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

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Message-ID: <20210816093452.GB3950@lst.de>
Date:   Mon, 16 Aug 2021 11:34:52 +0200
From:   Christoph Hellwig <hch@....de>
To:     Hillf Danton <hdanton@...a.com>
Cc:     syzbot <syzbot+1fb38bb7d3ce0fa3e1c4@...kaller.appspotmail.com>,
        axboe@...nel.dk, Christoph Hellwig <hch@....de>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in bdev_evict_inode

On Sun, Aug 15, 2021 at 09:49:30PM +0800, Hillf Danton wrote:
> After putting bdi in wb_exit(), wb->bdi is no longer stable. To fix the uaf,
> add the WB_put bit to avoid derefering a unstable pointer.
> 
> Only for thoughts.

This doesn't help with the fact that the bdi needs to be alive
until after inode_detach_wb is called.  I posted a patch for that last
week, although I'm about to post a v2 as there are more lingering issues
in this area.