dm crypt: fix crash by adding missing check for auth key size

If dm-crypt uses authenticated mode with separate MAC, there are two
concatenated part of the key structure - key(s) for encryption and
authentication key.

Add a missing check for authenticated key length.  If this key length is
smaller than actually provided key, dm-crypt now properly fails instead
of crashing.

Fixes: ef43aa38 ("dm crypt: add cryptographic data integrity protection (authenticated encryption)")
Cc: stable@vger.kernel.org # 4.12+
Reported-by: Salah Coronya <salahx@yahoo.com>
Signed-off-by: Milan Broz <gmazyland@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-crypt.c

@@ -1954,10 +1954,15 @@ static int crypt_setkey(struct crypt_config *cc)
 	/* Ignore extra keys (which are used for IV etc) */
 	subkey_size = crypt_subkey_size(cc);
 
-	if (crypt_integrity_hmac(cc))
+	if (crypt_integrity_hmac(cc)) {
+		if (subkey_size < cc->key_mac_size)
+			return -EINVAL;
+
 		crypt_copy_authenckey(cc->authenc_key, cc->key,
 				      subkey_size - cc->key_mac_size,
 				      cc->key_mac_size);
+	}
+
 	for (i = 0; i < cc->tfms_count; i++) {
 		if (crypt_integrity_hmac(cc))
 			r = crypto_aead_setkey(cc->cipher_tfm.tfms_aead[i],