Re: KASAN: use-after-free Read in debugfs_remove (2)

[Greg KH]

On Mon, Apr 23, 2018 at 07:34:45PM +0900, Tetsuo Handa wrote:
> >From be88e559ec13f49b1c3aec2457c14c70f6b1926a Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Date: Mon, 23 Apr 2018 11:21:03 +0900
> Subject: [PATCH] bdi: Fix use after free bug in debugfs_remove()
> 
> syzbot is reporting use after free bug in debugfs_remove() [1].
> 
> This is because fault injection made memory allocation for
> debugfs_create_file() from bdi_debug_register() from bdi_register_va()
> fail and continued with setting WB_registered. But when debugfs_remove()
> is called from debugfs_remove(bdi->debug_dir) from bdi_debug_unregister()
>  from bdi_unregister() from release_bdi() because WB_registered was set
> by bdi_register_va(), IS_ERR_OR_NULL(bdi->debug_dir) == false despite
> debugfs_remove(bdi->debug_dir) was already called from bdi_register_va().
> 
> Fix this by making IS_ERR_OR_NULL(bdi->debug_dir) == true.
> 
> [1] https://syzkaller.appspot.com/bug?id=5ab4efd91a96dcea9b68104f159adf4af2a6dfc1
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Reported-by: syzbot <syzbot+049cb4ae097049dac137@xxxxxxxxxxxxxxxxxxxxxxxxx>
> Fixes: 97f07697932e6faf ("bdi: convert bdi_debug_register to int")
> Cc: weiping zhang <zhangweiping@xxxxxxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>

Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>