPid must match that of the sibling */
- if (features->oVid != HID_ANY_ID && sibling->vendor != oVid)
+ if (features->oVid != HID_ANY_ID && data->vendor != oVid)
return false;
- if (features->oPid != HID_ANY_ID && sibling->product != oPid)
+ if (features->oPid != HID_ANY_ID && data->product != oPid)
return false;
/*
@@ -785,11 +805,11 @@ static bool wacom_are_sibling(struct hid_device *hdev,
* device path, while those with different VID/PID must share
* the same physical parent device path.
*/
- if (hdev->vendor == sibling->vendor && hdev->product == sibling->product) {
- if (!hid_compare_device_paths(hdev, sibling, '/'))
+ if (hdev->vendor == data->vendor && hdev->product == data->product) {
+ if (!wacom_compare_device_paths(hdev, data->phys, '/'))
return false;
} else {
- if (!hid_compare_device_paths(hdev, sibling, '.'))
+ if (!wacom_compare_device_paths(hdev, data->phys, '.'))
return false;
}
@@ -802,7 +822,7 @@ static bool wacom_are_sibling(struct hid_device *hdev,
* devices.
*/
if ((features->device_type & WACOM_DEVICETYPE_DIRECT) &&
- !(sibling_features->device_type & WACOM_DEVICETYPE_DIRECT))
+ !(data->device_type & WACOM_DEVICETYPE_DIRECT))
return false;
/*
@@ -810,17 +830,17 @@ static bool wacom_are_sibling(struct hid_device *hdev,
* devices.
*/
if (!(features->device_type & WACOM_DEVICETYPE_DIRECT) &&
- (sibling_features->device_type & WACOM_DEVICETYPE_DIRECT))
+ (data->device_type & WACOM_DEVICETYPE_DIRECT))
return false;
/* Pen devices may only be siblings of touch devices */
if ((features->device_type & WACOM_DEVICETYPE_PEN) &&
- !(sibling_features->device_type & WACOM_DEVICETYPE_TOUCH))
+ !(data->device_type & WACOM_DEVICETYPE_TOUCH))
return false;
/* Touch devices may only be siblings of pen devices */
if ((features->device_type & WACOM_DEVICETYPE_TOUCH) &&
- !(sibling_features->device_type & WACOM_DEVICETYPE_PEN))
+ !(data->device_type & WACOM_DEVICETYPE_PEN))
return false;
/*
@@ -836,7 +856,7 @@ static struct wacom_hdev_data *wacom_get_hdev_data(struct hid_device *hdev)
/* Try to find an already-probed interface from the same device */
list_for_each_entry(data, &wacom_udev_list, list) {
- if (hid_compare_device_paths(hdev, data->dev, '/')) {
+ if (wacom_compare_device_paths(hdev, data->phys, '/')) {
kref_get(&data->kref);
return data;
}
@@ -844,7 +864,7 @@ static struct wacom_hdev_data *wacom_get_hdev_data(struct hid_device *hdev)
/* Fallback to finding devices that appear to be "siblings" */
list_for_each_entry(data, &wacom_udev_list, list) {
- if (wacom_are_sibling(hdev, data->dev)) {
+ if (wacom_are_sibling(hdev, data)) {
kref_get(&data->kref);
return data;
}
@@ -858,18 +878,15 @@ static void wacom_release_shared_data(struct kref *kref)
struct wacom_hdev_data *data =
container_of(kref, struct wacom_hdev_data, kref);
- mutex_lock(&wacom_udev_list_lock);
list_del(&data->list);
- mutex_unlock(&wacom_udev_list_lock);
-
kfree(data);
}
static void wacom_remove_shared_data(void *res)
{
- struct wacom *wacom = res;
+ struct wacom *res_wacom = res;
struct wacom_hdev_data *data;
- struct wacom_wac *wacom_wac = &wacom->wacom_wac;
+ struct wacom_wac *wacom_wac = &res_wacom->wacom_wac;
if (wacom_wac->shared) {
data = container_of(wacom_wac->shared, struct wacom_hdev_data,
@@ -883,17 +900,19 @@ static void wacom_remove_shared_data(void *res)
rcu_dereference_protected(wacom_wac->shared->pen,
lockdep_is_held(&wacom_udev_list_lock));
- if (touch == wacom->hdev) {
+ if (touch == res_wacom->hdev) {
rcu_assign_pointer(wacom_wac->shared->touch, NULL);
rcu_assign_pointer(wacom_wac->shared->touch_input, NULL);
- } else if (pen == wacom->hdev) {
+ } else if (pen == res_wacom->hdev) {
rcu_assign_pointer(wacom_wac->shared->pen, NULL);
}
}
synchronize_rcu();
- kref_put(&data->kref, wacom_release_shared_data);
+ if (kref_put_mutex(&data->kref, wacom_release_shared_data, &wacom_udev_list_lock))
+ mutex_unlock(&wacom_udev_list_lock);
+
wacom_wac->shared = NULL;
}
}
@@ -916,7 +935,10 @@ static int wacom_add_shared_data(struct hid_device *hdev)
}
kref_init(&data->kref);
- data->dev = hdev;
+ strscpy(data->phys, hdev->phys, sizeof(data->phys));
+ data->vendor = hdev->vendor;
+ data->product = hdev->product;
+ data->device_type = wacom_wac->features.device_type;
list_add_tail(&data->list, &wacom_udev_list);
}
--
2.55.0.887.g758fc8c411-goog
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH 1/5] HID: wacom: Use hdev->product in wacom_setup_touch_input_capabilities
2026-08-25 15:12 [PATCH 1/5] HID: wacom: Use hdev->product in wacom_setup_touch_input_capabilities Lee Jones
` (3 preceding siblings ...)
