SUNRPC: Add RFC 8009 encryption KUnit tests

RFC 8009 provides sample encryption results. Add KUnit tests to
ensure our implementation derives the expected results for the
provided sample input.

I hate how large this test is, but using non-standard key usage
values means rfc8009_encrypt_case() can't simply reuse ->import_ctx
to allocate and key its ciphers; and the test provides its own
confounders, which means krb5_etm_encrypt() can't be used directly.
Tested-by: Scott Mayhew <smayhew@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/auth_gss/gss_krb5_crypto.c

@@ -886,8 +886,25 @@ gss_krb5_aes_decrypt(struct krb5_ctx *kctx, u32 offset, u32 len,
 	return ret;
 }
 
-static u32
-krb5_etm_checksum(struct crypto_sync_skcipher *cipher,
+/**
+ * krb5_etm_checksum - Compute a MAC for a GSS Wrap token
+ * @cipher: an initialized cipher transform
+ * @tfm: an initialized hash transform
+ * @body: xdr_buf containing an RPC message (body.len is the message length)
+ * @body_offset: byte offset into @body to start checksumming
+ * @cksumout: OUT: a buffer to be filled in with the computed HMAC
+ *
+ * Usually expressed as H = HMAC(K, IV | ciphertext)[1..h] .
+ *
+ * Caller provides the truncation length of the output token (h) in
+ * cksumout.len.
+ *
+ * Return values:
+ *   %GSS_S_COMPLETE: Digest computed, @cksumout filled in
+ *   %GSS_S_FAILURE: Call failed
+ */
+VISIBLE_IF_KUNIT
+u32 krb5_etm_checksum(struct crypto_sync_skcipher *cipher,
 		      struct crypto_ahash *tfm, const struct xdr_buf *body,
 		      int body_offset, struct xdr_netobj *cksumout)
 {
@@ -936,6 +953,7 @@ krb5_etm_checksum(struct crypto_sync_skcipher *cipher,
 	kfree_sensitive(checksumdata);
 	return err ? GSS_S_FAILURE : GSS_S_COMPLETE;
 }
+EXPORT_SYMBOL_IF_KUNIT(krb5_etm_checksum);
 
 /**
  * krb5_etm_encrypt - Encrypt using the RFC 8009 rules

net/sunrpc/auth_gss/gss_krb5_internal.h

@@ -221,6 +221,9 @@ int krb5_cbc_cts_encrypt(struct crypto_sync_skcipher *cts_tfm,
 			 struct crypto_sync_skcipher *cbc_tfm, u32 offset,
 			 struct xdr_buf *buf, struct page **pages,
 			 u8 *iv, unsigned int ivsize);
+u32 krb5_etm_checksum(struct crypto_sync_skcipher *cipher,
+		      struct crypto_ahash *tfm, const struct xdr_buf *body,
+		      int body_offset, struct xdr_netobj *cksumout);
 #endif
 
 #endif /* _NET_SUNRPC_AUTH_GSS_KRB5_INTERNAL_H */