[PATCH] i2c: fix use-after-free in debugfs directory during adapter removal

[Yun Zhou]

Move debugfs_remove_recursive() after device_unregister() in
i2c_del_adapter() to fix a race condition where a new i2c device probe
can access the adapter's already-freed debugfs dentry.

The race occurs when:
1. i2c_del_adapter() calls debugfs_remove_recursive(adap->debugfs),
   freeing the debugfs dentry.
2. Before device_unregister() completes, another thread writes to the
   sysfs 'new_device' attribute, triggering i2c_device_probe().
3. i2c_device_probe() calls debugfs_create_dir() with the stale
   adapter->debugfs pointer, causing a GPF in start_dirop() when
   trying to lock the freed inode.

Reported-by: syzbot+1e3d934ee3cff1ac188b@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=1e3d934ee3cff1ac188b
Fixes: 73febd775bdb ("i2c: create debugfs entry per adapter")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Yun Zhou <yun.zhou@xxxxxxxxxxxxx>
---
 drivers/i2c/i2c-core-base.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 3ec04787a737..9b0f3c783e9c 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -1826,8 +1826,6 @@ void i2c_del_adapter(struct i2c_adapter *adap)
 
 	i2c_host_notify_irq_teardown(adap);
 
-	debugfs_remove_recursive(adap->debugfs);
-
 	/* wait until all references to the device are gone
 	 *
 	 * FIXME: This is old code and should ideally be replaced by an
@@ -1839,6 +1837,8 @@ void i2c_del_adapter(struct i2c_adapter *adap)
 	device_unregister(&adap->dev);
 	wait_for_completion(&adap->dev_released);
 
+	debugfs_remove_recursive(adap->debugfs);
+
 	/* free bus id */
 	mutex_lock(&core_lock);
 	idr_remove(&i2c_adapter_idr, adap->nr);
-- 
2.43.0