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


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