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Date:   Wed, 4 Sep 2019 14:51:10 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Christoph Hellwig <hch@lst.de>, linux-fsdevel@vger.kernel.org,
        linux-xfs@vger.kernel.org, Goldwyn Rodrigues <rgoldwyn@suse.de>,
        Matthew Bobrowski <mbobrowski@mbobrowski.org>
Subject: Re: [PATCH 2/2] iomap: move the iomap_dio_rw ->end_io callback
 into a structure
Message-ID: <20190904125110.GB17285@lst.de>
References: <20190903130327.6023-1-hch@lst.de> <20190903130327.6023-3-hch@lst.de> <20190903161446.GH29434@bombadil.infradead.org>
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On Tue, Sep 03, 2019 at 09:14:46AM -0700, Matthew Wilcox wrote:
> On Tue, Sep 03, 2019 at 03:03:27PM +0200, Christoph Hellwig wrote:
> > Add a new iomap_dio_ops structure that for now just contains the end_io
> > handler.  This avoid storing the function pointer in a mutable structure,
> > which is a possible exploit vector for kernel code execution, and prepares
> > for adding a submit_io handler that btrfs needs.
> 
> Is it really a security win?  If I can overwrite dio->end_io, I can as
> well overwrite dio->dops.

Which you'd then need to point to another place where you can stuff
function pointer.  Not impossible, but just another hoop to jump
through.  At least until we add run-time checks that ops structures
are in read-only memory, which sounds more sensible than some of the
other security hardening patches floating around.