From d1c89acf70a794b78c5daaff206d734e36bbec6d Mon Sep 17 00:00:00 2001
From: Andrew Deason <adeason@sinenomine.net>
Date: Tue, 30 Jan 2024 20:44:48 -0600
Subject: [PATCH] roken: Declare ct_memcmp in hcrypto kernel roken.h

Currently, we build roken's ct.c for our kernel module to provide
ct_memcmp(). We declare a prototype for ct_memcmp() in krb5_locl.h,
and all of our kernel callers of ct_memcmp() include krb5_locl.h, so
all callers get a prototype and avoid "implicit declaration" compiler
warnings.

However, roken's ct.c itself does not include krb5_locl.h, so it
doesn't get a prototype for ct_memcmp(). This is dangerous, since if
the prototype ever slightly differs from the implementation for any
reason, it could cause a variety of issues.

This also causes warnings when building against a Linux 6.8 kernel
(which sets the -Wmissing-declarations and -Wmissing-prototypes
compiler flags as default). Linux 6.8 commit:
 'Makefile.extrawarn: turn on missing-prototypes globally' (0fcb70851f).

When building against a kernel with CONFIG_WERROR=y, the build fails.

We cannot change ct.c, since it is an external source file. To fix
this, instead move the prototype of ct_memcmp() to our stub
kernel-only roken.h header, which is included by ct.c. Make
krb5_locl.h also include roken.h when building kernel code, so all of
the ct_memcmp() callers also get the prototype.

While we're here, add some informative comments and an include guard
to our previously-blank roken.h stub.

Written in collaboration with cwills@sinenomine.net.

Reviewed-on: https://gerrit.openafs.org/15620
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit be236069e9d26339ed5f9939965bca0dd3f8bf4e)

Change-Id: I1112881938b0585263871f8f83d63b8909b12f0d
---

diff --git a/src/crypto/hcrypto/kernel/roken.h b/src/crypto/hcrypto/kernel/roken.h
index e69de29..f8c2334 100644
--- a/src/crypto/hcrypto/kernel/roken.h
+++ b/src/crypto/hcrypto/kernel/roken.h
@@ -0,0 +1,17 @@
+#ifndef OPENAFS_HCRYPTO_KERNEL_ROKEN_H
+#define OPENAFS_HCRYPTO_KERNEL_ROKEN_H
+
+/*
+ * This is a stub roken.h used for building roken code (or roken-using code) in
+ * the kernel. For userspace code, use a real roken.h. This just contains a few
+ * prototypes of roken functions we actually use in kernel code.
+ */
+
+#ifndef KERNEL
+# error "This header is for kernel code only"
+#endif
+
+/* ct.c */
+int ct_memcmp(const void *p1, const void *p2, size_t len);
+
+#endif /* OPENAFS_HCRYPTO_KERNEL_ROKEN_H */
diff --git a/src/crypto/rfc3961/krb5_locl.h b/src/crypto/rfc3961/krb5_locl.h
index eb279a9..6e70673 100644
--- a/src/crypto/rfc3961/krb5_locl.h
+++ b/src/crypto/rfc3961/krb5_locl.h
@@ -5,6 +5,7 @@
 #ifdef KERNEL
 
 #include "config.h"
+#include <roken.h>
 
 #else
 #include <afsconfig.h>
@@ -285,11 +286,6 @@
 krb5_error_code krb5_enctype_to_string(krb5_context context,
 				       krb5_enctype etype,
 				       char **string);
-#ifdef KERNEL
-/* Roken provides this in userspace, but we're on our own in the kernel. */
-int ct_memcmp(const void *p1, const void *p2, size_t len);
-#endif
-
 
 #include "crypto.h"