linux-kernel - Re: [rfc 1/4] mm: Introduce may_adjust

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Message-ID: <CAGXu5j+QHcrYjT8F9TZLA8YbJzZed28scp2y22QNO20sRF8Ndw@mail.gmail.com>
Date:	Thu, 24 Jul 2014 12:18:56 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrew Vagin <avagin@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>,
	Julien Tinnes <jln@...gle.com>
Subject: Re: [rfc 1/4] mm: Introduce may_adjust_brk helper

On Thu, Jul 24, 2014 at 9:46 AM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> To eliminate code duplication lets introduce may_adjust_brk
> helper which we will use in brk() and prctl() syscalls.
>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Andrew Vagin <avagin@...nvz.org>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Serge Hallyn <serge.hallyn@...onical.com>
> Cc: Pavel Emelyanov <xemul@...allels.com>
> Cc: Vasiliy Kulikov <segoon@...nwall.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Michael Kerrisk <mtk.manpages@...il.com>
> Cc: Julien Tinnes <jln@...gle.com>
> ---
>  include/linux/mm.h |   14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> Index: linux-2.6.git/include/linux/mm.h
> ===================================================================
> --- linux-2.6.git.orig/include/linux/mm.h
> +++ linux-2.6.git/include/linux/mm.h
> @@ -18,6 +18,7 @@
>  #include <linux/pfn.h>
>  #include <linux/bit_spinlock.h>
>  #include <linux/shrinker.h>
> +#include <linux/resource.h>
>
>  struct mempolicy;
>  struct anon_vma;
> @@ -1780,6 +1781,19 @@ extern struct vm_area_struct *copy_vma(s
>         bool *need_rmap_locks);
>  extern void exit_mmap(struct mm_struct *);
>
> +static inline int may_adjust_brk(unsigned long rlim,
> +                                unsigned long new_brk,
> +                                unsigned long start_brk,
> +                                unsigned long end_data,
> +                                unsigned long start_data)
> +{
> +       if (rlim < RLIMIT_DATA) {

Won't rlim always be the value from a call to rlimit(RLIMIT_DATA)? Is
there a good reason to not just put the rlimit() call in
may_adjust_brk()? This would actually be an optimization in the
prctl_set_mm case, since now it calls rlimit() unconditionally, but
doesn't need to.

-Kees

> +               if (((new_brk - start_brk) + (end_data - start_data)) > rlim)
> +                       return -ENOSPC;
> +       }
> +       return 0;
> +}
> +
>  extern int mm_take_all_locks(struct mm_struct *mm);
>  extern void mm_drop_all_locks(struct mm_struct *mm);
>
>



-- 
Kees Cook
Chrome OS Security
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