overlayfs: move xattr tables to .rodata

This makes it harder for accidental or malicious changes to
ovl_trusted_xattr_handlers or ovl_user_xattr_handlers at runtime.

Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: linux-unionfs@vger.kernel.org
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20230930050033.41174-28-wedsonaf@gmail.com
Acked-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: wedsonaf

fs/overlayfs/super.c

@@ -484,13 +484,13 @@ static const struct xattr_handler ovl_other_xattr_handler = {
 	.set = ovl_other_xattr_set,
 };
 
-static const struct xattr_handler *ovl_trusted_xattr_handlers[] = {
+static const struct xattr_handler * const ovl_trusted_xattr_handlers[] = {
 	&ovl_own_trusted_xattr_handler,
 	&ovl_other_xattr_handler,
 	NULL
 };
 
-static const struct xattr_handler *ovl_user_xattr_handlers[] = {
+static const struct xattr_handler * const ovl_user_xattr_handlers[] = {
 	&ovl_own_user_xattr_handler,
 	&ovl_other_xattr_handler,
 	NULL