[PATCH 5.10.y] HID: magicmouse: do not keep a stale msc->input if no input is claimed

[Sasha Levin <sashal@kernel.org>]

From: Jose Villaseñor Montfort <pepemontfort@gmail.com>

[ Upstream commit 0af3b89705688af01aa06025b84fa7a1e06ba6cc ]

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/20260728185542.65F091F000E9@smtp.kernel.org/
Cc: stable@vger.kernel.org
Signed-off-by: Jose Villaseñor Montfort <pepemontfort@gmail.com>
Reviewed-by: Alec Hall <signshop.alec@gmail.com>
Tested-by: Alec Hall <signshop.alec@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/hid/hid-magicmouse.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/hid/hid-magicmouse.c b/drivers/hid/hid-magicmouse.c
index afde78319b996..e39e32680feee 100644
--- a/drivers/hid/hid-magicmouse.c
+++ b/drivers/hid/hid-magicmouse.c
@@ -627,6 +627,16 @@ static int magicmouse_probe(struct hid_device *hdev,
 		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 (!msc->input) {
 		hid_err(hdev, "magicmouse input not registered\n");
 		ret = -ENOMEM;
-- 
2.53.0