avcodec/h264_parse: Check picture structure when initializing weight table

Fixes: runtime error: index 49 out of bounds for type 'int [48][2][2]'
Fixes: 2159/clusterfuzz-testcase-minimized-5267945972301824

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/h264_parse.c

@@ -26,7 +26,8 @@
 
 int ff_h264_pred_weight_table(GetBitContext *gb, const SPS *sps,
                               const int *ref_count, int slice_type_nos,
-                              H264PredWeightTable *pwt, void *logctx)
+                              H264PredWeightTable *pwt,
+                              int picture_structure, void *logctx)
 {
     int list, i, j;
     int luma_def, chroma_def;
@@ -98,6 +99,7 @@ int ff_h264_pred_weight_table(GetBitContext *gb, const SPS *sps,
             }
 
             // for MBAFF
+            if (picture_structure == PICT_FRAME) {
                 pwt->luma_weight[16 + 2 * i][list][0] = pwt->luma_weight[16 + 2 * i + 1][list][0] = pwt->luma_weight[i][list][0];
                 pwt->luma_weight[16 + 2 * i][list][1] = pwt->luma_weight[16 + 2 * i + 1][list][1] = pwt->luma_weight[i][list][1];
                 for (j = 0; j < 2; j++) {
@@ -105,6 +107,7 @@ int ff_h264_pred_weight_table(GetBitContext *gb, const SPS *sps,
                     pwt->chroma_weight[16 + 2 * i][list][j][1] = pwt->chroma_weight[16 + 2 * i + 1][list][j][1] = pwt->chroma_weight[i][list][j][1];
                 }
             }
+        }
         if (slice_type_nos != AV_PICTURE_TYPE_B)
             break;
     }

libavcodec/h264_parse.h

@@ -55,7 +55,8 @@ typedef struct H264POCContext {
 
 int ff_h264_pred_weight_table(GetBitContext *gb, const SPS *sps,
                               const int *ref_count, int slice_type_nos,
-                              H264PredWeightTable *pwt, void *logctx);
+                              H264PredWeightTable *pwt,
+                              int picture_structure, void *logctx);
 
 /**
  * Check if the top & left blocks are available if needed & change the

libavcodec/h264_parser.c

@@ -202,7 +202,7 @@ static int scan_mmco_reset(AVCodecParserContext *s, GetBitContext *gb,
     if ((p->ps.pps->weighted_pred && slice_type_nos == AV_PICTURE_TYPE_P) ||
         (p->ps.pps->weighted_bipred_idc == 1 && slice_type_nos == AV_PICTURE_TYPE_B))
         ff_h264_pred_weight_table(gb, p->ps.sps, ref_count, slice_type_nos,
-                                  &pwt, logctx);
+                                  &pwt, p->picture_structure, logctx);
 
     if (get_bits1(gb)) { // adaptive_ref_pic_marking_mode_flag
         int i;

libavcodec/h264_slice.c

@@ -1801,7 +1801,8 @@ static int h264_slice_header_parse(const H264Context *h, H264SliceContext *sl,
         (pps->weighted_bipred_idc == 1 &&
          sl->slice_type_nos == AV_PICTURE_TYPE_B)) {
         ret = ff_h264_pred_weight_table(&sl->gb, sps, sl->ref_count,
-                                  sl->slice_type_nos, &sl->pwt, h->avctx);
+                                  sl->slice_type_nos, &sl->pwt,
+                                  picture_structure, h->avctx);
         if (ret < 0)
             return ret;
     }