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

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Message-ID: <YmkB7JdGPFQD+5Nt@kroah.com>
Date:   Wed, 27 Apr 2022 10:42:20 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Masahiro Yamada <masahiroy@...nel.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 Wed, Jan 12, 2022 at 04:14:00AM +0900, Masahiro Yamada wrote:
> 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__ */

Sorry for the long delay, but yes, this does seem to resolve the issue
for me.  I'll respin this and resend, thanks!

greg k-h