avformat/mov: Error on too large stsd entry counts.

Entries are always at least 8 bytes per the parsing code, so if we
see an impossible entry count avoid massive allocations. This is
similar to an existing check in mov_read_stsc().

Since ff_mov_read_stsd_entries() does eof checks, an alternative
approach could be to clamp the entry count to atom.size / 8.
Signed-off-by: Dale Curtis <dalecurtis@chromium.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mov.c

@@ -2558,7 +2558,8 @@ static int mov_read_stsd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     avio_rb24(pb); /* flags */
     entries = avio_rb32(pb);
 
-    if (entries <= 0) {
+    /* Each entry contains a size (4 bytes) and format (4 bytes). */
+    if (entries <= 0 || entries > atom.size / 8) {
         av_log(c->fc, AV_LOG_ERROR, "invalid STSD entries %d\n", entries);
         return AVERROR_INVALIDDATA;
     }