[PATCH weston v3] pixman: Destroy pixman images when underlying buffer is destroyed

[Pekka Paalanen]

On Tue, 19 Nov 2013 15:44:44 +0100
Lubomir Rintel <lkundrak at v3.sk> wrote:

> While the pixman image might be attached, the underlying buffer might be
> already gone under certain circumstances. This is easily reproduced by
> attempting to resize gnome-terminal on a fbdev backend.
> 
> $ WAYLAND_DEBUG=1 strace -emunmap weston --backend=fbdev-backend.so
> ...
> [1524826.942] wl_shm at 7.create_pool(new id wl_shm_pool at 23, fd 40, 1563540)
> [1524827.315] wl_shm_pool at 23.create_buffer(new id wl_buffer at 24, 0, 759, 515, 3036, 0)
> ...
> [1524829.488] wl_surface at 14.attach(wl_buffer at 24, 0, 0)
> [1524829.766] wl_surface at 14.set_buffer_scale(1)
> [1524829.904] wl_surface at 14.damage(0, 0, 759, 515)
> [1524830.248] wl_surface at 14.frame(new id wl_callback at 25)
> [1524830.450] wl_surface at 14.commit()
> ...
> [1524846.706] wl_shm at 7.create_pool(new id wl_shm_pool at 26, fd 40, 1545000)
> [1524847.215] wl_shm_pool at 26.create_buffer(new id wl_buffer at 27, 0, 750, 515, 3000, 0)
> [1524847.735] wl_buffer at 24.destroy()
> [1524847.953]  -> wl_display at 1.delete_id(24)
> [1524848.144] wl_shm_pool at 23.destroy()
> munmap(0xb5b2e000, 1563540)             = 0
> [1524849.021]  -> wl_display at 1.delete_id(23)
> [1524849.425] wl_surface at 14.attach(wl_buffer at 27, 0, 0)
> [1524849.730] wl_surface at 14.set_buffer_scale(1)
> [1524849.821] wl_surface at 14.damage(0, 0, 750, 515)
> <No commit yet, so drawing is attempted from older buffer that used to be
>  attached to the surface, which happens to come from a destroyed pool,
>  resulting it an invalid read from address 0xb5b2e000>
> 
> Signed-off-by: Lubomir Rintel <lkundrak at v3.sk>
> ---
> Changes to v2:
>   - Added listener instead of checking the buffer mapping,
>     as suggested by Pekka Paalanen
>   - Added more context to the commit message
> Changes to v3:
>   - Removed unnecessary buffer unreferences and signal handler unhook
>     of itself after it was called, suggested by Pekka Paalanen
>   - Unhook the signal if we destroy the surface or reattach the buffer
>     to avoid circular attachment or call after the surface state is gone
> 
> On Tue, 2013-11-19 at 14:23 +0200, Pekka Paalanen wrote:
> > Otherwise looks good.
> > 
> > We have the trade-off between less code (the first version of the
> > patch), and not having a lingering ps->image referring to unusable
> > memory (the second version of the patch). IMHO the latter is cleaner.
> 
> I've found another issue; if a surface is removed, the destroy handler
> will use-after-free the ps. Therefore I'm unhooking it once before ps
> vanishes if it exists and only if it exists -- as the image data might
> as well be a color fill without actual buffer attached.
> 
> I found no better way of discovering whether it's appropriate to unhook
> (buffer attached) or not (nothing attached or color-filled) that looking
> at the notify callback pointer. It works well enough for me byt maybe
> there's a cleaner solution?

Right, looks like it should work. Another way would be to ensure, that
buffer_destroy_listener.link is always removable. You can do that by
initializing it with and always after remove calling wl_list_init() on
it. That way wl_list_remove()'ing it is never illegal.


Thanks,
pq

>  src/pixman-renderer.c | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/src/pixman-renderer.c b/src/pixman-renderer.c
> index b719829..c2c6ca9 100644
> --- a/src/pixman-renderer.c
> +++ b/src/pixman-renderer.c
> @@ -42,6 +42,7 @@ struct pixman_surface_state {
>  	pixman_image_t *image;
>  	struct weston_buffer_reference buffer_ref;
>  
> +	struct wl_listener buffer_destroy_listener;
>  	struct wl_listener surface_destroy_listener;
>  	struct wl_listener renderer_destroy_listener;
>  };
> @@ -450,6 +451,22 @@ pixman_renderer_flush_damage(struct weston_surface *surface)
>  }
>  
>  static void
> +buffer_state_handle_buffer_destroy(struct wl_listener *listener, void *data)
> +{
> +	struct pixman_surface_state *ps;
> +
> +	ps = container_of(listener, struct pixman_surface_state,
> +			  buffer_destroy_listener);
> +
> +	if (ps->image) {
> +		pixman_image_unref(ps->image);
> +		ps->image = NULL;
> +	}
> +
> +	ps->buffer_destroy_listener.notify = NULL;
> +}
> +
> +static void
>  pixman_renderer_attach(struct weston_surface *es, struct weston_buffer *buffer)
>  {
>  	struct pixman_surface_state *ps = get_surface_state(es);
> @@ -499,6 +516,13 @@ pixman_renderer_attach(struct weston_surface *es, struct weston_buffer *buffer)
>  		buffer->width, buffer->height,
>  		wl_shm_buffer_get_data(shm_buffer),
>  		wl_shm_buffer_get_stride(shm_buffer));
> +
> +	if (ps->buffer_destroy_listener.notify)
> +		wl_list_remove(&ps->buffer_destroy_listener.link);
> +	ps->buffer_destroy_listener.notify =
> +		buffer_state_handle_buffer_destroy;
> +	wl_signal_add(&buffer->destroy_signal,
> +		      &ps->buffer_destroy_listener);
>  }
>  
>  static void
> @@ -506,7 +530,8 @@ pixman_renderer_surface_state_destroy(struct pixman_surface_state *ps)
>  {
>  	wl_list_remove(&ps->surface_destroy_listener.link);
>  	wl_list_remove(&ps->renderer_destroy_listener.link);
> -
> +	if (ps->buffer_destroy_listener.notify)
> +		wl_list_remove(&ps->buffer_destroy_listener.link);
>  
>  	ps->surface->renderer_state = NULL;
>