[PATCH] i3c: master: Fix info leak and UAF in device unregister path

[Adrian Hunter]

i3c_master_unregister_i3c_devs() clears i3cdev->dev->desc before
calling device_unregister().  During device_unregister(),
device_del() emits a KOBJ_REMOVE uevent and unbinds the driver while
the device descriptor is still expected to be valid.  As a result,
i3c_device_uevent() and a racing modalias_show() can observe a NULL
desc and fall back to an uninitialized stack struct i3c_device_info,
leaking kernel stack contents in the generated modalias.  Driver
.remove() callbacks may also encounter an unexpected NULL desc during
unbind.

Keep desc valid until device_unregister() has completed.  Since
device_unregister() drops the device reference and may free the device,
take an extra reference with get_device() before unregistering.  Clear
desc afterwards and release the extra reference with put_device().
This preserves the release-time invariant that desc must be NULL while
avoiding both the information leak and a potential use-after-free from
writing desc after the device has been released.

Reported-by: sashiko-bot@xxxxxxxxxx
Link: https://lore.kernel.org/linux-i3c/20260702190003.8BF741F000E9@xxxxxxxxxxxxxxx/
Fixes: 3a379bbcea0a ("i3c: Add core I3C infrastructure")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
 drivers/i3c/master.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
index 659c14c2c192..433dc7531701 100644
--- a/drivers/i3c/master.c
+++ b/drivers/i3c/master.c
@@ -3083,11 +3083,12 @@ static void i3c_master_unregister_i3c_devs(struct i3c_master_controller *master)
 		if (!i3cdev->dev)
 			continue;
 
-		i3cdev->dev->desc = NULL;
-		if (device_is_registered(&i3cdev->dev->dev))
+		if (device_is_registered(&i3cdev->dev->dev)) {
+			get_device(&i3cdev->dev->dev);
 			device_unregister(&i3cdev->dev->dev);
-		else
-			put_device(&i3cdev->dev->dev);
+		}
+		i3cdev->dev->desc = NULL;
+		put_device(&i3cdev->dev->dev);
 		i3cdev->dev = NULL;
 	}
 }
-- 
2.53.0