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Date: Tue, 17 Apr 2012 23:19:16 +0400
From: Cyrill Gorcunov <gorcunov@openvz.org>
To: Kees Cook <keescook@chromium.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        Pavel Emelyanov <xemul@parallels.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH c/r -mm] c/r: prctl: Simplify PR_SET_MM on mm::code/data
 assignment
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On Tue, Apr 17, 2012 at 11:22:06AM -0700, Kees Cook wrote:
> On Mon, Apr 16, 2012 at 3:55 PM, Cyrill Gorcunov <gorcunov@openvz.org> wrote:
> > The mm::start_code, end_code, start_data, end_data members
> > are set during startup of executable file and are not changed
> > after.
> >
> > But the program itself might map new executable or/and data areas in
> > time so the original values written into mm fields mentioned above
> > might not have correspond VMA area at all, thus if one try to
> > use this prctl codes without underlied VMA, the error will be
> > returned.
> >
> > Drop this requirement. This shrinks the code and eliminates
> > redundant calls to vma_flags_mismatch. The worst thing one can
> > do (if say to write some bad values here) -- the weird results
> > will be shown in /proc/$pid/statm or in /proc/pid/stat.
> >
> > Still, assignement of data on stack (such as command line and
> > environment variables) requires the underlied VMA to exist.
> >
> > Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
> 
> Since this is CAP_SYS_RESOURCE, and mmap_min_addr is CAP_SYS_RAWIO,
> how about a lower-bounds check against mmap_min_addr? (We're already
> doing the TASK_SIZE upper check, so this additional sanity checking
> seems reasonable to me.)

I think this is good idea, thanks Kees. I'll check it out.

	Cyrill