linux-kernel - Re: NULL pointer dereference in i2c-hid

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Message-ID: <20141211140307.GE1300@lahna.fi.intel.com>
Date:	Thu, 11 Dec 2014 16:03:07 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Gabriele Mazzotta <gabriele.mzt@...il.com>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	benjamin.tissoires@...hat.com, aduggan@...aptics.com,
	jkosina@...e.cz
Subject: Re: NULL pointer dereference in i2c-hid

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)
--
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