linux-kernel - Re: [RFC 2/2] Arch: Kconfig: Disable obsolete syscalls

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Date:	Wed, 12 Feb 2014 21:23:19 +0800
From:	Fabian Frederick <fabf@...net.be>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, rdunlap <rdunlap@...radead.org>
Subject: Re: [RFC 2/2] Arch: Kconfig: Disable obsolete syscalls

On Wed, 12 Feb 2014 13:13:14 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Wed, 12 Feb 2014 21:04:40 +0800 Fabian Frederick <fabf@...net.be> wrote:
> 
> > fs: sysfs syscall: Disable if DISABLE_OBSOLETE_SYSCALLS
> > 
> > sysfs syscall is obsolete (cf man sysfs).
> > 
> > Don't define fs_index, fs_name, fs_maxindex functions when
> > DISABLE_OBSOLETE_SYSCALLS is defined.
> > In that case, SYSCALL_DEFINE3(sysfs...) returns automatically -EINVAL.
> > 
> 
> Are there any other syscalls which will fall under
> CONFIG_DISABLE_OBSOLETE_SYSCALLS?
> 
> There are plenty of other syscalls which can be disabled via Kconfig. 
> As far as I recall, they each use their own CONFIG_foo.
> 
> So I'm thinking it would be better to add a CONFIG_SYS_SYSFS or
> whatever which enables this syscall only.  It defaults to y.

I thought it would be interesting to directly disable all of its but 
honestly I don't know if there are a lot so your solution seems interesting :)
Thanks for your help !

> 
> > --- a/fs/filesystems.c
> > +++ b/fs/filesystems.c
> > @@ -121,6 +121,7 @@ int unregister_filesystem(struct file_system_type * fs)
> >  
> >  EXPORT_SYMBOL(unregister_filesystem);
> >  
> > +#ifndef CONFIG_DISABLE_OBSOLETE_SYSCALLS
> >  static int fs_index(const char __user * __name)
> >  {
> >  	struct file_system_type * tmp;
> > @@ -199,6 +200,12 @@ SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
> >  	}
> >  	return retval;
> >  }
> > +#else
> > +SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
> > +{
> > +	return -EINVAL;
> > +}
> > +#endif /*CONFIG_DISABLE_OBSOLETE_SYSCALLS*/
> 
> And this should be done in kernel/sys_ni.c along with all the others.
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