linux-kernel - Re: [syzbot] KASAN: use-after-free Read in disk_part_iter

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Date:   Mon, 22 Mar 2021 08:49:45 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Christoph Hellwig <hch@....de>
Cc:     syzbot <syzbot+8fede7e30c7cee0de139@...kaller.appspotmail.com>,
        Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [syzbot] KASAN: use-after-free Read in disk_part_iter_next (2)

On Mon, Mar 22, 2021 at 8:18 AM Christoph Hellwig <hch@....de> wrote:
>
> I've been running the reproducer on a KASAN enable VM for about
> 15 minutes now, but haven't been able to reproduce it.
>
> Is there a way to inject this proposed fix into the syzbot queue?

Hi Christoph,

Yes, since this bug has a reproducer, syzbot can test patches. See:

http://bit.do/syzbot#testing-patches

It would be, for example:

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master


> diff --git a/block/partitions/core.c b/block/partitions/core.c
> index 1a7558917c47d6..f5d5872b89d57e 100644
> --- a/block/partitions/core.c
> +++ b/block/partitions/core.c
> @@ -288,15 +288,12 @@ struct device_type part_type = {
>  void delete_partition(struct block_device *part)
>  {
>         xa_erase(&part->bd_disk->part_tbl, part->bd_partno);
> -       kobject_put(part->bd_holder_dir);
> -       device_del(&part->bd_device);
> -
> -       /*
> -        * Remove the block device from the inode hash, so that it cannot be
> -        * looked up any more even when openers still hold references.
> -        */
>         remove_inode_hash(part->bd_inode);
>
> +       synchronize_rcu();
> +
> +       kobject_put(part->bd_holder_dir);
> +       device_del(&part->bd_device);
>         put_device(&part->bd_device);
>  }

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