Commit 1c24e5fc authored Jul 19, 2025 by Hans de Goede Committed by Wolfram Sang Jul 28, 2025

i2c: core: Fix double-free of fwnode in i2c_unregister_device()



Before commit df6d7277 ("i2c: core: Do not dereference fwnode in struct
device"), i2c_unregister_device() only called fwnode_handle_put() on
of_node-s in the form of calling of_node_put(client->dev.of_node).

But after this commit the i2c_client's fwnode now unconditionally gets
fwnode_handle_put() on it.

When the i2c_client has no primary (ACPI / OF) fwnode but it does have
a software fwnode, the software-node will be the primary node and
fwnode_handle_put() will put() it.

But for the software fwnode device_remove_software_node() will also put()
it leading to a double free:

[   82.665598] ------------[ cut here ]------------
[   82.665609] refcount_t: underflow; use-after-free.
[   82.665808] WARNING: CPU: 3 PID: 1502 at lib/refcount.c:28 refcount_warn_saturate+0xba/0x11
...
[   82.666830] RIP: 0010:refcount_warn_saturate+0xba/0x110
...
[   82.666962]  <TASK>
[   82.666971]  i2c_unregister_device+0x60/0x90

Fix this by not calling fwnode_handle_put() when the primary fwnode is
a software-node.

Fixes: df6d7277 ("i2c: core: Do not dereference fwnode in struct device")
Cc: stable@vger.kernel.org
Signed-off-by: Hans de Goede <hansg@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

parent f61389a9

drivers/i2c/i2c-core-base.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -1066,6 +1066,12 @@ void i2c_unregister_device(struct i2c_client *client)
		of_node_clear_flag(to_of_node(fwnode), OF_POPULATED);
		else if (is_acpi_device_node(fwnode))
		acpi_device_clear_enumerated(to_acpi_device_node(fwnode));

		/*
		* If the primary fwnode is a software node it is free-ed by
		* device_remove_software_node() below, avoid double-free.
		*/
		if (!is_software_node(fwnode))
		fwnode_handle_put(fwnode);

		device_remove_software_node(&client->dev);