linux-kernel - Re: [PATCH] Input: wacom_w8001 - Ignore bogus idx values in interrupt

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Date:	Mon, 23 May 2016 11:00:39 -0700
From:	Ping Cheng <pinglinux@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Chris J Arges <christopherarges@...il.com>,
	linux-input <linux-input@...r.kernel.org>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	Benjamin Tissoires <benjamin.tissoires@...il.com>,
	Ping Cheng <pingc@...om.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Input: wacom_w8001 - Ignore bogus idx values in interrupt

On Mon, May 23, 2016 at 9:52 AM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
> On Sun, May 22, 2016 at 10:21:45PM -0700, Ping Cheng wrote:
>> Hi Chris,
>>
>> On Sun, May 22, 2016 at 6:42 PM, Chris J Arges
>> <christopherarges@...il.com> wrote:
>> > I've noticed crashes when using my x60t using a coreboot bios. When using
>> > the pen I can produce a crash simply by tapping a few times. This
>> > generates an event which has an idx of 0xc. This in turn crashes the
>> > machine because the array access is greater than W8001_MAX_LENGTH. This
>> > patch checks for bogus values and filters them in order to prevent crashes.
>>
>> Thank you for submitting a patch in addition to reporting the issue.
>>
>> > Signed-off-by: Chris J Arges <christopherarges@...il.com>
>> > ---
>> >  drivers/input/touchscreen/wacom_w8001.c | 9 +++++++++
>> >  1 file changed, 9 insertions(+)
>> >
>> > diff --git a/drivers/input/touchscreen/wacom_w8001.c b/drivers/input/touchscreen/wacom_w8001.c
>> > index bab3c6a..c858200 100644
>> > --- a/drivers/input/touchscreen/wacom_w8001.c
>> > +++ b/drivers/input/touchscreen/wacom_w8001.c
>> > @@ -283,6 +283,15 @@ static irqreturn_t w8001_interrupt(struct serio *serio,
>> >         unsigned char tmp;
>> >
>> >         w8001->data[w8001->idx] = data;
>> > +
>> > +       /* ignore bogus idx values */
>> > +       if (w8001->idx >= W8001_MAX_LENGTH) {
>> > +               pr_info("w8001: ignored interrupt: data 0x%02x idx %d\n", data,
>> > +                       w8001->idx);
>> > +               w8001->idx = 0;
>> > +               return IRQ_HANDLED;
>> > +       }
>> > +
>>
>> I don't have an x60t system to test with. I wonder if your system
>> supports two finger touch or not. We at least have a bug in the code
>> since W8001_MAX_LENGTH should be 13 instead of 11. How come no one had
>> encountered that issue before?
>>
>> I'm going to email a patch to the list. Please test it and let us know
>> your result. Maybe we still need your patch if your device doesn't
>> support two finger touch or the idx=0xc can't be fixed by
>> W8001_MAX_LENGTH=13.
>
> Just so we are clear this version of the patch is buggy as we check the
> index only after [potentially] writing past the array bounds of
> w8001->data[].

Thanks for the heads up. I noticed that last night. Since it breaks
two-finger touch, we won't use it anyway.

My other patch is still necessary though. You'll need to change:

From: wacom <wacom@...alhost.localdomain>

to

From: Ping Cheng <pingc@...om.com>

I made it on a brand new system, which I didn't setup the environment
properly. I can update the patch if that's what you like...

Ping