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

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

[Chris J Arges]

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.

Signed-off-by: Chris J Arges <christopherarges@gmail.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;
+	}
+
 	switch (w8001->idx++) {
 	case 0:
 		if ((data & W8001_LEAD_MASK) != W8001_LEAD_BYTE) {
-- 
2.7.4

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

[Ping Cheng]

Hi Chris,

On Sun, May 22, 2016 at 6:42 PM, Chris J Arges
<christopherarges@gmail.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@gmail.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.

Thanks,

Ping

>         switch (w8001->idx++) {
>         case 0:
>                 if ((data & W8001_LEAD_MASK) != W8001_LEAD_BYTE) {
> --
> 2.7.4
>
> --
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Re: [PATCH] Input: wacom_w8001 - Ignore bogus idx values in interrupt

[Dmitry Torokhov]

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@gmail.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@gmail.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.

-- 
Dmitry

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

[Ping Cheng]

On Mon, May 23, 2016 at 9:52 AM, Dmitry Torokhov
<dmitry.torokhov@gmail.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@gmail.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@gmail.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@localhost.localdomain>

to

From: Ping Cheng <pingc@wacom.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