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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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