From 9aa237cf66495b2426ddde8532e9b08a0ed83aaa Mon Sep 17 00:00:00 2001 From: Wei Jie LAW <98lawweijie@gmail.com> Date: Wed, 9 Sep 2026 09:15:13 +0800 Subject: [PATCH] HID: wacom: fix OOB read in wacom_wac_pen_serial_enforce() The 'wacom_wac_pen_serial_enforce()' function may calculate and pass an invalid offset to hid_field_extract(), resulting in memory reads at incorrect addresses -- possibly beyond the end of the report. If a field in the HID descriptor lists more usages than its Report Count actually reserves space for, the function's inner 'j' will walk past the end of the field: for (i = 0; i < report->maxfield; i++) { for (j = 0; j < report->field[i]->maxusage; j++) { ... value = hid_field_extract(hdev, raw_data + 1, offset + j * size, size); A descriptor listing 12288 usages against Report Count 1 has the loop extract the usage at index 12287 from bit offset 98296 -- about 12 KB past a 2-byte received report. The value is stored in wacom_wac->serial[0] and can reach userspace as an MSC_SERIAL event, making this an information disclosure. Clamp the loop to field->report_count, the number of value slots the report holds. Value slots past the last declared usage are still scanned; they reuse that usage (HID 1.11, 6.2.2.8). Verified on v6.12.105 with a UHID reproducer: a 2-byte report from such a descriptor trips KASAN before the patch and not after it. Fixes: 83417206427b ("HID: wacom: Queue events with missing type/serial data for later processing") Suggested-by: Jason Gerecke Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-5 Assisted-by: GLM:glm-5.3 Signed-off-by: Wei Jie Law <98lawweijie@gmail.com> Reviewed-by: Jason Gerecke Signed-off-by: Jiri Kosina --- drivers/hid/wacom_sys.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c index 0eafa483b7f7..40770affdbde 100644 --- a/drivers/hid/wacom_sys.c +++ b/drivers/hid/wacom_sys.c @@ -113,8 +113,9 @@ static int wacom_wac_pen_serial_enforce(struct hid_device *hdev, /* Queue events which have invalid tool type or serial number */ for (i = 0; i < report->maxfield; i++) { - for (j = 0; j < report->field[i]->maxusage; j++) { - struct hid_field *field = report->field[i]; + struct hid_field *field = report->field[i]; + + for (j = 0; j < field->report_count; j++) { struct hid_usage *usage = &field->usage[j]; unsigned int equivalent_usage = wacom_equivalent_usage(usage->hid); unsigned int offset;