Reviewed-by: Dmitry Savin <envelsavinds@xxxxxxxxx>
On Tue, 22 Jul 2025 at 09:00, Qasim Ijaz <qasdev00@xxxxxxxxx> wrote:
>
> 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 vulnerability by ensuring the descriptor size is
> greater than or equal to 608 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: c8000deb6836 ("HID: multitouch: Add support for GT7868Q")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Qasim Ijaz <qasdev00@xxxxxxxxx>
> Reviewed-by: Dmitry Savin <envelsavinds@xxxxxxxxx>
> ---
> drivers/hid/hid-multitouch.c | 25 ++++++++++++++++---------
> 1 file changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
> index 7ac8e16e6158..af4abe3ba410 100644
> --- a/drivers/hid/hid-multitouch.c
> +++ b/drivers/hid/hid-multitouch.c
> @@ -1461,18 +1461,25 @@ 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 (rdesc[607] == 0x15) {
> - rdesc[607] = 0x25;
> - dev_info(
> - &hdev->dev,
> - "GT7868Q report descriptor fixup is applied.\n");
> + if (*size >= 608) {
> + if (rdesc[607] == 0x15) {
> + rdesc[607] = 0x25;
> + dev_info(
> + &hdev->dev,
> + "GT7868Q report descriptor fixup is applied.\n");
> + } else {
> + dev_info(
> + &hdev->dev,
> + "The byte is not expected for fixing the report descriptor. \
> + It's possible that the touchpad firmware is not suitable for applying the fix. \
> + got: %x\n",
> + rdesc[607]);
> + }
> } else {
> dev_info(
> &hdev->dev,
> - "The byte is not expected for fixing the report descriptor. \
> -It's possible that the touchpad firmware is not suitable for applying the fix. \
> -got: %x\n",
> - rdesc[607]);
> + "GT7868Q fixup: report descriptor only %u bytes, skipping\n",
> + *size);
> }
> }
>
> --
> 2.39.5
>
