linux-kernel - Re: perf_copy_attr pointer arithmetic weirdness

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Date:	Sat, 19 Sep 2009 10:06:09 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ian Schram <ischram@...enet.be>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	xiaoguangrong@...fujitsu.com, Paul Mackerras <paulus@...ba.org>
Subject: Re: perf_copy_attr pointer arithmetic weirdness


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, 2009-09-18 at 21:26 +0200, Ian Schram wrote:
> > There is some -to me at least- weird code in per_copy_attr. Which supposedly
> > checks that all bytes trailing a struct are zero.
> > 
> > It doesn't seem to get pointer arithmetic right. Since it increments
> > an iterating pointer by sizeof(unsigned long) rather than 1.
> > 
> > I believe this has an impact on the exploitability of the recent buffer overflow
> > in the perf_copy_attr function. I'm pretty sure I'm not the only one who noticed
> > this, but i couldn't find it being mentioned. For some reason people prefer
> > mmaping something at zero these days?
> > 
> > I have appended a patch locating the issue. The PTR_ALIGN stuff right above it
> > doesn't seem to take any boundary conditions into account which is probably not
> > a good thing either.
> 
> sizeof(struct perf_counter_attr) should always be a multiple of u64, and
> we can indeed read beyond the tail boundary, but that should be ok,
> worst that can happen is that we fail the read..
> 
> Ugh on the ptr arith, one wonders how many stupid bugs one can make in
> such a piece of code... :/
> 
> > signed-of-by Ian Schram <ischram@...enet.be>
> 
> Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

Ian, you meant Signed-off-by, not signed-of-by, right?

	Ingo
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