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

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Message-ID: <20210825092731.GA1328@lst.de>
Date:   Wed, 25 Aug 2021 11:27:31 +0200
From:   Christoph Hellwig <hch@....de>
To:     Hillf Danton <hdanton@...a.com>
Cc:     syzbot <syzbot+2c98885bcd769f56b6d6@...kaller.appspotmail.com>,
        axboe@...nel.dk, josef@...icpanda.com, linux-block@...r.kernel.org,
        Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        nbd@...er.debian.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in nbd_genl_connect (2)

On Wed, Aug 25, 2021 at 04:55:25PM +0800, Hillf Danton wrote:
> Because no nbd is kfreed without being removed from the nbd idr, finding
> a freed nbd in the idr with nbd_index_mutex held means the nbd is not a
> valid pointer, and fix the uaf by cutting the chance for invalid nbd.
> 
> Only for thoughts now.

That is a bug, but not really the problem here.  I think the issue
is the completion issue that Tetsuo reported.  Looking into that at
the moment.