[PATCH] Input: synaptics-rmi4 - fix input device name lifetime with hid-rmi

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

rmi_driver_set_input_name() allocates the input device name string
using devm_kasprintf(&rmi_dev->dev, ...). When the input device is
supplied by a transport driver via rmi_dev->xport->input (such as
hid-rmi), the input device's lifetime is owned by the transport device
rather than rmi_dev.

When rmi_remove() in hid-rmi calls rmi_unregister_transport_device()
before hid_hw_stop(), or if rmi_driver_probe() fails after setting the
name, or if rmi_dev is unbound via sysfs, devres releases the name
string while the HID input device remains registered, causing a
use-after-free when input->name is later accessed (for example when
generating the KOBJ_REMOVE uevent or reading /proc/bus/input/devices).

Allocate the name string on input->dev.parent instead of &rmi_dev->dev:
- For hid-rmi, input->dev.parent is &hdev->dev, whose driver devres
  group is released in hid_device_remove() after rmi_remove() and
  hid_hw_stop() have unregistered the input device.
- When rmi_driver_probe() allocates the input device itself via
  devm_input_allocate_device(), input->dev.parent is &rmi_dev->dev, and
  the subsequent input_register_device() call pushes the unregistration
  devres action onto &rmi_dev->dev after the name allocation, so the
  input device is unregistered before the name is freed.

Fixes: 2b6a321da9a2 ("Input: synaptics-rmi4 - add support for Synaptics RMI4 devices")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/input/rmi4/rmi_driver.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/input/rmi4/rmi_driver.c b/drivers/input/rmi4/rmi_driver.c
index a349dfd17519..4ab00b2cf4f0 100644
--- a/drivers/input/rmi4/rmi_driver.c
+++ b/drivers/input/rmi4/rmi_driver.c
@@ -361,7 +361,14 @@ static void rmi_driver_set_input_name(struct rmi_device *rmi_dev,
 	const char *device_name = rmi_f01_get_product_ID(data->f01_container);
 	char *name;
 
-	name = devm_kasprintf(&rmi_dev->dev, GFP_KERNEL,
+	/*
+	 * Allocate the name string on the input device's parent rather than
+	 * rmi_dev->dev so that when the input device is supplied by a
+	 * transport driver (such as hid-rmi), the name string is not freed
+	 * when rmi_dev is torn down before the transport unregisters its
+	 * input device.
+	 */
+	name = devm_kasprintf(input->dev.parent, GFP_KERNEL,
 			      "Synaptics %s", device_name);
 	if (!name)
 		return;
-- 
2.56.0.rc1.315.gc6ed9934b7-goog


-- 
Dmitry