HID: multitouch: fix slab out-of-bounds access in mt_report_fixup()

JIRA: https://issues.redhat.com/browse/RHEL-124612
CVE: CVE-2025-39806

commit 0379eb8
Author: Qasim Ijaz <qasdev00@gmail.com>
Date:   Sun Aug 10 19:09:24 2025 +0100

    HID: multitouch: fix slab out-of-bounds access in mt_report_fixup()

    A malicious HID device can trigger a slab out-of-bounds during
    mt_report_fixup() by passing in report descriptor smaller than
    607 bytes. mt_report_fixup() attempts to patch byte offset 607
    of the descriptor with 0x25 by first checking if byte offset
    607 is 0x15 however it lacks bounds checks to verify if the
    descriptor is big enough before conducting this check. Fix
    this bug by ensuring the descriptor size is at least 608
    bytes before accessing it.

    Below is the KASAN splat after the out of bounds access happens:

    [   13.671954] ==================================================================
    [   13.672667] BUG: KASAN: slab-out-of-bounds in mt_report_fixup+0x103/0x110
    [   13.673297] Read of size 1 at addr ffff888103df39df by task kworker/0:1/10
    [   13.673297]
    [   13.673297] CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Not tainted 6.15.0-00005-gec5d573d83f4-dirty #3
    [   13.673297] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/04
    [   13.673297] Call Trace:
    [   13.673297]  <TASK>
    [   13.673297]  dump_stack_lvl+0x5f/0x80
    [   13.673297]  print_report+0xd1/0x660
    [   13.673297]  kasan_report+0xe5/0x120
    [   13.673297]  __asan_report_load1_noabort+0x18/0x20
    [   13.673297]  mt_report_fixup+0x103/0x110
    [   13.673297]  hid_open_report+0x1ef/0x810
    [   13.673297]  mt_probe+0x422/0x960
    [   13.673297]  hid_device_probe+0x2e2/0x6f0
    [   13.673297]  really_probe+0x1c6/0x6b0
    [   13.673297]  __driver_probe_device+0x24f/0x310
    [   13.673297]  driver_probe_device+0x4e/0x220
    [   13.673297]  __device_attach_driver+0x169/0x320
    [   13.673297]  bus_for_each_drv+0x11d/0x1b0
    [   13.673297]  __device_attach+0x1b8/0x3e0
    [   13.673297]  device_initial_probe+0x12/0x20
    [   13.673297]  bus_probe_device+0x13d/0x180
    [   13.673297]  device_add+0xe3a/0x1670
    [   13.673297]  hid_add_device+0x31d/0xa40
    [...]

    Fixes: c8000de ("HID: multitouch: Add support for GT7868Q")
    Cc: stable@vger.kernel.org
    Signed-off-by: Qasim Ijaz <qasdev00@gmail.com>
    Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
    Signed-off-by: Jiri Kosina <jkosina@suse.com>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

drivers/hid/hid-multitouch.c

@@ -1461,6 +1461,14 @@ static const __u8 *mt_report_fixup(struct hid_device *hdev, __u8 *rdesc,
 	if (hdev->vendor == I2C_VENDOR_ID_GOODIX &&
 	    (hdev->product == I2C_DEVICE_ID_GOODIX_01E8 ||
 	     hdev->product == I2C_DEVICE_ID_GOODIX_01E9)) {
+		if (*size < 608) {
+			dev_info(
+				&hdev->dev,
+				"GT7868Q fixup: report descriptor is only %u bytes, skipping\n",
+				*size);
+			return rdesc;
+		}
+
 		if (rdesc[607] == 0x15) {
 			rdesc[607] = 0x25;
 			dev_info(