Re: NULL pointer dereference in i2c-hid

From: Andrew Duggan <aduggan@synaptics.com>
To: Gabriele Mazzotta <gabriele.mzt@gmail.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: <linux-input@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<benjamin.tissoires@redhat.com>, <jkosina@suse.cz>
Subject: Re: NULL pointer dereference in i2c-hid
Date: Thu, 11 Dec 2014 10:40:05 -0800	[thread overview]
Message-ID: <5489E505.3050903@synaptics.com> (raw)
In-Reply-To: <2128690.c90ERDd9ZP@xps13>

On 12/11/2014 10:16 AM, Gabriele Mazzotta wrote:
> On Thursday 11 December 2014 16:03:07 Mika Westerberg wrote:
>> On Thu, Dec 11, 2014 at 10:58:01AM +0200, Mika Westerberg wrote:
>>> On Wed, Dec 10, 2014 at 06:04:51PM +0100, Gabriele Mazzotta wrote:
>>>> my laptop uses a touchpad that needs hid-rmi along with i2c-hid to work.
>>>> i2c-hid and hid-rmi can be loaded and unloaded independelty from each
>>>> other, however since 34f439e4afcd ("HID: i2c-hid: add runtime PM support")
>>>> if I unload hid-rmi and after it I also unload i2c-hid, I get a NULL
>>>> pointer dereference.
>>> I'll look into this.
>>>
>>> I can reproduce this easily with i2c-hid + hid-multitouch following your
>>> directions.
>> Can you try the below patch?
>>
>> I think we shouldn't free buffers yet in ->stop() because we need the
>> command buffer sending power commands to the device. Also it seems that
>> ->start() re-allocates buffers anyway if maximum size increases.
>>
>> It shouldn't even leak memory as we release buffers at ->remove()
>> anyway.
>>
>> diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c
>> index 62cec01937ea..68a8c938feea 100644
>> --- a/drivers/hid/i2c-hid/i2c-hid.c
>> +++ b/drivers/hid/i2c-hid/i2c-hid.c
>> @@ -705,12 +705,7 @@ static int i2c_hid_start(struct hid_device *hid)
>>   
>>   static void i2c_hid_stop(struct hid_device *hid)
>>   {
>> -	struct i2c_client *client = hid->driver_data;
>> -	struct i2c_hid *ihid = i2c_get_clientdata(client);
>> -
>>   	hid->claimed = 0;
>> -
>> -	i2c_hid_free_buffers(ihid);
>>   }
>>   
>>   static int i2c_hid_open(struct hid_device *hid)
> Yes, it works, thanks.
>
> This change seems to also prevent kernel ooops when I unload either
> i2c-hid or i2c-designware-platform while the touchpad is in use,
> thing that is likely to happen because of the other bug I reported.
>
> Speaking of it, does any of you have any suggestion on how to debug it?
I was able to reproduce the initial issue by unloading hid-rmi and 
i2c-hid while holding my fingers on the touchpad. Mika's patch fixes it 
for me.

For the original bug, you can modprobe i2c-hid debug=1 and we can see 
what data the touchpad is reporting. That might help narrowing down if 
it's noise which the touchpad thinks are fingers or if there is a 
problem with the I2C lines causing spurious interrupts.

Andrew