sunrpc: remove incorrect HMAC request initialization

make_checksum_hmac_md5() is allocating an HMAC transform and doing
crypto API calls in the following order:

    crypto_ahash_init()
    crypto_ahash_setkey()
    crypto_ahash_digest()

This is wrong because it makes no sense to init() the request before a
key has been set, given that the initial state depends on the key.  And
digest() is short for init() + update() + final(), so in this case
there's no need to explicitly call init() at all.

Before commit 9fa68f62 ("crypto: hash - prevent using keyed hashes
without setting key") the extra init() had no real effect, at least for
the software HMAC implementation.  (There are also hardware drivers that
implement HMAC-MD5, and it's not immediately obvious how gracefully they
handle init() before setkey().)  But now the crypto API detects this
incorrect initialization and returns -ENOKEY.  This is breaking NFS
mounts in some cases.

Fix it by removing the incorrect call to crypto_ahash_init().
Reported-by: Michael Young <m.a.young@durham.ac.uk>
Fixes: 9fa68f62 ("crypto: hash - prevent using keyed hashes without setting key")
Fixes: fffdaef2 ("gss_krb5: Add support for rc4-hmac encryption")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

net/sunrpc/auth_gss/gss_krb5_crypto.c

@@ -237,9 +237,6 @@ make_checksum_hmac_md5(struct krb5_ctx *kctx, char *header, int hdrlen,
 
 	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
 
-	err = crypto_ahash_init(req);
-	if (err)
-		goto out;
 	err = crypto_ahash_setkey(hmac_md5, cksumkey, kctx->gk5e->keylength);
 	if (err)
 		goto out;