[PATCH 7.2 59/82] HID: magicmouse: do not keep a stale msc->input if no input is claimed

7.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jose Villaseñor Montfort <[email protected]>

commit 0af3b89705688af01aa06025b84fa7a1e06ba6cc upstream.

magicmouse_input_mapping() caches the first hid_input's input_dev in
msc->input while the report descriptor is parsed, and the rest of the
driver treats a non-NULL msc->input as proof that an input device was
registered.

That does not hold on the hid-input error path. If hidinput_connect()
fails -- for instance because input_register_device() returns an error --
it unwinds through hidinput_disconnect(), which frees every input_dev it
created, including the one cached in msc->input.

The failure does not abort the probe. hid_connect() only skips the claim:

	if ((connect_mask & HID_CONNECT_HIDINPUT) && !hidinput_connect(hdev,
				connect_mask & HID_CONNECT_HIDINPUT_FORCE))
		hdev->claimed |= HID_CLAIMED_INPUT;

and the "device has no listeners" bailout below it does not fire for this
driver, which sets ->raw_event; on the USB Magic Mouse 2 / Magic Trackpad
2 paths hidraw and hiddev are claimed as well. hid_hw_start() therefore
returns 0 and magicmouse_probe() continues with msc->input pointing at
freed memory. Being non-NULL, it passes the "input not registered" check
in probe and the NULL checks in ->raw_event and ->event, so the next
input report dereferences freed memory.

Clear msc->input when the HID core did not claim an input device, so the
existing NULL checks cover this case as well.

Fixes: f1a9a149abc8 ("HID: magicmouse: fix race between input_register() and probe()")
Link: https://lore.kernel.org/linux-input/[email protected]/
Cc: [email protected]
Signed-off-by: Jose Villaseñor Montfort <[email protected]>
Reviewed-by: Alec Hall <[email protected]>
Tested-by: Alec Hall <[email protected]>
Signed-off-by: Jiri Kosina <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/hid/hid-magicmouse.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/drivers/hid/hid-magicmouse.c
+++ b/drivers/hid/hid-magicmouse.c
@@ -922,6 +922,16 @@ static int magicmouse_probe(struct hid_d
 		return ret;
 	}
 
+	/*
+	 * When hidinput_connect() fails it frees every input device it
+	 * created, but that does not fail hid_hw_start(): the core simply
+	 * does not claim an input. msc->input, cached in ->input_mapping
+	 * while the report descriptor was parsed, would then be a dangling
+	 * pointer that passes every NULL check. Trust the core's claim.
+	 */
+	if (!(hdev->claimed & HID_CLAIMED_INPUT))
+		msc->input = NULL;
+
 	if (is_usb_magicmouse2(id->vendor, id->product) ||
 	    is_usb_magictrackpad2(id->vendor, id->product)) {
 		timer_setup(&msc->battery_timer, magicmouse_battery_timer_tick, 0);