[FFmpeg-devel] [PATCH v2] avcodec/hevc/hevcdec: Do not allow slices to depend on failed slices

[Michael Niedermayer]

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

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
---
 libavcodec/hevc/hevcdec.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/libavcodec/hevc/hevcdec.c b/libavcodec/hevc/hevcdec.c
index 0e4b26dad3b..80d59ab1916 100644
--- a/libavcodec/hevc/hevcdec.c
+++ b/libavcodec/hevc/hevcdec.c
@@ -621,6 +621,10 @@ static int hls_slice_header(SliceHeader *sh, const HEVCContext *s, GetBitContext
 
         if (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, "dependent slice failed\n");
+            return AVERROR_INVALIDDATA;
+        }
 
         slice_address_length = av_ceil_log2(sps->ctb_width *
                                             sps->ctb_height);
@@ -893,9 +897,6 @@ static int hls_slice_header(SliceHeader *sh, const HEVCContext *s, GetBitContext
         } else {
             sh->slice_loop_filter_across_slices_enabled_flag = 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;
@@ -3155,8 +3156,11 @@ static int decode_slice(HEVCContext *s, const H2645NAL *nal, GetBitContext *gb)
     int ret;
 
     ret = hls_slice_header(&s->sh, s, gb);
-    if (ret < 0)
+    if (ret < 0) {
+        //The code is not capable to rewind from an error, the state now is inconsistant so we cannot use it on depandant slices
+        s->slice_initialized = 0;
         return ret;
+    }
 
     if ((s->avctx->skip_frame >= AVDISCARD_BIDIR && s->sh.slice_type == HEVC_SLICE_B) ||
         (s->avctx->skip_frame >= AVDISCARD_NONINTRA && s->sh.slice_type != HEVC_SLICE_I) ||
-- 
2.45.2