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

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
[off-list ref] wrote:

quoted

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.

quoted

Signed-off-by: Chris J Arges <redacted>
---
 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