drm_prime: double free bug

This commit fixes a bug where handle for a framebuffer gets double
freed.
It seems to happen that the same prime fd gets two framebuffers.
As the prime fd is the same the resulting prime handle is also the
same.
This means one handle but 2 framebuffers and can lead to the following
chain:

1. The first framebuffer gets deleted the handle gets also freed via
the ioctl.

2. In startup phase not all 4 dumb buffers for overlay drawing
are set up. It can happen that the last dumb buffer gets the
handle we freed above.

3. The second framebuffer gets freed and the handle will be
freed again resulting that the 4's dumb buffer handle is not
backed by a buffer.

4. Drm prime continues to assign handles to its prime fds an
will lead to have this handle which was just freed to
reassign again but to an prime buffer.

5.Now the overlay should be drawn into dumb buffer 4 which
still has the same handle but is backed by the wrong buffer.
This leads to two different behaviors:

- MPV crashes as the drm prime buffers size als calculated
by the decoder output format. The overlay output format
differs and it takes more space. SO the size check
in kernel fails.

- MPV is continuing play. This happens when the decoders
allocates a bigger buffer than needed for the overlay.
For example overlay is Full HD and decoder output is 4k.
This leads to the behavior das the overlay wil be drawn
into the wrong buffer as its a drm prime buffer and results
in a flicker every fourth step.

1 files changed, 9 insertions, 3 deletions

diff --git a/video/out/opengl/hwdec_drmprime_drm.c b/video/out/opengl/hwdec_drmprime_drm.c
index bc9f548019..66d3497807 100644
--- a/video/out/opengl/hwdec_drmprime_drm.c
+++ b/video/out/opengl/hwdec_drmprime_drm.c
@@ -55,6 +55,8 @@ struct priv {
     struct mp_rect src, dst;
 
     int display_w, display_h;
+
+    struct drm_prime_handle_refs handle_refs;
 };
 
 static void set_current_frame(struct ra_hwdec *hw, struct drm_frame *frame)
@@ -68,7 +70,7 @@ static void set_current_frame(struct ra_hwdec *hw, struct drm_frame *frame)
     // is not being displayed when we release it.
 
     if (p->ctx) {
-        drm_prime_destroy_framebuffer(p->log, p->ctx->fd, &p->old_frame.fb);
+        drm_prime_destroy_framebuffer(p->log, p->ctx->fd, &p->old_frame.fb, &p->handle_refs);
     }
 
     mp_image_setrefp(&p->old_frame.image, p->last_frame.image);
@@ -183,7 +185,7 @@ static int overlay_frame(struct ra_hwdec *hw, struct mp_image *hw_image,
             int dstw = MP_ALIGN_UP(p->dst.x1 - p->dst.x0, 2);
             int dsth = MP_ALIGN_UP(p->dst.y1 - p->dst.y0, 2);
 
-            if (drm_prime_create_framebuffer(p->log, p->ctx->fd, desc, srcw, srch, &next_frame.fb)) {
+            if (drm_prime_create_framebuffer(p->log, p->ctx->fd, desc, srcw, srch, &next_frame.fb, &p->handle_refs)) {
                 ret = -1;
                 goto fail;
             }
@@ -222,7 +224,7 @@ static int overlay_frame(struct ra_hwdec *hw, struct mp_image *hw_image,
     return 0;
 
  fail:
-    drm_prime_destroy_framebuffer(p->log, p->ctx->fd, &next_frame.fb);
+    drm_prime_destroy_framebuffer(p->log, p->ctx->fd, &next_frame.fb, &p->handle_refs);
     return ret;
 }
 
@@ -288,6 +290,10 @@ static int init(struct ra_hwdec *hw)
         goto err;
     }
 
+    if (has_prime) {
+        drm_prime_init_handle_ref_count(p, &p->handle_refs);
+    }
+
     disable_video_plane(hw);
 
     p->hwctx = (struct mp_hwdec_ctx) {