2026-08-25 15:12 ` [PATCH 5/5] HID: wacom: Redesign shared sibling data lifecycle Lee Jones
@ 2026-08-27 2:48 ` Ping Cheng
4 siblings, 0 replies; 6+ messages in thread
From: Ping Cheng @ 2026-08-27 2:48 UTC (permalink / raw)
To: Lee Jones
Cc: Ping Cheng, Jason Gerecke, Jiri Kosina, Benjamin Tissoires,
Aaron Skomra, Dmitry Torokhov, Peter Hutterer, linux-input,
linux-kernel
Hi Lee,
Thank you for your effort and persistence! We (Wacom and Wacom's
customers) are lucky to have people like you working in this
community!
In addition to making sure that you know your contribution is greatly
appreciated, I am giving you an initial testing feedback so you know
you are on the right track.
I manually tested a few older and new Wacom tablets. Some of them have
touch switches, some don't. They all worked well!
Two more details I'd like to share.
The first one is about the touch-only tablet. In all the models of
Wacom tablets, there was only one model that is touch-only. It was a
Bamboo Touch (model CTT-460) released on September 24, 2009. So, it
was more than 17 years ago. However, the quality of Wacom tablets are
so high, it is possible that some people are still using those ones
;).
The second one is about the type of touch on/off switches. There are
two types of touch on/off switches: it can be a soft key or hardware
switch. The hardware touch switch is easy to understand. The soft key
touch switch is actually an on-screen display in the shape of fingers,
where the touch on/off is controlled by the driver: [1]. This softkey
touch switch, somehow, is not reported to the userland by the existing
driver. Your patchset doesn't show it either.
I will do more testing to figure out the root cause of the softkey issue.
Cheers,
Ping
[1] ttps://github.com/linuxwacom/input-wacom/blob/master/4.18/wacom_wac.c#L2063
On Tue, Aug 25, 2026 at 10:09 AM Lee Jones <lee@kernel.org> wrote:
>
> Replace the lookup-dependent 'wacom_wac->shared->touch->product' references
> with 'hdev->product' inside wacom_setup_touch_input_capabilities() since
> 'hdev' is already available (via container_of) and represents the touch
> device itself.
>
> Signed-off-by: Lee Jones <lee@kernel.org>
> ---
>
> v7 -> v8: New patch
>
> drivers/hid/wacom_wac.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
> index a29bf051ada7..4436faf2d2bb 100644
> --- a/drivers/hid/wacom_wac.c
> +++ b/drivers/hid/wacom_wac.c
> @@ -3953,8 +3953,8 @@ int wacom_setup_pen_input_capabilities(struct input_dev *input_dev,
> int wacom_setup_touch_input_capabilities(struct input_dev *input_dev,
> struct wacom_wac *wacom_wac)
> {
> + struct hid_device *hdev = container_of(wacom_wac, struct wacom, wacom_wac)->hdev;
> struct wacom_features *features = &wacom_wac->features;
> -
> if (!(features->device_type & WACOM_DEVICETYPE_TOUCH))
> return -ENODEV;
>
> @@ -3963,9 +3963,11 @@ int wacom_setup_touch_input_capabilities(struct input_dev *input_dev,
> else
> __set_bit(INPUT_PROP_POINTER, input_dev->propbit);
>
> - if (features->type == HID_GENERIC)
> + if (features->type == HID_GENERIC) {
> + hid_dbg(hdev, "generic touch setup\n");
> /* setup has already been done */
> return 0;
> + }
>
> input_dev->evbit[0] |= BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
> __set_bit(BTN_TOUCH, input_dev->keybit);
> @@ -3997,19 +3999,17 @@ int wacom_setup_touch_input_capabilities(struct input_dev *input_dev,
> input_dev->evbit[0] |= BIT_MASK(EV_SW);
> __set_bit(SW_MUTE_DEVICE, input_dev->swbit);
>
> - if (wacom_wac->shared->touch->product == 0x361) {
> + if (hdev->product == 0x361) {
> input_set_abs_params(input_dev, ABS_MT_POSITION_X,
> 0, 12440, 4, 0);
> input_set_abs_params(input_dev, ABS_MT_POSITION_Y,
> 0, 8640, 4, 0);
> - }
> - else if (wacom_wac->shared->touch->product == 0x360) {
> + } else if (hdev->product == 0x360) {
> input_set_abs_params(input_dev, ABS_MT_POSITION_X,
> 0, 8960, 4, 0);
> input_set_abs_params(input_dev, ABS_MT_POSITION_Y,
> 0, 5920, 4, 0);
> - }
> - else if (wacom_wac->shared->touch->product == 0x393) {
> + } else if (hdev->product == 0x393) {
> input_set_abs_params(input_dev, ABS_MT_POSITION_X,
> 0, 6400, 4, 0);
> input_set_abs_params(input_dev, ABS_MT_POSITION_Y,
> @@ -4039,8 +4039,8 @@ int wacom_setup_touch_input_capabilities(struct input_dev *input_dev,
> fallthrough;
>
> case WACOM_27QHDT:
> - if (wacom_wac->shared->touch->product == 0x32C ||
> - wacom_wac->shared->touch->product == 0xF6) {
> + if (hdev->product == 0x32C ||
> + hdev->product == 0xF6) {
> input_dev->evbit[0] |= BIT_MASK(EV_SW);
> __set_bit(SW_MUTE_DEVICE, input_dev->swbit);
> wacom_wac->has_mute_touch_switch = true;
> --
> 2.55.0.887.g758fc8c411-goog
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread