On Apr 6, 2012, at 9:54 AM, Chris Wilson wrote: > On Fri, 6 Apr 2012 09:46:46 -0400, Xi Wang <xi.wang at 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 at 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. Let it overflow the 32-bit multiplication and turn the call to: exec2_list = kmalloc(0, ...); Then the subsequent call to i915_gem_do_execbuffer(..., exec2_list) may read exec2_list, which is out of bounds. - xi
