linux-kernel - Re: [rfc 1/3] fs, proc: Add start_data, end_data, start

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Date:	Fri, 2 Dec 2011 11:23:32 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Andrew Vagin <avagin@...nvz.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Vasiliy Kulikov <segoon@...nwall.com>
Subject: Re: [rfc 1/3] fs, proc: Add start_data, end_data, start_brk members
 to /proc/$pid/stat

On Thu, Dec 1, 2011 at 11:28 PM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> On Fri, Dec 02, 2011 at 03:24:06AM +0300, Alexey Dobriyan wrote:
>> > > +         cputime_to_clock_t(cgtime),
>> > > +         mm ? (permitted ? mm->start_data : 1) : 0,
>> > > +         mm ? (permitted ? mm->end_data : 1) : 0,
>> > > +         mm ? (permitted ? mm->start_brk : 1) : 0);
>> > >   if (mm)
>> > >           mmput(mm);
>> > >   return 0;
>> >
>> > Thanks for using "permitted" here. :)
>>
>> And these are new fields, so "1" hack is unnecessary.
>
> I perhaps miss some history here, you mean just print 0
> instead of 1, right?

The history is that when "0" is seen for start_code, tools like "ps"
assumed the process was a kernel thread, so "1" was used as a hack to
not break userspace reporting. So yeah, since this is a new field,
it's fine to just do:

+         (mm && permitted) ? mm->start_data : 0,
+         (mm && permitted) ? mm->end_data : 0,
+         (mm && permitted) ? mm->start_brk : 0,

-Kees

-- 
Kees Cook
ChromeOS Security
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