[FFmpeg-devel] [PATCH v3] avcodec/decode: guard against NULL hw_frames_ctx

[Dmitry Rogozhkin <dmitry.v.rogozhkin-at-intel.com@ffmpeg.org>]

Guard against segfault running VLC decoding under msys2 [1]:

Thread 33 received signal SIGSEGV, Segmentation fault.
[Switching to Thread 37728.0xadd0]
ff_hwaccel_frame_priv_alloc (avctx=0x6447b00, hwaccel_picture_private=0x65dfd00)
    at libavcodec/decode.c:1848
1848        frames_ctx = (AVHWFramesContext *)avctx->hw_frames_ctx->data;
(gdb) bt
    at libavcodec/decode.c:1848
    at libavcodec/h264_slice.c:208
    first_slice=1) at libavcodec/h264_slice.c:1599
    at libavcodec/h264_slice.c:2130
    at libavcodec/h264dec.c:652
    got_frame=0x646e4b0, avpkt=0x64522c0) at libavcodec/h264dec.c:1048

(gdb) p avctx
$1 = (AVCodecContext *) 0x6447b00
(gdb) p avctx->hw_frames_ctx
$2 = (AVBufferRef *) 0x0

v2: check for free_frame_priv (Hendrik)
v3: return EINVAL (Christoph Reiter)

See[1]: https://github.com/msys2/MINGW-packages/pull/19050
Fixes: be07145109 ("avcodec: add AVHWAccel.free_frame_priv callback")
CC: Lynne <dev@lynne.ee>
CC: Christoph Reiter <reiter.christoph@gmail.com>
Signed-off-by: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
---
 libavcodec/decode.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/libavcodec/decode.c b/libavcodec/decode.c
index ad39021..50c3995 100644
--- a/libavcodec/decode.c
+++ b/libavcodec/decode.c
@@ -1838,17 +1838,25 @@ int ff_copy_palette(void *dst, const AVPacket *src, void *logctx)
 int ff_hwaccel_frame_priv_alloc(AVCodecContext *avctx, void **hwaccel_picture_private)
 {
     const FFHWAccel *hwaccel = ffhwaccel(avctx->hwaccel);
-    AVHWFramesContext *frames_ctx;
 
     if (!hwaccel || !hwaccel->frame_priv_data_size)
         return 0;
 
     av_assert0(!*hwaccel_picture_private);
 
-    frames_ctx = (AVHWFramesContext *)avctx->hw_frames_ctx->data;
-    *hwaccel_picture_private = ff_refstruct_alloc_ext(hwaccel->frame_priv_data_size, 0,
-                                                      frames_ctx->device_ctx,
-                                                      hwaccel->free_frame_priv);
+    if (hwaccel->free_frame_priv) {
+        AVHWFramesContext *frames_ctx;
+
+        if (!avctx->hw_frames_ctx)
+            return AVERROR(EINVAL);
+
+        *hwaccel_picture_private = ff_refstruct_alloc_ext(hwaccel->frame_priv_data_size, 0,
+                                                          frames_ctx->device_ctx,
+                                                          hwaccel->free_frame_priv);
+    } else {
+        *hwaccel_picture_private = ff_refstruct_allocz(hwaccel->frame_priv_data_size);
+    }
+
     if (!*hwaccel_picture_private)
         return AVERROR(ENOMEM);
 
-- 
1.8.3.1

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