crypto: vmac - require a block cipher with 128-bit block size

The VMAC template assumes the block cipher has a 128-bit block size, but
it failed to check for that.  Thus it was possible to instantiate it
using a 64-bit block size cipher, e.g. "vmac(cast5)", causing
uninitialized memory to be used.

Add the needed check when instantiating the template.

Fixes: f1939f7c ("crypto: vmac - New hash algorithm for intel_txt support")
Cc: <stable@vger.kernel.org> # v2.6.32+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/vmac.c

@@ -655,6 +655,10 @@ static int vmac_create(struct crypto_template *tmpl, struct rtattr **tb)
 	if (IS_ERR(alg))
 		return PTR_ERR(alg);
 
+	err = -EINVAL;
+	if (alg->cra_blocksize != 16)
+		goto out_put_alg;
+
 	inst = shash_alloc_instance("vmac", alg);
 	err = PTR_ERR(inst);
 	if (IS_ERR(inst))