HID: wacom: fix OOB read in wacom_wac_pen_serial_enforce()

Overview

In the Linux kernel, the following vulnerability has been resolved:

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.

Affected

• Linux >= 83417206427bdf0fef9fa69957807194f25923c3 < 9aa62f967b6a4bb30aa3b778e02c8a5ca6bcde51
• Linux >= 83417206427bdf0fef9fa69957807194f25923c3 < 26471d954bbfbfb9032994f7f485802ee20e0582
• Linux >= 83417206427bdf0fef9fa69957807194f25923c3 < 456afe4707e23cc114ad833197f63b52bb8fd1e7
• Linux >= 83417206427bdf0fef9fa69957807194f25923c3 < 65e7c4b5366b770c60dfefac3f1d06e33a9e411e
• Linux >= 83417206427bdf0fef9fa69957807194f25923c3 < eaa7d29341ef4b91e84ad097562982288a7c376c
• Linux >= 83417206427bdf0fef9fa69957807194f25923c3 < c3129e6f26e18c0886ede7265f187a7ec289e1d1
• Linux >= 83417206427bdf0fef9fa69957807194f25923c3 < 4b09b7c84b8633cd041181616bd15bf5e73c164d
• Linux >= 83417206427bdf0fef9fa69957807194f25923c3 < 9aa237cf66495b2426ddde8532e9b08a0ed83aaa
• Linux 4.16

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.