Re: [PATCH v2 RESEND] HID: multitouch: fix slab out-of-bounds access in mt_report_fixup()

[Jiri Kosina]

On Sun, 10 Aug 2025, Qasim Ijaz 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 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: c8000deb6836 ("HID: multitouch: Add support for GT7868Q")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Qasim Ijaz <qasdev00@xxxxxxxxx>
> Reviewed-by: Jiri Slaby <jirislaby@xxxxxxxxxx>
> ---
> v2:
> - Simplify fix with a if-size check after discussion with Jiri Slaby
> - Change explanation of bug to reflect inclusion of a if-size check

Applied to hid.git#for-6.17/upstream-fixes, thanks.

-- 
Jiri Kosina
SUSE Labs