linux-kernel - Re: [PATCH] export: fix string handling of namespace in EXPORT_SYMBOL

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Message-ID: <CAK7LNASC+PBFqbsAFWbePoEjL5d21z95Nb84AHTkPjiMcWG_Gg@mail.gmail.com>
Date:   Wed, 12 Jan 2022 04:14:00 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Jessica Yu <jeyu@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        Matthias Maennich <maennich@...gle.com>
Subject: Re: [PATCH] export: fix string handling of namespace in EXPORT_SYMBOL_NS

On Sat, Jan 8, 2022 at 11:04 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.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@...e.cz>
> Cc: Emil Velikov <emil.l.velikov@...il.com>
> Cc: Jessica Yu <jeyu@...nel.org>
> Cc: Quentin Perret <qperret@...gle.com>
> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Cc: Matthias Maennich <maennich@...gle.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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