jpeg2000: Check that we have enough components for MCT

Avoid overread.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavcodec/jpeg2000dec.c

@@ -343,6 +343,13 @@ static int get_cod(Jpeg2000DecoderContext *s, Jpeg2000CodingStyle *c,
     tmp.nlayers    = bytestream2_get_be16u(&s->g);
     tmp.mct        = bytestream2_get_byteu(&s->g); // multiple component transformation
 
+    if (tmp.mct && s->ncomponents < 3) {
+        av_log(s->avctx, AV_LOG_ERROR,
+               "MCT %d with too few components (%d)\n",
+               tmp.mct, s->ncomponents);
+        return AVERROR_INVALIDDATA;
+    }
+
     if ((ret = get_cox(s, &tmp)) < 0)
         return ret;