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SubjectRe: [patch 1/2] c/r: prctl: Add ability to set new mm_struct::exe_file
On Thu, Mar 22, 2012 at 04:38:43PM -0700, Eric W. Biederman wrote:
> Cyrill Gorcunov <gorcunov@openvz.org> writes:
>
> > On Mon, Mar 19, 2012 at 03:46:49PM -0700, Andrew Morton wrote:
> >> > >>
> >> > >> What is this mysterious "security reason"?
> >> > >>
> >> > >
> >> > > Oh, sorry I should have included Matt's comment here
> >>
> >> Please send a patch with the updated changelog and improved comment?
> >>
> >
> > Andrew, take a look please, will the changelog and comments look
> > better?
>
> Can you change this to take an actual address and get the exe_file
> from an mmapped area and make certain that the mmaped_area is already
> mapped MAP_EXEC.

Do you mean PROT_EXEC/VM_EXEC?

>
> That will prevent out-right lies.
>
> At least then we will know that exe_file will at least be a file that is
> mapped executable in the process's address space. It's not a lot better
> but it makes /proc/<pid>/exe at almost as trustable as it is now.

I don't dislike the idea. However just because it's mapped with one of
those flags does not mean that a single instruction of it will ever be
executed. So it's not much better than using the fd :/.

Perhaps there is some way to use the userspace stack and/or regs to get
a reasonable instruction pointer, lookup its VMA, and use that? I'm not
sure that would work for c/r though...

Cheers,
-Matt



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