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Date:   Mon, 26 Nov 2018 18:36:19 +0800
From:   PanBian <bianpan2016@163.com>
To:     Carlos Maiolino <cmaiolino@redhat.com>
Cc:     "Darrick J. Wong" <darrick.wong@oracle.com>,
        linux-xfs@vger.kernel.org, Brian Foster <bfoster@redhat.com>,
        Dave Chinner <dchinner@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] xfs: libxfs: move xfs_perag_put late
Message-ID: <20181126103619.GA95394@bp>
Reply-To: PanBian <bianpan2016@163.com>
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 <20181126093139.cgojlmtubzuzdb23@hades.usersys.redhat.com>
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On Mon, Nov 26, 2018 at 10:31:39AM +0100, Carlos Maiolino wrote:
> On Sat, Nov 24, 2018 at 05:44:20PM +0800, Pan Bian wrote:
> > The function xfs_alloc_get_freelist calls xfs_perag_put to drop the
> > reference. In this case, pag may be released. However,
> > pag->pagf_btreeblks is read and write after the put operation. This may
> > result in a use-after-free bug. This patch moves the put operation late.
> > 
> 
> The patch looks reasonable, can you detail more how did you find it? Via code
> inspection of you hit this user-after-free in some way?

I wrote a tool to check such bugs statically. It first scans the source code 
to extract paired alloc/free functions. Equipped with such functions, it
performs an intra-procedural data flow analysis to detect mismatched
alloc/free bugs and use-after-free bugs.

Best regards,
Pan Bian