Re: NULL pointer dereference in i2c-hid

From: Andrew Duggan
Date: Thu Dec 11 2014 - 13:41:34 EST

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
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()

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.

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