[FFmpeg-devel] [PATCH] avutil/hwcontext_dxva2: No longer improperly freeing IDirect3DSurface9 objects

Aaron Levinson alevinsn at aracnet.com
Tue May 16 14:09:28 EEST 2017


Purpose: No longer improperly freeing IDirect3DSurface9 objects in
hwcontext_dxva2.c.  Added dxva2_pool_release_dummy() and using it in
call to av_buffer_create() in dxva2_pool_alloc().  Prior to this
change, av_buffer_create() was called with NULL for the third
argument, which indicates that av_buffer_default_free() should be used
to free the buffer's data.  Eventually, it gets to buffer_pool_free()
and calls buf->free() on a surface object (which is
av_buffer_default_free()).  This can result in a crash when the debug
version of the C-runtime is used on Windows.  While it doesn't appear
to result in a crash when the release version of the C-runtime is used
on Windows, it likely results in memory corruption, since av_free() is
being called on memory that was allocated using
IDirectXVideoAccelerationService::CreateSurface().

Signed-off-by: Aaron Levinson <alevinsn at aracnet.com>
---
 libavutil/hwcontext_dxva2.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/libavutil/hwcontext_dxva2.c b/libavutil/hwcontext_dxva2.c
index 4ed0d56..6c41788 100644
--- a/libavutil/hwcontext_dxva2.c
+++ b/libavutil/hwcontext_dxva2.c
@@ -121,6 +121,13 @@ static void dxva2_frames_uninit(AVHWFramesContext *ctx)
     }
 }
 
+static void dxva2_pool_release_dummy(void *opaque, uint8_t *data)
+{
+    // important not to free anything here--data is a surface object
+    // associated with the call to CreateSurface(), and these surfaces are
+    // released in dxva2_frames_uninit()
+}
+
 static AVBufferRef *dxva2_pool_alloc(void *opaque, int size)
 {
     AVHWFramesContext      *ctx = (AVHWFramesContext*)opaque;
@@ -130,7 +137,7 @@ static AVBufferRef *dxva2_pool_alloc(void *opaque, int size)
     if (s->nb_surfaces_used < hwctx->nb_surfaces) {
         s->nb_surfaces_used++;
         return av_buffer_create((uint8_t*)s->surfaces_internal[s->nb_surfaces_used - 1],
-                                sizeof(*hwctx->surfaces), NULL, 0, 0);
+                                sizeof(*hwctx->surfaces), dxva2_pool_release_dummy, 0, 0);
     }
 
     return NULL;
-- 
2.10.1.windows.1



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