i2c: core: fix debugfs UAF on adapter removal

i2c_del_adapter() frees the adapter's debugfs directory before it
unregisters the adapter device, but the new_device sysfs attribute
stays writable until device_del(). A write racing with removal still
reaches i2c_device_probe(), which passes the freed adap->debugfs to
debugfs_create_dir() as the new client's parent:

  BUG: KASAN: slab-use-after-free in lookup_noperm_common+0x407/0x430
  Read of size 4 at addr ffff88803ef87810 by task syz.0.61/6090
   lookup_noperm_common+0x407/0x430
   simple_start_creating+0x9c/0x110
   debugfs_start_creating+0xdb/0x1a0
   debugfs_create_dir+0x24/0x350
   i2c_device_probe+0x814/0xbf0

It's technically possible to create a client after i2c_deregister_clients
has run. That client will never be unregistered and make
wait_for_completion hang.

Close the window by removing the new_device attribute at the start of
i2c_del_adapter(). device_remove_file() will drain any clients left.

Fixes: 73febd775bdb ("i2c: create debugfs entry per adapter")
Reported-by: syzbot+23ad911c819b923238b7@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=23ad911c819b923238b7
Signed-off-by: Vasileios Almpanis <vasilisalmpanis@gmail.com>
Cc: <stable@vger.kernel.org> # v6.8+
Tested-by: syzbot+23ad911c819b923238b7@syzkaller.appspotmail.com
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://patch.msgid.link/20260812-i2c-v2-1-5efaab4c3334@gmail.com

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index fb25704219c7552e34ffab0d53faf23e2377dcba..ddaacf876dada92c1ffafd2d5d1e4b83c8f0101f 100644 (file)
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -1816,6 +1816,12 @@ void i2c_del_adapter(struct i2c_adapter *adap)
                return;
        }
 
+       /*
+        * This drains any in-flight writers, so all
+        * clients will be caught by i2c_deregister_clients().
+        */
+       device_remove_file(&adap->dev, &dev_attr_new_device);
+
        i2c_acpi_remove_space_handler(adap);
 
        i2c_deregister_clients(adap);