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    SubjectRe: KASAN: use-after-free Read in debugfs_remove (2)
    On Mon 23-04-18 19:34:45, Tetsuo Handa wrote:
    > From be88e559ec13f49b1c3aec2457c14c70f6b1926a Mon Sep 17 00:00:00 2001
    > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    > 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@I-love.SAKURA.ne.jp>
    > Reported-by: syzbot <syzbot+049cb4ae097049dac137@syzkaller.appspotmail.com>
    > Fixes: 97f07697932e6faf ("bdi: convert bdi_debug_register to int")
    > Cc: weiping zhang <zhangweiping@didichuxing.com>
    > Cc: Jan Kara <jack@suse.cz>
    > Cc: Jens Axboe <axboe@kernel.dk>

    Looks good to me. You can add:

    Reviewed-by: Jan Kara <jack@suse.cz>

    Jens, can you please merge this fix? Thanks!

    Honza

    > ---
    > mm/backing-dev.c | 1 +
    > 1 file changed, 1 insertion(+)
    >
    > diff --git a/mm/backing-dev.c b/mm/backing-dev.c
    > index 023190c..7fe73fa 100644
    > --- a/mm/backing-dev.c
    > +++ b/mm/backing-dev.c
    > @@ -115,6 +115,7 @@ static int bdi_debug_register(struct backing_dev_info *bdi, const char *name)
    > bdi, &bdi_debug_stats_fops);
    > if (!bdi->debug_stats) {
    > debugfs_remove(bdi->debug_dir);
    > + bdi->debug_dir = NULL;
    > return -ENOMEM;
    > }
    >
    > --
    > 1.8.3.1
    >
    --
    Jan Kara <jack@suse.com>
    SUSE Labs, CR

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