linux-kernel - Re: [PATCH] block: Avoid accessing an already freed kobject in delete

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Date:   Tue, 6 Jul 2021 06:12:17 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Rajat Asthana <thisisrast7@...il.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Rajat Asthana <rajatasthana4@...il.com>, axboe@...nel.dk,
        damien.lemoal@....com, jack@...e.cz, rafael@...nel.org,
        syzbot+7d6c5587ec9cff5be65c@...kaller.appspotmail.com,
        linux-kernel@...r.kernel.org, ming.lei@...hat.com,
        linux-block@...r.kernel.org, hare@...e.de,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] block: Avoid accessing an already freed kobject in
 delete_partition

On Tue, Jul 06, 2021 at 06:31:11AM +0530, Rajat Asthana wrote:
> 
> 
> On 03/07/21 10:56 am, Christoph Hellwig wrote:
> > This should be fixed properly by:
> > 
> > "block: check disk exist before trying to add partition"
> 
> Hi Christoph, thanks a lot for suggesting this fix. I have been
> working on implementing this and have tried the following:
> - I checked if the the kobject of device structure embedded in
>   gendisk structure is not NULL, to add the partition.
>   This didn't work.
> 
> - Then I checked the if kobject of the block_device struct (part0)
>   embedded in the gendisk struct is not NULL, to add the partition.
>   This also didn't work.
> 
> - Then I checked the i_state of the bd_inode field of block_device
>   struct embedded in the gendisk struct. I checked if the I_FREEING or
>   I_WILL_FREE fields are not set. The reason behind doing this was
>   to confirm that we only create partition on the disks which are not
>   being freed.
> 
> Am I going in the right direction? Can you point me to the correct
> direction if I am not?

No.  There should be no need to check anything, but the code needs
to ensure that the block device is alive.  I think the above mentioned
patch (now in Jens' tree) does that, so please try it.