linux-kernel - Re: [PATCH] asm-generic: {get,put}_user ptr argument evaluate only 1 time

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Date:	Thu, 16 Jul 2015 22:33:23 +0900
From:	Yoshinori Sato <ysato@...rs.sourceforge.jp>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] asm-generic: {get,put}_user ptr argument evaluate only 1 time

On Thu, 16 Jul 2015 15:40:31 +0900,
Geert Uytterhoeven wrote:
> 
> Hi Sato-san,
> 
> On Thu, Jul 16, 2015 at 7:15 AM, Yoshinori Sato
> <ysato@...rs.sourceforge.jp> wrote:
> > Current implemantation ptr argument evaluate 2 times.
> > It'll be an unexpected result.
> >
> > Signed-off-by: Yoshinori Sato <ysato@...rs.sourceforge.jp>
> 
> Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> 
> > ---
> >  include/asm-generic/uaccess.h | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/asm-generic/uaccess.h b/include/asm-generic/uaccess.h
> > index 72d8803..1b813fb 100644
> > --- a/include/asm-generic/uaccess.h
> > +++ b/include/asm-generic/uaccess.h
> > @@ -163,9 +163,10 @@ static inline __must_check long __copy_to_user(void __user *to,
> >
> >  #define put_user(x, ptr)                                       \
> >  ({                                                             \
> > +       __typeof__((ptr)) __p = (ptr);                          \
> >         might_fault();                                          \
> > -       access_ok(VERIFY_WRITE, ptr, sizeof(*ptr)) ?            \
> > -               __put_user(x, ptr) :                            \
> > +       access_ok(VERIFY_WRITE, __p, sizeof(*__p)) ?            \
> > +               __put_user(x, __p) :                            \
> 
> For safety, you may want to change "x" to "(x") while at it.

That's right.
I'll sent v2.

> >                 -EFAULT;                                        \
> >  })
> >
> > @@ -225,9 +226,10 @@ extern int __put_user_bad(void) __attribute__((noreturn));
> >
> >  #define get_user(x, ptr)                                       \
> >  ({                                                             \
> > +       __typeof__((ptr)) __p = (ptr);                          \
> >         might_fault();                                          \
> > -       access_ok(VERIFY_READ, ptr, sizeof(*ptr)) ?             \
> > -               __get_user(x, ptr) :                            \
> > +       access_ok(VERIFY_READ, __p, sizeof(*__p)) ?             \
> > +               __get_user(x, __p) :                            \
> 
> Likewise.
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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

-- 
Yoshinori Sato
<ysato@...rs.sourceforge.jp>
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