Re: [PATCH] export: fix string handling of namespace in EXPORT_SYMBOL_NS

Masahiro Yamada
2022-01-11T19:15:01Z

On Sat, Jan 8, 2022 at 11:04 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> Commit c3a6cf19e695 ("export: avoid code duplication in
> include/linux/export.h") broke the ability for a defined string to be
> used as a namespace value. Fix this up by adding another layer of
> indirection to preserve the previous functionality.
>
> Fixes: c3a6cf19e695 ("export: avoid code duplication in include/linux/export.h")
> Cc: Miroslav Benes <mbenes@suse.cz>
> Cc: Emil Velikov <emil.l.velikov@gmail.com>
> Cc: Jessica Yu <jeyu@kernel.org>
> Cc: Quentin Perret <qperret@google.com>
> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> Cc: Matthias Maennich <maennich@google.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> Note, I found this while forward porting an out-of-tree Android kernel
> patch from 5.4 to 5.10 that used module namespaces to help wall-off vfs
> symbols from being used by non-filesystem modules. This issue does not
> affect any in-kernel code, so I am not so sure if it really is needed
> here, but it does restore the previous functionality that was being used
> in older kernels so it might be good to put back in case others want to
> do much the same thing.
>
> include/linux/export.h | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/export.h b/include/linux/export.h
> index 27d848712b90..9a992809f57d 100644
> --- a/include/linux/export.h
> +++ b/include/linux/export.h
> @@ -162,8 +162,10 @@ struct kernel_symbol {
>
> #define EXPORT_SYMBOL(sym) _EXPORT_SYMBOL(sym, "")
> #define EXPORT_SYMBOL_GPL(sym) _EXPORT_SYMBOL(sym, "_gpl")
> -#define EXPORT_SYMBOL_NS(sym, ns) __EXPORT_SYMBOL(sym, "", #ns)
> -#define EXPORT_SYMBOL_NS_GPL(sym, ns) __EXPORT_SYMBOL(sym, "_gpl", #ns)
> +#define _EXPORT_SYMBOL_NS(sym, ns) __EXPORT_SYMBOL(sym, "", #ns)
> +#define _EXPORT_SYMBOL_NS_GPL(sym, ns) __EXPORT_SYMBOL(sym, "_gpl", #ns)
> +#define EXPORT_SYMBOL_NS(sym, ns) _EXPORT_SYMBOL_NS(sym, ns)
> +#define EXPORT_SYMBOL_NS_GPL(sym, ns) _EXPORT_SYMBOL_NS_GPL(sym, ns)
>
> #endif /* !__ASSEMBLY__ */
>
> --
> 2.34.1
>

I see __stringify() a few files above.
So, you can use it here as well.

Does the following code work? (untested)

diff --git a/include/linux/export.h b/include/linux/export.h
index 27d848712b90..5910ccb66ca2 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -2,6 +2,8 @@
#ifndef _LINUX_EXPORT_H
#define _LINUX_EXPORT_H

+#include <linux/stringify.h>
+
/*
* Export symbols from the kernel to modules. Forked from module.h
* to reduce the amount of pointless cruft we feed to gcc when only
@@ -154,7 +156,6 @@ struct kernel_symbol {
#endif /* CONFIG_MODULES */

#ifdef DEFAULT_SYMBOL_NAMESPACE
-#include <linux/stringify.h>
#define _EXPORT_SYMBOL(sym, sec) __EXPORT_SYMBOL(sym, sec,
__stringify(DEFAULT_SYMBOL_NAMESPACE))
#else
#define _EXPORT_SYMBOL(sym, sec) __EXPORT_SYMBOL(sym, sec, "")
@@ -162,8 +163,8 @@ struct kernel_symbol {

#define EXPORT_SYMBOL(sym) _EXPORT_SYMBOL(sym, "")
#define EXPORT_SYMBOL_GPL(sym) _EXPORT_SYMBOL(sym, "_gpl")
-#define EXPORT_SYMBOL_NS(sym, ns) __EXPORT_SYMBOL(sym, "", #ns)
-#define EXPORT_SYMBOL_NS_GPL(sym, ns) __EXPORT_SYMBOL(sym, "_gpl", #ns)
+#define EXPORT_SYMBOL_NS(sym, ns) __EXPORT_SYMBOL(sym, "",
__stringify(ns))
+#define EXPORT_SYMBOL_NS_GPL(sym, ns) __EXPORT_SYMBOL(sym, "_gpl",
__stringify(ns))

#endif /* !__ASSEMBLY__ */

--
Best Regards
Masahiro Yamada