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HID: wacom: Fix Use-After-Free in wacom_bamboo_pad

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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_sibling_pending() and
   wacom_mode_change_work() to avoid warnings (while lockless access in
   the latter remains a pre-existing issue).

Cc: stable@vger.kernel.org
Fixes: 8c97a76546 ("HID: wacom: add full support of the Wacom Bamboo PAD")
Signed-off-by: Lee Jones <lee@kernel.org>
Acked-by: Ping Cheng <ping.cheng@wacom.com>
Tested-by: Ping Cheng <ping.cheng@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
This commit is contained in:
Lee Jones 2026-09-09 11:12:26 +00:00 committed by Jiri Kosina
parent ef32877368
commit 3a523ecf9a
3 changed files with 34 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
drivers/hid/wacom_sys.c
View File

@ -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);
}
}
@ -2361,14 +2368,17 @@ static void wacom_set_shared_values(struct wacom_wac *wacom_wac)
}
if (wacom_wac->features.device_type & WACOM_DEVICETYPE_TOUCH) {
if (wacom_wac->shared->touch == wacom->hdev || !wacom_wac->shared->touch) {
struct hid_device *touch =
rcu_dereference_protected(wacom_wac->shared->touch,
lockdep_is_held(&wacom_udev_list_lock));
if (touch == wacom->hdev || !touch) {
wacom_wac->shared->type = wacom_wac->features.type;
wacom_wac->shared->touch = wacom->hdev;
rcu_assign_pointer(wacom_wac->shared->touch, wacom->hdev);
rcu_assign_pointer(wacom_wac->shared->touch_input, wacom_wac->touch_input);
}
} else if (wacom_wac->features.device_type & WACOM_DEVICETYPE_PEN) {
/* Pairs with smp_load_acquire() in wacom_sibling_pending() */
smp_store_release(&wacom_wac->shared->pen, wacom->hdev);
rcu_assign_pointer(wacom_wac->shared->pen, wacom->hdev);
}
}
@ -2384,8 +2394,7 @@ static bool wacom_sibling_pending(struct wacom *wacom)
return false;
if (wacom->wacom_wac.shared) {
/* Pairs with smp_store_release() in wacom_set_shared_values() */
if (smp_load_acquire(&wacom->wacom_wac.shared->pen))
if (rcu_access_pointer(wacom->wacom_wac.shared->pen))
return false;
}
@ -2852,16 +2861,19 @@ 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;

13
drivers/hid/wacom_wac.c
View File

@ -3307,6 +3307,7 @@ 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;
/*
@ -3319,13 +3320,11 @@ 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;
}

4
drivers/hid/wacom_wac.h
View File

@ -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;
};