linux-kernel - Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe

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Date:	Thu, 8 Mar 2012 12:06:17 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Oleg Nesterov <oleg@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Will Drewry <wad@...omium.org>
Subject: Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file v3

On Thu, Mar 8, 2012 at 12:02 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Thu, Mar 8, 2012 at 11:40 AM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
>> On Thu, Mar 08, 2012 at 11:31:58AM -0800, Kees Cook wrote:
>> ...
>>> > +       err = -EACCES;
>>> > +       if (!S_ISREG(dentry->d_inode->i_mode)   ||
>>> > +           exe_file->f_path.mnt->mnt_flags & MNT_NOEXEC)
>>> > +               goto exit;
>>>
>>> I'm starting to notice that this pattern (testing ISREG and
>>> MNT_NOEXEC) is getting repeated a few times in the kernel, and at
>>> least the no-new-privs patch (not yet in -mm but hopefully soon given
>>> the seccomp_filter work) updates this pattern everywhere. Perhaps this
>>> should be extracted into a helper first, and then this patch can call
>>> that helper here? (And then nnp can just update the single helper.)
>>>
>>
>> I can do that if Andrew agree.
>
> I'm a bit lost.  nnp updates the MNT_NOSUID checks, not the MNT_NOEXEC
> checks.  (And the effects of the two flags is different in selinux for
> historical reasons.)  I'm sure I'm missing something.

Oops, you're right. Regardless, we might want helpers anyway. Better
to have single places to do these tests.

-Kees

-- 
Kees Cook
ChromeOS Security
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