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    Subject[PATCH 4.4 20/20] drm/i915: fix use-after-free in page_flip_completed()
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Andrey Ryabinin <aryabinin@virtuozzo.com>

    commit 5351fbb1bf1413f6024892093528280769ca852f 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
    (cherry picked from commit 05c41f926fcc7ef838c80a6a99d84f67b4e0b824)
    Signed-off-by: Jani Nikula <jani.nikula@intel.com>
    Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    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
    @@ -3948,10 +3948,10 @@ static void page_flip_completed(struct i
    drm_crtc_vblank_put(&intel_crtc->base);

    wake_up_all(&dev_priv->pending_flip_queue);
    - queue_work(dev_priv->wq, &work->work);
    -
    trace_i915_flip_complete(intel_crtc->plane,
    work->pending_flip_obj);
    +
    + queue_work(dev_priv->wq, &work->work);
    }

    void intel_crtc_wait_for_pending_flips(struct drm_crtc *crtc)

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