Add stricter checking on mac key lengths.

Negative lengths are always invalid.  The key length should also
be zero for hash algorithms that do not accept a key.

admbugs:	949
Reported by:	Yuval Kanarenstein <yuvalk@ssd-disclosure.com>
Reviewed by:	cem
MFC after:	1 week
Sponsored by:	Chelsio Communications
Differential Revision:	https://reviews.freebsd.org/D23094

sys/opencrypto/cryptodev.c

@@ -585,8 +585,8 @@ cryptof_ioctl(
 		if (thash) {
 			cria.cri_alg = thash->type;
 			cria.cri_klen = sop->mackeylen * 8;
-			if (thash->keysize != 0 &&
-			    sop->mackeylen > thash->keysize) {
+			if (sop->mackeylen > thash->keysize ||
+			    sop->mackeylen < 0) {
 				CRYPTDEB("invalid mac key length");
 				error = EINVAL;
 				SDT_PROBE1(opencrypto, dev, ioctl, error,