mov: don't overwrite existing indexes.

Prevents all kind of badness if files contain multiple
indexes.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org

libavformat/mov.c

@@ -1727,6 +1727,7 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
     unsigned int stps_index = 0;
     unsigned int i, j;
     uint64_t stream_size = 0;
+    AVIndexEntry *mem;
 
     /* adjust first dts according to edit list */
     if (sc->time_offset && mov->time_scale > 0) {
@@ -1755,12 +1756,13 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
 
         if (!sc->sample_count)
             return;
-        if (sc->sample_count >= UINT_MAX / sizeof(*st->index_entries))
+        if (sc->sample_count >= UINT_MAX / sizeof(*st->index_entries) - st->nb_index_entries)
             return;
-        st->index_entries = av_malloc(sc->sample_count*sizeof(*st->index_entries));
-        if (!st->index_entries)
+        mem = av_realloc(st->index_entries, (st->nb_index_entries + sc->sample_count) * sizeof(*st->index_entries));
+        if (!mem)
             return;
-        st->index_entries_allocated_size = sc->sample_count*sizeof(*st->index_entries);
+        st->index_entries = mem;
+        st->index_entries_allocated_size = (st->nb_index_entries + sc->sample_count) * sizeof(*st->index_entries);
 
         for (i = 0; i < sc->chunk_count; i++) {
             current_offset = sc->chunk_offsets[i];
@@ -1844,12 +1846,13 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
         }
 
         av_dlog(mov->fc, "chunk count %d\n", total);
-        if (total >= UINT_MAX / sizeof(*st->index_entries))
+        if (total >= UINT_MAX / sizeof(*st->index_entries) - st->nb_index_entries)
             return;
-        st->index_entries = av_malloc(total*sizeof(*st->index_entries));
-        if (!st->index_entries)
+        mem = av_realloc(st->index_entries, (st->nb_index_entries + total) * sizeof(*st->index_entries));
+        if (!mem)
             return;
-        st->index_entries_allocated_size = total*sizeof(*st->index_entries);
+        st->index_entries = mem;
+        st->index_entries_allocated_size = (st->nb_index_entries + total) * sizeof(*st->index_entries);
 
         // populate index
         for (i = 0; i < sc->chunk_count; i++) {