4.16-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> commit f53823c18131e755905b4f654196fd2cc3953f6e upstream. 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> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/backing-dev.c | 1 + 1 file changed, 1 insertion(+) --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -126,6 +126,7 @@ static int bdi_debug_register(struct bac bdi, &bdi_debug_stats_fops); if (!bdi->debug_stats) { debugfs_remove(bdi->debug_dir); + bdi->debug_dir = NULL; return -ENOMEM; }
