Re: [PATCH][RFC] Make /proc/<pid> chmod'able

[Bodo Eggert]

On Mon, 14 Mar 2005, Albert Cahalan wrote:
> On Mon, 2005-03-14 at 10:42 +0100, Rene Scharfe wrote:
> > Albert Cahalan wrote:

> > Why do you think users should not be allowed to chmod their processes' 
> > /proc directories?  Isn't it similar to being able to chmod their home 
> > directories?  They own both objects, after all (both conceptually and as 
> > attributed in the filesystem).
> 
> This is, to use your own word, "cloaking". This would let
> a bad user or even an unauthorized user hide from the admin.

NACK, the admin (and with the new inherited capabilities all users with 
cap_???_override) can see all processes. Only users who don't need to know
won't see the other user's processes.

> Note that the admin hopefully does not normally run as root.

su1 and sudo exist.

> Even if the admin were not running as a normal user, it is
> expected that normal users can keep tabs on each other.
> The admin may be sleeping. Social pressure is important to
> prevent one user from sucking up all the memory and CPU time.

Privacy is important, too. Imagine each user can see the CEO (or the
admin) executing "ee nakedgirl.jpg".

> > > Note: I'm the procps (ps, top, w, etc.) maintainer.
> > > 
> > > Probably I'd have to make /bin/ps run setuid root
> > > to deal with this. (minor changes needed) The same
> > > goes for /usr/bin/top, which I know is currently
> > > unsafe and difficult to fix.

I used unpatched procps 3.1.11, and it worked for me, except pstree.

> > Why do ps and top need to be setuid root to deal with a resticted /proc? 
> >     What information in /proc/<pid> needs to be available to any and all 
> > users?
> 
> Anything provided by traditional UNIX and BSD systems
> should be available.

e.g. the buffer overflow in sendmail? Or all the open relays? :)

The demands to security and privacy have increased. Linux should be able 
to provide the requested privacy.

> Users who want privacy can get their
> own computer. So, these need to work:
> 
> ps -ef
> ps -el
> ps -ej
> ps axu
> ps axl
> ps axj
> ps axv
> w
> top

Works as intended. Only pstree breaks, if init isn't visible.

> > > If you restricted this new ability to root, then I'd
> > > have much less of an objection. (not that I'd like it)
> > 
> > How about a boot parameter or sysctl to enable the chmod'ability of 
> > /proc/<pid>, defaulting to off?  But I'd like to resolve your more 
> > general objections above first, if possible. :)

I'd prefer a minimum and a maximum mask. If the admin wants to enforce 
privacy, he can do it, and if he wants the users to spy on each other, so 
be it.
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