Re: perf_copy_attr pointer arithmetic weirdness

[Ingo Molnar <mingo@elte.hu>]

* Peter Zijlstra <peterz@infradead.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@telenet.be>
> 
> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

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

	Ingo