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Subject[PATCH 3.2 01/59] drm/i915: fix use-after-free in page_flip_completed()
3.2.92-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andrey Ryabinin <aryabinin@virtuozzo.com>

commit 05c41f926fcc7ef838c80a6a99d84f67b4e0b824 upstream.

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@virtuozzo.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170126143211.24013-1-aryabinin@virtuozzo.com
[bwh: Backported to 3.2:
- Uusing schedule_work() instead of queue_work()
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/gpu/drm/i915/intel_display.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6995,9 +6995,9 @@ static void do_intel_finish_page_flip(st
&obj->pending_flip.counter);

wake_up(&dev_priv->pending_flip_queue);
- schedule_work(&work->work);
-
trace_i915_flip_complete(intel_crtc->plane, work->pending_flip_obj);
+
+ schedule_work(&work->work);
}

void intel_finish_page_flip(struct drm_device *dev, int pipe)
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