avcodec/h264: Increase field_poc to 64bit in ff_h264_init_poc() to detect overflows

Fixes: Integer overflow
Fixes: 5746/clusterfuzz-testcase-minimized-6270097623613440

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

libavcodec/h264_parse.c

@@ -271,7 +271,7 @@ int ff_h264_init_poc(int pic_field_poc[2], int *pic_poc,
                      int picture_structure, int nal_ref_idc)
 {
     const int max_frame_num = 1 << sps->log2_max_frame_num;
-    int field_poc[2];
+    int64_t field_poc[2];
 
     pc->frame_num_offset = pc->prev_frame_num_offset;
     if (pc->frame_num < pc->prev_frame_num)
@@ -337,6 +337,10 @@ int ff_h264_init_poc(int pic_field_poc[2], int *pic_poc,
         field_poc[1] = poc;
     }
 
+    if (   field_poc[0] != (int)field_poc[0]
+        || field_poc[1] != (int)field_poc[1])
+        return AVERROR_INVALIDDATA;
+
     if (picture_structure != PICT_BOTTOM_FIELD)
         pic_field_poc[0] = field_poc[0];
     if (picture_structure != PICT_TOP_FIELD)

libavcodec/h264_parser.c

@@ -449,8 +449,10 @@ static inline int parse_nal_units(AVCodecParserContext *s,
             /* Decode POC of this picture.
              * The prev_ values needed for decoding POC of the next picture are not set here. */
             field_poc[0] = field_poc[1] = INT_MAX;
-            ff_h264_init_poc(field_poc, &s->output_picture_number, sps,
+            ret = ff_h264_init_poc(field_poc, &s->output_picture_number, sps,
                              &p->poc, p->picture_structure, nal.ref_idc);
+            if (ret < 0)
+                goto fail;
 
             /* Continue parsing to check if MMCO_RESET is present.
              * FIXME: MMCO_RESET could appear in non-first slice.

libavcodec/h264_slice.c

@@ -1607,8 +1607,10 @@ static int h264_field_start(H264Context *h, const H264SliceContext *sl,
             (h->mb_height * h->mb_stride - 1) * sizeof(*h->slice_table));
     }
 
-    ff_h264_init_poc(h->cur_pic_ptr->field_poc, &h->cur_pic_ptr->poc,
+    ret = ff_h264_init_poc(h->cur_pic_ptr->field_poc, &h->cur_pic_ptr->poc,
                      h->ps.sps, &h->poc, h->picture_structure, nal->ref_idc);
+    if (ret < 0)
+        return ret;
 
     memcpy(h->mmco, sl->mmco, sl->nb_mmco * sizeof(*h->mmco));
     h->nb_mmco = sl->nb_mmco;