[PATCH] drm/i915: fix use-after-free in page_flip_completed()

[Chris Wilson]

On Thu, Jan 26, 2017 at 05:32:11PM +0300, Andrey Ryabinin wrote:
> page_flip_completed() dereferences 'work' variable after executing
> queue_work(). This is not safe as the 'work' item might be already freed
> by queued work:
> 
>     BUG: KASAN: use-after-free in page_flip_completed+0x3ff/0x490 at addr ffff8803dc010f90
>     Call Trace:
>      __asan_report_load8_noabort+0x59/0x80
>      page_flip_completed+0x3ff/0x490
>      intel_finish_page_flip_mmio+0xe3/0x130
>      intel_pipe_handle_vblank+0x2d/0x40
>      gen8_irq_handler+0x4a7/0xed0
>      __handle_irq_event_percpu+0xf6/0x860
>      handle_irq_event_percpu+0x6b/0x160
>      handle_irq_event+0xc7/0x1b0
>      handle_edge_irq+0x1f4/0xa50
>      handle_irq+0x41/0x70
>      do_IRQ+0x9a/0x200
>      common_interrupt+0x89/0x89
> 
>     Freed:
>      kfree+0x113/0x4d0
>      intel_unpin_work_fn+0x29a/0x3b0
>      process_one_work+0x79e/0x1b70
>      worker_thread+0x611/0x1460
>      kthread+0x241/0x3a0
>      ret_from_fork+0x27/0x40
> 
> Move queue_work() after	trace_i915_flip_complete() to fix this.
> 
> Fixes: e5510fac98a7 ("drm/i915: add tracepoints for flip requests & completions")
> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>

That's old, and indeed does seem to be present from that commit and not
exposed by something later.

Cc: <stable at vger.kernel.org> # v2.6.36+
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre