[FFmpeg-cvslog] avformat/mov: validate chunk_count vs stsc_data

[chcunningham]

ffmpeg | branch: release/3.4 | chcunningham <chcunningham at chromium.org> | Thu Feb  7 14:58:17 2019 -0800| [08b159fd0d9ddcc3a26fe96ca754d77f1de3c40a] | committer: Michael Niedermayer

avformat/mov: validate chunk_count vs stsc_data

Bad content may contain stsc boxes with a first_chunk index that
exceeds stco.entries (chunk_count). This ammends the existing check to
include cases where chunk_count == 0. It also patches up the case
when stsc refers to unknown chunks, but stts has no samples (so we
can simply ignore stsc).

Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 1c15449ca9a5bfa387868ac55628397273da761f)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=08b159fd0d9ddcc3a26fe96ca754d77f1de3c40a
---

 libavformat/mov.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 27c103ba43..19884b73e8 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -2496,8 +2496,11 @@ static inline int64_t mov_get_stsc_samples(MOVStreamContext *sc, unsigned int in
 
     if (mov_stsc_index_valid(index, sc->stsc_count))
         chunk_count = sc->stsc_data[index + 1].first - sc->stsc_data[index].first;
-    else
+    else {
+        // Validation for stsc / stco  happens earlier in mov_read_stsc + mov_read_trak.
+        av_assert0(sc->stsc_data[index].first <= sc->chunk_count);
         chunk_count = sc->chunk_count - (sc->stsc_data[index].first - 1);
+    }
 
     return sc->stsc_data[index].count * (int64_t)chunk_count;
 }
@@ -3822,6 +3825,13 @@ static int mov_read_trak(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
     c->trak_index = -1;
 
+    // Here stsc refers to a chunk not described in stco. This is technically invalid,
+    // but we can overlook it (clearing stsc) whenever stts_count == 0 (indicating no samples).
+    if (!sc->chunk_count && !sc->stts_count && sc->stsc_count) {
+        sc->stsc_count = 0;
+        av_freep(&sc->stsc_data);
+    }
+
     /* sanity checks */
     if ((sc->chunk_count && (!sc->stts_count || !sc->stsc_count ||
                             (!sc->sample_size && !sc->sample_count))) ||
@@ -3830,7 +3840,7 @@ static int mov_read_trak(MOVContext *c, AVIOContext *pb, MOVAtom atom)
                st->index);
         return 0;
     }
-    if (sc->chunk_count && sc->stsc_count && sc->stsc_data[ sc->stsc_count - 1 ].first > sc->chunk_count) {
+    if (sc->stsc_count && sc->stsc_data[ sc->stsc_count - 1 ].first > sc->chunk_count) {
         av_log(c->fc, AV_LOG_ERROR, "stream %d, contradictionary STSC and STCO\n",
                st->index);
         return AVERROR_INVALIDDATA;