linux-kernel - Re: [PATCH 1/4] um: Fix _FORTIFY_SOURCE=2 support for kernel modules

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Message-Id: <201106291742.24137.richard@nod.at>
Date:	Wed, 29 Jun 2011 17:42:23 +0200
From:	Richard Weinberger <richard@....at>
To:	Vitaliy Ivanov <vitalivanov@...il.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: [PATCH 1/4] um: Fix _FORTIFY_SOURCE=2 support for kernel modules

Am Mittwoch 29 Juni 2011, 17:37:54 schrieb Vitaliy Ivanov:
> On Tue, Jun 28, 2011 at 1:15 AM, Richard Weinberger <richard@....at> wrote:
> > When UML is compiled with _FORTIFY_SOURCE we have to
> > export all _chk() functions which are used in modules.
> > For now it's only the case for __sprintf_chk().
> > 
> > Tested-by: Florian Fainelli <florian@...nwrt.org>
> > Reported-by: Florian Fainelli <florian@...nwrt.org>
> > Signed-off-by: Richard Weinberger <richard@....at>
> > ---
> >  arch/um/os-Linux/user_syms.c |    5 +++++
> >  1 files changed, 5 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/um/os-Linux/user_syms.c b/arch/um/os-Linux/user_syms.c
> > index 05f5ea8..45ffe46 100644
> > --- a/arch/um/os-Linux/user_syms.c
> > +++ b/arch/um/os-Linux/user_syms.c
> > @@ -113,3 +113,8 @@ EXPORT_SYMBOL(__stack_smash_handler);
> > 
> >  extern long __guard __attribute__((weak));
> >  EXPORT_SYMBOL(__guard);
> > +
> > +#ifdef _FORTIFY_SOURCE
> > +extern int __sprintf_chk(char *str, int flag, size_t strlen, const char
> > *format); +EXPORT_SYMBOL(__sprintf_chk);
> > +#endif
> > --
> 
> Can you please clarify why it's needed? I use FORTIFY_SOURCES on
> Linus' tree UML on Ubuntu w/ no problems and w/o this patch...

The problem appears only when a UML kernel module is using sprintf().
E.g: CONFIG_UML_WATCHDOG.
Then loading the module will fail because of the missing symbol __sprintf_chk().

Thanks,
//richard
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