Re: [PATCH 1/2] drm/i915: fix integer overflow in i915_gem_execbuffer2()

[Chris Wilson <chris@chris-wilson.co.uk>]

On Fri, 6 Apr 2012 10:01:36 -0400, Xi Wang <xi.wang@gmail.com> wrote:
> On Apr 6, 2012, at 9:54 AM, Chris Wilson wrote:
> 
> > On Fri, 6 Apr 2012 09:46:46 -0400, Xi Wang <xi.wang@gmail.com> wrote:
> >> On Apr 6, 2012, at 9:36 AM, Chris Wilson wrote:
> >> 
> >>> On Fri,  6 Apr 2012 08:58:18 -0400, Xi Wang <xi.wang@gmail.com> wrote:
> >>>> A large args->buffer_count from userspace may overflow the allocation
> >>>> size, leading to out-of-bounds access.
> >>>> 
> >>>> Use kmalloc_array() to avoid that.
> >>> 
> >>> I can safely say that exec list larger than 4GiB is going to be an
> >>> illegal operation and would rather the ioctl failed outright with
> >>> EINVAL.
> >> 
> >> On 32-bit platform?
> > 
> > On any platform. The largest it can legally be is a few tens of megabytes.
> 
> IDGI.  First we come to i915_gem_execbuffer2() from ioctl:
> 
>   exec2_list = kmalloc(sizeof(*exec2_list)*args->buffer_count, ...);
> 
> args->buffer_count is passed from userspace so it can be any value.

That I agreed with, I just disagree with how you chose to handle it.
Rather than continue on and attempt to vmalloc a large array we should
just fail the ioctl with EINVAL.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre