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Message-ID: <aH9zl18IqvL7l9pX@gmail.com>
Date: Tue, 22 Jul 2025 12:19:01 +0100
From: Qasim Ijaz <qasdev00@...il.com>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: jikos@...nel.org, bentiss@...nel.org, linux-input@...r.kernel.org,
linux-kernel@...r.kernel.org, stable@...r.kernel.org,
Dmitry Savin <envelsavinds@...il.com>
Subject: Re: [PATCH RESEND] HID: multitouch: fix slab out-of-bounds access in
mt_report_fixup()
On Tue, Jul 22, 2025 at 11:16:15AM +0200, Jiri Slaby wrote:
> On 22. 07. 25, 10:00, 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 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@...r.kernel.org
> > Signed-off-by: Qasim Ijaz <qasdev00@...il.com>
> > Reviewed-by: Dmitry Savin <envelsavinds@...il.com>
> > ---
> > 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",
>
> This is wrong. You have all the spaces/tabs in the string now. Drop all the
> backslashes, and open and close the string on every line.
>
> > + rdesc[607]);
> > + }
>
> As this is superlong and superindented, perhaps introduce a new function for
> these devices?
>
> > } 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",
>
> This was horrid too, yeah.
>
> > - rdesc[607]);
> > + "GT7868Q fixup: report descriptor only %u bytes, skipping\n",
>
> A predicate missing. Eg. "has only", or "is only".
>
Thanks for the feedback Jiri, I took the advice on board, is something
like this better?
static const __u8 *mt_report_fixup(struct hid_device *hdev, __u8 *rdesc,
unsigned int *size)
{
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(
&hdev->dev,
"GT7868Q fixup: report descriptor fixup is applied.\n");
} else {
dev_info(&hdev->dev,
"GT7868Q fixup: offset 607 is %x (expected 0x15), "
"descriptor may be malformed, skipping\n",
rdesc[607]);
}
}
return rdesc;
}
the key changes I made are:
- Move size check to the top, this way the indentation level is decent
- get rid of message backslashes
- shorten the fixup failure message when rdesc[607] is not 0x15 and make
it a bit clearer since this message was the longest - just a minor
cleanup
- added "is only %u bytes" as you suggested
if this is all good I can send v2.
Thanks
qasim
> > + *size);
> > }
> > }
>
> thanks,
> --
> js
> suse labs
>
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