[PATCH] drm: fix drm_framebuffer cleanup.

[Rob Clark]

On Fri, Nov 9, 2012 at 1:39 AM, Inki Dae <inki.dae at samsung.com> wrote:
> This patch fixes access issue to invalid memory region.
>
> crtc had only one drm_framebuffer object so when framebuffer
> cleanup was requested after page flip, it'd try to disable
> hardware overlay to current crtc.
> But if current crtc points to another drm_framebuffer,
> This may induce invalid memory access.

btw, this should instead be done by holding a ref to the GEM
object(s)..  or these days you can increment the reference count on
the fb and let the fb hold ref's to the GEM object(s) (which makes it
a bit easier to deal with multi-planar formats)

BR,
-R

> Assume that some application are doing page flip with two
> drm_framebuffer objects. At this time, if second drm_framebuffer
> is set to current crtc and the cleanup to first drm_framebuffer
> is requested once drm release is requested, then first
> drm_framebuffer would be cleaned up without disabling
> hardware overlay because current crtc points to second
> drm_framebuffer. After that, gem buffer to first drm_framebuffer
> would be released and this makes dma access invalid memory region.
>
> This patch adds drm_framebuffer to drm_crtc structure as member
> and makes drm_framebuffer_cleanup function check if fb->crtc is
> same as desired fb. And also when setcrtc and pageflip are
> requested, it makes each drm_framebuffer point to current crtc.
>
> Signed-off-by: Inki Dae <inki.dae at samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park at samsung.com>
> ---
>  drivers/gpu/drm/drm_crtc.c |    7 ++++---
>  include/drm/drm_crtc.h     |    1 +
>  2 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index ef1b221..5c04bd4 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -386,7 +386,7 @@ void drm_framebuffer_remove(struct drm_framebuffer *fb)
>
>         /* remove from any CRTC */
>         list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
> -               if (crtc->fb == fb) {
> +               if (fb->crtc == crtc) {
>                         /* should turn off the crtc */
>                         memset(&set, 0, sizeof(struct drm_mode_set));
>                         set.crtc = crtc;
> @@ -2027,6 +2027,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
>         set.mode = mode;
>         set.connectors = connector_set;
>         set.num_connectors = crtc_req->count_connectors;
> +       fb->crtc = crtc;
>         set.fb = fb;
>         ret = crtc->funcs->set_config(&set);
>
> @@ -3635,8 +3636,8 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
>                         spin_unlock_irqrestore(&dev->event_lock, flags);
>                         kfree(e);
>                 }
> -       }
> -
> +       } else
> +               fb->crtc = crtc;
>  out:
>         mutex_unlock(&dev->mode_config.mutex);
>         return ret;
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index 3fa18b7..92889be 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -256,6 +256,7 @@ struct drm_framebuffer {
>         struct kref refcount;
>         struct list_head head;
>         struct drm_mode_object base;
> +       struct drm_crtc *crtc;
>         const struct drm_framebuffer_funcs *funcs;
>         unsigned int pitches[4];
>         unsigned int offsets[4];
> --
> 1.7.4.1
>
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