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

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Message-ID: <20220614071757.GA1207@lst.de>
Date:   Tue, 14 Jun 2022 09:17:57 +0200
From:   Christoph Hellwig <hch@....de>
To:     dsterba@...e.cz,
        syzbot <syzbot+d2dd123304b4ae59f1bd@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, clm@...com, dsterba@...e.com,
        hch@....de, josef@...icpanda.com, linux-btrfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, syzkaller-bugs@...glegroups.com,
        willy@...radead.org
Subject: Re: [syzbot] KASAN: use-after-free Read in
 copy_page_from_iter_atomic (2)

On Mon, Jun 13, 2022 at 09:39:12PM +0200, David Sterba wrote:
> On Fri, Jun 10, 2022 at 12:10:19AM -0700, syzbot wrote:
> > syzbot has bisected this issue to:
> > 
> > commit 4cd4aed63125ccd4efc35162627827491c2a7be7
> > Author: Christoph Hellwig <hch@....de>
> > Date:   Fri May 27 08:43:20 2022 +0000
> > 
> >     btrfs: fold repair_io_failure into btrfs_repair_eb_io_failure
> 
> Josef also reported a crash and found a bug in the patch, now added as
> fixup that'll be in for-next:

The patch looks correct to me.  Two things to note here:

 - I hadn't realized you had queued up the series.  I've actually
   started to merge some of my bio work with the bio split at
   submission time work from Qu and after a few iterations I think
   I would do the repair code a bit differently based on that.
   Can you just drop the series for now?
 - I find it interesting that syzbot hits btrfs metadata repair.
   xfstests seems to have no coverage and I could not come up with
   a good idea how to properly test it.  Does anyone have a good
   idea on how to intentially corrupt metadata in a deterministic
   way?