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

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Date:   Mon, 10 Jan 2022 17:38:54 +0000
From:   Matthias Maennich <maennich@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     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>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [PATCH] export: fix string handling of namespace in
 EXPORT_SYMBOL_NS

On Sat, Jan 08, 2022 at 03:04:15PM +0100, Greg Kroah-Hartman 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>

Reviewed-by: Matthias Maennich <maennich@...gle.com>

Cheers,
Matthias

>---
>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
>