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

Greg Kroah-Hartman
2022-04-27T08:42:34Z

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@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__ */

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