mov: validate number of DataReferenceBox entries against box size

Avoids a 2G memory allocation and parsing of random data in
mov_read_dref(). The fuzzed sample sample.mp4_s224424 triggers this.

libavformat/mov.c

@@ -351,6 +351,7 @@ static int mov_read_chpl(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     return 0;
 }
 
+#define MIN_DATA_ENTRY_BOX_SIZE 12
 static int mov_read_dref(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 {
     AVStream *st;
@@ -364,7 +365,8 @@ static int mov_read_dref(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
     avio_rb32(pb); // version + flags
     entries = avio_rb32(pb);
-    if (entries >= UINT_MAX / sizeof(*sc->drefs))
+    if (entries >  (atom.size - 1) / MIN_DATA_ENTRY_BOX_SIZE + 1 ||
+        entries >= UINT_MAX / sizeof(*sc->drefs))
         return AVERROR_INVALIDDATA;
     av_free(sc->drefs);
     sc->drefs = av_mallocz(entries * sizeof(*sc->drefs));