Re: [PATCH] HID: rmi: check sanity of the incoming report

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

On Sep 08 2014 or thereabouts, Andrew Duggan wrote:
> On 09/05/2014 06:57 AM, Benjamin Tissoires wrote:
> >In the Dell XPS 13 9333, it appears that sometimes the bus get confused
> >and corrupts the incoming data. It fills the input report with the
> >sentinel value "ff". Synaptics told us that such behavior does not comes
> >from the touchpad itself, so we filter out such reports here.
> >
> >Unfortunately, we can not simply discard the incoming data because they
> >may contain useful information. Most of the time, the misbehavior is
> >quite near the end of the report, so we can still use the valid part of
> >it.
> >
> >Fixes:
> >https://bugzilla.redhat.com/show_bug.cgi?id=1123584
> >
> >Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> >---
> >  drivers/hid/hid-rmi.c | 31 ++++++++++++++++++++++++++-----
> >  1 file changed, 26 insertions(+), 5 deletions(-)
> >
> >diff --git a/drivers/hid/hid-rmi.c b/drivers/hid/hid-rmi.c
> >index 8389e81..db92c3b 100644
> >--- a/drivers/hid/hid-rmi.c
> >+++ b/drivers/hid/hid-rmi.c
> >@@ -320,9 +320,6 @@ static int rmi_f11_input_event(struct hid_device *hdev, u8 irq, u8 *data,
> >  	int offset;
> >  	int i;
> >-	if (size < hdata->f11.report_size)
> >-		return 0;
> >-
> >  	if (!(irq & hdata->f11.irq_mask))
> >  		return 0;
> >@@ -332,9 +329,13 @@ static int rmi_f11_input_event(struct hid_device *hdev, u8 irq, u8 *data,
> >  		int fs_bit_position = (i & 0x3) << 1;
> >  		int finger_state = (data[fs_byte_position] >> fs_bit_position) &
> >  					0x03;
> >+		int position = offset + 5 * i;
> >+
> >+		if (position + 5 > size)
> >+			/* partial report, go on with what we received */
> >+			break;
> >-		rmi_f11_process_touch(hdata, i, finger_state,
> >-				&data[offset + 5 * i]);
> >+		rmi_f11_process_touch(hdata, i, finger_state, &data[position]);
> >  	}
> >  	input_mt_sync_frame(hdata->input);
> >  	input_sync(hdata->input);
> >@@ -412,9 +413,29 @@ static int rmi_read_data_event(struct hid_device *hdev, u8 *data, int size)
> >  	return 1;
> >  }
> >+static int rmi_check_sanity(struct hid_device *hdev, u8 *data, int size)
> >+{
> >+	int valid_size = size;
> >+	/*
> >+	 * On the Dell XPS 13 9333, the bus sometimes get confused and fills
> >+	 * the report with a sentinel value "ff". Synaptics told us that such
> >+	 * behavior does not comes from the touchpad itself, so we filter out
> >+	 * such reports here.
> >+	 */
> >+
> >+	while ((data[valid_size - 1] == 0xff) && valid_size > 0)
> >+		valid_size--;
> >+
> >+	return valid_size;
> >+}
> >+
> >  static int rmi_raw_event(struct hid_device *hdev,
> >  		struct hid_report *report, u8 *data, int size)
> >  {
> >+	size = rmi_check_sanity(hdev, data, size);
> >+	if (size < 2)
> >+		return 0;
> >+
> >  	switch (data[0]) {
> >  	case RMI_READ_DATA_REPORT_ID:
> >  		return rmi_read_data_event(hdev, data, size);
> I think there should also be a check in rmi_f30_input_event to make sure
> that the F30 data is also valid. The F30 data is at the end of the HID
> report so if the F30 interrupt bit is set, but the value in the report is FF
> then there might be some unintended button events. I think checking that
> size > 0 would be sufficient to make sure the F30 data is valid.

Yeah :(
Actually, I am missing too checks in f11 and f30. If the size is <= 0,
then bail out before doing anything.

> 
> Other then that, the sanity check and validation in rmi_f11_input_event look
> good to me.
> 
> Andrew