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    SubjectRe: [PATCH 1/4] um: Fix _FORTIFY_SOURCE=2 support for kernel modules
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    On Wed, Jun 29, 2011 at 17:42, Richard Weinberger <richard@nod.at> wrote:
    > Am Mittwoch 29 Juni 2011, 17:37:54 schrieb Vitaliy Ivanov:
    >> On Tue, Jun 28, 2011 at 1:15 AM, Richard Weinberger <richard@nod.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@openwrt.org>
    >> > Reported-by: Florian Fainelli <florian@openwrt.org>
    >> > Signed-off-by: Richard Weinberger <richard@nod.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().

    What about changing harddog_user.c to not use sprintf(), but snprintf()?

    Besides, the code does look fishy to me:

    char pid_buf[sizeof("nnnnn\0")];
    sprintf(pid_buf, "%d", os_getpid());

    os_getpid() returns int:

    int os_getpid(void)
    {
    return syscall(__NR_getpid);
    }

    but sys_getpid() returns long.

    So we truncate a (possibly 64-bit number) to 32-bit, and format it
    in a buffer that has space for 5 chars only...

    Gr{oetje,eeting}s,

                            Geert

    --
    Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

    In personal conversations with technical people, I call myself a hacker. But
    when I'm talking to journalists I just say "programmer" or something like that.
                                    -- Linus Torvalds
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