[FFmpeg-cvslog] avcodec/hevc/hevcdec: Don't add to null pointer

[Vitaly Buka]

ffmpeg | branch: master | Vitaly Buka <vitalybuka at google.com> | Thu Jan 16 15:49:19 2025 -0800| [c5287178b4dc373e763f7cd49703a6e3192aab3a] | committer: James Almer

avcodec/hevc/hevcdec: Don't add to null pointer

`POS(1,` and `POS(2,` may trigger UBSAN report:
"runtime error: applying non-zero offset 304 to null pointer"

Looks like values are not used without `chroma_format_idc`,
so maybe there is no other issues than the UB.

Can't reproduce with "fate".

Signed-off-by: Vitaly Buka <vitalybuka at google.com>
Signed-off-by: James Almer <jamrial at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=c5287178b4dc373e763f7cd49703a6e3192aab3a
---

 libavcodec/hevc/hevcdec.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/libavcodec/hevc/hevcdec.c b/libavcodec/hevc/hevcdec.c
index 3655ed0039..7d3e844945 100644
--- a/libavcodec/hevc/hevcdec.c
+++ b/libavcodec/hevc/hevcdec.c
@@ -2040,9 +2040,10 @@ static void hls_prediction_unit(HEVCLocalContext *lc,
                                 int x0, int y0, int nPbW, int nPbH,
                                 int log2_cb_size, int partIdx, int idx)
 {
-#define POS(c_idx, x, y)                                                              \
+#define POS(c_idx, x, y)                                                          \
+    &s->cur_frame->f->data[c_idx] ?                                               \
     &s->cur_frame->f->data[c_idx][((y) >> sps->vshift[c_idx]) * linesize[c_idx] + \
-                           (((x) >> sps->hshift[c_idx]) << sps->pixel_shift)]
+                           (((x) >> sps->hshift[c_idx]) << sps->pixel_shift)] : NULL
     const HEVCContext *const s = lc->parent;
     int merge_idx = 0;
     struct MvField current_mv = {{{ 0 }}};