SUNRPC: Improve Kerberos confounder generation

Other common Kerberos implementations use a fully random confounder
for encryption. The reason for this is explained in the new comment
added by this patch. The current get_random_bytes() implementation
does not exhaust system entropy.

Since confounder generation is part of Kerberos itself rather than
the GSS-API Kerberos mechanism, the function is renamed and moved.

Note that light top-down analysis shows that the SHA-1 transform
is by far the most CPU-intensive part of encryption. Thus we do not
expect this change to result in a significant performance impact.
However, eventually it might be necessary to generate an independent
stream of confounders for each Kerberos context to help improve I/O
parallelism.

Reviewed-by: Simo Sorce <simo@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/net/sunrpc/auth_gss/gss_krb5_internal.h b/net/sunrpc/auth_gss/gss_krb5_internal.h
new file mode 100644
index 000000000000..16a83d507075
--- /dev/null
+++ b/net/sunrpc/auth_gss/gss_krb5_internal.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 or BSD-3-Clause */
+/*
+ * SunRPC GSS Kerberos 5 mechanism internal definitions
+ *
+ * Copyright (c) 2022 Oracle and/or its affiliates.
+ */
+
+#ifndef _NET_SUNRPC_AUTH_GSS_KRB5_INTERNAL_H
+#define _NET_SUNRPC_AUTH_GSS_KRB5_INTERNAL_H
+
+void krb5_make_confounder(u8 *p, int conflen);
+
+#endif /* _NET_SUNRPC_AUTH_GSS_KRB5_INTERNAL_H */