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Date:   Fri, 18 May 2018 23:23:08 +0300
From:   Roman Kagan <rkagan@virtuozzo.com>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] idr: fix invalid ptr dereference on item delete
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        Matthew Wilcox <willy@infradead.org>,
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On Fri, May 18, 2018 at 10:50:25AM -0700, Matthew Wilcox wrote:
> It'd be nice if you cc'd the person who wrote the code you're patching.
> You'd get a response a lot quicker than waiting until I happened to
> notice the email in a different forum.

I sent it to someone called "Matthew Wilcox <mawilcox@microsoft.com>".
Also I cc'd that guy when I only started to point the finger at IDR as
the suspected culprit in that syzcaller report.  I thought it was him
who wrote the code...

> Thanks for finding the situation that leads to the bug.  Your fix is
> incorrect; it's legitimate to store a NULL value at offset 0, and
> your patch makes it impossible to delete.  Fortunately, the test-suite
> covers that case ;-)

How do you build it?  I wish I had it when debugging but I got linking
errors due to missing spin_lock_init, so I decided it wasn't up-to-date.

Thanks,
Roman.

P.S. I'll forward your message to all the recepients of my patch, to let
them know it's wrong and you have a better one.