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    SubjectRe: [kernel-hardening] Re: [PATCH] proc: restrict access to /proc/interrupts
    On 11/07/2011 01:23 PM, Linus Torvalds wrote:
    > On Mon, Nov 7, 2011 at 12:47 PM, H. Peter Anvin <> wrote:
    >> You didn't really get my point. There are global nodes which are
    >> dynamic, and more importantly the *set* changes across the system life.
    >> A global policy option is a lot easier to deal with for the vast
    >> majority of users who don't need fine grain control.
    > I want *one* global policy that the kernel would actually know about:
    > is the user physically at the machine right now.
    > Sadly, I don't think the kernel has any good way to figure that out
    > automatically.
    > Because quite frankly, a lot of the /proc files should be "root or
    > desktop user". If you control the hardware, you should damn well be
    > able to see the interrupt counts in order to do bug reports etc
    > without having to 'sudo' or similar.
    > I realize that pam & co could give us this info, or we could just add
    > a new capability flag, but I think this is something where the kernel
    > really could just do the RightThing(tm) automatically, and screw the
    > crazy login managers, odd policies (I really don't believe that adding
    > magic selinux rules actually improves security all that much, because
    > it's too painful and too hard to know for any normal user).
    > The person in front of the hardware really *is* fundamentally special.
    > Right now all the distros do magic things with the audio device
    > because they know the person in front of the machine is special. But
    > all those things are ad-hoc per device, and never cover things like
    > random /proc files etc.

    I was going to say "let's just have the login manager add a group to the
    desktop user's permission set" but then I realized that this would be
    really bad because of setgid files.

    Which exposes a real problem with chgrp and setgid files overall.

    The way setgid works effectively means that any user can become a member
    of any group that they have at any time been a member of, simply by
    "stashing" a copy of the group as a setgid file:

    cp /bin/sh my-saved-group
    chgrp mygroup my-saved-group
    chmod g+s my-saved-group

    This is rather messy, because gids are otherwise a very nice capability


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