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

[Matthias Maennich]

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@xxxxxxx>
> Cc: Emil Velikov <emil.l.velikov@xxxxxxxxx>
> Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> Cc: Quentin Perret <qperret@xxxxxxxxxx>
> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Cc: Matthias Maennich <maennich@xxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

Reviewed-by: Matthias Maennich <maennich@xxxxxxxxxx>

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