Re: [PATCH 6/8] Input: psmouse - add support for SMBus companions

From: Benjamin Tissoires
Date: Fri Mar 10 2017 - 12:55:28 EST

On Mar 09 2017 or thereabouts, Dmitry Torokhov wrote:
> From: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
> This provides glue between PS/2 devices that enumerate the RMI4 devices
> and Elan touchpads to the RMI4 (or Elan) SMBus driver.
> The SMBus devices keep their PS/2 connection alive. If the initialization
> process goes too far (psmouse_activate called), the device disconnects
> from the I2C bus and stays on the PS/2 bus, that is why we explicitly
> disable PS/2 device reporting (by calling psmouse_deactivate) before
> trying to register SMBus companion device.
> The HID over I2C devices are enumerated through the ACPI DSDT, and
> their PS/2 device also exports the InterTouch bit in the extended
> capability 0x0C. However, the firmware keeps its I2C connection open
> even after going further in the PS/2 initialization. We don't need
> to take extra precautions with those device, especially because they
> block their PS/2 communication when HID over I2C is used.
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> ---

Hi Dmitry,

There is an issue with this patch. The platform_data provided by the
caller of psmouse_smbus_init() may be dereference, leading to a dangling
pointer on the stack in rmi4.

There is no guarantees rmi-smbus will get probed directly and even if it
does, a later rmmod/modprobe might happen and won't have access to the
platform data.

See below for a patch that solves this. Feel free to squash it, change it
and remove the terrible commit message.