Re: [PATCH V2 03/17] asm-generic: fcntl: compat: Remove duplicate definitions

[Guo Ren]

On Mon, Jan 10, 2022 at 9:35 PM Arnd Bergmann <arnd@xxxxxxxx> wrote:
>
> On Tue, Dec 28, 2021 at 3:39 PM <guoren@xxxxxxxxxx> wrote:
> >
> > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> >
> > Remove duplicate F_GETLK64,F_SETLK64,F_SETLKW64 definitions in
> > arch/*/include/asm/compat.h.
> >
> > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
>
> Unfortunately, this one does not look correct to me:
>
> > @@ -116,7 +116,7 @@
> >  #define F_GETSIG       11      /* for sockets. */
> >  #endif
> >
> > -#ifndef CONFIG_64BIT
> > +#if !defined(CONFIG_64BIT) || defined(CONFIG_COMPAT)
> >  #ifndef F_GETLK64
> >  #define F_GETLK64      12      /*  using 'struct flock64' */
> >  #define F_SETLK64      13
>
> The problem here is that include/uapi/ headers cannot contain checks for
> CONFIG_* symbols because those may have different meanings in user space
> compared to kernel.
>
> This is a preexisting problem in the header, but I think the change
> makes it worse.
>
> With the current behavior, user space will always see the definitions,
> unless it happens to have its own definition for CONFIG_64BIT already.
> On 64-bit parisc, this has the effect of defining the macros to the
> same values as F_SETOWN/F_SETSIG/F_GETSIG, which is potentially
> harmful. On MIPS, it uses values that are different from the 32-bit numbers
> but are otherwise unused. Everywhere else, we get the definition from
> the 32-bit architecture in user space, which will do nothing in the kernel.
>
> The correct check for a uapi header would be to test for
> __BITS_PER_LONG==32. We should probably do that here, but
> this won't help you move the definitions, and it is a user-visible change
> as the incorrect definition will no longer be visible. [Adding Jeff and Bruce
> (the flock mainainers) to Cc for additional feedback on this]
>
> For your series, I would suggest just moving the macro definitions to
> include/linux/compat.h along with the 'struct compat_flock64'
> definition, and leaving the duplicate one in the uapi header unchanged
> until we have decided on a solution.
Okay.

>
>         Arnd



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/