avcodec/hevc/hevcdec: Do not allow slices to depend on failed slices

An alternative would be to leave the context unchanged on failure of hls_slice_header()

Fixes: out of array access
Fixes: NULL pointer dereference
Fixes: 69584/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HEVC_fuzzer-5931086299856896
Fixes: 69724/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HEVC_fuzzer-5104066422702080
Fixes: 70422/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HEVC_fuzzer-5908731129298944

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 5d9544cfb0)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/hevcdec.c

@@ -658,6 +658,10 @@ static int hls_slice_header(HEVCContext *s)
 
         if (s->ps.pps->dependent_slice_segments_enabled_flag)
             sh->dependent_slice_segment_flag = get_bits1(gb);
+        if (sh->dependent_slice_segment_flag && !s->slice_initialized) {
+            av_log(s->avctx, AV_LOG_ERROR, "Independent slice segment missing.\n");
+            return AVERROR_INVALIDDATA;
+        }
 
         slice_address_length = av_ceil_log2(s->ps.sps->ctb_width *
                                             s->ps.sps->ctb_height);
@@ -946,9 +950,6 @@ static int hls_slice_header(HEVCContext *s)
         } else {
             sh->slice_loop_filter_across_slices_enabled_flag = s->ps.pps->seq_loop_filter_across_slices_enabled_flag;
         }
-    } else if (!s->slice_initialized) {
-        av_log(s->avctx, AV_LOG_ERROR, "Independent slice segment missing.\n");
-        return AVERROR_INVALIDDATA;
     }
 
     sh->num_entry_point_offsets = 0;
@@ -3037,8 +3038,11 @@ static int decode_nal_unit(HEVCContext *s, const H2645NAL *nal)
     case HEVC_NAL_RASL_N:
     case HEVC_NAL_RASL_R:
         ret = hls_slice_header(s);
-        if (ret < 0)
+        if (ret < 0) {
+            // hls_slice_header() does not cleanup on failure thus the state now is inconsistant so we cannot use it on depandant slices
+            s->slice_initialized = 0;
             return ret;
+        }
         if (ret == 1) {
             ret = AVERROR_INVALIDDATA;
             goto fail;